California Precast Bridge Design In the Past - Precast / Prestressed ...

California Department of Transportation 

Caltrans Precast Bridge Design 

Overview 

Jim Ma, P.E. 

October 15, 2008 

15 th Annual CALTRANS/PCMAC Bridge Seminar 

Sacramento, California

California Department of Transportation 

Presentation Outlines 

1. California Precast Bridge Design 

Past 

Present 

Future 

2. Precast Bridge Design Issues 

Precast Girder Connection Design and Details 

Precast Girder End Stress Control and Girder Camber 

Design 

New LRFD I-Girder XS Sheet 

Precast Girder Design Software

California Precast Bridge Design In the Past 

Precast Bridge Types and Shapes 

Most Common Precast Bridges 

Before Year of 1998 

– Short Span Bridges 

– Widening Bridges 

– Bridges in Remote Area 

Most Common Used Shapes 

– California I-Girders 

– California Voided Slabs 

– Precast Box Beams 

– Delta Girders 

– Rectangular Girders 

– Double T Girders

California Precast-Pretensioned Girders 

Normal Shapes and Span Length Summary 

(Before Year of 1998) 

Girder Type Possible Span Length Preferred Span Length 

California I-Girder 50’ to 125’ 50’ to 95’ 

California Voided Slab 20’ to 70’ 20’ to 50’ 

Precast Box Beam 40’ to 120’ 40’ to 100’ 

Delta Girder 90’ to 120’ 90’ to 100’ 

Double T Girder 30’ to 90’ 30’ to 60’ 

Rectangular Girder 30’ to 100’ 30’ to 100’

California Precast Bridge Design In the Past 

Precast Advantages: 

Rapid construction 

Minimize falsework 

Reduce traffic disruptions 

on-site 

Improve safety for traffic and 

construction workers 

Minimize environmental 

impact 

Increase product quality 

Precast Challenges: 

Longer Span 

Seismic Design 

Construction Cost

California Precast Bridge Design In the Past

California Long Span Girder Section 

• California Bulb-Tee Girder: 

Used to Achieve Longer Span Lengths 

and Spliced Girders with 8” Web Width 

Simple Pre-tensioned D/S = 0.050 

Multi-Span Cont. for LL D/S = 0.045 

Spliced Multi-Span w/P-T 

Debonded Strands preferred 

D/S = 0.040 

145’ Girder was transported 

Span Lengths up to 200+ feet 

When Segments are spliced 

Together with Post-Tensioning

California Long Span Girder Section 

• California Bath-Tub Girder: 

Precast Alternative to Typical 

California CIP Box-Girder Shape 

Same D/S Ratio as Bulb-Tee 

Limitations Include Fabrication 

Complexity, High Cost, Hauling 

Weight.

California Precast-Pretensioned Girders 

Normal Shapes and Span Length Summary 

Girder Type Possible Span Length Preferred Span Length 

California I-Girder 50’ to 125’ 50’ to 95’ 

California Bulb-Tee Girder 80’ to 150’ 95’ to 150’ 

California Bath-Tub Girder 80’ to 150’ 80’ to 100’ 

California Voided Slab 20’ to 70’ 20’ to 50’ 

Precast Box Beam 40’ to 120’ 40’ to 100’ 

Delta Girder 90’ to 120’ 90’ to 100’ 

Double T Girder 30’ to 90’ 30’ to 60’ 

Rectangular Girder 30’ to 100’ 30’ to 100’

California Precast Bridge Design In Last Ten Years 

To Compete CIP PS Box Girder Bridges, Post-Tensioned Spliced 

Precast Girder Bridges have been introduced to achieve 

competitive longer spans in California. 

PC Girder: 30’-150’ 

PT PC Spliced: 100’-350’ 

PC Segmental: 250’-450’

Two Methods for Post-Tensioning Spliced Girders 

Method 1: Splicing Girders Supported on Limited Falsework

Two Methods for Post-Tensioning Spliced Girders 

Method 2: Splicing Girders on the Ground (Without Falsework)

Spliced Precast Girder Fabrication

Spliced Precast Girder Construction Sequence 

Two Span Spliced Girder Construction Sequence


Two Span Spliced Girder Construction Sequence


Three Span Spliced Girder Construction Sequence

Spliced Precast Girder Construction Sequence



Multi-Span Spliced Girder Construction Sequence

Strong-Back Construction


(Bread and Butter Type) 

1a. Construct abutments, bent footings, and columns 

1b. Fabricate PC/PS girders off-site at same time 

2. Erect temporary supports 

3. Place PC/PS girders on temporary supports


4. Construct CIP end diaphragms, bent cap, and intermediate diaphragms. 

5. Allow CIP portions to reach min concrete strength 

6. Place deck concrete 

7. Post-tension superstructure 

8. Remove temp supports, and complete construction









Spliced Precast Girder Construction Summary 

Advantages of this type: 

Very limited falsework 

Maximize vertical clearance 

Continuous superstructure with no joints 

Integral system between superstructure, bent 

cap and columns 

Seismic resistance connection 

Could be pinned at column bottom 

Smaller footing size, reduce cost 

Aesthetically pleasant

Curved Precast Spliced Girder Bridge Possible



Precast Spliced Girder Bridge Construction

Precast Spliced Girder Bridge Construction

Precast Spliced Girder Design Software Available 

CONSPLICE

Precast Spliced Girder Bridge Summary 

Precast Spliced Girder Bridge Summary 

Benefits of Using Spliced Precast Girder 

Longer span lengths to reduce the number of piers, Avoid 

obstacles on the ground, Improve safety, Reduce 

environmental impact. 

Rapid construction, Reduce congestion, traffic delays, and 

the total project cost. 

Eliminating superstructure joints to improve structural 

performance (including seismic performance), Reduce 

long-term maintenance cost, Increase service life. 

Minimizing bridge superstructure depth to obtain required 

vertical clearance for traffic or railway. 

Minimizing falsework to improve the flow of traffic and 

Improve safety for traffic and construction workers. 

Increase girder spacing, reduce girder lines and bridge cost

Benefits of Spliced Precast Girders 

Typical Cast-in-Place Falsework

California Precast Bridge Design In the Future 

Accelerated Bridge Construction using Precast Products 

Reduce on-site construction time and reduce traffic impact 

Off-site bridge elements fabrication 

Fast track process 

Improve work zone safety


High Performance Concrete 

Longer bridge spans 

Shallower girder section 

Increase girder spacing and reduce numbers 

of girders 

Increase structure durability and has longer 

bridge life


Self-Consolidated Concrete (SCC) 

Better workability in narrow area 

No vibration needed 

Faster construction 

Less noise and better working environment


New Efficient Precast Girder Shape (CA Super Girder) 

Longer span length over 180’ possible 

More competitive to CIP PS box girder 

Reduce construction cost 

Give engineers more options


Lightweight Concrete 

Lower superstructure weight 

Possible smaller substructure 

Reduced girder transportation and handling 

cost 

Less seismic loads


Welded Wire Reinforcement in Precast Girder Application 

High production rates and could reduce 40-50% labor cost 

Increase accuracy by using automatic machines 

High quality material & easier inspection 

Could be large rebars such as #6, #7, #8

Precast Bridge Design Issues 


Precast Girder End Stress Control and Girder Camber 

Design 

New LRFD I-Girder XS Sheet 

Precast Girder Design Software

Precast Girder Connection Design and Details

Precast Girder Connection Design and Details


Several Typical Precast Girder/Bent Cap Connections: 

Drop Bent Cap Connection 

Inverted-T Cap Connection 

Integral Bent Cap Connection 

Integral Drop Bent Cap Connection


Drop Bent Cap Connection 

Continuous superstructure 

Pinned between superstructure 

and cap 

Column/footing connection has 

to be fixed 

Extend PC girder bottom 

strands


Inverted-T Bent Cap Connection 

Semi-continuous superstructure 

Considered as pinned between 

superstructure and cap 

Column/footing connection has to 

be fixed


Integral Bent Cap Connection 


Fixed between 

superstructure and cap 

Column/footing connection 

could be pinned 

Good seismic connection


Integral Drop Bent Cap Connection 


Fixed between superstructure and 

cap 

Column/footing connection could 

be pinned 

Good seismic connection

Precast Girder End Stress Control and Girder Camber Design 

Draping or Harping Strands 

• Reduce eccentricity at ends 

• Raise center group of 

strands until stress limits are 

satisfied


Debonding or Shielding Strands 

• Reduce prestress force at ends by 

preventing bond of selected 

strands with concrete 

• Increase number of debonded 

strands until stress limits are 

satisfied


Debonded Strands Location and Design Requirements 

LRFD 5.11.4.2 with CA Amendment requires: 

• Number of strands debonded ≤ 33% of total strands 

• Number of strands debonded in any row ≤ 50% of total 

strands in that row 

• Exterior strands in each row must be fully bonded 

• All limit states must be satisfied


Debonded Strands Location and Design Requirements 

Adding Top Strands 

• Debond top strands in center portion 

of the girder and bond strand about 

10’-15’ at end of girder 

• Reduce moment at ends by adding 

strands at the top of the girder 

• Must provide access hole for cutting 

strands after diaphragm are cast and 

cured, but before the deck slab is 

placed


Adding Mild Reinforcement 

• If tensile stress > . 0948 f ′ , but not more than 0. 

ci 

Add mild reinforcement to resist the tensile force 

0 24 f ′ ci


Increasing Compressive Strength of 

Concrete at Release f ′ ci 

• Increase f ′ ci until stress limits are 

satisfied 

• Use reasonable value for f ′ ci that can be 

achieved economically by local producers 

• Maintain reasonable balance between ′ ci 

f and f ′ 

c


Determination of Build-Up or Haunch 

Current MTD 11-8 States: 

• At support: min. 2” haunch 

• At midspan: min. 0” haunch 

Uncertainty to determine camber 

• Concrete strength (Ec) 

• Concrete weight 

• Girder length or support length 

• Creep and shrinkage 

• Numbers of days for deck 

placement 

Suggest: min. 2” haunch at midspan

Precast Girder Special Provision 

Design Engineer is responsible to review and verify 

manufacture precast shop drawings 

The Contractor is responsible for deflection calculations 

and adjustments for deck concrete placement such as 

meeting the min. vertical clearance, maintaining deck 

profile grade and cross slope etc. 

Temporary lateral bracing shall be designed and 

constructed 

Temporary falsework shall be designed and constructed 

if used and should be approved by the Engineer 

The Contractor shall submit girder lifting plan including 

procedure and sequencing for hauling, unloading, lifting, 

and erecting girders

New LRFD Precast I-Girder XS Sheet 

Revised New LRFD Drawing Details

New LRFD Precast I-Girder XS Sheet 

Revised New LRFD Drawing Details 

Prestressing table provides 

calculated P-jacking force. Precaster 

manufacture can determine the 

numbers of strands for the shop 

drawing and fabrication. 

No more standard shear stirrups 

provided. 

Added end block is optional. 

Added 0.6” strand min. clearance 

based on AASHTO LRFD.

LRFD Precast Girder Software Update 

PSBeam V3 

Precast Prestressed Concrete Bridge Girder 

Design per AASHTO and Caltrans


CONSPAN 

Precast Prestressed Concrete Bridge Girder 

Design per AASHTO and Caltrans


CONSPLICE 

Specifically Developed for Post-Tensioned Post Tensioned Splice 

Precast Girder Design and Analysis

Thank You !

California Precast Bridge Design In the Past - Precast / Prestressed ...

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