Lateral load response of unbraced steel building frames

Abstract

The standard CAN3-S16.1-M84 "Steel structures for buildings — limit states design" recognizes three sets of assumptions in the analysis, design, and construction of steel buildings. In two of them the connections are assumed to be either fully rigid (continuous construction, clause 8.2) or completely free (simple construction, clause 8.3.1). In the third type of construction, termed here as "special simple construction" (clause 8.3.2), the beam-to-column connections are assumed to be completely free (pinned) to resist gravity loads and are assumed to be rigid to resist the lateral loads due to earthquake or wind. Such connnections are designed for moments due to lateral loads only, and thus they are more flexible and may yield at ultimate load levels. This paper illustrates the analysis and design of two (one 5-storey and the other 10-storey) office buildings assumed to be located in Hamilton, Ontario, on the basis of special simple construction. Using realistic connection behaviour, the influence of connection flexibility and strength on the performance of these buildings is studied. In the nonlinear static analysis, the buildings have been subjected to gravity loads and incremental lateral loads until failure. For comparison purposes, the building frames were also analysed and designed, based on continuous construction assumptions. The results showed increased drifts and decreased overall strength due to connection flexibility and strength. Thus, the system based on continuous construction structurally performs better than the system based on special simple construciton. As far as the economy is concerned both systems appear to be equivalent. Key words: building design, steel structures, flexible connections, analysis, wind load, earthquake load, strength.