Elastic-plastic analysis of framed structures under dynamic loads

In this research, the hardening plastic hinge model is developed to be used under any dynamic loads or earthquakes in addition to the static loads. A numerical example is analyzed to check the reliability of the new model and its results. The results obtained were accepted. A parametric study is made on an eight -story two-bay steel frame under real records of El-centro earthquake to study the effect of coss section of beams and columns, the first floor height and the floor mass. After reaching the most resistant frame, the frame is analyzed WIder real records of six earthquakes to check its response to different earthquakes. The following conclusions are obtained :1) There is no close relation between the maximum peak acceleration of the earthquake and its hazard.2) The cross section of the exterior columns is a very effective parameter in the design of any frame to resist the earthquakes. The greater the cross section, the more resistant the frame.3) The cross section of the interior columns has 110 great effect on theresponse of frames so, it is recommended to have the same crosssection of the interior columns, which is obtained from the design under vertical loads because they are already exposed to large values of normal loads.4) The cross section of the beams has a considerabler effect on the response of frames. The strong beams may lead to to the formation of plastic hinges in the columns, which leads to a sudden failure.5) The first floor height affects the response of the frames, but it is not a dominant factor in the frame behavior. So, the required first floor, height can be obtained but with increasing the cross section of the exterior columns to maintain the same stiffness.6) The floor mass has a great effect on the response of the frames. The smaller the floor mass is, the more safe the structure.7)The formation of the plastic hinge in beams before columns is greatly recommended because the fonnation of the plastic hinges in columns indicates the development of the failure mechanism• in a short time.