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The previous paper (Part 1) described the magunitude of plastic deformation introduced into beam-ends. In this paper (Part 2), based on the same numerical results, we deal with hysteretic behavior. Cumulative plastic rotation, the increment of plastic rotation during each half-cycle of vibration, and the hysteretic process of plastic rotation are discussed. A method is proposed to approximate damage to the beams in steel moment frames subjected to strong ground motions.

The previous paper proposed a seismic design procedure to estimate the ductility demanded of beams in steel frames that sustain overall collapse mechanisms. In this paper, a method is presented to predict a collapse mechanism that can form with the greatest probability in a frame structure under severe earthquake excitations, and the amplification factor of the ductility demand is determined based on the predicted collapse mechanism. Seismic responses of steel frames sustaining various collapse mechanisms are examined numerically. The results of the proposed method favor the overestimation of ductility demand for frames sustaining partial collapse mechanisms in a few stories but the approximation of the upper limit of numerical results.

This paper presents a seismic design procedure to estimate the ductility demanded of beams in strong column - weak beam steel frames. Critical parameters that control the earthquake response of steel frames are characterized and incorporated into the equivalent SDOF representation. Maximum and cumulative plastic rotations induced into beam-ends are derived in explicit forms as functions of these parameters, and accuracy of the estimated rotations is demonstrated through the comparison with numerical results.