Response of Continuous Steel I-Girder Bridges Subject to Temperature Variation

Abstract

Thermal deformation of the superstructure in continuous slab-on-girder bridges must be freely permitted to avoid potential adverse behavior due to the development of thermal forces. The use of fixed and guided bearings can introduce a significant amount of restraint against thermal deformation that, if not accommodated by the supporting piers, will lead to thermal stresses throughout the structure, most notably in substructure elements (piercaps, bearing assemblies, bearing anchor bolts). The potential effects of restrained thermal deformation in steel I-girder bridges have not been clearly demonstrated. Additionally, the method provided in AASHTO specifications for orienting guided expansion bearings on horizontally curved bridges could foster the development of thermal stresses.

The main goal of this work is to demonstrate and quantify the effect of restrained thermal deformation in an in-service horizontally curved continuous steel I-girder bridge. A second goal is to determine what bearing arrangement scheme is most preferable for minimizing thermal forces. The study presented here includes a comprehensive background discussion, detailed literature review on current concepts regarding the behavior of horizontally curved bridges subject to thermal loads, consequences of inhibited thermal deformation, findings from a field investigation of an in-service steel I-girder bridge, and finite element analysis (FEA).

Finite element analysis is utilized to verify whether or not behaviors documented during a field investigation of the in-service bridge are a result of restrained thermal deformation of the steel I-girder superstructure. During the field inspection, several unfavorable conditions were observed including bent bearing anchor bolts, deformation around the bearing devices, and significant cracking of the reinforced concrete support piers. To investigate these behaviors, 3D finite element modeling of the bridge was completed. Analysis of the FEA study indicates that these behaviors likely result from restrained thermal deformation of the bridge's superstructure. It is found that while lateral pier flexure allows thermal stresses in the superstructure to remain at an acceptable level, stresses in the substructure exceed critical values.

Additionally, FEA is employed to determine what bearing arrangement scheme is preferred for maximizing thermal deformation of the bridge's horizontally curved superstructure, thereby minimizing the possibility that harmful effects may develop. The bridge's geometry, span configuration and location of the support piers remain unchanged so that only the boundary conditions are modified. The study shows that placing fixed bearing assemblies near the bridge's point of zero movement and employing expansion bearing devices at all other support locations results in the most preferable state of stress throughout the bridge.