Evaluation of Ultimete Limit State Strength of Steel Structures

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The purpose of this study is to find the failure mechanism of frame in ultimate state which dissipates a input energy to the frame by earthquake excitations or wind loading.There were three types of tests conducted static tests, earthquake response tests and dynamic response tests by wind loading.All these tests were conducted on 3-story frames and were controlled by the On-line test technique.The test results are summarized below:(1) The strength observed at the static tests is much higher than the strength which is calculated by a simple plastic analysis for perfectly elastoplastic materials. In order to evaluate correctly the strength of frame, it is very important to take into account the strain-hardening effect at the strength analysis of frame.(2) The trajectories of the inertial forces are crowed along the line representing the ratio between the inertial forces during the 1st mode vibration. It suggests the possibility of representing the dynamic load effects by an equivalent static load.It is possible to develop the simple ultimate state aseismatic design method characterized by equivalent static parameters, in the case of comparatively small effects of higher mode of vibration in frames.Considering the interactive effects between velosity of frame and wind verosity at the wall exposing to the wind, the dynamic loading distribution exerting at the each floor of frame is nearly equal to the static wind loading distribution. The 1st mode vibration in dynamic response, however, are dominant. Then, there are no interactive relation between the ratios of the work done by the static shear force at the each floor and by the dynamic loads.