3.12 Buried Structures - Kansas Department of Transportation

Kansas Department of Transportation 

Design Manual 

3.12 Buried Structures 

Table of Contents 

3.12 Buried Structures ..................................................................................................................1 

3.12.1 Geometry .............................................................................................................1 

3.12.1.1 Definitions ...............................................................................................................1 

3.12.1.2 Length ......................................................................................................................3 

3.12.1.3 Skew or Rotation Angle ..........................................................................................3 

3.12.1.4 Wingwalls ................................................................................................................4 

3.12.2 Material .............................................................................................................19 

3.12.2.1 Concrete ................................................................................................................19 

3.12.2.2 Reinforcing ............................................................................................................19 

3.12.2.3 Material Density ....................................................................................................19 

3.12.3 Loads .................................................................................................................20 

3.12.3.1 Vehicle Load (LL) .................................................................................................20 

3.12.3.2 Dynamic Load Allowance (IM) ............................................................................20 

3.12.3.3 Distribution ............................................................................................................21 

3.12.3.4 Live Load Surcharge (LS) .....................................................................................21 

3.12.3.5 Future Wearing Surface (DW) ..............................................................................21 

3.12.3.6 Earth and Water Pressure (EV)(EH)(WA) ............................................................21 

3.12.3.7 Earth Surcharge (ES) .............................................................................................23 

3.12.3.7 Fill Height (Hf) ......................................................................................................24 

3.12.3.8 Summary of Low Fill Culvert Protection ..............................................................28 

3.12.4 Load Factors and Modifiers ..............................................................................29 

3.12.4.1 Load Factors ..........................................................................................................29 

3.12.4.2 Load Modifiers ......................................................................................................29 

3.12.5 Soils Information ...............................................................................................29 

3.12.5.1 Introduction ...........................................................................................................29 

3.12.5.2 Soils Data ..............................................................................................................30 

3.12.5.3 Bearing Capacity ...................................................................................................30 

3.12.5.4 Backfill ..................................................................................................................30 

3.12.5.5 Camber ..................................................................................................................31 

3.12.6 Analysis and Design ..........................................................................................33 

3.12.6.1 Analysis .................................................................................................................33 

3.12.6.2 Design Summary ...................................................................................................34 

3.12.6.3 Detailing ................................................................................................................37 

3.12.6.4 Practical Considerations for Structure Type .........................................................38 

3.12.7 Wingwall Structural Considerations .................................................................39 

3.12.7.1 Assumptions ..........................................................................................................39 

3.12.7.2 Earth Pressure ........................................................................................................40 

3.12.8 Precast Members ...............................................................................................44 

3.12.8.1 Box Culverts ..........................................................................................................44 

3.12.8.2 Precast Arch Culverts ............................................................................................47 

Volume III US (LRFD) 

Version 9/13 

3 - 12 - i 

Bridge Section


Design Manual 

3.12.9 Miscellaneous ....................................................................................................52 

3.12.9.1 Guardrail ................................................................................................................52 

3.12.9.1.1 Sidewalks, Fence, Slab Rest ............................................................................52 

3.12.9.2 Vehicle Grate .........................................................................................................52 

3.12.9.3 Entrance Bevel ......................................................................................................52 

3.12.9.4 Hubguard ...............................................................................................................53 

3.12.9.5 Strike Line .............................................................................................................53 

3.12.9.6 Weep Holes ...........................................................................................................53 

3.12.9.7 Seal Course ............................................................................................................53 

3.12.9.8 Scour Apron ..........................................................................................................54 

3.12.9.9 Soil Saver ..............................................................................................................54 

List of Figures 

Figure 3.12.1.1-1 Single/Multiple Cell RCB ..................................................................................5 

Figure 3.12.1.1-2 RCB Plan Views ................................................................................................6 

Figure 3.12.1.1-3 Box Size Definitions ..........................................................................................7 

Figure 3.12.1.1-4 Bridge Box, 10’ to 20’ Structure (500 Series), or Road Culvert .......................8 

Figure 3.12.1.2-1 RCB Plan View and Section ..............................................................................9 

Figure 3.12.1.3-1 Normal, Skewed and Rotated Crossing ...........................................................10 

Figure 3.12.1.4-1 Wingwall Flare Angle ......................................................................................11 

Figure 3.12.1.4-2 Embankment at Wingwalls ..............................................................................12 

Figure 3.12.1.4-3 Wingwall Dimensions for 0 Degree Skew RCB’s ...........................................13 

Figure 3.12.1.4-4 Wingwall Dimensions for 30 Degree Skewed RCB’s .....................................14 

Figure 3.12.1.4-5 Wingwall Dimensions for 45 Degree Skewed RCB’s .....................................15 

Figure 3.12.1.4-6 Straight Wingwall Details ................................................................................16 

Figure 3.12.1.4-7 Wingwall Dimensions for Straight Wings .......................................................17 

Figure 3.12.1.4-8 Straight Wingwall Plan Details ........................................................................18 

Figure 3.12.3.1-1 Live Load Distribution ....................................................................................20 

Figure 3.12.3.6-1 Summary of Loading Conditions .....................................................................22 

Figure 3.12.3.6-2 Buoyancy Effects on Backfill Materials ..........................................................23 

Figure 3.12.3.7-1 Design Fill Height Category ...........................................................................24 

Figure 3.12.3.7-3 Unequal Fill Height .........................................................................................27 

Figure 3.12.5.5-1 Settlement of Culvert .......................................................................................32 

Figure 3.12.6.1-1 Model of Culvert ..............................................................................................33 

Figure 3.12.6.2-1 Strength Design ................................................................................................35 

Figure 3.12.7.2-1 Design Assumptions - Vertical Cantilever .......................................................42 

Figure 3.12.7.2-2 Typical Backfill and Toe Dimensions ..............................................................43 

Figure 3.12.8.1-1 Precast Box Culvert Details .............................................................................46 

Figure 3.12.8.2-1 Precast Arch Details .........................................................................................50 

Figure 3.12.8.2-2 Closure Pour ....................................................................................................51 

Figure 3.12.9.1-1 Minimum Box Length With Guardrail ............................................................55 

Figure 3.12.9.6-1 RCB Auxiliary Details (Std BR020b) ..............................................................56 

Figure 3.12.9-3 Typical Culvert Extensions (Std RD080) ...........................................................57 

Figure 3.12.9-4 Bridge Excavation (Std BR100) ..........................................................................58 


Version 9/13 3 - 12 - ii 

Bridge Section


Design Manual 

Figure 3.12.9-5 Alignment & Details for Guardrail Protection on Low Fill Culverts (Std RD617c) 

59 

List of Tables 

Table 3.12.4.1-1 LRFD Load Factors. ..........................................................................................29 

Appendixs 

Appendix A Kansas Automated RCB System ...............................................................................1 

Appendix B Wingwall Moment & Reaction Coefficients ..............................................................1 

Appendix C LRFD RCB Mathcadd Loads ..................................................................................... 1 

Appendix D Doubly Reinforced and Shear Capactiy of Concrete .................................................1 

Appendix E Miscellaneous Example Details ..................................................................................1 

References 

REFERENCES ...............................................................................................................................1 


Version 9/13 

3 - 12 - iii 

Bridge Section


Design Manual 

Disclaimer: 

Disclaimer:ThisdocumentisprovidedforusebypersonsoutsideoftheKansasDepartmentof 

Transportationasinformationonly.TheKansasDepartmentofTransportation,theStateofKansas,its 

officersoremployees,bymakingthisdocumentavailableforusebypersonsoutsideofKDOT,donot 

undertakeanydutiesorresponsibilitiesofanysuchpersonorentitywhochoosestousethisdocument. 

ThisdocumentshouldnotbesubstitutedfortheexerciseofapersonsownUProfessionalEngineering 

JudgementU.Itistheusersobligationtomakesurethathe/sheusestheappropriatepractices.Any 

personusingthisdocumentagreesthatKDOTwillnotbeliableforanycommercialloss;inconvenience; 

lossofuse,time,data,goodwill,revenues,profits,orsaving;oranyotherspecial,incidental,indirect,or 

consequentialdamagesinanywayrelatedtoorarisingfromuseofthisdocument. 

TypographicConventions: 

Thetypographicalconventionforthismanualisasfollows: 

 

NonitalicreferencesrefertolocationswithintheKDOTBridgeDesignManuals(eithertheLRFDorLFD), 

orHyperlinksshowninred,asexamples: 

 

 

Section3.2.9.12Transportation 

Table3.9.21DeckProtection 

 

 

ItalicreferencesandtextrefertolocationswithintheAASHTOLRFDDesignManual,forexample: 

 

Article5.7.3.4 

 

ItalicreferenceswithaLFDlabelandtextrefertolocationswithintheAASHTOLFDStandard 

Specifications,forexample: 

 

LFDArticle3.5.1 


Version 9/13 3 - 12 - iv 

Bridge Section


Design Manual 

3.12 Buried Structures 

The following criteria are intended as guidelines in the structural design and detail of cast-inplace 

(CIP) reinforced concrete box culverts. The criteria are applicable to culverts for which 

KDOT has direct design responsibility and for which KDOT has a responsibility for plan review. 

It is not intended that these guidelines answer all questions of design or details of design. Additional 

information will be added to this document, as needed, for clarification. It is expected that 

the applicability of these guidelines to actual field conditions or to designs outside the limits considered 

in this report will be verified by an Engineer. The hydraulic design and selection of culvert 

size are discussed in other documents. 

This section also contains information on precast box culverts and precast arch strucures. 

Reference to the “KDOT Design Engineer” considered to be appropriately either the State Road 

Engineer or the State Bridge Engineer. 

Unless otherwise noted, AASHTO references are to the 2007 American Association of State 

Highway and Transportation Official’s LRFD Specifications for Highway Bridges, including the 

2009 interims. 

3.12.1 Geometry 

3.12.1.1 Definitions 

For purposes of this report, a reinforced concrete box culvert is considered to consist of two components: 

a rectangular conduit (box, barrel, etc.) to convey water and a retaining structure (headwalls, 

wingwalls, etc.) to prevent erosion of the embankment fill. The wingwalls provide a 

hydraulic transition at the entrance and exit of the conduit. 

The standard designation for the size of a box culvert shall be the span followed by the rise (see 

Figure 3.12.1.1-1 Single/Multiple Cell RCB). For example, a 10 x 8 designation is a box culvert 

with a span of 10 ft. and a rise (height) of 8 ft. The designation for a multiple cell box culvert shall 

be the number of cells followed by the cell size. For example, a 3-10 x 8 is a triple cell box culvert 

with each cell measuring 10 ft. span by 8 ft. rise. For Standard Box Culverts, all cells of a multiple 

cell box culvert shall be the same size. The span by rise designation shall be measured as the clear 

distance from the inside faces of walls, and the clear inside distance from top to bottom slabs. For 

normal practice, the rise dimension is considered vertical and the end face of the RCB is assumed 

to be constructed vertical. The span by rise designation is an indication of the hydraulic flow area. 

The structural-design span length for slab and wall members shall be determined by the applicable 

AASHTO specifications. 


Version 9/13 3 -12 - 1 

Bridge Section


Design Manual 

For purposes of classification, a box culvert can be classified as a Bridge Box, a 10 ft. to 20 ft. 

Structure (Formerly known as ‘500’ Series), or a Road Culvert. (See Figure 3.12.1.1-2 RCB Plan 

Views, Figure 3.12.1.1-3 Box Size Definitions, and Figure 3.12.1.1-4 Bridge Box, 10’ to 20’ 

Structure (500 Series), or Road Culvert 

Bridge Box: A bridge box is defined as a structure having a length greater than 20 ft. measured 

along the centerline of the roadway from the inside faces of both exterior walls (including 

all span widths and the thickness of all interior walls). The total length along the centerline 

of project shall consider the effects of the skew or rotation. For example, a 20 x 10 box culvert 

constructed normal to centerline of project is not a bridge. A 20 x 10 box culvert constructed 

skewed or rotated to centerline of project would be classified as a bridge. A 2-10 

x 8 box culvert would be classified as a bridge, i.e. two (2) 10 ft. clear spans plus an interior 

wall exceeds 20 ft. 

10 ft. to 20 ft. Structures, (Formerly known as ‘500’ Series Boxes): Box culverts with a total 

width of 10 ft. or greater (measured perpendicular to the centerline of box) to less than or 

equal to 20 ft. (measured along the centerline of the roadway) are considered 10 ft. to 20 

ft. Structures. Measurements are taken from the inside faces of both exterior walls and 

include all span widths and the thicknesses of all interior walls.) 

Road Culvert: A Road Culvert is defined as a structure having a length of less than 10 ft. from the 

inside faces of both exterior walls measured perpendicular to the centerline of the box. 

RCB vs. RFB: Box culverts are further defined as RCB’s (“Pinned”) and RFB’s (“Fixed”). 

A “Pinned” box is designed with the walls and slabs assumed to be simple spans 

(independent of one another). Normally there is only one layer of steel in the walls of 

pinned boxes (unless the cell height is greater than 10 ft.). In addition, pinned boxes do not 

have fillets in the corners of the box. 

“Fixed” (also referred to as Rigid Frame) boxes are designed with the slabs and walls 

assumed to be continuous (connected to one another). Therefore, in Rigid Frame Boxes 

(RFB’s), there will always be an L-shaped reinforcing bar in the corners of the box near 

the outside face. This corner reinforcing bar distributes some of the load from the slab to 

the wall and vice-versa. Rigid Frame culverts always have two layers of steel in the wall. 

All KDOT Rigid Frame Boxes have fillets in the corners of the box. This fillet helps 

provide rigidity to the frame. 

On the Plan/Profile Sheets and Title Sheet, in the note that specifies location, size and type 

of box culverts; label “pinned” boxes as RCB’s, and label “fixed” boxes as RFB’s. 

The State Road Office is responsible for the design and detail generation of “Road Culverts” and 

“10 ft. to 20 ft. Structures”. The State Bridge Office is responsible for “Bridge Boxes”. The 10 ft. 

to 20 ft. structures have a unique serial number for their respective county. This requires coordination 

with the Bridge Special Assignments Section in acquiring a serial number. 


Version 9/13 3 - 12 - 2 

Bridge Section


Design Manual 

3.12.1.2 Length 

The length of an RCB is considered to be the horizontal length measured along the centerline of 

the culvert from exterior face to exterior face and shall be rounded up to the nearest inch. The 

Roadway length (right or left) is the horizontal distance from the centerline of roadway (or project) 

to the roadway side of the hubguard and is measured normal (90) to the centerline of roadway 

(or project). The ‘Roadway Length’ is a parameter used in determining guardrail 

requirements, encroachments in the safety recovery zone, and other features of Geometric Roadway 

Design. As an example, a 10 x 8 x 272’-3” RCB has a horizontal length (to the nearest inch) 

of 272’-3”, but may have combinations of ‘Roadway Left’ and ‘Roadway Right’ depending on 

the grade of the box and the angle of skew or rotation. Roadway lengths are rounded to the nearest 

0.01 ft. (see Figure 3.12.1.2-1 RCB Plan View and Section). For normal practice, it is sufficient to 

station the location to the nearest ft. 

3.12.1.3 Skew or Rotation Angle 

A skewed RCB is defined as an RCB that intersects the centerline of project at an angle other than 

90 and has an entrance and exit face that is parallel to the centerline of project. 

A rotated RCB is defined as an RCB that intersects the centerline of project at an angle other than 

90° and has an entrance and exit face that is normal to the centerline of the RCB. For rotated 

structures the roadway length reference location is the inside of the hubguard closest to the road. 

This location is also used to determine the minimum structure dimension when providing a structure 

which is outside of the clear zone and thus may not need guardrail. 

The skew angle or rotation angle is the acute angle measured from a line normal to the centerline 

of project. A skew angle (or rotation angle) is considered a ‘right’ skew (or rotation) when the 

acute angle of intersection from a line normal to the centerline of project and the centerline of the 

RCB is measured clockwise. Conversely, a ‘left’ skew angle is measured counterclockwise (see 

Figure 3.12.1.3-1 Normal, Skewed and Rotated Crossing). 

Ordinary design practice allows normal (90 crossing) box culverts to be rotated to angles up to 

15 degrees. Standard skewed boxes of 30 skew and 45 skew angles may be used at skewed 

waterway crossings with local channel realignment to improve the approach and exit direction of 

the stream. 


Version 9/13 3 -12 - 3 

Bridge Section


Design Manual 

3.12.1.4 Wingwalls 

Wingwalls are referred to as ‘flared’ when the axis of the wingwall forms an acute angle with the 

centerline axis of the box. ‘Straight’ wingwalls are an extension or continuation of the box walls. 

(See Figure 3.12.1.4-8 Straight Wingwall Plan Details) Wingwalls constructed at 90 to the barrel 

or constructed parallel to centerline of roadway are not considered hydraulically efficient and are 

not recommended for use on KDOT Standard RCB’s. Flared wingwalls will be used on the Standards 

at the entrance ends of culverts for hydraulic reasons. However, straight wings may be 

specified at the entrance end when the hydraulics and additional costs are adequately considered. 

Straight wings, compared to flared wings, for a rise of 8.0 ft. or less may be economically specified 

for single cell boxes. For multiple cell boxes, the cost for straight wings, including the floor, 

may exceed the cost for flared wings; however, at sites where erosion aprons are specified, 

straight wings may be appropriate. Otherwise, ‘flared’ wings will be used at the exit end. 

The ‘flare’ angle for normal or rotated culverts will be 45 degrees. For Standard 30 and 45 

skewed boxes, the ‘flare’ angle will be as shown on Figure 3.12.1.4-1 Wingwall Flare Angle. 

The reference point for wingwall geometry is considered the intersection of the back face of the 

wingwall and the exterior face of the box. The length of the wingwall is measured from the free 

end to the reference point along the back face of the wall. (see Figure 3.12.1.4-2 Embankment at 

Wingwalls) 

Length of flared walls will be based on a local embankment slope behind the wing of 3.5:1 and a 

2:1 slope in front of the wing. (see Figure 3.12.1.4-2 Embankment at Wingwalls) The computed 

length of the wall will be rounded up to the next 6 inches. The elevation at the end of flared walls 

shall be computed from the flow line with a 2:1 slope and the height at the end of the wing shall 

be rounded up to the nearest inch. Flared wingwalls are available for standard box heights from 3 

ft. to 20 ft. (See Figure 3.12.1.4-3 Wingwall Dimensions for 0 Degree Skew RCB’s, Figure 

3.12.1.4-4 Wingwall Dimensions for 30 Degree Skewed RCB’s, and Figure 3.12.1.4-5 Wingwall 

Dimensions for 45 Degree Skewed RCB’s for flared wingwall dimensions) 

Length of straight walls will be based on a local embankment slope beyond the hubguard of 3:1. 

(see Figure 3.12.1.4-6 Straight Wingwall Details) The computed length of the wall will be 

rounded up to the next 6 inches. The elevation at the end of the straight walls shall be computed at 

the end of the wall as h/4 above the flow line (2.5 ft. maximum) and rounded up to the nearest 

inch. (see Figure 3.12.1-8) Straight wingwalls are available for standard box heights from 2 ft. to 

10 ft. (See Figure 3.12.1.4-7 Wingwall Dimensions for Straight Wings for straight wingwall 

dimensions) 


Version 9/13 3 - 12 - 4 

Bridge Section


Design Manual 

Figure 3.12.1.1-1 Single/Multiple Cell RCB 


Version 9/13 3 -12 - 5 

Bridge Section


Design Manual 

Figure 3.12.1.1-2 RCB Plan Views 


Version 9/13 3 - 12 - 6 

Bridge Section


Design Manual 

Figure 3.12.1.1-3 Box Size Definitions 


Version 9/13 3 -12 - 7 

Bridge Section


Design Manual 

Figure 3.12.1.1-4 Bridge Box, 10’ to 20’ Structure (500 Series), or Road Culvert 


Version 9/13 3 - 12 - 8 

Bridge Section


Design Manual 

Figure 3.12.1.2-1 RCB Plan View and Section 


Version 9/13 3 -12 - 9 

Bridge Section


Design Manual 

Figure 3.12.1.3-1 Normal, Skewed and Rotated Crossing 


Version 9/13 3 - 12 - 10 

Bridge Section


Design Manual 

Figure 3.12.1.4-1 Wingwall Flare Angle 


Version 9/13 3 -12 - 11 

Bridge Section


Design Manual 

Figure 3.12.1.4-2 Embankment at Wingwalls 


Version 9/13 3 - 12 - 12 

Bridge Section


Design Manual 

Figure 3.12.1.4-3 Wingwall Dimensions for 0 Degree Skew RCB’s 


Version 9/13 3 -12 - 13 

Bridge Section


Design Manual 

Figure 3.12.1.4-4 Wingwall Dimensions for 30 Degree Skewed RCB’s 


Version 9/13 3 - 12 - 14 

Bridge Section


Design Manual 

Figure 3.12.1.4-5 Wingwall Dimensions for 45 Degree Skewed RCB’s 


Version 9/13 3 -12 - 15 

Bridge Section


Design Manual 

Figure 3.12.1.4-6 Straight Wingwall Details 


Version 9/13 3 - 12 - 16 

Bridge Section


Design Manual 

Figure 3.12.1.4-7 Wingwall Dimensions for Straight Wings 


Version 9/13 3 -12 - 17 

Bridge Section


Design Manual 

Figure 3.12.1.4-8 Straight Wingwall Plan Details 


Version 9/13 3 - 12 - 18 

Bridge Section


Design Manual 

3.12.2 Material 

3.12.2.1 Concrete 

Grade 4.0(AE) 

Grade 4.0 

f’c = 4,000 psi 

f’c = 4,000 psi 

Grade 4.0 concrete shall be used for design and construction of Reinforced Concrete Boxes 

except that Grade 4.0 (AE) concrete shall be used in the top slab at locations where the top slab is 

the riding surface (or where the actual fill is 2 ft. less) and it is expected that the top slab will be 

exposed to frequent applications of deicing salts. Air-entrained concrete should be used in conjunction 

with epoxy-coated reinforcing steel (see Section 3.12.6.3 Detailing for corrosion protection 

for reinforcing). 

When specified by the plans or required by the Plan Engineer, a seal course of unreinforced concrete 

(Commercial Grade) may be used. 

3.12.2.2 Reinforcing 

ASTM A615 Grade 60 Fy = 60 ksi 

Maximum length of bars #5 through #11 shall not exceed 60.0 ft. Maximum length of #3 and #4 

bars shall be 40.0 ft. This is a field handling consideration. See Section 3.12.6.3 Detailing for size, 

spacing, and clearance requirements. 

3.12.2.3 Material Density 

The following densities are assumed for design purposes (taken from Table 3.5.1-1): 

Concrete ..............................................................150 pcf 

Asphalt ................................................................135 pcf 

Compacted Sand .................................................115 pcf 

Loose (Dumped Sand) ........................................100 pcf 

Compacted Sand-Gravel .....................................120 pcf 

Soil .......................................................................120 pcf 


Version 9/13 3 -12 - 19 

Bridge Section


Design Manual 

3.12.3 Loads 

3.12.3.1 Vehicle Load (LL) 

KDOT uses a one ft. strip method to analyze the top slab of culverts. The HS20 live load or design 

tandem only shall be used (Article 3.6.1.3.3 for spans in the longitudinal direction), whichever 

produces the greatest stress. Per Article 3.6.1.3, the lane load included in the HL-93 load is not 

used for box culverts. Where traffic travels parallel to the span, the designs will be limited to one 

lane loaded and use a multiple presence factor of 1.2 per Article C3.6.1.3.3. In rare cases where 

the traffic travels perpendicular to the span a special analysis is required. KDOT will not make 

any corrections for skewed structures, per Article 12.11.2.4. Live load need not be considered for 

single cell structures where the fill is greater than 8 ft., or for multi-cell structures with the fill 

height greater than the overall box width. See Appendix C LRFD RCB Mathcadd Loads for 

example calculations. 

Figure 3.12.3.1-1 Live Load Distribution 

3.12.3.2 Dynamic Load Allowance (IM) 

Impact shall be applied as per Article 3.6.2.2, and will have influence only to a depth of 8 ft. for 

single cell structures or to a depth of fill equal to the out-to-out dimension for multi-cell structures. 


Version 9/13 3 - 12 - 20 

Bridge Section


Design Manual 

3.12.3.3 Distribution 

Per Article 4.6.2.10, where the depth of fill is less than 2.0 ft., the live load shall be distributed 

over a distance E, measured perpendicular to the span, and E span measured parallel to the span per 

Equations 4.6.2.10.2-1 and Equations 4.6.2.10.2-2 respectfully. KDOT uses 1.00 for the Live 

Load Distribution Factor (LLDF). This assumes the distribution of the live load through depth of 

fill will be consistent with soil. 

When the depth of fill is 2.0 ft. or more (Article 3.6.1.2.6), the live load is distributed over a rectangular 

area starting from a contact patch of 10 in. x 20 in. per Article 3.6.1.2.5. KDOT uses a 

22.5 degree angle, 0.500:1 from each side of the patch to the top of the culvert. This article also 

allows the use of a 0.575:1 factor for granular fill which would increase the size of the rectangular 

area and decrease the load intensity. Unless special circumstances exist, which would change the 

overburden material on the culvert from that covered in KDOT’s Standard Specifications, the 

default of 0.500:1 is used. 

For the design of KDOT ‘Standard Culverts’, it is assumed that the culvert is founded on a yielding 

foundation using embankment construction methods. The vertical earth load shall be the soil 

weight with applicable design factors. 

The foundation is considered to be on springs (compression only) derived from an average modulus 

of subgrade reaction of 125 pci. These springs replace the distribution of load (reaction) to the 

bottom slab specified in Article 12.11.2.3. The passive resistance of the walls is similar to the 

floor. The value of the reaction is half that of the floor reaction. These spring supports, representing 

the soil, at the foundation are based on a modulus of subgrade reaction recommended by 

KDOT’s Geotechnical Engineer. This may be unconservative for culverts founded on rock. Structures 

founded on rock may require a special design, and can be investigated for by adjusting the 

spring constant and determining the effects. 

3.12.3.4 Live Load Surcharge (LS) 

KDOT will use a live load surcharge as stated in Article 3.11.6.4, where vehicular load is expected 

to act on the surface of the backfill within a distance equal to one-half of the wall height. The 

range of values are from 2.0 ft. to 4.0 ft. of equivalent soil. (see Figure 3.12.3.6-1 Summary of 

Loading Conditions) 

3.12.3.5 Future Wearing Surface (DW) 

KDOT policy is to use a paved surface on top of the standard RCB’s. An allowance for future 

wearing surface (FWS) will not be used in the design of an RCB ‘At Grade’ box. When the top 

slab is the wearing surface, FWS should be considered. 

3.12.3.6 Earth and Water Pressure (EV)(EH)(WA) 

Coulomb Earth Pressure Theory is appropriate for walls with no heels and backfill materials 

which may not be free draining; see Article C 3.11.5.3 for additional information. Rankine Earth 


Version 9/13 3 -12 - 21 

Bridge Section


Design Manual 

Pressure Theory uses equivalent earth pressure and is appropriate for long heeled cantilever walls 

and backfill material which is free draining. Acceptable backfill materials will meet criteria 

specified in the 3.12.5.4 Backfill. 

The following values are used for the design of KDOT Standard Reinforced Concrete Box Culverts: 

Saturated Soil Unit Weight ...................................................... 135 pcf 

Soil Weight Unit Weight ......................................................120 pcf 

Coefficient of ‘at-rest’ earth .................................................... 0.50 

Because the designer may not be sure which method of construction will occur in the field, KDOT 

assumes that “Embankment” rather than “Trench” type construction is used. This assumption 

results in conservative values for the unfactored vertical earth loads per Article 12.11.2.2. 

Figure 3.12.3.6-1 Summary of Loading Conditions 


Version 9/13 3 - 12 - 22 

Bridge Section


Design Manual 

Figure 3.12.3.6-2 Buoyancy Effects on Backfill Materials 

Water Effects: 

The height of the water table will be taken to be level with the top of the box. The internal effect 

assumes that the box is completely full. The soil below the top of the barrel is considered submerged; 

soil in the EH (earth horizontal) load is buoyant. Use the effective unit weight to calculate 

this force effect, except for structures with fill heights less than 10 ft. as described below. 

Hydrostatic forces (WA) are applied to both the exterior and interior portions of the barrel that 

maximize the force effects. The vertical force effect for (WA) is used on the bottom slab. These 

two effects are to be considered independent effects which are combined to maximized the greatest 

effect. The assumed effects of water and buoyancy are shown in Figure 3.12.3.6-2 Buoyancy 

Effects on Backfill Materials. 

Special Considerations: 

In Kansas, road ditches and creeks in small drainage areas have a water surface elevation which 

changes rapidly with each hydraulic event. The probability of saturating the soil in the backfill, as 

described in the previous section, is low. The Standard KDOT RCB with less than 10 ft. of fill 

will not be designed for this condition, as it would be overly conservative most of the time. If the 

designer anticipates the possibility of a sustained high water event, for example in a flood plain or 

at a detention storage location, then a custom design may be warranted. 

3.12.3.7 Earth Surcharge (ES) 

Occasionally, construction activities require accelerated settlement by loading portions of the new 

roadway embankment with excessive overburden. The Standard KDOT RCB was not designed 

for this loading condition. If the Engineer anticipates this construction condition, a special analysis 

will be done to evaluate the potentials for distress in the box culvert. 


Version 9/13 3 -12 - 23 

Bridge Section


Design Manual 

3.12.3.7 Fill Height (H f ) 

For normal crowned roadways, the design fill height will be measured from the top of the riding 

surface at the outside edge of the shoulder to top of box. A structure with “0.0 ft.” of design fill 

height should be only used when traffic is directly on the top of the box. For traffic directly on the 

structure, adjust the top bar reinforcement cover to a minimum of 3 in. 

For super-elevated roadways, extreme sloping boxes, or unusual cross-sections, judgment will be 

exercised in determining the design fill height. In all cases, the fill height will be noted on the 

plans for review and future reference. KDOT’s practice requires that one fill height be used for the 

structural design of the entire length of the box. 

Figure 3.12.3.7-1 Design Fill Height Category 

Category 

‘At Grade’ Box 

‘Low Fill’ Box 

‘Moderate Fill’ Box 

‘High Fill’ Box 

Design Fill Height 

0.0 to 2.0 ft., or* where top slab is driving surface. 

Over 2.0 ft. to 10.0 ft. 

Over 10.0 ft. to 20.0 ft. 

Over 20.0 ft. to 50.0 ft. 

*Note: Driving directly on the top slab or with a nomial amount of pavement is the only time 0.0 

ft. should be used as the fill height. 

For superelevated roadway sections as shown in the graphic, the design fill height may be either a 

minimum fill, or a maximum fill section. Investigate both to determine the most conservative 

design. 


Version 9/13 3 - 12 - 24 

Bridge Section


Design Manual 

Fill Heights: 

1) The designer needs to specify the proper depth of fill on the RCB. Design fills 

should be specified as follows: 

Actual Fill 

Fill to specify 

on plans 

0 < 0.5 ft. 0.0* 

> 0.5 ft. < 2 ft. 2 ft. 

> 2 ft. < 3 ft. 3 ft. 

> 3 ft. < 5 ft. 5 ft. 

> 5 ft. < 10 ft. 10 ft. 

> 10 ft. < 15 ft. 15 ft. 

> 15 ft. < 20 ft. 20 ft. 

> 20 ft. < 25 ft. 25 ft. 

> 25 ft. < 30 ft. 30 ft. 

> 30 ft. < 35 ft. 35 ft. 

> 35 ft. < 40 ft. 40 ft. 

> 40 ft. < 45 ft. 45 ft. 

> 45 ft. < 50 ft. 50 ft. 

* Special Case when traffic is directly on top slab. 

2) Below is a graphical representation showing the importance of specifying the 

proper amount of fill. Arbitrarily adding fill height does not necessarily provide a 

stronger RCB. In some instances, engineering judgment may be required to 

specify the proper amount of fill (i.e.; RCB Extensions, RCB's under superelevated 

roadways). 

For fill heights < 10’-0”, the Designer (software) will investigate 5 ft., 3 ft. and 2 

ft. fill heights to determine the most conservative design. 

The fill heights used in the RCB Program rounds the actual fill to the Design fill 

height. It is KDOT’s policy to round actual fill height of 4.99 ft. and less to the 

most conservative value of 2 ft. which is governed by the truck loadings. Round 

fill heights of 5.00 ft. and greater to the next conservative fill value in which earth 

pressure controls. 


Version 9/13 3 -12 - 25 

Bridge Section


Design Manual 

For ‘At Grade’ Boxes an equivalent soil fill height should be used, considering mass and thickness 

of the pavement, pavement base, and sub-base. The design value shall be noted on the plans. 

For other than ‘At Grade’ Boxes, the weight of pavement and base may be assumed as earth density 

at 120 pcf. 

Design Fills over 50.0 ft. will be considered as special circumstances and will require a review by 

the KDOT Design Engineer.The design fill value is a representative design parameter not 

intended for use in field construction or for hydraulic analysis. 

In special circumstances where unusual variance in fill heights may occur and savings may be 

effected as in the case of large and/or long boxes under ‘high fill’, more than one Design Fill 

Height may be used and shall be so noted on the plans. Culverts designed with more than one 

Design Fill Height will require a documented economic analysis to be reviewed by the KDOT 

Design Engineer. Where a design life is needed for economic evaluation, a design life of 75 years 

will be assumed. The minimum length of culvert section with multiple Design Fill Height shall be 

60.0 ft. 

Unequal Fill: For locations where unequal fill could be a concern, such as when a box culvert is 

installed parallel to the embankment slope, use an RFB. When the differential in fill height is 

equal to or greater than 20% a special analysis is required. 


Version 9/13 3 - 12 - 26 

Bridge Section


Design Manual 

Figure 3.12.3.7-3 Unequal Fill Height 

Structure Top Slab Protection: 

For box structures where the design fill height is less than or equal to 2 ft. , measured at the outside 

edge of the shoulder, the box will have a multi-layer protection system. Cast-in-place box 

structures will have 100% epoxy coated reinforcement in the barrel, not just the top slab portion 

as in past practice. Wings need not have epoxy protection. Air Entrained (AE) concrete will be 

used for the top of slab when a design fill height is less than or equal to 2 ft. The exterior (dirt 

side) portion of the top slab plus 12 in. of the top of the exterior wall will be protected by an 

approved non-coal tar “Bridge Backwall Protection System” comprised of needle punched bentonite 

panels. 

For box structures using a precast alternate, the concrete will provide for a low permeability structure. 

For design fill heights less than or equal to 2 ft. use an “Bridge Back wall Protection System” 

in the cast in place structure is required. Epoxy reinforcement is not required for precast structures. 

For structures where the driving surface is the top slab and hot mix asphalt will be placed directly 

on the top slab there are two additional requirements. The designer will use “Pavement Waterproofing 

Membrane” from Section 800 and increase the cover to the top mat of reinforcement to a 

minimum of 3 in. by adding 1 in. of concrete. In-leiu of the waterproofing membrane the Contractor 

may supply a minium of 3 in. of dirt to thermaly insulate the backwall protection from the 

hot mix asphalt. 

* See Section 3.12.3.8 for summary of protection for all culvert types. 


Version 9/13 3 -12 - 27 

Bridge Section


Design Manual 

3.12.3.8 Summary of Low Fill Culvert Protection 

Precast Culvert (Special Provision 07-07019) 

Precast Arch 

• Fill less than or equal 3 feet 

• Epoxy reinforcement in entire precast arch and closure pour 

• Pavement waterproofing membrane over closure + 18 in. 

• Air entrained concrete for entire arch 

• Bridge Backwall Protection covering the middle 1/3 of top of the structure 

• 2 feet of aggregate on top and sides 

Precast Rigid Frame 


• Epoxy reinforcement in entire precast frame 

• Air entrained concrete for entire frame 

• Bridge Backwall Protection covering the entire top + 12 in. down the sides 

• 2 feet of aggregate on top and sides 

Precast Box Culvert (Special Provision 07-07-07017) 


• Epoxy reinforcement for entire box or Bridge Backwall Protection covering the entire top + 

12 in. down the sides 

• Air entrained concrete for entire box 

• Additional 1 1/4 in. clearance for top mat in top slab 

Cast-In-Place Box Culvert (Bridge Standard per RCB Program + BR020B) 


• Epoxy reinforcement for entire box and Bridge Backwall Protection covering the entire top + 

12 in. down the sides 

• Air entrained concrete for top slab 


Version 9/13 3 - 12 - 28 

Bridge Section


Design Manual 

3.12.4 Load Factors and Modifiers 

3.12.4.1 Load Factors ( ) 

The factors below are taken from Table 3.4.1-2 to maximize the effects to the structure. 

Table 3.12.4.1-1 LRFD Load Factors. 

Load 

* For special designs. 

3.12.4.2 Load Modifiers ( ) 

At the Strength Limit State buried structures are considered redundant for live loads and nonredundant 

for earth fill per Article 12.5.4. KDOT RCB Standards use a load modifier 1.00 for all 

force effects instead of 1.05 for earth fill. However, for all custom /non-standard designs use a 

load modifier of 1.05 for earth fill. 

3.12.5 Soils Information 

Strength I Load Factors 

Minimum 

Maximum 

Service I Load Factors 

DC 0.90 1.25 1.00 

DW 0.65 1.50 1.00 

LL,IM,LS 0.00 1.75 1.00 

EH 0.50 

(Article 3.11.7) 

1.35 1.00 or 0.50 


EV 0.90 1.30 1.00 

WA 0.00 1.00 1.00 

* ES 0.50 


1.50 1.00 or 0.50 

3.12.5.1 Introduction 

This information is intended to be used to select the proper backfill for a box, to guide the 

designer in ascertaining soil properties for normal foundation conditions, and calculating the 

required camber for boxes under fills of less than 20 ft. in height. 


Version 9/13 3 -12 - 29 

Bridge Section


Design Manual 

3.12.5.2 Soils Data 

Soil data for the design of boxes may be obtained from a special investigation of the proposed 

site. A KDOT Soil Survey or data from a Soil Conservation Service (SCS) Soil Survey may be 

use for this purpose. The majority of boxes will probably be designed using the SCS data, since 

most drainage structures will not warrant a special investigation or may not be located on the state 

system. Therefore, the soil classifications used in this report will be those of the Unified Soil 

Classification System. 

The information of interest to designers in the SCS Soil Surveys is contained in the Engineering 

Index Properties table and the detailed soil maps. The soil maps are used to identify the soil type 

in the area of the project, and the Engineering Index Properties give the classification and index 

properties of the soil. This information may then be used to identify the type of footings and backfill 

required to properly construct the box. 

3.12.5.3 Bearing Capacity 

The design of footings should be done using a nominal bearing pressure of 6000 psf unless the 

box is sited in a soil of low bearing capacity. Soils with a low bearing capacity are CH, MH, OH, 

and OL type soils. Footings in low bearing capacity soils should be designed using an nominal 

bearing pressure of 4500 psf. In both cases a value of 0.45 should be used. 

3.12.5.4 Backfill 

Soil used to backfill reinforced concrete boxes shall have a liquid limit less than 50, and a plasticity 

index less than 22. Backfill soil shall be essentially free of all organic matter. High plasticity 

and organic soils are not considered free draining materials and should not be used. Soils unacceptable 

for use as backfill are CH, MH, OH, and OL type soils. Where soils of this type are 

encountered, a clean, granular backfill will be required. Specifying granular backfill in areas 

where there are expansive soils, will help reduce soil pressures and are consistent with design 

assumptions. 


Version 9/13 3 - 12 - 30 

Bridge Section


Design Manual 

3.12.5.5 Camber 

Unless other information is furnished by a soils report, camber will be shown for design fill 

heights over 20 ft. The camber used will vary linearly from the maximum deflection to zero 

deflection at the end of the box. 

If a field investigation will not be performed to determine foundation settlement, an estimate may 

be determined from the report, “Guidelines on the Use of Soils Information for Box Design”. The 

graph in Figure 3.12.5.5-1 Settlement of Culvert, contains a set of five settlement curves for five 

generalized soil types. These curves relate fill height to settlement up to a maximum fill height of 

20 ft. For fill heights greater than 20 ft., settlement may be estimated by adding together the 

equivalent thicknesses. (ie the settlement for 30 ft. of fill equals to the settlements for 10 ft. plus 

20 ft. added together) 

The five settlement curves were developed using the assumption of a 20 ft. compressible layer. If 

there is less than 20 ft. of compressible material below the culvert in the foundation, the settlement 

may be proportioned relative to the thickness of the compressible layer. (ie the settlement for 

a culvert with a 10 ft. compressible layer would be taken as 0.5 that shown for that curve) 


Version 9/13 3 -12 - 31 

Bridge Section


Design Manual 

Figure 3.12.5.5-1 Settlement of Culvert 


Version 9/13 3 - 12 - 32 

Bridge Section


Design Manual 

3.12.6 Analysis and Design 

3.12.6.1 Analysis 

The existing box standards (barrel portion) where checked against the 2007 LRFD AASTHO 

Specifications including 2009 Interims. The reinforced concrete box (RCB) model consisted of 

two node prismatic beam elements with three degrees of freedom per node. The tops of the walls 

for the RCB are considered to be pinned with no rotational resistance. This “pinned” condition is 

created by releasing the moment continuity at the end of the wall member which frames into the 

either the top slab or the bottom slab. The rigid frame box (RFB) model is similar except the fillets 

in the corners are stepped beam elements. The supports are linear translation springs representing 

a yielding support based on the modulus of subgrade reaction. This differs from Article 

12.11.2.3. All models are planer and represent a 1.0 ft. slice, which maximizes the live load loading 

patches and minimizes two way action. This one way action (beam action) is a conservative 

assumption. The discretization is shown below in Figure 3.12.6.1-1 Model of Culvert. Nodes are 

placed at 1.0 ft. increments and at critical locations such as midpoint of the span and at fillet toes. 

The live load was evaluated by the use of influence lines. A unit load was placed on the top slab 

and moved in three inch increments. All points of analysis whether located on the floor, walls, or 

slab had their own slab live load influence lines (one for each force type of moment, shear and 

axial) generated by retreiving the force at the analysis point for each movement of the point load 

along the slab. All design truck and tandem possibilities are then applied and distributed per Article 

3.12.3.3. The maximum and minimum force effects are then calculated for each point. The 

controlling effects are combined into strength, service limit states. Concrete design calculation are 

done for the given results (loads) and compared to the capacities (resistances) provided. 

Figure 3.12.6.1-1 Model of Culvert 


Version 9/13 3 -12 - 33 

Bridge Section


Design Manual 

3.12.6.2 Design Summary 

All structures are designed for traffic to be parallel to the span using a single lane loaded with a 

multiple presence factor of 1.2. per Article C12.11.2.1. No design adjustments are made for skew 

effect. 

Loads: 

Live loads for the top of slab consist of axle load of the design truck or design tandem without 

lane loads per Article 3.6.1.3. Where the live load and impact force effects in Article 3.6.1.2.6 

exceed the effects from Article 4.6.2.10, use the latter. KDOT will use only Article 3.6.1.2.6 for 

fill heights greater than 2 ft. For the design tandem, where wheels overlap the total load will be 

uniform over the area. Live load effects are neglected for single cell structures with fill greater 

than 8 ft. or multi-cell structures where the fill is greater than the out-to-out dimension of the barrels. 

(See Figure 3.12.3.1-1 Live Load Distribution) 

Coulomb earth pressure theory will be used for the barrel designs per the definition in Article 

3.11.5.3. The vertical earth load (EV) is based on Article 12.11.2.2.1 using embankment construction 

methods, assuming that compacted fill is placed along the sides of the barrel. Assuming 

compacted fill effectively limits the soil-structure interaction factor for embankment construction. 

Design Assumptions: 

For the design of the KDOT Standard RCB’s, it is assumed that the culvert is founded on a yielding 

foundation. 

• For design, span lengths shall be considered as center to center of supports for continuous and 

rigid joints. The location of the design negative bending moment shall be taken at the face of 

support, except where fillets are used in determining the structural stiffness of the member, in 

which case the design moment may be at the toe of the fillet as allowed by Article 12.11.4.2. 

• The Service I Limit State is used to evaluated cracking per Article 12.5.2. Strength is used to 

evaluate shear, moment and thrust capacities per Article 12.5.3. Extreme Event Loading 

where not considered in design per Article 12.6.1 and Article C12.5.3. 

• The design shear will be taken at a distance of d v away from the inside face for pinned boxes 

per Article 5.8.3.2 and d v away from the toe of the fillet for fixed boxes per Article 

C5.13.3.6.1-1. Shear capacity will be based on the shear capacity of the concrete per Article 

5.13.3.6.2 and the unused flexural reinforcement as capacity per ACI and dowel action Article 

5.10.11.4.4. See “Appendix D Doubly Reinforced and Shear Capactiy of Concrete” for 

additional information. 

• KDOT will apply distribution steel requirements found in Article 5.14.4.1, to the top slab 

with fill heights 2 ft. and less. 

• Rigid Frame Structures (RFB) are designed and detailed to resist bending moments thoughout 

the structure acting continously between all adjacent members. RCB’s will be considered 


Version 9/13 3 - 12 - 34 

Bridge Section


Design Manual 

a pinned frame acting as simple beams in the corners. For RCB’s intermediate supports at 

walls in multiple cell boxes are considered as knife edge supports. 

• Because the bottom slab is cast against foundation stabilization, none of the bottom of the 

bottom slab is neglected for computation of design depth. 

• Use shear 

= 0.85 and moment 

= 0.90 per Table 12.5.5-1 for buried structures. This 

assumes tension controlled regions. Flexure and axial force interaction and design capacities 

are evaluated as rectangular column sections as shown below. 

• For minimum reinforcement requirements as described in Article 5.7.3.3.2. the phi factor 

implied in the 1.2xM cr is 1.0. the gross concrete section is used as well as a singly reinforced 

cracked section for calculating As req’d . 

Figure 3.12.6.2-1 Strength Design 


Version 9/13 3 -12 - 35 

Bridge Section


Design Manual 

Design Assumptions - Continued 

• Crack Control provisions (Article 5.7.3.4) are checked only when the concrete stress on the 

gross section at the Service Limit State is greater than 80% of the Modulus of Rupture as 

described in Article 5.4.2.6. The RCB design program uses the worst case Class II exposure 

factor (0.75) for the top slab members when the fill is at 0 ft. For all other members the program 

uses Class I exposure factor (1.00). At the Service Limit State the stress in the tension 

reinforcement is calculated using a doubly reinforce section as decribed in Appendix D Doubly 

Reinforced and Shear Capactiy of Concrete or calculated using Article C.12.11.3 in members 

with high compressive forces. 

• Where earth pressure may reduce the effects caused by other loads, Article 3.11.7 allows a 

50% reduction in these force effects. This is reflected in Table 3.12.4.1-1 LRFD Load Factors. 

Special Design: 

• For culverts founded on rock, an evaluation of the RCB height, depth of fill, and depth of 

trench shall be made to determine if the Standard RCB is applicable for construction on a 

rock foundation. Use a minimum average modulus of subgrade reaction of 400 lbs/in 3 for 

culverts founded in rock. The designer may give considerations to using a three sided structure 

if the founding materials are not prone to scour actions. All boxes constructed without a 

floor (bottom slab) will be designed as Rigid Frames. 


Version 9/13 3 - 12 - 36 

Bridge Section


Design Manual 

3.12.6.3 Detailing 

Skewed or Rotated RCB: 

Skewed or rotated structures will be designed and detailed with reinforcing, placed normal to the 

centerline of the box. 

Reinforcing: 

Truss bars (crank shaft bars) for single cell Rigid Frames or for multiple cell RCB design will normally 

not be required and are not recommended. Spacing of the interior face of reinforcing may 

be independent of the exterior face for rigid frame boxes. However, for ease of placing, it is preferable 

that all reinforcing in a particular face (exterior or interior) shall be placed at the same 

spacing. For normal practice it is intended that the wall reinforcing will be placed vertical. Detailing 

practice will reflect that intention. Minimum spacing shall be 5 in. centers. Spacing increments 

will be in ½ in. intervals. The limits of bar shall be #4 through #11 sizes. 

New Boxes: 

• All clearances are 2 in. where permanently in contact with the earth and 1½ in. otherwise. 

Because KDOT concrete mixes are cement rich with a low W/C ratio, the cover on the nonearth 

contact face was reduced by ½ in. (per Article 5.12.3). The clearance for the bottom mat 

of reinforcement will be 2 in. Table 5.12.3-1 states that members cast against the earth will 

have 3 in. of clearance. However, because KDOT uses a granular foundation stabilization, it 

is not considered cast against the earth. This is considered a Class I exposure for crack control. 

• For the top of the top slab with a fill height of 0 ft., Class II exposure is used for crack control; 

otherwise Class I is used. 

• When the top slab will be exposed to frequent applications of deicing salts, epoxy coated 

reinforcing bars and air-entrained (AE) concrete should be specified in the top slab. Epoxy 

coated bars and (AE) concrete should not normally be specified for box sizes less than 6 ft. x 

6 ft. or when the roadway is not surfaced. The default for the RCB design program is to use 

epoxy reinforcement and (AE) concrete when the fill height equal to or less than 2 ft. 

Box Extensions: 

• All of the above criteria may also apply to box culvert extensions. Normally, epoxy coated 

reinforcing and (AE) concrete will not be used for extensions except in urban areas where the 

extension will be subject to deicing salts. 

• The depth of fill to specify for extensions shall be the fill depth at the end of the existing box 

culvert. 

• See road design standard drawing RD080 (Figure 3.12.9-3 Typical Culvert Extensions (Std 

RD080) for extension details. 


Version 9/13 3 -12 - 37 

Bridge Section


Design Manual 

Member Size: 

Thickness of concrete members shall be designed in increments of ½ in. The wall thickness shall 

preferably be not less than 2/3 the largest slab thickness. The minimum wall thickness shall not be 

less than 7 in. for spans 6 ft. and greater, and not less than 6 in. for spans less than 6 ft. Minimum 

slab thickness will be 6 in. The minimum fillet size shall be 4 in. x 4 in. 

3.12.6.4 Practical Considerations for Structure Type 

For purposes of structural discussion and design, an RCB will be referenced as a Rigid Frame or 

as a Pinned Frame. Ordinary design procedure will assume all exterior corners to be pinned or 

rigid, i.e., no mixing of pinned and rigid joints. (See Section 3.12.1.1 Definitions for additional 

definitions). 

As a general rule, pinned boxes (RCB’s) for culverts with spans 10 ft. or less are more economical 

than rigid frame boxes (RFB’s). However, for mainline structures on State routes do not use a 

pinned type (RCB) structure for fill heights less 5.0 ft. 

Framing costs per unit volume for fixed boxes less than 6.0 ft. are higher than average. It is 

suggested that concrete cost be increased 20% for cost comparisons. Basic concrete and 

reinforcing steel costs may be estimated at $359/cu.yd. and $0.71/lb. respectively. 


Version 9/13 3 - 12 - 38 

Bridge Section


Design Manual 

3.12.7 Wingwall Structural Considerations 

3.12.7.1 Assumptions 

• All flared wingwalls have cantilever retaining walls with freestanding detached stem walls. 

The footings are detailed as attached and continuous with the culvert floor. One way action 

(beam design) is used based on a 1’-0” strip taken at the maximum wall height. This configuration 

allows some settlement to occur at the wing ends without causing distress in the barrel 

of the culvert. 

• For lateral earth pressure the Rankine Earth Pressure Theory as defined in Article C 3.11.5.3 

is used with the coefficient of active earth equal to 0.33. This theory is consistent with a long 

heeled cantilever with free draining granular material. Granular backfill materials consistent 

with SB or SCA materials as specified on Figure 3.12.9.6-1 RCB Auxiliary Details (Std 

BR020b) are used. 

• Wingwalls for culverts with a rise over 16 ft. shall have a site evaluation of foundation and 

backfill conditions to determine if actual field conditions will approximate the assumptions 

of design. Where conditions are different, the KDOT Design Engineer shall be notified. 

• Because of continuity in the footing, between the wing wall and the barrel, stability is met 

when the resultant of the force reactions act within the middle one-half of the base for soils 

and the middle three-fourths when founded on rock. This check is made at the Service Limit 

State. Therefore, no Load Factors will be applied to earth pressures for stability analysis. The 

height of the wall used for the stability check is at 3/4th of the maximum wing wall height. 

• Unless otherwise determined by a soils analysis, the foundation will be over-excavated and 

backfilled with 6 inches of granular material (Foundation Stabilization) to aid in the sliding 

friction factor. The Sliding resistance for the wall footing is considered the sum of the soil 

plus the one-half of the shear resistance of the concrete footing. 

• LRFD Strength I and Service I Limit States will be used for Structural Design of Members. 

See Load Combinations of Tables) 3.4.1-1 and -2 for additional information. The following 

load factors where used: 

DC stability 0.90 

DC bearing 1.25 

EV stability 1.00 

EV bearing 1.35 

EH 1.50 

Class I Exposure 1.00 


Version 9/13 3 -12 - 39 

Bridge Section


Design Manual 

Assumptions Continued: 

• Clearance to reinforcing will be 2 in. from formed surfaces in contact with the earth and 

1 1/2 in. clear for surfaces that are not. For the bottom of the footings cast on foundation stabilization 

the clearance to the reinforcing steel will be 2 in., and the top reinforcing steel 

cover is 2 in. regardless of fill height. 

• Fatigue limit state need not be investigated according to Article 5.5.3. 

• Member sizes will preferably remain constant throughout the length of the wall. The minimum 

wingwall thickness will be 7 in. The front face will be reinforced for shrinkage and 

temperature for walls over 9 in. thick. The footing will be detailed monolithic with the bottom 

slab of the RCB. Reinforcement will extend continuously from the wall footing into the 

bottom slab. 

3.12.7.2 Earth Pressure 

Founding Material: 

All box culverts and wingwall are supported by 6” of Foundation Stabilization Foundation per 

Section 204 of KDOT Standard Specifications “Excavation and Backfill for Structures”. Verification 

of founding material below that shall be estimated from a KDOT Soils Report when available, 

from site knowledge, or from the “Soil Conservation Service - County Soil Survey” reports, 

which are on file in the KDOT Bridge Section or available from the SCS Office in Salina. As a 

general guideline, soils judged as high-plasticity clays, fat clays, expansive clays, or organic clays 

will be considered poor foundation for culverts and will not be used. Soils that are classified as 

CH, OH, OL, or MH fall within the description of poor soils. High water table levels are considered 

poor foundation conditions and require evaluation to determine if the standard wingwalls are 

adequate. 

Backfill Material: 

The Standard KDOT wingwall design is based on backfill material consistent with SB-1, SB-2, 

SCA-2, SCA-3 and SCA-5 per Bridge Standard BR020. This material is described in Section 

1107 of the KDOT Standard Specifications “Aggregates for Backfill”. This is a granular material 

that is free draining, and is consistent with the design assumptions used for cantilevered, freestanding 

wingwalls. 

Live Load Surcharge: 

A value of 2.0 ft. will be included in the design of all wingwalls in consideration of traffic loading 

and construction equipment loading when the distance from wingwall to the traveled roadway is 

less than half the height of the wall. 


Version 9/13 3 - 12 - 40 

Bridge Section


Design Manual 

Design Parameters: 

The following will be assumed for the Standard KDOT wingwall design: 

• All passive pressure in front of the toe and wall will be neglected. 

• Wingwalls are designed as vertical cantilever walls: (See Figure 3.12.7.2-1 Design Assumptions 

- Vertical Cantilever) 

• Wingwall Design Soil Parameters as follows: 

Lateral Pressure ........................................... Rankine Active Earth Pressure Theory 

Live Load Surcharge ...................... Use 2’-0” of overburden as equivalent force 

Granular Backfill Material.....................................................................Density 120 pcf 

Ultimate Bearing Pressure ...............................................................................6,000 psf 

Phi Factor for Bearing is ..........................................................................................0.45 

Phi Factor for Sliding is ..........................................................................................0.80 

Coefficient or Active Earth Pressure....................................................................... 0.33 

Internal Friction Angle............................................................................................ 30 

Stability..................Check that the resultant is within the middle 1/2 of the footing 

(using 3/4 of the maximum wall height) 

• A friction factor of 0.50 assumes that the foundation condition will be a granular material 

with a tan = 0.50. 


Version 9/13 3 -12 - 41 

Bridge Section


Design Manual 

Figure 3.12.7.2-1 Design Assumptions - Vertical Cantilever 


Version 9/13 3 - 12 - 42 

Bridge Section


Design Manual 

Figure 3.12.7.2-2 Typical Backfill and Toe Dimensions 


Version 9/13 3 -12 - 43 

Bridge Section


Design Manual 

3.12.8 Precast Members 

3.12.8.1 Box Culverts 

When specifying bridge sized cast-in-place reinforced concrete boxes on plans, allow the Contractor 

the option of using precast boxes when extenuating circumstances requires their use. In no 

case shall a precast option be granted if: 1) the structure is on highly erodible soils or poor foundation 

materials 2) the top of the structure will be the wearing surface 3) the structure will be 

located within an MSE wall. For non-bridge sized structures see Volumn I, Part C Section 10 of 

the Road Design Manual. 

Precast boxes shall meet the same load requirements as cast-in-place box culverts. The design 

shall be a rigid frame design to account for loads expected during construction and shipping. The 

precast sections shall meet the requirements ASTM C1577 except as noted in this section. The 

precast box design software “BOXCAR” has been updated and is now acceptable for use on 

KDOT projects. Versions of “BOXCAR” 1.95 or later are acceptable. 

Fill heights of less than 2 ft. require a distribution slab. A cast-in-place distribution slab shall be 6 

in. thick with #4 bars at 1.5 ft. transversely and #5 bars at 1 ft. along the barrel. Substitution of an 

equivalent welded wire fabric is acceptable. Precast distribution slabs with the same reinforcement 

may be used for fill heights over 1 ft. Center the joints over the barrel segments. Provide a 

minimum of 3 in. of granular material between the barrel and the precast distribution slab. 

In general, do not allow precast boxes for multiple-cell installations (greater than two cells wide) 

unless there is economic justification. 

A special cast-in-place end section shall be required to transition from precast sections to flared 

wingwalls. See Figure 3.12.8.1-1 Precast Box Culvert Details (Standard BR031) for additional 

details. Flared wingwalls are required to be cast-in-place. Straight wingwalls may be precast sections 

and may be placed without a cast-in-place transition. 

Clearances to reinforcing shall be a minimum of 1¼ in. from all faces, except when the depth of 

fill is less than 2 ft., in which case the clearance to reinforcing in the top of the slab shall be 2½ in. 

Epoxy-coated reinforcing shall be as noted in Section 3.12.6.3 Detailing. Welded wire fabric is an 

acceptable substitute. 

Longitudinal reinforcing for shrinkage and temperature requirements shall be a minimum of 0.06 

sq. in. per ft. 

Shop drawings will be required, detailing all phases of construction, including layout, joint 

details, lifting devices, casting methods, construction placement and details of cast-in-place segments 

or transitions that may be required. The weights of the precast sections and proposed transportation 

methods shall be noted on the shop drawings. Copies of over height and overload 

permits, when required, shall be submitted with the shop drawings. 


Version 9/13 3 - 12 - 44 

Bridge Section


Design Manual 

Review of some typical Precast Box Culverts Question and Answers 

1) Is a precast option prohibited by Plan Note? (CIP only) 

Precast allowed unless shown on the Plan Details 

2) Does the box design meet the minimum ASTM C 1577 requirement details? 

Yes, this is the LRFD equivalent to C 1433, use Table 2 for member sizes, members will be 

at a minimum 3/4 the thickness of the CIP equivalent RFB, but no smaller than 6”. 

3) Can the precast option be an arch culvert? 

Yes, see Section 3.12.8.2 Precast Arch Culverts for criteria. 

4) Was the box designed with BOXCAR software 1.95 or later? 

No, a structural review is needed. 

5) Do low fill boxes require a distribution slab? 

Yes, see Figure 3.12.8.1-1 Precast Box Culvert Details (Standard BR031) for additional 

criteria. (Note: Min. 3 in. granular material cushion between box/slab) 

6) Are multiple single cells allowed (or double cells required)? 

Yes, multi-cells are allowed, but ties between cells may be required – also the Contractors 

Engineer is required to develop plan details. 

7) Is a transition section to CIP end section with flared wings required? 

Yes, with a maximum transition of 4:1, the Contractors Engineer is required to develop 

plan details. (Straight wings may be precast without transition) 

8) Design criteria: 

• > 2 ft. Fill min. 1.25 in. clearance, uncoated rebar 

• < 2 ft. Fill min. 2.5 in. clearance, epoxy coated rebar required 

• Min. shrinkage & temperature requirement (0.06 in 2 /ft) 

• Slab & wall thicknesses will be > 75% of the CIP Standard. 

• See KDOT Std. Specs. 735 for additional information 

• Substitution of equivalent WWF: 

(If cross-sectional area is less than rebar, structural review is needed) 

9) Are Precast Box Culverts > 10 ft. reviewed by KDOT? 

Yes, All culverts are reviewed by KDOT. 

10) Are Precast Arch Culverts reviewed by KDOT? 

Yes, All culverts are reviewed by KDOT. 

11) What is the design criteria for the CIP end sections and wings? 

The minimum will be the equivalent CIP KDOT Standard and not the section provided 

in #2 above. The Contractors Engineer will detail transitions for differences in member 

thicknesses. 


Version 9/13 3 -12 - 45 

Bridge Section


Design Manual 

Figure 3.12.8.1-1 Precast Box Culvert Details 


Version 9/13 3 - 12 - 46 

Bridge Section


Design Manual 

3.12.8.2 Precast Arch Culverts 

Precast Arch Culverts may offer a cost-effective, convenient alternative that can be considered on 

certain projects. Bottomless culverts are well suited for areas where spread footings or pedestal 

walls can be keyed into non-erodible bedrock, the use of a natural channel may be advantageous 

to mitigate environmental concerns. The following design limitations, design responsibilities, site 

limitations and plan processing procedures are noted. Questions relative to the interpretation of 

these requirements should be directed to the State Bridge Office for clarification. 

* Note: Fully resolved forces will result in the accounting of the forces through 

connections and members resulting in minimal damage to the arch structure or 

headwall. Contact the Local Projects Team Leader for barrier loading requirements. 

** Use granular backfill meeting the requirements of SB-1,SB-2,SCA-2, 3 or 5. 

Design Criteria: 

Items Grade Separation Stream Crossing 

Maximum Span: 60’-0” 42’-0” 

Live Load: HL-93 HL-93 

Foundation: 

Span Bridge Criteria per 

Section 3.4.1 

1. The structure will be designed in accordance with the current AASHTO LRFD edition 

and latest interim requirements for structurally reinforced concrete structures. 

2. The design plans will include a Contour Map, Construction Layout and Geology Sheet 

with Geology Report. The Geology Report shall bear the seal of the Professional 

Geologist. The geology sheet will show the limits of the maximum potential scour 

line, include long-term degradation, contraction scour, local scour and lateral 

migration. 

3. Skews in excess of 45 will not be permitted. 

Span Bridge Criteria per 

Section 2.3.9 and 3.4.1 

Wings/Headwall: Precast (free-standing) CIP (free-standing) 

Free Board: N/A 2’-0” @ Overtop 

Minimum Fill: 2’-0” 2’-0” 

Backfill Material: 

Granular for Arch, and 

precast wings per manufacture 

requirements 

Granular for Arch ** 

BR020b materials for the 

CIP wings 

Barrier: *TL-4 fully resolved *TL-4 fully resolved 


Version 9/13 3 -12 - 47 

Bridge Section


Design Manual 

4. Rise measured from top of cast-in-place footing to the bottom of the bridge’s top slab 

shall, in excess of 16 ft. will not be permitted. 

5. A minimum cover of 2 ft., measured from the pavement surface at the roadway edge, 

will be provided. Provide distribution slab. See Figure 3.12.8.1-1 Precast Box Culvert 

Details (Standard BR031) for additional criteria. 

6. The bottom of the foundation footings shall be a minimum of 4 ft. below streambed 

thalweg elevation unless field conditions dictate otherwise. 

7. Streambed slab, cut-off wall or other suitable means is required unless streambed is 

non-erodible bedrock. 

Design Responsibilities: 

1. Foundation and bridge sizing consideration will follow all span structure requirements 

including design high water and free board clearances. Show the maximum potential 

scour on the geology sheet. 

2. For stream crossings, hydraulics and waterway opening requirements should be 

handled similar to other bridge projects with bridge hydraulics evaluated as 

appropriate for the spans involved. Stream Stability analysis shall be performed per 

Section 2.3.9. Include a completed Hydraulic Assessment Checklist (HAC) for each 

proposed site. The HAC can be downloaded at: http://kart.ksdot.org 

3. Foundation borings are required for all projects. The soils and foundations design 

including precast portions (i.e. slope stability, settlement, spread footings, piling, 

etc....) will be performed and sealed by a Licensed Professional Engineer. Suppliers of 

three-sided precast concrete bridges should be contacted for precast loads, reactions, 

etc. to be utilized in the foundation designs. 

4. The actual design and rating of the Precast Arch Culverts is the responsibility of the 

supplier. Shop plans for the Arch Culvert sections along with formal structural 

calculations will be submitted to the State Bridge Office for approval. Shop plans shall 

be certified by the supplier as being designed and load rated in accordance with 

current AASHTO LRFD Specifications. The supplier should also indicate additional 

backfilling requirements beyond those found in the KDOT Specifications. Show the 

limits of those backfilling requirements. 

5. Precast wings and headwall are not allowed for stream crossings. CIP end section 

requirements will follow BR031. See Figure 3.12.8.1-1 Precast Box Culvert Details 

for additional criteria. 


Version 9/13 3 - 12 - 48 

Bridge Section


Design Manual 

Plan Processing Procedures: 

1. Arch spans with be consistent with current procedures for all bridge projects. Field 

Check plans, geotechnical and geological investigations will be required for all 

projects utilizing Precast Arch Culverts. 

2. Final plans for the Arch Culverts should: 

a. identify the size (span x rise) of the bridge, 

b. identify the length of the bridge, 

c. indicate the skew angle of the bridge (in 1 degree increments), 

d. include the detailed design of all foundation units (whether cast-in-place or 

precast) and other cast-in-place or precast portions (such as headwalls, wingwalls, 

toe walls, etc....) and 

e. include the pay item, Arch Culvert (span x rise) (Precast), Lin. Ft. 

Details: 

The connection of the exterior to first interior arch segment as shown in Figure 3.12.8.2- 

1 Precast Arch Details helps distribute horizontal earth and vehicular impact loads 

imparted to the headwall. The joint seal system consists of butyl rope placed in the joint, 

with the adjacent areas of the joint primed. A water-proof rubber seal is then bonded 

over the joint per KDOT’s specifications. 


Version 9/13 3 -12 - 49 

Bridge Section


Design Manual 

Figure 3.12.8.2-1 Precast Arch Details 


Version 9/13 3 - 12 - 50 

Bridge Section


Design Manual 

Figure 3.12.8.2-2 Closure Pour 

Protection: 

For arch structures which are assembled from two separate halves and require a closure pour at 

the crown of the structure, it shall be detailed and constructed as shown in Figure 3.12.8.2-2 Closure 

Pour, a butyl rope will be placed in the beveled joint where the two arch halves meet and 

where the individual arch sections abut at the sides. A longitudinal section at the crown will be 

protected by coating the cured closure pour concrete with a primer recommend by the manufacturer 

and covered by an rubber adhered to the primer. The closure pour concrete shall be Gr. 4.0 

(AE) Air maintained placed and consolidated according to KDOT Specifications. 


Version 9/13 3 -12 - 51 

Bridge Section


Design Manual 

3.12.9 Miscellaneous 

3.12.9.1 Guardrail 

Unless there is a sidewalk on the bridge, it is desirable that bridge rails on ‘At Grade’ and ‘Low- 

Fill’ Boxes be limited to installations in excess of 50 ft. total span. Where guardrail is required, it 

preferably shall be continuous over culverts less than 50 ft. total span. For installations that 

require a bridge rail, a Corral rail will be used, unless determined otherwise at field check. The 

minimum length of boxes for guardrail installation will be as shown in Figure 3.12.9.1-1 Minimum 

Box Length With Guardrail. The designer will consider corral rail for fill heights up to 1’- 

0”. Corral rail should be use when warranted by traffic count, height of drop into the structure, or 

route classification. When guardrail is used, consult Road Design for guidance. 

3.12.9.1.1 Sidewalks, Fence, Slab Rest 

In certain conditions urban environments may require non-standard RCB details. Appendix E 

Miscellaneous Example Details has example details successfully used in the past. These details 

incorporated approach slabs and slab rests mounted to the structure, sidewalks, bridge railing and 

pedestrian fencing. Guardrail mounting details and criteria can be found at Figure 3.12.9.1-1 Minimum 

Box Length With Guardrail. 

3.12.9.2 Vehicle Grate 

At locations where a vehicular grate over the culvert opening may be needed, refer to FHWA publication 

“Safety Treatment of Roadside Cross-Drainage Structures” 

(FHWA/TX-82/37 + 280-1). 

3.12.9.3 Entrance Bevel 

A 45 bevel shall be provided on the soffit of the top slab at all upstream entrances to enhance the 

flow at high stages. The bevel shall be sized as shown below. (Reference: “HEC-13,” d = 

0.042H). 

Rise 

Bevel 

Less than 8.0 ft. 

4 inches 

8.0 ft. to 12.0 ft. 6 inches 

Greater than 12.0 ft. to 16.0 ft. 8 inches 

Greater than 16.0 ft. to 20.0 ft. 10 inches 


Version 9/13 3 - 12 - 52 

Bridge Section


Design Manual 

3.12.9.4 Hubguard 

The “hubguard” is a detail at the top slab at the end of the RCB to retain a minimum depth of fill 

to establish vegetation and prevent embankment erosion. In some instances, the hubguard retains 

the roadway surfacing and shoulder. The minimum height of the hubguard shall be 5 in. above the 

culvert. 

The hubguard height “h” and width “t” varies depending on the box span length. See sketch 

below. 

For spans < 16 ft.; h = 1.50 ft., t = 0.75 ft. 

For spans > 16 ft.; h = 1.67 ft., t = 1.25 ft. 

The exception to the above criteria is when the value (S + 5 in.) exceeds 1.5 ft. (for spans less than 

16 ft.) or 1.67 ft. (for spans greater than or equal to 16 ft.). In this case, “h” will equal (S + 5 in.) 

up to a maximum of 1.75 ft. (for spans less than 16 ft.) or 1.92 ft. (for spans greater than or equal 

to 16 ft.). This may occur on culverts under high fills. For “h” greater than 1.75 ft. (or 11.92 ft.), 

the standard wingwall details may need to be modified to accommodate the increased hubguard 

height. However, this should be an infrequent occurrence. 

3.12.9.5 Strike Line 

For ease of construction, points outside the strike line will be constructed level with the flow line 

elevation at the strike line. This would include the top of the footing for the wingwalls and for 

floor slabs of skewed boxes outside the strike line. 

3.12.9.6 Weep Holes 

Weep holes are constructed to reduce water pressure behind the wingwalls. Unless a Soils Report 

or other evidence indicates there is groundwater problems, weep holes are not required in the barrel. 

See Figure 3.12.7.2-2 Typical Backfill and Toe Dimensions and Figure 3.12.9.6-1 RCB Auxiliary 

Details (Std BR020b) for drainage details and weep holes. 

3.12.9.7 Seal Course 

The seal course is an unreinforced concrete placement to aid in dewatering a site. It will not be 

used unless required by the field Engineer or specified on the plans. 


Version 9/13 3 -12 - 53 

Bridge Section


Design Manual 

3.12.9.8 Scour Apron 

An “apron” or “floating apron” is a slab on grade reinforced with welded wire mesh. The apron 

will include an erosion toe (at the free end) in addition to the wall toe and trenched to the same 

depth. The apron will not be structurally tied to the wall. The purpose of the apron is to reduce 

erosion at the exit end of the culvert. It will be used only when specified on the plans or required 

by the Engineer. 

3.12.9.9 Soil Saver 

A soil saver is a wall constructed across the stream bed at the end of the wings of the upstream 

entrance to the culvert. It provides a vertical drop in the stream bed. The soil saver functions as a 

grade control structure to aid in controlling erosion in the upstream drainage basin. 

In addition, the soil saver acts as a “Drop Inlet”. It allows a culvert that would otherwise be constructed 

on a steep slope, operating under inlet control with high exit velocities (> 15 ft./sec.); to 

be constructed on a flatter slope, operating under outlet control with reduced velocities. 

Current environmental concerns will limit the use of soil savers as they are considered impediments 

to upstream migration of aquatic life. Check with KDOT’s Environmental Section prior to 

using soil savers. The details for soil savers can be found on Road Design Standard Drawing 

RD520. 


Version 9/13 3 - 12 - 54 

Bridge Section


Design Manual 

Figure 3.12.9.1-1 Minimum Box Length With Guardrail 


Version 9/13 3 -12 - 55 

Bridge Section


Design Manual 

Figure 3.12.9.6-1 RCB Auxiliary Details (Std BR020b) 


Version 9/13 3 - 12 - 56 

Bridge Section


Design Manual 

Figure 3.12.9-3 Typical Culvert Extensions (Std RD080) 


Version 9/13 3 -12 - 57 

Bridge Section


Design Manual 

Figure 3.12.9-4 Bridge Excavation (Std BR100) 


Version 9/13 3 - 12 - 58 

Bridge Section


Design Manual 

Figure 3.12.9-5 Alignment & Details for Guardrail Protection on Low Fill Culverts 

(Std RD617c) 


Version 9/13 3 -12 - 59 

Bridge Section


Design Manual 

Appendix A Kansas Automated RCB System 

The Kansas automated RCB system generates plans for site specific reinforced box culverts based 

on fill depth. 

For reinforced concrete boxes from 3 ft. spans up to and including 20 ft. spans (single, double and 

triple cells), the system generates quantities and completed detail sheets. 

Plan Sheets Required: 

1) One sheet is required for barrel details (including RCB extensions). 

2) One sheet is required for wingwall details. Two sheets are needed if a straight and 

flared wing are used on a single box. 

3) One “RCB Auxiliary Detail” sheet is required per set of RCB plans. 

Request Form: to://kart.ksdot.org/ 

Users external to KDOT can request box details by filling out a “RCB Details Request Form” (A 

blank copy is included following this section) and returning it to the appropriate KDOT Unit 

(Bureau of Design or Bureau of Local Projects). This form is now electronic and can be submitted 

online by placing the e-mail address of the contact person on the form. 

Quantity calculations and detail generation are completely automated for all boxes. This includes 

barrel and wing details. The system creates completed detail sheets in an Microstation graphics 

file and a computer report with pertinent data. 

Available Standards: 

The reinforced box culverts shown in the chart on the following page are available for use. 

These boxes are designed for fill heights ranging from 0 ft. through 50 ft. The following options 

are available: 

1) Pinned Boxes (RCB) or Rigid Frame Boxes (RFB). 

2) 0, 30, or 45 degree skews 

3) Flared wingwalls are available for all box heights. Straight wingwalls are available for 

box heights 10 ft. and less. (All wingwalls less than or equal to 23 ft. in length are 

attached to the exterior wall of box). On skewed boxes, if the long wing is detached 

from the wall of the box, the short wing is also detached even though it may be less 

than 23 ft. in length. 


Version 9/13 3 -12 - A - 1 

Bridge Section


Design Manual 

Chart showing available box sizes with maximum fill depths 


Version 9/13 3 - 12 - A - 2 

Bridge Section


Design Manual 

Chart showing available wing sizes and skews 


Version 9/13 3 -12 - A - 3 

Bridge Section


Design Manual 

Pinned vs. Fixed: (See Section 3.12.6.4 Practical Considerations for Structure Type) 

RCB Details Request Forms (4 pages) 

KDOT’s automated RCB request forms are available through the KDOT Authentication Resource 

Tracking (KART) http://kart.ksdot.org/ 


Version 9/13 3 - 12 - A - 4 

Bridge Section


Design Manual 

CLARIFICATION OF COMMON MISUNDERSTANDINGS 

FIGURES 

Figure 1 

Figure 2 


Version 9/13 3 -12 - A - 5 

Bridge Section


Design Manual 

Figure 3 

Figure 4 


Version 9/13 3 - 12 - A - 6 

Bridge Section


Design Manual 

Quantity calculations: 

1. Air entrained concrete quantities include the top slab, the hubguards and on skewed extensions, the top edge beam abutting the old 

hubguard (See Std. RD080 & RD510 SI). On rigid frame (fixed) boxes, the walls and fillets above the optional construction joint shown 

on the details are also air entrained concrete. Epoxy coated resteel includes all "S", "K" and "G" bars. 

2. Extensions: The software asks for the "Length of Existing Bottom Slab Beyond Outside Edge of Hubguard." This existing slab serves 

as part of the floor for the new extension. (See KDOT Standard Number RD080 & RD510 SI) Concrete corresponding to the volume 

(Normal width of box * Dimension A * Slab Thickness) of the existing slab is subtracted from the floor concrete quantities. This is the 

only adjustment to the box concrete quantities, even though the existing flared wings and footings would decrease the concrete needed. 

The program also adjusts (decreases) the number of F1, F2 and F3 bars and shortens the F4 bars. The length of the vertical wall bars (W1 

and W2) over the extension are not adjusted and may need to be shortened in the field. 

3. Hubguard concrete quantities are included in the box concrete. "G" bars are included in the box steel quantities. 

SPAN HUBGUARD WIDTH HUBGUARD HEIGHT 

< 16 feet (4.875 m) 9" (230 mm) 1'-6" (455 mm) - (slab thickness) 

> 16 feet (4.875 m) 1'-3" (380 mm) 1'-8" (510 mm) - (slab thickness) 

For all spans, hubguard height must be > 5" (125 mm). 

4. Box Length - On new boxes this dimension is used to calculate quantities. On extensions it is added to the details as information only. Box 

length is the total length of the box once construction is complete. 

Roadway - The Roadway is added to the details as information only. It is not used in any quantity calculations. The Roadway dimension is the 

total roadway once construction is complete. 

Extension Lengths - On extensions, this value is used to calculate quantities rather than the box length. 

Miscellaneous: 

1. Extensions - Match the existing box type (fixed or pinned). 

Submit your completed "KDOT STANDARD RCB/RFB DETAIL REQUEST FORM" to: 

(County and City Projects) 

Kansas Dept. of Transportation 

Bureau of Local Projects 

Attn: Ed Thorsel 

Dwight D. Eisenhower State Office Building 

700 SW Harrison Street 

Topeka, KS 66603-3754 

(State and Federal Projects) 

Kansas Dept. of Transportation 

Bureau of Design 

State Bridge Office 

Dwight D. Eisenhower State Office Building 

700 SW Harrison Street 

Topeka, KS 66603-3754 


Version 9/13 3 -12 - A - 7 

Bridge Section


Design Manual 

Sample Output: Automated Reinforced Concrete Box System (4 pages 

KKK KKKK DDDDDDDDD OOOOOOO TTTTTTTTTTT 

KKK KKKK DDDDDDDDDD OOOOOOOOO TTTTTTTTTTT 

KKK KKKK DDD DDD OOO OOO TTT 


KKKKKKK DDD DDD OOO OOO TTT 

KKKKK DDD DDD OOO OOO TTT 

KKKK DDD DDD OOO OOO TTT 

KKKKK DDD DDD OOO OOO TTT 

KKKKKKK DDD DDD OOO OOO TTT 


KKK KKKK DDDDDDDDDD OOOOOOOOO TTT 

KKK KKKK DDDDDDDDD OOOOOOO TTT 

AUTOMATED REINFORCED CONCRETE BOX SYSTEM 

SEE SPECIAL ASSIGNMENTS, BRIDGE DESIGN 

IF PROBLEMS ARE ENCOUNTERED 

Version 7.1.6 

1/10/12 Double 16 ft x 14 ft Fixed Box PAGE NO. 1 

Project Number:111-2 K-BNCH-04 

Final Data Input to RCB Software 

PROJECT NO. 111-2 K-BNCH-04 FALSEWORK INSPECTION REQ'D No 

BRIDGE NUMBER 22.22 FLOOR ELEV. BELOW FLOWLINE NO 

STATION 1+000 FLOOR ELEV. LT. 105.34 

COUNTY Anderson Co. FLOOR ELEV. RT. 104.22 

ROUTE 111 CROWN GRADE 130.22 

SERIAL NO. 99 FILL DEPTH 5 

CELLS 2 EPOXY & AIR Yes 

SKEW 45 LEFT WING Flared 

SKEW DIRECTION Left RIGHT WING Flared 

ROTATION 0 APRON Yes 

CELL SPAN 16 SOIL SAVER No 

CELL HEIGHT 14 DESIGN TYPE Fixed 

LENGTH LEFT 71.25 LEFT EXTENSION 0 

LENGTH RIGHT 76.25 RIGHT EXTENSION 0 

ROADWAY LEFT 70 DOWNSTREAM SIDE 2 

ROADWAY RIGHT 75 FLR. SLAB EXT. 0 

Design fill is adjusted to 5 ft. 


Version 9/13 3 - 12 - A - 8 

Bridge Section


Design Manual 



LIST OF BARS FOR BOX 

NEW BOX 

MARK SIZE SPACING NUMBER LENGTH 

in 

ft 

ft 

ft 

F1 5 6.0 226 34.167 

F2 6 6.0 572 8.916 

F3 7 6.0 226 12.000 

F4 4 0.0 160 37.917 

S1 6 6.0 226 34.167 

S2 6 6.0 570 8.416 

S3 7 6.0 226 14.500 

S4 4 0.0 80 37.917 

S5 4 0.0 72 37.917 

K1 6 6.00 256 18.250 

>>> K1 Bar INFO. INCREMENT 6.00 in SHORT 2.500 ft LONG 34.000 

K2 7 6.00 228 20.000 

>>> K2 Bar INFO. INCREMENT 6.00 in SHORT 6.000 ft LONG 34.000 

W1 5 12.0 298 15.417 

W2 6 12.0 296 15.417 

W3 4 0.0 204 37.917 

W4 5 12.0 296 15.417 

G1 8 0.0 4 48.333 

G2 10 0.0 4 48.333 

S2 HORIZONTAL LEG = 5.083 ft 

S2 VERTICAL LEG = 3.333 ft 

F2 VERTICAL LEG = 4.333 ft 

F2 HORIZONTAL LEG = 4.583 ft 

NUMBER OF F2 AND S2 BARS ON ONE END OF SKEWED BOX 

F2 BARS = 60 S2 BARS = 59 

CONCRETE MEMBER THICKNESSES 

SLAB 

= 10.500 in 

FLOOR = 11.000 in Note: Clearance 

EXTERIOR WALL = 10.000 in 

top slab = 2.0 in 

INTERIOR WALL = 10.000 in 

HUBGUARD + TOP SLAB = 1.667 ft 

TOP OF HUBGUARD TO TOP OF WINGS = 5.0 in 

LENGTH OF HUBGUARD 

= 48.790 ft 

LENGTH OF TRIANGULAR SECTION = 34.500 ft 


Version 9/13 3 -12 - A - 9 

Bridge Section


Design Manual 



FLARED WING COMPUTED BAR DATA 

MARK NUMBER LENGTH 

(ft) 

C2 1 48.500 

D2 31 6.750 

E2 4 41.500 

FLARED WING GEOMETRY VALUES 

'W' Apron Width = 38.558 ft 

'K' Tip to Tip = 98.827 ft 

FLARED WING COMPUTED BAR DATA 

MARK NUMBER LENGTH 

(ft) 

C2 1 48.500 

D2 31 6.750 

E2 4 41.500 

FLARED WING GEOMETRY VALUES 

'W' Apron Width = 38.558 ft 

'K' Tip to Tip = 98.827 ft 


Version 9/13 3 - 12 - A - 10 

Bridge Section


Design Manual 



RCB QUANTITIES SUMMARY 

GRADE 4.0 CONCRETE (TOTAL) (yd^3) 561.384 

BOX 362.849 

LEFT WING 85.760 

RIGHT WING 85.760 

APRON 27.015 

GRADE 4.0(AE) CONCRETE (TOTAL) (yd^3) 207.793 

( TOP SLAB OF BOX) 

FOUNDATION STABILIZATION (TOTAL) (yd^3) 164.661 

BOX 106.843 



APRON 24.735 

SOIL SAVER 0.000 

PLAIN REINFORCING STEEL (TOTAL) (lb) 20611.640 

BOX 0.000 


LEFT WING (WELDED WIRE FABRIC) 621.201 


RIGHT WING (WELDED WIRE FABRIC) 621.201 

APRON (WELDED WIRE FABRIC) 1505.723 

EPOXY COATED REINFORCING STL (TOTAL)(lb) 93920.020 

(BOX) 

GRANULAR BACKFILL (TOTAL) (yd^3) 758.000 



FILTER FACBRIC (TOTAL)(SUBSIDIARY)(yd^2) 656.000 



BR BCK PRT SYS (TOTAL)(SUBSIDIARY)(yd^2) 583.856 

BOX 583.856 

COST OF BOX (Conc, Reinf, Gran Back, and Fnd Stbl) 

COST OF CONCRETE = $ 

COST OF FND STBL = $ 

COST OF RESTEEL = $ 

COST OF GRAN BK = $ 

329.00 / yd^3 

41.51 / yd^3 

0.71 / lb 

46.00 / yd^3 

TOTAL COST = $ 376079.80 


Version 9/13 3 -12 - A - 11 

Bridge Section


Design Manual 

Typical RCB Details (2 sheets) 


Version 9/13 3 - 12 - A - 12 

Bridge Section


Design Manual 


Version 9/13 3 -12 - A - 13 

Bridge Section


Design Manual 

Appendix B Wingwall Moment & Reaction Coefficients 


Version 9/13 3 -12 - B - 1 

Bridge Section


Design Manual 

Volume III US (RLFD) 

Version 9/13 3 - 12 - B - 2 

Bridge Section


Design Manual 


Version 9/13 3 -12 - B - 3 

Bridge Section


Design Manual 

Appendix C LRFD RCB Mathcadd Loads 

1 Example of LRFD Loads for RCB Design 2/24 


LRFD Box Culvert Design Guidelines 

Copyright © 2007 Kansas Department of Transportation All rights reserved. 

Input 

RCB or RFB (use p for RCB and f for RFB) ....................................... Type "f" 

Cell Span measure for inside face of walls, (ft) .................................. Span 20ft 

Culvert Height measured from the top of floor to bottom of slab. (ft) ..... Height 8ft 

Fill Height from the top of pavement to top of slab,(ft) ......................... H 3ft 

Number of Cell in Structure ............................................................. Cell 2 

Unit weight of soil, (pcf) ..................................................................... γ soil 125 

lbf 

ft 3 

Coefficient of earth pressure................................................. k o 0.50 

Backfill Type (1.0 soil , 1.15 granular) ............................................ Fill 1.0 

Fillet Size ................................................................................... Fillet 16in 

Database 

box_type num_cel span height fill 

f 2 20 8 3 

f1_size f1_spabar f2_size f2_spabar f3_size 

6 5.5 6 6 8 

k o 

Return Box Geometry From Database 

Interior wall thickness,(in)............................................................... 

Exterior wall thickness, (in) ........................................................... 

Top slab thickness,(in) .................................................................. 

Wall int 

Wall ext 

Slab top 

8in 

9in 

12.5in 

Bottom slab thickness, (in) ............................................................ Slab bot 13.5in 


Version 9/13 3 -12 - C - 1 

Bridge Section


Design Manual 


3.11.5.5 Equivalent-Fluid Method of Estimating 

Rankine Lateral Earth Pressures 

The equivalent-fluid method may be used where Rankine earth pressure theory is 

applicable. The equivalent-fluid method shall only be used where 

the backfill is free-draining. If this criterion cannot be satisfied, the provisions of Articles 

3.11.3, 3.11.5.1 and 3.11.5.3 shall be used to determine horizontal earth 

pressure. 

If the backfill qualifies as free-draining (i.e., granular material with < 5 percent passing a 

No. 200 sieve), water is prevented from creating hydrostatic pressure. 

12.11.2.4 Distribution of Concentrated Loads in Skewed Box Culverts 

Wheel distribution specified in Article 12.11.2.3 need not be corrected for 

skew effects. 

The span length is not adjusted for skew, it is center-center of the walls perpendicular 

to the walls 

B c CellSpan 

Wall int ( Cell 1) 

2Wall ext z H Height Slab top Slab bot 

z' 

01 

ft 

z 

Dead Loads 

Loads 

self weight: 

The top slab weight is applied to the top of the box. The wall weight and the top slab weight 

are applied to the bottom slab in an upward uniform pressure. The bottom slab weight load is 

directly applied to the resisting soil. 

earth vertical 

The design fill is measured from the top of the top slab to the top of the pavement. A soil 

structure interaction factor is applied. Article 12.11.2.2.1 

F' e 1.0 0.20 

H Equation 12.11.2.2.1-2 

B c 

F e F' e if F' e 1.15 

1.15 otherwise 

F e shall not exceed 1.15 for installations with compacted fill along the sides of the 

box section, or 1.40 for installations with uncompacted fill along the sides of 

the box section. 


Version 9/13 3 - 12 - C - 2 

Bridge Section


Design Manual 


embankment construction: 

W e F e γ soil B c H 

Equation 12.11.2.2.1-1 

Loading per one foot strip 

W e 

EV ft 

EV 0.4 

kip 

B 

c 

ft 

earth horizontial: 

p EH ( z' ) k o γ soil z' 

ft 

Equation 3.11.5.1-1 

p EH ( H) 0.2 

kip 

ft 

p EH ( z) 0.8 

kip 

EH top p EH ( H) 

ft EH bot p EH () z 

Live Loads (Article 12.11.2.1) 

Article 3.6.1.3 Application of Design Vehicular Live Loads 

3.6.1.3.3 Design Loads for Decks, Deck Systems, and the Top Slabs of Box 

Culverts 

For top slabs of box culverts of all spans and for all other cases, including 

slab-type bridges where the span does not exceed 15.0 ft., only the axle 

loads of the design truck or design tandem. 

Article 3.6.1.2.6 Distribution for Wheels Through Earth Fill 

Live load shall be considered as specified in Article 3.6.1.3. Distribution of wheel loads 

and concentrated loads for culverts 

Multiple presence Factor Article 3.6.1.1.2, Distribution of wheel loads and concentrated 

loads for culverts with less than 2.0 ft.of fill shall be taken as specified in Article 

4.6.2.10. For traffic traveling parallel to the span, box culverts shall be designed for a 

single loaded lane with the single lane multiple presence factor applied to the load. 


Version 9/13 3 -12 - C - 3 

Bridge Section


Design Manual 


Article 4.6.2.10.2 Case 1: Traffic Travels Parallel to Span 

When traffic travels primarily parallel to the span, culverts shall be analyzed for a single loaded lane 

with the single lane multiple presence factor. 

Multiple Presence Factor..... (Article C12.11.2.1).................................... MPF 1.2 

The axle load shall be distributed to the top slab for determining moment, 

thrust, and shear as follows: 

Perpendicular to Span (width) 

E flow 

96 1.44 

Span 

 

 

ft in 

Equation 4.6.2.10.2-1 E flow 

E = equivalent distribution width perpendicular to span (in.) 

S = clear span (ft.) 

10.4 ft 

Distribution for Wheels Through Earth Fill (contact area factor) ................. LLDF 1.00 

Tire contact area (10 in x 20 in) parallel to span...................................... L t 10in 

Parallel to the Span (length): 

E span L t LLDFH 

Equation 4.6.2.10.2-2 E span 3.8ft 

E span = equivalent distribution length parallel to span / axle (in.) 

LT = length of tire contact area parallel to span, as specified in Article 3.6.1.2.5 (in.) 

LLDF = factor for distribution of live load with depth of fill, 1.15 or 1.00, as specified in Article 3.6.1.2.6 

H = depth of fill from top of culvert to top of pavement (in.) 

Loading patch E x E span 

Article 3.6.1.2.6 

32kip 

Truck MPF 

E 

E flow E ft 

Truck E 0.963 

kip 

span 

ft 

 

50kip 

Tandem MPF 

E 

E flow E ft 

Tandem E 1.505 

kip 

span 

ft 

In lieu of a more precise analysis, or the use of other acceptable approximate methods of 

load distribution permitted in Section 12, where the depth of fill is 2.0 ft. or greater, 

wheel loads may be considered to be uniformly distributed over a rectangular area with 

sides equal to the dimension of the tire contact area, as specified in Article 3.6.1.2.5, and 

increased by either 1.15 times the depth of the fill in select granular backfill, or the depth 

of the fill in all other cases. The provisions of Articles 3.6.1.1.2 and 3.6.1.3 shall apply. 

Where such areas from several wheels overlap, the total load shall be uniformly distributed 

over the area 


Version 9/13 3 - 12 - C - 4 

Bridge Section


Design Manual 


Distribution of Load to Top Slab 

Truck & Tandem 

Dist. of LL in the RCB width direction (flow) 

Dist W 20in 

LLDFH 

6ft 

Dist W 10.7 ft 

Dist. of LL in the RCB length direction (span) 

Truck Distr L_TR 10in 

LLDFH 

Distr L_TR 3.8 ft 

Tandem Distr L_T 10in 

4ft 

LLDFH 

Distr L_T 7.8 ft 

Loading patch Dist W x Dist L_TR or Dist L_T 

(Single HS 32 kip axle or 50 kip Double Tandem ) 

32kip 

Truck MPF 

fill 

 

Dist W Distr ft 

Truck fill 0.939 

kip 

 

L_TR 

ft 

50kip 

Tandem MPF 

fill 

 

Dist W Distr ft 

Tandem fill 0.718 

kip 

 

L_T 

ft 

For single-span culverts, the effects of live load may be neglected where the depth of fill is more 

than 8.0 ft. and exceeds the span length; for multiple span culverts, the effects may be neglected 

where the depth of fill exceeds the distance between faces of end walls. 


Version 9/13 3 -12 - C - 5 

Bridge Section


Design Manual 


Controlling Live Load Effect (s): 

LL truck 0 if H 8ft 

Cell = 1 

0 if H CellSpan 


 

 

 

1 

Truck E if H 2ft 

Truck fill if H 2ft 

LL truck 

0.939 

kip 

ft 

Distr truck E span if H 2ft 

Distr L_TR otherwise 

Distr truck 3.8 ft 

LL tandem 0 if H 8ft 

Cell = 1 

0 if H CellSpan 


 

 

Cell 1 

Tandem E if H 2ft 

Tandem fill if H 2ft 

LL tandem 

0.718 

kip 

ft 

Distr tandem E span if H 2ft 

Distr L_T otherwise 

Distr tandem 7.8 ft 

Fatigue uses only one truck / MPF and fixed axle of 30 ft. 

LL fat 

LL truck 

MPF 

LL fat 

0.8 

kip 

ft 

Note: RCB design does not require fatigue check 


Version 9/13 3 - 12 - C - 6 

Bridge Section


Design Manual 


12.11.2.3 Distribution of Concentrated Loads to 

Bottom Slab of Box Culvert 

The width of the top slab strip used for distribution of concentrated wheel loads, specified 

in Article 12.11.2, shall also be used for the determination of moments, shears, and thrusts 

in the side walls and the bottom slab. 

C12.11.2.3 

Restricting the live load distribution width for the bottom slab to the same width used for the 

top slab provides designs suitable for multiple loaded lanes, even though analysis is only 

completed for a single loaded lane (as discussed in Article C12.11.2.1). 

Impact Loading (Article 3.6.2.2) 

The live load dynamic allowance for culvert and shall be taken as: 

D E = the minimum depth of earth cover above the structure, (ft) 

IM = dynamic allowance, (%) > 0 % 

H 

All Limit States D E 

ft 

33 1.0 0.125D E 33 1.0 0.125D E 

IM 1 if 

1 1.0 Equation 3.6.2.2-1 

100 

100 

 

1.0 otherwise 

 

Fatigue Limit State 

IM 1.21 

IM fat 

15 1.0 0.125D E 15 1.0 0.125D E 

1 if 

100 

100 

1 1.0 Table 3.6.2.1-1 

1.0 otherwise 

 

 

IM fat 1.09 


Version 9/13 3 -12 - C - 7 

Bridge Section


Design Manual 


Live Load Surcharge (LS) Article 3.11.6.4 

A live load surcharge shall be applied where vehicular load is expected to act on the 

surface of the backfill within a distance equal to one-half the wall height behind the back 

face of the wall. If the surcharge is for a highway, the intensity of the load shall be 

consistent with the provisions of Article 3.6.1.2. 

Modified Boussinesq for Point 

H 1 ( 1.0ft ) if H 1.0ft H 1 3 ft 

H otherwise 

Note: This is taken at the max. location in plan using 

the Tandem = 25 kip. 

Total heigth of the Wall (ft)....... H LL H 1 Height 

H LL 11 ft 

H LL 12 

H LL 

x 1 1 y 1 1 

ft 

ft 

1 

Depth Below the Wheel (ft)....... Z ( x 1) 

ft 

x1 

12 

Distance(s) from Wall Face (ft)............ X ( y 1) ft 

1y 

Point Load (kip)....................... Q L 25kip 

Dimensionless Parameters...... 

n 

Z 

H 1 

m 

X 

H 1 

Modified Boussinesq Equation 

2 

0.28 n x 1 

F xy 

 

 

2 

0.16 n x1 

 

 

3 

1.77 m n 1y 

x 1 

if 

2 2 

m 1y 

2 n x1 

 

 

2 

m 0.4 1y 

3 otherwise 

 

 

Q L 

Δp LL F 

2 

H 

1 


Version 9/13 3 - 12 - C - 8 

Bridge Section


Design Manual 


The increase in pressure (in ksf) as a function of Depth for Point Load 

Z x 1 

0 

5 

Resultant of the Pressure Diagram (kip/ ft of wall) 

Δp LL.Res xy 

 

( 0ksf) if Z H x1 

1 

Δp LL xy 

otherwise 

10 

 

Δp LLx 5 

15 

0 1.510 4 

 

Equivalent Uniform Surcharge per foot of width on Exterior Wall 

Numerical Integration for the pressure on the wall ...... 

w LL1 y 

 

 

y 1 

Δp LL.Res ft ft 

12 

Height 

Res stack X ft 

 

w ft LL 

kip 

Maximum Effect from moving the Tadem .......... 

0.173 

kip 

max w LL 

ft 

Reduction Due to Earth Pressure (Article 3.11.7) 

For culverts and bridges and their components where earth pressure may reduce effects 

caused by other loads and forces, such reduction shall be limited to the extent earth 

pressure can be expected to be permanently present. In lieu of more precise information, 

a 50 percent reduction may be used, but need not be combined with the minimum load 

factor specified in Table 3.4.1-2. 


Version 9/13 3 -12 - C - 9 

Bridge Section


Design Manual 


Water Loads (Article 3.7) 

y 

01ft 

Height 

Designers need to consider load cases where the culvert is full of water as well as cases 

where the culvert is empty. A simple hydrostatic distribution is used for the water load: 

The vertical water force is assumed pass directly into the foundation material 

γ water 

62.4pcf 

p WA ( y) ( Height y) γ 

water ft 

p WA ( 0) 0.499 

kip 

ft 

WA p WA ( 0) 

p WA ( Height) 0.000 

kip 

ft 

Design Considerations 

Load Modifiers Ductility........................... 1.00 

Redundancy .................. 1.05 

Importance .................... 1.00 

η I 1.00 

η D 1.00 

η R 1.05 

12.5.4 Load Modifiers and Load Factors 

Load modifiers shall be applied to buried structures and tunnel liners as specified 

in Article 1.3, except that the load modifiers for construction loads should be 

taken as 1.0. For strength limit states, buried structures shall be considered 

non redundant under earth fill and redundant under live load and dynamic 

load allowance loads. Operational importance shall be determined on the basis 

of continued function and/or safety of the roadway. 

Load modifier for EV is 1.05 and 1.00 for LL + IM 

Wall Thickness 

Interior wall thickness,(in)............................................................... 

Exterior wall thickness, (in) ........................................................... 

Top slab thickness,(in) .................................................................. 

Wall int 

Wall ext 

Slab top 

8in 

9in 

12.5in 

Bottom slab thickness, (in) ............................................................ Slab bot 13.5in 


Version 9/13 3 - 12 - C - 10 

Bridge Section


Design Manual 


Earth Loads 

Loading Summary: 

_____________________________________________________________ 

Vertical ...............(entire top slab)................................ 

EV 

0.380 

kip 

ft 

Horizontal Pressure .................................... top .......... 

Horizontal Pressure ....................................bottom ....... 

EH top 

EH bot 

_____________________________________________________________ 

Live Loads 

Controlling Uniform Distributed LL ................................ 

LL truck 

LL tandem 

0.188 

kip 

ft 

0.823 

kip 

ft 

0.939 

kip 

ft 

0.718 

kip 

ft 

Length of Uniform Distributed LL in the Span Direction .... 

Horizontal surcharge ...( uniform on Ext. Walls).............. 

Distr truck 3.8 ft 

Distr tandem 7.8 ft 

0.173 

kip 

max w LL 

ft 

Fatigue Loads ___________________________________________________________ 

Uniform Distributed Fatigue Load ................................ 

LL fat 

0.783 

kip 

ft 

Impact 

________________________________________________________________ 

Dynamic Allowance for Truck and Tandem............................. IM 1.21 

Dynamic Allowance for Fatigue............................................ IM fat 1.09 

Water 

________________________________________________________________ 

Hydrostatic Water Pressure at the Bottom of the Ext. Walls ... 

WA 

0.499 

kip 

ft 

Note: Based on using a one foot strip for design. 


Version 9/13 3 -12 - C - 11 

Bridge Section


Design Manual 

Appendix D Doubly Reinforced and Shear Capactiy of Concrete 

Investigate Shear Capacity of Concrete Slab Under Earth Fill January 6, 2012 

Purpose: Hypothesize that shear capacity of concrete slabs under earth fill is greater than current 

AASHTO specifications allow. 

Doubly Reinforced Concrete Section With Moment and Axial Loads Less than Ultimate Strength 

F = 0 x 

M = 0 O 

Figure 1 

1 

N u A s f s = A' s f' s 

 

2 b k d A' 

s 

 

 

 

 

 

 

h 

N u d 

e = A' s f' s ( d d' ) 

2 

f c 

1 

2 b k d A' 

 

s 

f c 

d 

 

 

 

k d 3 

Where: 

N u ..................................... Applied Axial Force 

M u ..................................... Applied Moment 

kd...................................... Depth to the Neutral Axis 

f c = E c ε c 

f s = E s ε s 

f' s = 2 E s ε' s Due to creep and nonlinearity use 2n for compression steel 

Input: 

ϕ v 0.85 f y 60ksi f’ c 4ksi V p 0kip b v 12in h 11in 

ϕ c 0.8 E s 29000ksi 

V s 0kip 

d v 7.92in 

ϕ f 0.9 

V c 14.57kip 

d e 8.5in 

M u 28.375kip ft V u 29.37kip N u 4.17kip 

h 

d'' d e 

d'' 3 in 

2 

A s 1.58in 2 

A' s 1.896in 2 

A s 

p 

b v d e 

d' e 2.0in 

p' 

A' s 

b v d e 

M u 

e d'' e 84.655 in 

N u 

e 

9.959 E c 33 145 1.5 

d e 

f’ c 

psi 

psi 

E s 

n n 7.958 

E c 


Version 9/13 3 -12 - D- 1 

Bridge Section


Design Manual 

Guess: 

1 

j 0.84502 i 

d e 

1 j 

e 

m n p i ( 2n 1) p' 

The following was derived from Figure 1 for a cracked, doubly-reinforced concrete section using 

The equations from ACI Publication SP-3 "Reinforced Concrete Design Handbook - Working 

Stress Method" Third Edition, 1965: 

i 1.093 

m 0.412 

d' e 

q n p i ( 2n 1) p' 

q 0.2 

d e 

k m 2 2q m 

k 0.34275 

1 ( 2n 1) A' s d' e d' e 

 

1 

 

6 k b v d e k d e k d e 

z z 0.452 

1 ( 2n 1) A' s d' e 

 

1 

 

2 k b 

v d e k d e 

c k d e 

c 2.913 in 

j ( 1 z k) 

j 0.84502 

Once j = guessed value, continue... 

Calculate the Stresses: 

N u e 

f s 

f s 

f s 28.467 ksi 

ε s 

j A s i d e 

E s 

ε s 0.00098162 

f s k 

f c 

 

n 1 k 

f c 

f c 1.865 ksi 

ε c 

E c 

ε c 0.0005119 

d' e 

k 

d 

e 

f' s 2 f s f' s 

1 k 

f' s 9.308 ksi 

ε' s ε' s 0.00255427 

E c 

Sum of the Forces: 

N u 4.17 kip 

1 

2 f c b v k d e f' s A' s f s A s 5.279 kip 

M u 28.375 kip ft 

1 

2 f h k d e 

c b v k d e f' s A' h 

s d' 

h 

e f s A s d e 

28.698 kip ft 

2 3 

2 2 

Close enough. So OK. 


Version 9/13 3 - 12 - D - 2 

Bridge Section


Design Manual 

Now that the stresses and strains are calculated, try to justify higher shear capacity for this section. The section defined 

above fails for the applied shear load. For Article 5.8.3.4.2 let us try using the actual calculated strain to solve for shear. 

Article 5.8.3.4.2 

4.8 

51 

β 

β 2.765 

1 750 ε s s xe 

39 

 

in 

a g 0.75 s xe max 

12inmind e d' e d v 

 

s xe 12 in 

 

1.38 

 

a g 0.63 

f’ c 

V .c 0.0316 β ksi b v d v V .c 16.606 kip 

ϕ v V .c 14.11 kip 

ksi 

θ 29deg 3500deg ε s 

θ 32.436 deg 

V u 29.37 kip 

V r < V u 

Still No Good. 

This helps some, but Vs still = 0 and Vr is not greater than Vu. Let us see how much shear capacity is left in the existing 

reinforcing in dowel action. Article 5.10.11.4.4 allows for dowl action in a compression memember. 

Article 5.10.11.4.4 

Use leftover As for Dowel Action. Concrete shear, Vc = 0 but is replaced by the 0.75*Nu term in this calculation. 

Notice, we used a 0.6 factor on the available area for shear that is missing in AASHTO and ACI. 

f y f' s f y f s 

A s_comp_leftover A' s 

f 

A s_tension_leftover A s 

y 

f 

y 

A s_comp_leftover 1.602 in 2 

A s_tension_leftover 0.83 in 2 

A vf A s_tension_leftover A s_comp_leftover 

V n 0.6 A vf f y 0.75 N u V n 90.688 kip V r ϕ v V n 

V r 77.08 kip 

V u 29.37 kip 

V r > V u 

This helps as well, but since we don't strictly fall into the category of Article 5.10.11.4.4 for an RCB, the following approach 

will be followed: 

 

V .s 0.6 A s_tension_leftover A s_comp_leftover f y 

V c 14.57 kip (Concrete shear from unrefined method) 

 

 

 

V .r ϕ v V .s V c 

V .r 86.81 kip 

V u 29.37 kip 

V r > V u 

Conclusion: 

Using a more refined tension strain with the above relationship may yield higher values for calculating shear 

capacity. AASHTO 5.10.11.4.4 allows for dowel action in a compression member at an extreme event limit 

state. For concrete slabs under earth fill, using the left over tension and compression A s can enhance the 

shear capacity in the section. The conclusion is that KDOT will design our slabs for maximum moment and 

check the ultimate shear capacity of the section based on the left over A s using the above method. 


Version 9/13 3 -12 - D- 3 

Bridge Section


Design Manual 

Appendix E Miscellaneous Example Details 

Traffic directly on top of bridge approach slab rest. Sidewalk/Barrier/Fence Details 


Version 9/13 3-12 -E - 1 

Bridge Section


Design Manual 


Version 9/13 3-12 - E - 2 

Bridge Section


Design Manual 


Version 9/13 3-12 -E - 3 

Bridge Section


Design Manual 


Version 9/13 3-12 - E - 4 

Bridge Section


Design Manual 


Version 9/13 3-12 -E - 5 

Bridge Section


Design Manual 


Version 9/13 3-12 - E - 6 

Bridge Section


Design Manual 


Version 9/13 3-12 -E - 7 

Bridge Section


Design Manual 

REFERENCES 

AASHTO, (2007). LRFD Bridge Design Specification, 4 th ed. American Association of State 

Highway and Transportation Officials, Washington, DC. LRFDUS-4 

AASHTO, (2010). LRFD Bridge Construction Specification, 3 th ed. American Association of 

State Highway and Transportation Officials, Washington, DC. LRFDCONS-3 

AASHTO, (2011). The Manual for Bridge Evaluation, Second Edition, Washington, DC. 

ASTM Specifications, A615. Standard Specification for Deformed and Plain Carbon-Steel Bars 

for Concrete Reinforcement. 

ASTM Specifications, C1433. Standard Specification for Precast Reinforced Concrete 

Monolithic Box Sections for Culverts, Storm Drains, and Sewers. 

ASTM Specifications, C1577. Standard Specification for Precast Reinforced Concrete 

Monolithic Box Sections for Culverts, Storm Drains, and Sewers Designed According to 

AASHTO LRFD. 

FHWA, Safety Treatment of Roadside Cross-Drainage Structures, FHWA/TX-83/37+280-1) 

KDOT , (2007). Standard Specifications for State Road and Bridge Construction, 

SS204, Excavation and Backfill for Structures 

SS735, Precast Reinforced Concrete Box 

SS1107, Aggregates for Aggregate Base Construction Aggregate for Backfill. 


Version 9/13 3-12 - Ref 1 

Bridge Section


Design Manual 

Terzoghi, Peck.(1664). Soils Mechanics in Engineering Practice 

Transportation Research Board Paper No. TRB 00307759. Live Load Distribution on Concrete 

Box Culverts. 

TRR #1191. BOXCAR, (versions later than 1.95) 

Unified Soil Classification System in the Engineering Index properties table and the detailed 

soil maps of the soil Conservation Services County Soil Survey. Vol. 1-105. 


Version 9/13 3 - 12 - Ref 2 

Bridge Section

3.12 Buried Structures - Kansas Department of Transportation

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?