Recent Research on Steel Bridges

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2012 CTR Symposium

Michael EngelhardtTodd Helwig

Karl FrankEric Williamson

Richard Klingner

Investigators:

Recent Research on Steel Bridges

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• Project 0-5701Cross Frame and Diaphragm Layout and Connection DetailsCompleted 2010

• Project 0-6564Improved Cross Frame DetailsOn-Going Research

• Project 0-6719Strengthening Continuous Steel Girders With Post-Installed Shear ConnectorsOn-Going Research

Cross Frame and Diaphragm Layout and Connection Details

TxDOT Project 0-5701Completed 2010

Graduate Research Assistants: Craig Quadrato, Wei Wang, Andrew Wahr, Anthony Battistini

Faculty Researchers: Todd Helwig, Karl Frank, and Michael Engelhardt

TxDOT Project Coordinator: Kenneth OzunaTxDOT Project Director: Ken Lin

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Research Objectives

1. Investigate cross frame connection details for skewed steel girder bridges

2. Investigate different bracing layouts

3. Improve stability and fatigue performance

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Bearing Stiffeners

Bent Plate

Cross Frame

Bent Plate Detail for Connecting Cross-Frames to Girders at a Skew:

Current TxDOT Practice:

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Key Issue: Flexibility of Bent Plate Connection Detail

Key Objective: Develop Improved Connection Detail forAttaching Skewed Cross-Frames to Girder

Proposed Improved Connection:Half-Pipe Stiffener

Warping restraint

Half-Pipe Stiffener

Cross Frame

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• Stiffer cross-frame to girder connection• Provides warping restraint for girder – increases

girder stability

Potential Benefits of Half-Pipe Stiffener:

Bearing Stiffeners

Bent PlateCross Frame

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Major Research Activities

• Laboratory Tests– Connection Tests– Fatigue Testing– Large Scale Tests on Two and Three Girder Systems

• Computational Modeling

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Connection Testing and Analysis

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Fatigue Testing and Analysis

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Large Scale Testing

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Computational Modeling

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Results

Bent Plate Connection:– acceptable for end frames– avoid for intermediate cross frames– half-pipe stiffener provides a better alternative

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Results (cont.)

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• Increased stability and safety of girders during all stages of construction.

• Better control of end twist during construction .• Serves as bearing stiffener.• Potentially eliminate first line of intermediate

cross frames near support.

Benefits of half-pipe stiffener:

Results (cont.)

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Design of half-pipe stiffener:

• Hand calculation method – determine modified effective length of girder for buckling calculations.

• UT Bridge softwareUpdated to incorporate the half-pipe stiffener

Design of Half-Pipe StiffenerUT Bridge

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Results (cont.)

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Consider use of staggered intermediate cross-frames in skewed bridges.

– Avoid congestion near supports– Better fatigue performance due to lower induced

live load force

Continuous:

Staggered:

Improved Cross Frame DetailsTxDOT Project 0-6564Research In Progress

Graduate Research Assistants: Anthony Battistini, Wei Wang

Faculty Researchers:Todd Helwig, Michael Engelhardt, Karl Frank

TxDOT Project Director:Michelle Romage-Chambers

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Research Objective

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Investigate behavior of TxDOT standard cross frames: • Stiffness• Strength• Fatigue

Research Objective

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Develop and evaluate potential improvements to cross frame details.

• Single diagonal cross frames• Use of tubular members• Use of double-angle members• Unconventional connection details

Cross Frame Functions

• Critical for stability of steel bridges during construction

• Resist torsion in curved steel bridge systems

• Distribute lateral loadsand truck live loads

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Cross Frame Member and Connection Analysis

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T-Stem Detail

Cast Connection Detail

Knife Plate Detail

Single Angle Detail

Double Angle Detail

Component Stiffness, Strength and Fatigue

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Component Stiffness, Strength and Fatigue

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Cross Frame System Stiffness and Strength

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Cross Frame System Stiffness and Strength

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Cross Frame System Stiffness and Strength

Cross Frame System Stiffness and Strength

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Key Observations from Research Completed To-Date

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Standard TxDOT Single Angle Cross-Frame:• Behavior is complex due to use of single angle

members (unsymmetrical member, eccentric connections).

• Current methods used in design to calculate cross frame stiffness can lead to large errors.

• Fatigue behavior cannot be predicted by component level testing. Cross Frame fatigue behavior may be worse than previously assumed.

Key Observations from Research Completed To-Date (cont.)

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Promising approaches for improved cross frames:

• Single diagonal cross frame

• Tubular members or double angle members to minimize eccentric connections

• Knife plate connections for tubes

• Conventional gusset connections for double angles

Strengthening Continuous Steel GirdersWith Post-Installed Shear Connectors

Graduate Research Assistants: Kerry Kreitman and Hemal Patel

Faculty Researchers:Michael Engelhardt. Todd Helwig, Richard Klingner,and Eric Williamson

TxDOT Project Director: Yuan Zhao

TxDOT Project 0-6719

Research In Progress

Project Objective

Develop techniques to strengthen existing continuous multi-span non-composite steel girder bridges, through the use of post-installed shear connectors.

0-4124: Methods to Develop Composite Action in Non-Composite Bridge Floor Systems(completed 2007)

5-4124: Implementation Project: Bridge Strengthening Through the Use of Post-installed Shear Connectors (completed 2009)

Project 0-6719 builds on previous TxDOT Projects:

Key Concept:

Strengthen existing non-composite steel girder bridges….by developing composite action

Older Non-composite Bridge

steel girder

concrete deckPost-installedshear connector

Focus of Project 0-4124: Increase positive moment capacity

Bridge Near Hondo, Texas:Improvement in Load Rating -

Load Rating

Inventory Level

Operating Level

Before Retrofit After Retrofit

HS 10.6

HS 17.6

HS 17.5

HS 29.1

Increase in load rating: 65 %

Project 0-6719:

Extend concepts developed in 0-4124 and 5-4124:

Use post-installed shear connectors to strengthen continuous multi-span girders with inadequate flexural capacity in negative moment regions.

Challenge:

Composite action is less efficient in negative moment regions – concrete is in tension.

Possible Approaches:

Use post-installed shear connectors in negative moment region- using reinforcing steel for composite action

Use post-installed shear connectors in positive moment region – allow redistribution of moment from negative to positive moment regions

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Recent Research on Steel Bridges- Closing Comments -

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Overall Research Focus:

Improve safety and economy of new steel bridges.

Develop practical solutions to problems that arise in design and/or construction.

Develop methods to extend the life of existing steel bridges.