Simplified Method to Determine the Effect of Detailing on Cross-Frame Forces

Abstract

There are several issues that necessitate the use of steel I-girder bridges with skewed supports. Due to skew supports, the axis of rotation of bearing line cross-frame is not in line with the axis of rotation of girders, and connection points of intermediate cross-frames are either at different elevations or undergo different deflections. The consequence of this behavior is that the cross-frames fit between the girders at one loading stage and do not fit between the girders at other loading stages, depending on the detailing method used to detail the cross-frames. Additional structural responses, henceforth called lack-of-fit effects, are developed when cross-frames do not fit between the girders. These lack-of-fit effects can be estimated by different methods of analysis for different detailing methods. In addition to lack-of-fit effects, fit-up forces are required to fit the cross-frames between their connections to girder during erection, for total dead load (TDL) fit detailing method. Methods of analysis to estimate fit-up forces are not available. The objective of this paper is to introduce different methods that can be used to calculate lack-of-fit effects for the steel dead load (SDL) fit detailing method at the total dead load (TDL) stage and the TDL fit detailing method at the steel dead load (SDL) stage. A comparison of different methods is done to recommend a single simplified method of analysis that can be used to calculate lack-of-fit effects for both SDL fit and TDL fit detailing methods with reasonable accuracy. Analysis methods are proposed to estimate the fit-up forces. The main conclusion of this research is that improved 2D grid analysis can be used to estimate lack-of-fit effects for both TDL fit and SDL fit detailing methods and can also be used to determine fit-up forces for connecting girder and cross-frame detailed with TDL fit.