Seismic Damage Mechanism Of RC Frame Stuctures On The Slope

Step-terrace frame structure, a typical structure for mountainbuilding, has a very wide range of applications. This kind of structure is supported by pillars with different height, which results in a significant different mechanical performance between step-terrace structure and normal structures. Until now, there is no relevant design code for mountain buildings at home and abroad. And the seismic theoretical research for mountain frame structures is seriously lagging behind the needs of engineering practice. The plane model has long-being used as the main research object for the seismic response analysis of structures, as a result of the slow developing in multidimensional study for structures and the unit model adopted being unable to simulate the influence of some key problems such asthecoupling of flexural and axial action in both directions in frame column. On the other hand, the influence of the modeling methods, used for the seismic response analysis of mountain structures, is less researched. Therefore, it is necessary to study the correlation of seismic action between plane model and space model in mountain frame structures.The research objects are space step-terrace structure located in 8 degree seismic regions(0.2g) and the plane step-terrace structure extracted from space step-terrace structure in both directions. Perform-3D is used to analysis the seismic performance of the space step-terrace structure from both global and local level which is under the influence of near-fault ground motions and far-field ground motions. In addition, the correlation of seismic action between plane model and space step-terrace frame structure model under the influence of bi-directional earthquake is studied by being compared with space step-terrace frame structure model which is subjected to unidirectional earthquake.The main conclusions of this article are as follows:â‘  Compared to far-field ground motions, near-fault ground motions containing velocity pulse are rich in low-frequency components, which may have a more adverse impact on the long period(greater than 0.9s) structures; On the contrary, far-field ground motions are abound with high-frequency components, which may result in the short period(less than 0.9 s) structure damaged seriously. The seismic responses of space step-terrace frame structure are to be enlarged in different degree by near-fault ground motions containing velocity pulse. Judging from its max story drift ratio which exceed one-fiftieth, a limited plastic displacement angle provided GB50011, it is found that the consideration for the influence of the pulse in near-fault ground motions is insufficient in current codes. Meamwhile, the vertical groud motion in near-fault region which makes axial force of columns change violently, will significantly influence the flexural bearing capacity and shear bearing capacity of columns for the frame, and the capacity of columns may be controlled by the tension-bending and tension-shear forces.â‘¡ The seismic responses of space step-terrace frame structure in longitudinal slope direction(X direction) are rather close to that of plane step-terrace frame structure, while the responses in the other direction are quite different. So, it is feasible to replace the seismis responses of space step-terrace frame structure in longitudinal slope direction(X direction) with plane step-terrace frame structure in the same direction. And the above method may unreliable when it comes to the other direction.â‘¢ In terms of indicators of local reactions, for all three different models in the X direction, their rate of rod-end hinges, rod-end angle distribution and distribution of plastic hinges are quite consistent; The typical "beam-column hinges" mechanism is formed in all models. Compared with column-hinge, beam-hinge has a larger rotation amplitude and its distribution is more even; The column-hinges are mostly formed in one side and distributed unevenly, which results in the major damage appearing at the bottom of column in upper grounding floor. Under bi-directional seismic action, the number of column-hinges, the rotation value and the accumulated story drift in space step-terrace frame structure are significantly higher than those of the rest of both; The features of beam-hinges in all the three models are familiar; The number of beam-hinges, the rotation value and the accumulated story drift in space step-terrace frame structure under unidirectional seismic action are in the middle of the three.â‘£ Through a comparative analysis of seismic responses of the three different models in Y direction, it is found that the number of hinges, the maximum of rotation at rob end, the distribution of rotation after the yield of rob end, the distribution of plastic hinge and the accumulated story drift in the plane frame( Ydirection) have a great difference compared with the other two models.