Abstract
The response modification factor (R factor) is a crucial parameter for calculating the design seismic forces applied to a bridge structure. This factor considers the nonlinear performance of bridges during strong ground motions. Conventional bridge structures rely on the substructure components to resist earthquake forces. Accordingly, there are R factors available in the design codes based on the type of bridge substructure system. Lateral load resisting system of Integral Abutment Bridges (IABs) in the longitudinal direction is more complex than ordinary bridges. It involves the contributions from soils behind the abutments and soil/structure interaction (SSI) in addition to existing rigid connection between the superstructure and abutments. There is no R factor available in any design code throughout the world for IABs in the longitudinal direction that considers all these parameters. In this research, the Federal Emergency Management Agency publication FEMA P695 methodology has been applied to estimate the R factor for IABs. It is found that 3.5 could be a safe and valid R factor in the longitudinal direction for seismic design of such bridges.
Highlights
For many years, long span bridges were mainly designed and constructed as multiple supported spans until the moment distribution method was published in 1930 and facilitated the analysis of continuous spans and rigid frame bridges [1]
If all archetypes are put into one performance group, ACMRi = 2.61 which is above ACMR10% = 2.30
ACMRi for all archetypes is above ACMR20% = 1.73, except W30L2 that has an adjusted collapse margin ratios (ACMRs) value of 1.64 that is below the acceptable value
Summary
Long span bridges were mainly designed and constructed as multiple supported spans until the moment distribution method was published in 1930 and facilitated the analysis of continuous spans and rigid frame bridges [1]. The integral abutment bridge (IAB) benefits from continuity in a different way, namely between the superstructure and substructure, very similar to an arch bridge. This continuity eliminates the need for expansion joints at the abutments and due to extensive and costly problems associated with these joints, IABs are becoming a bridge system of choice throughout the world. In an earthquake, the unseating of the deck, which is a major problem in conventional bridges, is eliminated for IABs. Despite many advantages, secondary stresses due to thermal, shrinkage and creep are more of a concern for IABs. In general, the analysis of IABs is very complex and involves an indeterminate structure with soil/structure interaction (SSI) in its fullest form. Many researchers have worked on this complex SSI problem and suggested simplified analysis techniques for IABs under gravity, thermal and seismic actions [2,3,4,5,6,7,8]
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