Evaluation and Assessment the Effect of Overstrength Factor in Seismic Behavior of Steel Moment Resisting Frames

In recent years, the world - wide standard codes such as IBC2000 and NEHRP2000 have paid special attention to the coefficient over-strength factor. The effect of this parameter on saving the safety of structures from earthquake is quite postulated. This parameter associated with the Redundancy/ Reliability factor by which the structural safety is controlled is added into the above mentioned Codes from 1997. Describing the over-strength parameter, the role of effective factors on it, it's role on the seismic behavior of structure, quantitative description of the problem in terms of performing linear and non-linear analyzing of selected structures under incremental push-over analysis and determining this factor in performance pint of the structures constitute some sections of this article. Moreover, an important issue concerning the following question is investigated. That is, "Dose the unknown over-strength factor value incorporated in the structure through the design procedure suffices the structures for being safe or it should be sufficiently induced in structures for responding an appropriate non-linear performance".
In this article eight Moment Resisting Frames (MRF) with different number of stories and bays in two different systems, ordinary and special are studied and the results are assessed. These structures have been designed according to The Iranian standard 2800 and American IBC2000 Standard and the required over-strength values produced by the design procedure are determined and the results obtained from both Codes are compared and evaluated.