| The single-span frame structure has been widely used in the primary andsecondary school in our country since1990’s. It is found that the single-spanframe structure is damaged severely due to the insufficient structural redundancyin great earthquakes in the recent years, especially in the Chi-Chi Earthquake andthe Wenchuan Earthquake. It is urgently demanded in the newly revised codesthat the single-span frame structure should not be used in the teaching buildingswhich are classified as the category B building, and the existing single-spanframe teaching buildings must be evaluated and strengthened.Some common strengthening methods are compared in this paper. For theflexible arrangement, the convenient construction procedure and the reasonableconcept design, the wing wall strengthening method is widely adopted byengineers. However, the research about the strengthening method for the wingwall is rarely found. The calculation method and failure characteristics form ofthe wing wall strengthening are still in doubt. Therefore, the failure mechanism ofthe single-span frame structure and the seismic performance of the structurestrengthened by wing wall are studied through the large scale model simulated onthe shake table contrast test. The study in this paper is to lay the foundation forthe strengthening methods of multi-story single-span reinforced concrete framestructure which the effective collapse resistant capacity is obtained, and toprovide the basis for the corresponding standards.First of all, a typical single-span frame building is designed in this paper andstrengthened by wing walls. The influence on strengthening effect of the framestructure by different wing wall strengthening forms and dimension is studied. Byusing software ETABS and MIDAS, the strengthened and the unstrengthenedstructure are analyzed in three-dimensional elastic and elastoplastic way. Theresults show that the method of installing wing walls in two directions should beadopted for the two directions strengthening schemes, so that the seismic capacityas well as the deformation capacity is improved in both directions of the structure,in order to improve the strengthening effect obviously. The two directionsstrengthening scheme of500mm wing wall is selected for the follow-upstrengthening form of the shake table test. Secondly, two1:5large scale single-span frame structure of shake table testmodel are designed, which are strengthened structure and unstrengthenedstructure. The selection of the material, construction process, and the layout ofthe test equipments for the models are provided. The two test models are placedon the same shake table, the contrast test subjected to20seismic conditions areconducted. The El Centro Wave, the Taft Wave and the Wolong Wave areselected. From the failure phenomena and data results of test it is shown that, thecrack on the strengthened single-span frame structure model of beam is evenlydistributed and the energy dissipation range is wide, so the structure has a betterseismic performance, which the requirement in the corresponding current codecould be well satisfied. The beam hinges of the unstrengthened single-span framestructure model are concentrated at both ends of beams. Due to a limited numberof beams the column hinges is soon generated on the columns of theunstrengthened structure, which a hybrid system of beam hinge and column hingeis formed. At the same time, the ultimate bearing capacity of the structure isachieved easily and a domino collapse effect is formed which means, the seismicperformance is poor.Finally, the seismic elastoplastic analysis of the strengthened andunstrengthened models of the prototype structure is conducted by using largefinite element software MIDAS, subjected to the seismic conditions of0.05g,0.15g and0.20g of El Centro Wave. By compared the numerical simulationresults with the test results, it is can be seen that, by using lumped plastic hingefor the model unstrengthened of prototype structure the failure phenomena ofbeam and column are in good agreement with the test failure phenomena, whichmeans the simulation results are ideal. As the crack distribution on beams of thetest model strengthened by wing wall is dispersive, the simulation of thestrengthened structure by using the lumped plastic hinge is slightly worse than theunstrengthened one. Therefore, it is suggested to use the fiber hinge. |
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