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Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete.
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Home > Tools > Frequently Asked Questions
Q. With the advent and popularity of finite element analysis software, engineers can create sophisticated models of two-way slabs supported by columns. To comply with ACI 318, should a designer check punching shear stress with the simultaneous biaxial moments reported by such a model? A. The code equations were written at a time when structures were analyzed in independent directions. The approach of calculating shear stress independently has been proven to be conservative where frame lines are analyzed independently. Finite Element Modeling can provide a design that would be thinner than a traditional analysis. There is no rule of thumb that can identify when the design has become unconservative for this case. Some design engineers consider biaxial moments for two-way slabs and other elements such as corner columns when pushing the lower limits of the code. It would seem prudent that, if the designer is trying to get down to the half-inch, shear would be checked for the biaxial condition. References: ACI 318-19 Topics in Concrete: 318 Building Code; Design; Slab
Q. With the advent and popularity of finite element analysis software, engineers can create sophisticated models of two-way slabs supported by columns. To comply with ACI 318, should a designer check punching shear stress with the simultaneous biaxial moments reported by such a model?
A. The code equations were written at a time when structures were analyzed in independent directions. The approach of calculating shear stress independently has been proven to be conservative where frame lines are analyzed independently. Finite Element Modeling can provide a design that would be thinner than a traditional analysis. There is no rule of thumb that can identify when the design has become unconservative for this case. Some design engineers consider biaxial moments for two-way slabs and other elements such as corner columns when pushing the lower limits of the code. It would seem prudent that, if the designer is trying to get down to the half-inch, shear would be checked for the biaxial condition.
References: ACI 318-19
Topics in Concrete: 318 Building Code; Design; Slab
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