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Through the use of nonlinear time-history analysis, the displacement patterns of bridges subjected to transverse seismic attack are investigated. The variables considered in the study consist of bridge geometry, superstructure stiffness, substructure strength and stiffness, abutment support conditions, and earthquake ground motion. A series of three inelastic displacement pattern scenarios were identified: ͑1͒ rigid body translation ͑2͒ rigid body translation with rotation, and ͑3͒ flexible pattern. A relative stiffness index that is a function of the superstructure and substructure stiffness was shown to be a key variable in determining the type of displacement pattern a bridge is likely to follow. The results described in this paper have significant implications for performance-based seismic design procedures such as direct displacementbased design ͑DDBD͒. If the displacement pattern for a bridge can be identified with significant confidence at the start of the design process, application of approaches such as DDBD can be simplified. However, if the characteristics of the bridge are such that prescribing a pattern at the start of the process is not feasible, then an alternative approach must be employed for DDBD to proceed. Of the three displacement pattern scenarios defined in this paper, the first two require minimal effort in the design. For the third scenario, an iterative algorithm is proposed. Lastly, as a means for verification and demonstration, a series of bridges with various configurations was designed using DDBD for rigid body translation and flexible pattern scenarios. The designs for the flexible scenario showed good agreement with selected target profiles for bridges with up to five spans.

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Advancement in bridge design/construction technologies altered typical bridge parameters utilized in the development of AASHTO LRFD live-load distribution factors developed more than two decades ago. A girder bridge constructed using high-performance, high-strength concrete has been instrumented and tested under controlled-load condition. AASHTO LRFD distribution factors were compared to the factors computed from girders measured strains. AASHTO LRFD distribution factors were on average 21% higher than computed factors. A detailed finite element model (FEM) was developed and calibrated to match the controlled load test results. Several variations of the FEM were created to account for the presence of end & intermediate diaphragms, girders continuity, and bridge skewness. The addition of end diaphragms decreases distribution factors on average by 6% while addition of intermediate diaphragms redistributes the moments between interior and exterior girders. Effect of diaphragms was more evident for bridge with large skew angles and less significant for skew angles less than 20 • . Bridges with skewness have decreased distribution factors which was evident for skew angle in excess of 20 • ; AASHTO LRFD has good estimates of skewness effect on distribution factors. Considering the continuity effect in the calibrated FEM revealed that AASHTO LRFD distribution factors are overestimated on average by 17%.