2005-38 Analysis of Girder Differential Deflection and Web Gap by ColeBer


									Phase 1: Monitoring and Assessment Program for Wabasha County Bridge

This report documents the monitoring and assessment program used to investigate the dynamic
response and efficacy of the retrofit strategy for the Wabasha County Bridge.

This report is not available online. Please contact the Mn/DOT Library at (651) 296-2385 and
ask for research report #1998-22.

Phase 2: Analysis Tools and Rapid Screening Data for Distortional Fatigue in Steel Bridge

In this project, researchers sought to better understand bridge diaphragm deflection behavior and
advance the ability to estimate web gap distortional stress. Trends from the parametric studies
led to general observations that may assist in identifying fatigue-prone bridges.

This project led to the development of a formula for predicting diaphragm differential deflection
by an extensive parameter study on finite element models of bridges. The report can be found at

Phase 3: Assessment of Distortional Stresses in Multi-Girder Steel Bridges

Phase I resulted in a simple equation for estimating web gap stress using data collected during
field testing and subsequent finite modeling of a skew supported bridge with staggering bent-
plate diaphragms. Phase II produced an approximate method for predicting diaphragm
differential deflection of skew supported bridges with bent-plate diaphragms. Phase III
combined results of Phase I and Phase II into a useful method for predicting peak web gap stress
in skewed multi-girder steel bridges with staggered bent-plate diaphragms. This next step
developed a reliable procedure for the rapid assessment of distortional stresses in steel bridges
that includes a test of the applicability of this procedure to bridges with geometries differing
from those that formed the basis of the previous research. As a consequence of this research, the
authors propose changes and recommend modifications of previously developed methods of field
measurement and assessment. This report may be found at http://www.lrrb.org/pdf/200448.pdf

Phase 4 Analysis of Girder Differential Deflection and Web Gap Stress for Rapid
Assessment of Distortional Fatigue in Mulit-Girder Steel Bridges

The purpose this project was to refine and reformulate the previously developed equations of
estimating stresses in steel girder webs to out-of-plane distortion. In addition, this project
introduced dual-level analyses including both macro-models and micro-models of the two field-
monitored bridges.

With the completion of this study, a thorough finite element study for various bridges in the
Mn/DOT bridge inventory has been documented and proposed procedures for evaluating girder
differential deflections and web gap stresses have been calibrated to increase prediction

These prediction tools should prove to be effective for the rapid assessment of bridges
susceptible to distortional fatigue problems. The only shortcoming of this study is that the
technique for incorporating lateral deflection in the web gap stress prediction formula has not
been fully validated. Therefore, the report suggested that future research be done to verify
and/or modify the proposed procedure for web gap lateral deflection with field measurements
and detailed finite element analyses (for example, using the dual-level analysis procedure
developed as part of this study). This report may be found at: http://www.lrrb.org/pdf/200538.pdf

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