Beam Shear Design with Welded Wire Fabric: ACI 318 vs. AASHTO LRFD

摘要

Since 1963, the shear design of reinforced and prestressed concrete beams hasbecome unnecessarily complicated. There are currently two different procedures used to design and detail the steel shear reinforcement in concrete beams. The first method, used by the American Concrete Institute (ACI), is purely empirical. Their current design guide, the Building Code Requirements for Structural Concrete (ACI 318-95) and Commentary (ACI 318R-95) uses the results of beam tests to produce the current code shear reinforcement requirements. The second method, recently adopted by the American Association of State Highway and Transportation Officials (AASHTO) in their Load and Resistant Factor Design (LRFD) code is called the Modified Compression Field Theory (MCFT) approach. The MCFT approach, also referred to as the General method, was developed by Professor Michael P. Collins at the University of Toronto. The MCFT approach models the beam's steel reinforcement as a variable angle truss. According to Collins, the resulting steel shear reinforcement is designed based on a 'physically significant' quantity. The method relates the average strain in the longitudinal steel reinforcement with the principal strains in the beam. The AASHTO method greatly simplifies the design approach, since the same equations apply to both prestressed and non-prestressed concrete beams and to any beam geometry.