Load and resistance factor design of cold-formed steel structural members

In a traditional design, the Allowable Stress method has long been used for the design of cold-formed steel structures. In this design approach, the allowable stress is always used to prevent the possible structural failure by using an appropriate factor of safety selected primarily on the basis of engineering judgment and long-time experience. Recently, the concepts of risk and reliability analysis have been successfully applied to many fields of engineering. By applying the theories of probability and statistics, the load and resistance design criteria for steel structures have been developed for the design of hot-rolled steel shapes and built-up members. This method is based on the ultimate strength and serviceability of the structural members and connections. In order to develop the new design criteria for cold-formed steel structural members, a research project entitled Load and Resistance Factor Design (LRFD) of Cold-Formed Steel has been recently conducted at the University of Missouri-Rolla and Washington University. This study has included the selection of a probabilistic model, the evaluation of load factors, the calibration of safety indexes for the allowable stress design criteria issued by the American Iron and steel Institute, and the determination of resistance factors. Based on the safety indexes selected for cold-formed steel structural members and connections, the load and resistance factor design criteria for cold-formed steel have been developed by using the first order probabilistic theory and the statistical data on mechanical properties of materials and the test results obtained from previous research. In this method, appropriate load factors and resistance factors are applied to specified loads and nominal resistance to ensure that the limit state is not exceeded. Because these factors reflect the uncertainties of analysis, design, loading, material properties and fabrication, this design method can provide a more uniform overall safety and structural reliability --Abstract, pages ii-iii