UBC Theses and Dissertations
Pseudo non-linear seismic analysis for damage evaluation of concrete structures Mital, Subodh Kumar
Inelastic behavior is inevitable in most structures subjected to strong earthquake forces. Any rational design procedure, therefore, should attempt to estimate the amount of inelastic behavior to be expected in each member of the structure. Methods of dynamic response analysis based on linear elastic assumptions can be carried out conveniently and economically. Such methods, however, can not provide any direct information on the inelastic behavior of the structure. On the other hand, time-step analysis programs can 'truly' simulate the non-linear behavior of the structure but are seldom used because of their cost and complexity. There is, therefore, a need for practical and efficient methods which can account for the inelastic behavior. Some methods for estimating the inelastic response and damage patterns of structures under ground motions are presented. One is the Modified Substitute Structure Method which is now revised so that the structure can be analysed for gravity loads prior to the seismic analysis. The other method which is proposed here uses a static analysis. The structure is first analysed for gravity loads and then lateral seismic forces (as given by the appropriate codes) are applied. The amplitude of the lateral forces is gradually increased, maintaining the specified pattern; a plastic hinge is placed where a member has yielded and the structure stiffness matrix revised each time. This process is continued until the structure has reached a predetermined displacement. At this point, the rotation of the plastic hinges is known and then the member curvature ductilities can be calculated. Thus, an idea is obtained, of the damage pattern in the structure. A computer program has also been written for analysing the structures by 'Freeman's Method' to predict the inelastic response of structures under severe ground motion. The method gives the overall inelastic response without predicting the pattern of local damage. These various methods are then compared by analyzing two idealized structures. A third, real structure, an office/residential building in downtown Vancouver is also analysed by these methods and the results compared with those obtained by a time-step analysis program DRAIN-2D. These methods appear to give good results and it is hoped that they will be found useful by practising engineers. A user's guide and the listing of these programs are included in the appendices.
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