Influence of Thermal Sweep on Girder Stability during Construction

Abstract

During construction, girder stability of precast, prestressed concrete bridge girders is adversely affected by fabrication imperfections. Consequently, limits on lateral sweep imperfection caused by fabrication tolerances are imposed by design standards, thus reducing the possibility of girder instability and rollover. However, thermal sweep, induced by solar heating during early stages of construction, can add to pre-existing fabrication tolerances thereby amplifying girder imperfections and reducing stability. In the present study, lateral thermal gradients available in the literature were adopted and enhanced for purposes of computing thermal girder sweep. A variety of girder types—PCI BT-63, Florida-I Beams, and AASHTO Type-V—were then investigated to quantify the influence that lateral thermal sweep has on the stability of individual precast concrete bridge girders under lateral wind load. Previously validated finite element analysis modeling and analysis techniques were used to conduct a parametric study that included 10 girder types, varying span lengths, and five geographic locations. Results revealed that thermal sweep may cause wind carrying capacity reductions of the order of 30 to 60% for typical span lengths, and even greater reductions at span lengths that approach maximum design limits. Consequently, it is crucial that thermal sweep, caused by environmental solar-heating conditions, be considered in construction-stage girder stability analyses.