The Effect of Frame Dimensions on the Strength Reduction Factor of Intermediate Steel Moment Resisting Frames

Each frame has a layout which may be different from the layouts of other frames. This difference may be stemmed from differences between bay lengths or frame dimensions in frames. So, investigation on how these differences can affect the parameters, which govern the design of structure, becomes very important. One of the effective parameters which reduce the elastic spectra into inelastic form is so-called strength reduction factor. In most codes, this factor is constant and does not depend on several factors such as differences between layouts. In this study some 5 story intermediate moment resisting frames with different bay layouts are designed, their over strength, ductility and strength reduction factors are calculated by performing triangular pushover analysis and the influence of different frame layouts on strength reduction factor is evaluated. The results indicated that bay length is an ignored significant factor that can affect the strength reduction factors and the major impact on strength reduction is due to the bay-span rather than to its number of bays. the difference between frames withlong bays and short bays is calculated to be as high as 35 percent.