Research On Novel Embedded Damage-controllable Rocking Wall-frame And Its Seismic Performance

The existing seismic design enhances the seismic capacity of the structure by increasing its strength and ductility,without concerning the repairability.The restraints at foundations or joints of rocking structures are released so that the rocking motions can occur during earthquakes.Damage at main structure is limited by concentrated displacement at rocking interfaces.The rocking structure is easy to be repaired and is an ideal type of sustainable damage-controllable structure.In this paper,the existing researches on rocking structures are classified,and then the research status and applications of different types of rocking wall structures are introduced in detail.In response to the deficiencies of existing research,a novel damage-controllable rocking wall with resilient corners and replaceable damper is developed innovatively,which is embedded in the frame to form a novel embedded damage-controllable rocking wall-frame structure.The seismic behavior of the proposed novel structure is analyzed from the component level and structural level through experimental research,theoretical analysis and finite element simulation.Subsequently,an innovative design method of the novel embedded damage-controllable rocking wall-frame for retrofitting is developed.The novel damage-controllable rocking wall consists of rocking elements,connecting beams,unbounded post-tensioned tendons and replaceable dampers.Cyclic tests on the novel walls were conducted by changing the conditions of dampers,corner elastomers and tendons,in which two sets of reusable reinforced concrete rocking elements were repeatedly used.The energy dissipation,deformation and self-centering capacity of the novel damage-controllable rocking wall were explored through the tests,and the features consisting of controllable damage,small residual displacement and convenient repair are verified.The motion of the novel damage-controllable rocking wall is divided as before rocking phase and after rocking phase.A new analytical model is developed to calculate the deformation of damaged rocking elements before rocking,with a new effective stiffness ratio accounting for the plastic deformation and a proposed damage influence coefficient accounting for the effects of damaged corners.A simplified rigid model is used to derive the geometric characteristics and hysteretic behavior of the damage-controllable rocking wall in the after rocking phase,and the influence of the anchor position of the pre-stressed tendons and the vertical displacement during rocking are concerned.A segmented analytical model of the novel damage-controllable rocking wall is proposed by combining two analytical models in the before rocking phase and the after rocking phase,and its accuracy is verified by experiments and simulations.Based on the analytical model,it is concluded that increasing the stiffness of the resilient corners,the area and the initial force of the tendons can increase the stiffness and bearing capacity of the wall;the enhanced yield force of damper can significantly improve the bearing capacity and energy dissipation,but will also weaken the self-centering ability of the wall,so the yield force of damper should not be too large.Based on two different software,ABAQUS and PERFORM-3D,the solid finite element model and the fiber macroscopic model of the novel damage-controllable rocking wall are simulated.The ABAQUS solid finite element model can simulate the slip and incongruous motion of the rocking elements,the rotation of the upper connecting beam and the change of the tendon force,during the reversed cyclic loading.The hysteretic curve of the solid finite element model is basically consistent with that of the experiment and the segment analytical models.The PERFORM-3D fiber macroscopic model,in which the rocking interface is simulated by Shear Wall unit without tension stress and the damper is simulated by Seismic Isolator unit,can basically simulate the motion of the novel rocking wall,and the hysteretic curve of which is almost the same as that of the analytical model.The characteristics of the novel embedded damage-controllable rocking wall-frame are investigated through the embedded segmented rocking wall-frame using elastic-perfectly plastic material.A calculation model,in which the ability of the frame to restrain the rocking wall is simplified as the stiffness at some position of the elastic beam with both ends fixed,is proposed and its accuracy is verified by the solid finite element model.A fiber macroscopic model for the embedded segmented rocking wall-frame is proposed,and the accuracy of the model is cross-validated with the solid finite element model.The simulation results of the embedded segmented rocking wall-frame show that,obvious vertical displacement at the contact position in beam is induced by the uplift of the embedded rocking wall;the inter-layer displacement angle of the multi-layer structure tend to be uniform,but the deformation shape of the structure is still shear type;the smaller the span of the frame or the larger the aspect ratio of the embedded rocking wall,the stronger the stiffness and bearing capacity,and the more uniform the inter-layer displacement of the structure.The span of the beam should not be too small and the aspect ratio(width to height ratio)of the rocking wall should not be too large to prevent the beam and floor from damage caused by large deformation.Using the solid finite element model and the fiber macroscopic model,which have been proved effective,the seismic performance of an eight-layer frame is compared with that of the corresponding novel embedded damage-controllable rocking wall-frame and other types of wall-frame through push-over analysis and seismic response analysis.The first-order mode period of the novel embedded damage-controllable rocking wall-frame is much smaller than that of the original frame,so it is necessary to consider the change of the seismic force of the novel structure when the mode period is reduced.The traditional shear wall-frame can achieve excellent structural performance under suitable design,which is a simple and well structural system if there is no requirement for the ability to control residual displacement.The capacity of the novel embedded damage-controllable rocking wall-frame to control the maximum displacement and residual displacement is the best when retrofitting an existing building,but the seismic performance of this structure is close to that of the traditional shear wall-frame when constructing a new building.Since the novel damage-controllable rocking wall is a type of prefabricated component,it is suitable for strengthening existing frames when the construction period is tight and the cost is allowed.The mode and seismic response analysis of linear multi-degree-of-freedom systems show that,the mode shapes and the corresponding mass participation coefficients are constant when the structural stiffness of each floor changes in same proportion,and the ratio of the square of the mode period is equal to the reciprocal of the structural stiffness ratio;the greater the difference in structural stiffness from the bottom to the top and the more the number of grades,the closer the shape of the first-order mode is to a straight line,while the corresponding mass participation coefficient is smaller.For the structure in which the first-order mode contributes the main response,the seismic strengthening can be performed by improving the lateral stiffness to suppress the displacement,and then the bearing capacity of the new component is designed according to the increment of the seismic force.A design method of the novel embedded damage-controllable rocking wall-frame for retrofitting is developed in this paper,combining the conclusions above with the existing research result of controlling the inter-layer displacement angle uniform using the wall and the considering of limiting the adverse effect caused by uplift of the rocking wall.A five-layer frame case is strengthened by this design method.The accuracy of the design theory and the reliability of the retrofitted structure are confirmed by time history analysis and seismic fragility analysis.