| The reconnaissance report of Wenchuan Earthquake indicates that there werealmost no plastic hinges in the end of beams in reinforced concrete frames while plastichinges in the end of columns existed universally. Considering this, new edition ofChinese design code adjusted the seismic measures in Intensity Region7(SeismicCategory3) in order to ensure reasonable energy consumption mechanism. On the otherhand, with the development of technology, dynamic time-history analysis of structureshas advanced from plane analysis to3D analysis, from macro-model such as story basedmodel to micro-model such as fiber model, and from uniaxial input to bi-directionalinput of ground motion records. With the support of new technology, this paperre-evaluated the effectiveness of the seismic measures for structures in Intensity Region7(0.15g) and confirmed the analysis performance of the nonlinear dynamic analysisprogram PERFORM3D.Based on the research background mentioned above, the research work completedin this paper is as follows:①The current common section simulation methods were introduced briefly. Thefiber model and plastic hinge model that were suitable for frame structures wereintroduced in detail and their advantages and shortcomings were summarized in order toprovide theoretical support for the nonlinear analysis modeling of frame structures inthis paper.②T he multi-story and multi-span reinforced concrete frame located in IntensityRegion7(0.15g) was modeled and designed according to Code for Design of ConcreteStructures (GB50010-2010) and Code for Seismic Design of Buildings (GB50011-2010).③7groups of ground motion records from different earthquake events wereselected and scaled using the rare earthquake code spectrum as target spectrum and themean spectrum of period range T~1.5T as intensity index.④T he response rule of various seismic indexes of the structure with bi-directionalground motion records was provided utilizing the nonlinear dynamic analysis programPERFORM3D.The main conclusions are as follows:①When the structures are predicted to be strongly nonlinear or enter the soften phase, plastic hinge model is better than fiber model. However, when simulating thecoupling of axial force and bi-directional moment and new material and irregularsection, fiber model is more satisfied than plastic hinge mode. Engineers should choosereasonable method according to practical simulating conditions.②Through the introduction and comparison of common methods of selectingground motion records, this paper regards that general selecting methods such asmethods based on earthquake rupture distance and record station are preferable whenresearch work is focused on a large region while methods base on the deaggregationresults and conditional mean spectrum do a better job in reflecting the specialty of agiven site.③F rom the macro-response of structures, the seismic detailing measures forIntensity Region7(0.15g) in current Chinese design code could prevent structures fromoverall collapse or local story-centered collapse, however, plastic hinges mainlyoccurred in the end of columns and hence the energy dissipation mechanism werebeams and columns combined. Form the micro-response aspect, though the number ofplastic hinges in the end of columns was large, the maximum strain of reinforcementand curvature and rotation demand were not large hence the crush of column ends didnot happen. From both aspects, it could be concluded that the seismic detailingmeasures for Intensity Region7(0.15g) in current Chinese design code are effectivegenerally. It is not recommended to enhance the column moment coefficient and basecolumn moment coefficient in order to pursue ideal beam end plastic hinge mechanism,which will lead to irrational quantity of longitudinal reinforcement in columns andproblems for construction.④As a nonlinear dynamic analysis commercial program, PERFORM3D hasalready been widely used in coastal area. Its function of behavior evaluation, modelsimplification and efficiency of computation are satisfied. However, the analysis resultsare monotonous and some data could not be provided, which will lead to problems inthe processing of results and hence limit in the practice. |
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