Parametric Study on the Applicability of AASHTO LRFD for Simply Supported Reinforced Concrete Skewed Slab Bridges

Simplified code provisions can be used for the analysis and design of straight slab bridges. However, several studies question the appropriateness of simplified procedures for skewed geometries. This paper provides practical insights to the designer regarding the effects of skewness in reinforced concrete slab bridges by evaluating how simplified and more refined analysis procedures impact the design magnitudes and resulting reinforcement layouts. The methods used for this study are analytical and numerical case studies. Eighty case study slab bridges with varying lengths, widths, and skew angles are subjected to the AASHTO HL-93 loading. Then, the governing moments and shear forces are determined using the AASHTO LRFD simplified procedures with hand calculations, and using linear finite element analysis (LFEA). Afterwards, the reinforcement is designed according to the AASHTO LRFD design provisions. From these case studies, it is found through the LFEA that increasing skew angles result in decreasing amounts of longitudinal reinforcement and increasing amounts of transverse flexural reinforcement. Comparing the reinforcement layouts using AASHTO LRFD-based hand calculations and LFEA, we find that using LFEA reduces the total weight of steel reinforcement needed. Moreover, as the skew increases, LFEA captures increased shear forces at the obtuse corner that AASHTO LRFD does not. In conclusion, it is preferable to design the reinforcement of skewed reinforced concrete slab bridges using LFEA instead of hand calculations based on AASHTO LRFD for cost reduction and safety in terms of shear resistance in the obtuse corners.

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