Experimental Study On Collapse Mechanism Of Typical RC Frame Structures

Multi-story reinforced concrete(RC)frame structures are widely used for schools,hospitals and other public buildings.A large amount of RC frames collapsed fragilely in the past several mega-earthquakes and left tremendous casualties.The facts show that present understanding on the collapse mechanism of RC frame structure is far beyond correct.There is a big difference between reality and expectation.Therefore,the design level of collapse resistance of structures is far from satisfactory.So far the understanding of the collapse mechanism of RC frame structure concentrates on the “side sway mechanism”,accordingly present code requires engineers to improve the design value of the bending moment of frame columns in order to achieve the goal of strong column and weak beam".In fact,a large number of deformation pattern of RC frame with the vertical and horizontal infilled walls cannot be explained by such a theory.One RC frame structure in the meizoseismal area of the Great Wenchuan Earthquake,Xuankou middle school building was chosen as the analytical prototype here.According to the similarity ratio of 1:4,we reproduced the columns,beams and floors of this building.In particular,we set up fully infilled wall in the transversal direction and half-height continuous infilled walls in the longitudinal direction in strict accordance with actual structure details.Then shaking table model test was conducted to study the seismic performance of the structure.Among which,the conclusion was reached that the collapse mechanism of RC frame structures can be summarized as “Condense the seismic force and destroy the column one by one”.Major achievements of the dissertation are summed up as follows.1.The test showed that because of the restriction of transversal infilled wall,each floor of the structure moved back and forth in translational motion without torsional effect along the longitudinal direction,although the structure is eccentric in this direction.2.Given the only longitudinally translational motion,seismic inertia force was distributed according to the stiffness of the column and highly concentration of internal forces induced by bad configuration with local half-height continuous infilled walls(spandrel walls)led weight-bearing key members to fail one after one,then the total structure collapsed.3.Each floor only moved along the longitudinal direction,so the same displacement occurred at the column in the bottom story.In this case,the story-drift angles(inclination)of the columns constrained by local half-height continuous infilled walls were significantly greater than the ones of the unconstrained columns.Therefore,these columns were the first to fail under the effect of gravity,resulting in a larger collapse of the structure.