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This paper presents a study that investigated the effect of substructure stiffness on the performance of short- and medium-length steel integral abutment bridges (IABs) built on clay under thermal load effects. Various parameters, such as pile size and orientation, pile type, and foundation soil stiffness, were considered in the study. Detailed, three-dimensional (3-D), finite element (FE) models were developed to capture the behavior of IABs. Field measurements from a IAB were used to validate the 3-D FE model developed with LUSAS software. With the use of validated models, a parametric study was carried out to study the effect of these parameters on the performance of IABs under thermal loading with AASHTO load and resistance factor design temperature ranges. The study showed that the substructure stiffness had a significant effect on the stress level induced by thermal loads in various components of the substructure and superstructure. The results also showed significant variations in displacement and stress between interior and exterior locations in relatively wide IABs. The study showed that prestressed concrete piles could form a viable alternative to steel H-piles for short-span bridges. The stress level from thermal loading in the various components of the bridge could be reduced significantly if the top part of the pile were placed in an enclosure filled with crushed stone or loose sand.

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This paper presents a simple approach to calculate the displacements and the rotations induced by thermal loading in integral abutment bridges (IABs). The approach was derived from the results of a parametric study that investigated the effect of substructure stiffness on the performance of short- and medium-length steel IABs built on clay and sand under thermal load effects. Various parameters, such as pile size and orientation, pile material, and foundation soil stiffness, were considered in the study. Detailed three-dimensional (3-D) finite element (FE) models using the software LUSAS were developed to capture the overall behavior of IABs. The developed 3-D FE model was calibrated with field measurements obtained from a previous study. A parametric study was carried out with the calibrated models to study the effects of the above parameters on the performance of IABs under thermal loading using the AASHTO load and resistance factor design temperature ranges. The study showed that most parameters have significant effects on the displacement and rotation of the abutment and the supporting piles. Also, for relatively wide IABs, there were significant variations in the displacement and rotations in the substructure elements between interior and exterior locations. This approach, which used simple equations and charts and included parameters such as the length of the bridge, the stiffness of the foundation soil, and the pile location, provided results that were comparable with those of a detailed FE analysis.

This paper presents an analytical approach for predicting the length limits of integral bridges built on cohesive soils based on the flexural strength of the abutments and the low cycle fatigue performance of the steel H-piles at the abutments under cyclic thermal loading. First, H-piles that can accommodate large inelastic deformations are determined considering their local buckling instability. Then, a damage model is used to determine the maximum cyclic deformations that such piles can sustain. Next, nonlinear static pushover analyses of typical integral bridges subjected to cyclic thermal variations are conducted to study the effect of various geometric, structural, and geotechnical parameters on their performance. Equations are derived by using the analyses results to determine the maximum length limits of integral bridges built on cohesive soils. It is found that the maximum length limits of integral bridges is affected by the stiffness of the deck, height of the abutment, properties, and orientation of the piles as well as stiffness of the cohesive soils.Key words: bridges, integral, steel, piles, fatigue, inelastic, thermal, clay, soil, length.