STUDY ON SEISMIC DESIGN CRITERIA FOR STEEL FRAMES CONSIDERING DEGRADING LOAD-DEFLECTION CURVES

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The results obtained from this project are summarizes as follows :1.Based on numerical response analyzes of shear-type lumped mass models with perfect elasto-plastic load-deflection relationships, a basic law that governs distributions of damages is determined as a function of the strength distribution of structures. For a single-degree-of-freedom system, one quarter of the energy input due to ground motions is assumed to be absorbed first by plastic deformation in one direction, and then the rest of the energy is assumed to be distributed during the following reversals of plastic deflections according to the above-mentioned damage distribution law. Thus, the concentration of plastic deformation on one direction is determined in a quantitative manner.2.The influence of the shape of loas-deflection curves on the seismic response of steel frames is discussed based on the two rules described above. For shear-type models with bi-linear load-deflection relationships, the damage concentratio … More n on weak stories is found to depend on the rigidity ratio between elastic and plastic branch. A formula is derived to evaluate the energy absorption capacity of a single-degree system with tri-linear load-deflection relationship consisting of elastic, hardening, and degrading parts. These results coincide with the results of numerical response analysis.3.Steel frames with rectangular hollow section columns and wide flange beams under strong ground motions are analyzed numerically. The results show the damage disperses throughout the stories because of the yielding of connection panels. In addition, steel frames are designed according to allowable stress design criteria to see ultimate behavior of the frames. The results show frames tend to be of weak beam type structures.4.The computer program for non-linear static and dynamic analysis of plane frames is developed to study the damage distribution in steel frames. The generalized plastic hinge method is used for members to incorporate stain hardening effects. The elasto-plastic behavior including bauschinger effect of joint panels are also taken into account. Less