Texas DOT Experience with Prefabricated Bridge ... - MCEER

Texas DOT Experience with
Prefabricated Bridge
Construction
Lloyd M. Wolf, P.E.
TxDOT Bridge Division
September 2005

Logistics of
CIP Construction

Benefits of Prefabricated
Construction
TIME
COST
QUALITY
SAFETY

Replication
of Form

Redfish Bay Precast Caps
Nueces County
SH 361
(1994)

Grout Pocket

Pierce Elevated Freeway
Bridge Replacement
IH 45
Downtown Houston, TX
(1997)

“Bolted”
Connection

Pierce Elevated
• Precast deck panels
• Precast concrete
beams
•Prefabricated steel
bents
• Precast bent caps

Development of a Precast
Bent Cap System
TxDOT Research Project 1748
The University of Texas at Austin
Center for Transportation Research

Sponsored Research
•Various connection
types
•System performance
•Design guidelines in
code-like format
•Sample details
•Grout performance
specification
•Construction issues

Design Philosophy
• Limit States
–Strength
–Serviceability
–Fatigue and Fracture
–Extreme Event
• Ductility
•Redundancy
• Structural Integrity

Grout Pockets
• Technique
– precast voids/pockets in cap to contain
column connectors
• Advantages
– flexibility in size and shape
– large construction tolerances
– simple grouting operation
• Disadvantages
– cracking potential at large top surface
– congestion of reinforcement
– larger volume of grout

Grouted Vertical Ducts
• Technique
– steel corrugated ducts embedded in cap to
house column connectors
• Advantages
– inexpensive stay-in-place ducts
– minimal reinforcement congestion
– limited exposed top surface
– minimal volume of grout
• Disadvantages
– more difficult grout placement

Bolted Connection
• Technique
– ducts embedded in cap house threaded rods
tensioned at the top surface
• Advantages
– cap setting via leveling plates/nuts
– post-tensioning option
– resistance to larger moments
• Disadvantages
– more difficult grouting operations
– protecting/recessing top anchorage

Analysis Guidelines
• Structural Analysis
– simplified approach: actions based on worst case of
pinned vs. fixed connection at top of column/pile
– general approach: estimate connection stiffness
– load factor actions at connection increased by 30%
• Strength
– P-M analysis of connector cross-section
– shear friction, V n = cA g + µ [A v f y + P c ]
– joint shear, V n = 12 b j h

Serviceability Guidelines
• bedding layer opening (location of neutral axis)
• if connectors experience tension
– control of crack width via Gergley-Lutz equation (validity?)
– durability enhancement
• connector coatings
• embedment of column or pile into cap
• limit pocket/duct height below top of cap
• external sealants
• drip beads
• waterstops
– bent deflections

Select Trial Bent Configuration
Analyze & Design Bent,
Bent Cap, & Columns
Determine Connection Actions
Select Trial Connector Configuration
Analyze Connector Configuration
Determine Connector Type & Embedment
Select Confining & Auxiliary Reinforcement

Connection Details
• min. connector area of 0.7% for columns and 1.0% for piles
• #7 - #11 rebar (≤75 ksi); 7/8” to 1-1/2” bolts (≤ 150 ksi)
• min. of 4 connectors per column and 3 per pile
• grout pocket
– connector placement tolerance of ± 1” long, ± 2” trans, ± 1” vert
– trapezoidal cross-section with a downward narrowing 2° taper
– min. clear connector spacing the larger of d b and 1”
• vertical ducts and bolted connections
– connector placement tolerance of ± 1” long, trans, and vert
– max 5” duct dia.
– duct length ≥ connector embedment + 3”
– min. clear duct spacing the larger of 1-1/2” and 4/3 x max. aggr.

Connection Details (cont’d)
• connection embedment (top of column or pile)
– surface-flush: bedding layer thickness of 1-1/2” to 4”
– embedded: 2” to 5” from bottom surface of cap
• confinement
– spirals or closed ties required (ACI mins for shear)
– vertical spacing of 2” to 6”
• development length
0.022dbfy
– grout pocket………………….l d =
f '
c
– grouted vertical duct…………l d =
0.024d
f '
c
b
f
y
– 50% increase for close connector/duct spacings

Research Report 1748-2
• Contains Full Description of
– Research
– Testing
– Design Procedures and Recommendations
• Availability
– Center for Transportation Research Library
• Phone 512-232-3126
• ctrlib@utexas.edu

Research Project 4176
“Development of Precast Bridge Construction
Systems” – Report to be Published 3-2006
• Investigation of:
– Metal vs Plastic Ducts (25% Cap. Reduction)
– Misplaced Connectors in Ducts (Off Center –
20% Cap. Reduction)
– Connector Embedment Depth
• Availability
– Center for Transportation Research Library
• Phone 512-232-3126
• ctrlib@utexas.edu

Lake Ray Hubbard
Precast Caps
Rockwall County
SH 66
(2002)

Lake Belton
Precast
Hammer Head Caps
Bell County
SH 36
(2004)

Plan View of Project
PHASE 1 CONSTRUCTION
PHASE 2 CONSTRUCTION

New Structure
• Construction Began Sept. 2002
• Phase I: $20.0M ($47/SF)
• 3840 ft Total Length
• Twin 40 ft Roadways
• Phased Construction
• 32 ~ 120 ft Prestressed
Concrete U54 Beam Spans
• 8” Composite Slab: 4” CIP
Topping & PCP SIP Forms
• Twin Independent Substructures

Cross-Section of New Structure

Overall Bent Design

Bent Cap Design

Precast
Connection
Forces

Service Level
Section Behavior
Critical Bar
Neutral Axis
Service Stress

Precast Connection Design

Precast Connection Design

Research Project 4085
“Preventing Premature Concrete Deterioration
Due to ASR/DEF in New Concrete”
Report Pending
• Investigation and Report Include:
– Causes (Materials Evaluation)
– Mitigation (Materials Selection, Construction)
– Specifications and Recommended Practice
• Availability
– Center for Transportation Research Library
• Phone 512-232-3126
• ctrlib@utexas.edu

Cap Fabrication
• Construction according
to Item 420
• Mass concrete placement
– Max 160 deg F absolute
and 35 deg F differential
• Off-the-form finish
160
• Approved grout tubes
140
• Full curing w/ interruption 120
allowance to turn over 100
forms (3000 psi)
80
• Avoid damaging members 60
Absolute Temp (F)
Core
Surface
Differential
0 50 100 150
Time (Hours)
50
40
30
20
10
0
Temp Differential (F)

Cap Fabrication
• Concrete Specifications
• Fabricator Requirements
• Concrete Work Plan

Concrete Specification
Requirements
• 7 % Entrained Air
• 160° F Max. Temperature [+/-]
•35° F Max. Differential
Temperature
• Concrete Appearance Specification

Fabricator Concrete
Requirements
• Workable Concrete, 7 1/2” to 8”
Slump
• High-Early Strengths
• Rotate the Casting Bed within
24 hours

Concrete Work Plan
• Type III Portland Cement- 6 sacks/ CY
• Class C Fly Ash - 20% Replacement
• Grade I River Sand
• Grade 5 Crushed Limestone - CA Factor
0.81
• Water Cement Ratio - 4.0 gal/sack
• Air Entrainment, Water Reducing and
Retarding Agents used.

Connection Mock-Up and
Grouting Tests

5’x5’ Connection Block Mock-Up
• Record
Temperatures
• Concrete Finish -
Appearance
• Placement of
Grouting Hardware
• Grouting Test -
Contractor

Connection Block Mock-Up

Concrete Mix Results
• 8” Slump Achieved
• 20 Hr. Strength = 4,822 psi >3.0 ksi
• 7- Day fc = 9,125 psi
• 28- Day fc = 9,960 psi >3.6 ksi
• Max. Temp. = 154° F

Bedding Layer and Connection Bars
Mock-Up

Grout Mixing

Grout Pumping

Flow
Cone
Test

2” x 2”
Grout Cubes
3” x 6”
Cylinders

Bedding
Layer
Evaluation

Bridge Construction

Storage

Cap Transport
• Reverses in-place load condition
• Heavy (75 tons) & Short/ special permit req’d.

Cap
Placement

On the Right Track

LP340/SH6 at IH35
Complete Prefabricated
Superstructure and
Substructure
Bell, McLennan & Bosque Counties
IH 35
(2004)

Typical Superstructure and Interior Bent

Construction
Sequence

Pretopped Steel Tub Girder
38 in depth=115 ft span 46 in depth=130 ft span

Closure Strip

LP340/SH6 at IH-35
Prefabricated Concrete Superstructure
40 in depth=115 ft span

Simulated
Bearing Seats

Pre-topped Slab

Transverse
Screed

Reinforcing Steel Placement

Forming Closure Strips

Slab Pour

Remove
Form

Transportation to and Erection at
Bridge Site

Research Project 4122
“Development of CIP Slabs Connecting
Precast Slab and Steel Girder Assemblies”
Report to be Published 3-2006
• Investigation of:
– Closure Strip Behavior
• Service Load
• Ultimate Strength
• Availability
– Center for Transportation Research Library
• Phone 512-232-3126
• ctrlib@utexas.edu

STEEL BEAMS
ON SINGLE COLUMN BENTS
46' ROADWAY
56' ROADWAY

Prefabricated Columns

Setting Prefabricated Column Shell

Elevation
Control

Casting
Concrete
Core

Texas State
Historic Railroad
Bridge Replacements
From Palestine to Rusk
in conjunction with
Texas Parks and Wildlife Department
(1996 and 2003)

Dry Creek Bridge

Double Tee Connection

Thank You
Lloyd M. Wolf, PE
lwolf@dot.state.tx.us
512-416-2279