Steel Girder Stability during Bridge Erection: AASHTO LRFD Check on L/b Ratios |
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Authors: | John S Hastings Qiuhong Zhao Edwin G Burdette |
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Affiliation: | 1Civil Engineer Manager I, Tennessee Dept. of Transportation (TDOT), Suite 1100 James K. Polk Building, Nashville, TN 37243-0349, E-mail: john.s.hastings@state.tn.us 2Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of Tennessee, 109A Perkins Hall, Knoxville, TN 37996-2010, E-mail: qzhao@utk.edu 3Professor, Dept. of Civil and Environmental Engineering, Univ. of Tennessee, 115 Perkins Hall, Knoxville, TN 37996-2010. E-mail: eburdett@utk.edu
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Abstract: | The erection of steel plate girders during the construction process of a steel bridge is a complex operation, which is often left to the contractor and/or the subcontractor to plan and execute. Rules of thumb have been developed through experience to check the lateral torsional buckling of the steel girder during erection using the maximum L/b (unbraced length/compressive flange width) ratio, below which no lateral torsional buckling would occur. Although the L/b ratio check has proven to be useful and convenient on-site, it is necessary to provide a more rational basis for the rules of thumb, and find the maximum L/b ratios by checking the lateral torsional buckling failure of girders under erection according to the latest AASHTO LRFD code. A series of parametric studies were conducted on cantilever and simply supported girders under self-weight as well as self-weight plus wind load, in order to: (1) check the rules of thumb on L/b ratios and (2) determine the effects of girder flange width, flange thickness, web depth, web thickness, and yield strength on the maximum L/b ratio and girder stability during erection. From the results, rules of thumb were modified for girders with common shapes, and it was obvious that (1) self-weight plus wind load controls the girder stability during erection in most cases and (2) flange width and web depth have the most effects on the maximum L/b ratio and girder stability during erection. |
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Keywords: | Bridges steel Bridges girder Buckling Construction |
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