Simplified shear provisions of the AASHTO LRFD Bridge Design Specifications

摘要

Existing shear-design provisions are based on experimental test data, the equilibrium condition of members in the ultimate limit state, and comprehensive behavioral models for capacity. While there is consensus among researchers as to the components that contribute to shear resistance, there is considerable disagreement about the relative magnitude of the contributions, the factors that influence the contributions, and their significance for different design conditions. The wide variations in the forms of the shear-design specifications used in different influential codes of practice may result in the amount of shear reinforcement required by one code being two to three times that required by another code for the same section and factored sectional forces. It is not possible to make a full assessment of the appropriateness of existing design provisions using the results of experimental test data only because what researchers have tested in laboratories does not provide good representation of the types of structures or the loadings used in the field. To this end, design databases of representative design sections are useful for comparing required strengths p_v,f_y of shear reinforcement by different methods with each other and with the predictions of numerical methods. Simplified shear-design provisions were developed for the AASHTO LRFD specifications that are a modified version of the AASHTO standard specifications. These provisions will usually provide for a more conservative design, while in some situations other influential provisions, such as the general procedure of the LRFD specifications, may not. The general procedure of AASHTO LRFD specifications' SDM relies on tables for the evaluation of β and θ, the values of which control the contributions of concrete and transverse reinforcement to shear strength as well as the equation for the strain ε_x at mid-depth. Those tables can be replaced by the equations for the same three quantities in the CSA Design of Structural Concrete without a loss in accuracy or conservatism.