Comparison of LRFD and allowable stress design criteria for the design of multi-story frames

Abstract

Load and Resistance Factor Design is a set of specifications for the design of steel structures. It is based on a consistent probability of failure and the concept of limit states. The main difference between LRFD and the traditional Allowable Stress Design method is the use of load and resistance factors, which account for the variability of parameters affecting the design. The purpose of this study is to compare both design methods. To do so, a computer program for the design of steel frames according to LRFD criteria is created. Three frame structures are designed using this program, then compared to the same structures designed according to the ASD procedures. The results indicated that LRFD criteria yield a structure similar to that designed according to ASD, with a moderate saving in steel weight. Both methods were found to be similar in terms of complexity and effort to complete calculations. An advantage found in using LRFD was that engineers can develop a better understanding of the behavior of material and structures under the influence of different load conditions.