Doctoral Dissertation Defense


Comprehending Performance of Cross Frames in Skewed Straight Steel I-Girder Bridges


Jawad Hussain Gull

The effects of support in steel bridges can present significant challenges during construction.  The tendency of the girder to twist or layovers during the construction can present a particularly challenging problem regarding detailing the cross-frames that provide bracing to the steel girders. Methods of detailing cross-frames have been investigated in the past to identify some of the issues related to behavior of straight and skewed steel bridges. However, the absence of complete and simplified design approach has led to disputes between stakeholders, costly repairs and delays in construction.

The main objective of this research is to develop a complete and simplified design approach considering construction, fabrication and detailing of straight skewed I-girder bridges. This objective is achieved by comparing component of structural responses affected by different detailing methods and recommending methods of analysis to evaluate them, developing methods to estimate fit-up forces and recommending practices to reduce these forces, recommending methods of calculating cambers, and developing a design flowchart for each detailing method.

Girder layovers, flange lateral bending stress, cross-frame forces, component of vertical deflections, component of vertical reactions and lateral reactions or lateral displacements are affected by detailing methods and are referred as lack-of-fit effects. It has been found that lack-of-fit effects for the Final Fit detailing method at the steel dead load stage are equal and opposite to the lack-of-fit effects for the Erected Fit detailing method at the total dead load stage. The improved 2D grid analysis is recommended for estimating these lack-of-fit effects for different detailing methods. 3D erection simulations are developed for estimating fit-up forces required to attach the cross-frames to girders. The maximum fit-up force estimated from the improved 2D grid analysis shows a reasonable agreement with the maximum fit-up force obtained from the erection simulations. The erection sequence that reduces the maximum fit-up force is found by erection simulations. The line girder analysis is recommended for calculating cambers for the Final Fit detailing method. A combination of line girder analysis and 2D grid analysis should be used to calculate cambers for the Erected Fit detailing method. Finally, flowcharts are developed that facilitate the selection of a detailing method and show the necessary design checks.


Date: February 20, 2014 Department: Civil and environmental engineering
Time: 11:00 a.m. Major Professor: Dr. Atorod Azizinamini
Place: Engineering Center, EC 2461