Study On Seismic Performance Of Frame Structure With Additional Shear Wall

After the Wenchuan earthquake,the seismic fortification categories of some key public buildings in China were adjusted from the original standard fortification to fortified emphasis,in order to improve their seismic resistance.Therefore,the existing buildings that were previously constructed according to the standard defense requirements cannot meet the current seismic defense requirements,thus requiring seismic strengthening measures.Many of these buildings are reinforced concrete frame structures.Therefore,it is meaningful to study seismic retrofitting of reinforced concrete frame structures.The increase of seismic fortification categories will raise the seismic performance requirements of reinforced concrete frame structures.It is very tedious and uneconomical to strengthen each node and each component of the structure individually.Properly adding some shear walls in the frame can not only improve the seismic bearing capacity of the structure,but also transform the original frame structure into a frame-shear wall structure.In a frame-shear wall structure,the seismic performance level of the frame can remain unchanged,avoiding the need for reinforcing each node and each component individually.After adding partial shear walls to a framed structure,its seismic performance cannot be analyzed as a monolithic frame-shear wall structure.One reason is that the forces acting on the interface between the new and old concrete in the structure with added shear walls are different from those in the monolithic frame-shear wall structure.Another reason is that the added shear walls do not bear the vertical compression stress generated by the loads.This paper uses numerical analysis to examine the differences in seismic performance,such as failure mode,bearing capacity,and ductility,between a framed structure with added partial shear walls and a monolithic frame-shear wall structure.The study also investigates the influence of concrete strength and the connection method between the added shear walls and the frame on the bearing capacity of the structure.The contents were as following:(1)The ABAQUS software was used to establish the framework structural model of the added shear walls,investigating the parameter settings of the new and old concrete interface and the method of vertical load application.The simulation results were compared with the experimental results,verifying the reliability of the interface treatment method.(2)Create framework models of five newly added shear walls with a height-to-width ratio of 1.5:SW0 refers to a monolithic frame-shear wall structure.SW1-4 refer to the frame structures of newly added shear walls.Among them,for SW1,all distributed reinforcement of the newly added shear wall is inserted into the frame,and the material strength level is the same;SW2 has the same connection method as SW1,but the concrete strength of the newly added shear wall is one level higher than the original frame;For SW3 and SW4,the horizontal distributed reinforcement of the newly added shear walls is not inserted into the frame column,but the concrete strength level of the newly added shear wall in SW3 is the same as SW0;The concrete strength level of the newly added shear wall in SW4 has been raised by one level compared to the original frame.Applying low-cycle fatigue loads to all models separately,the collapse modes and seismic performance,as well as properties such as bearing capacity,stiffness,and ductility of the structures,were analyzed.(3)Based on the collapse mode of the structure and the simulated unit stress results,a calculation formula for the shear bearing capacity of a frame structure with additional partial shear walls can be derived.The results show that: By combining Coulomb-friction model and cohesive force model,it is possible to simulate the force behavior of the interface between old and new concrete;As the bond strength between new and old concrete is relatively weak,the cracking load,yield load,and peak load of the frame structure with additional partial shear walls are all smaller than those of the monolithic frame-shear wall structure.Even if the concrete strength of the newly added shear walls is increased by one level higher than the original framework,it is still less than the load-bearing capacity of the monolithic frame-shear wall structure.Therefore,the load-bearing capacity should not be calculated based on the monolithic structure alone.The ductility of the frame structure with newly added shear walls is slightly better than that of the monolithic structure.The way of not connecting the newly added shear walls with the frame columns results in slightly lower load-bearing capacity and ductility than inserting distributed reinforcements into the frame,but the difference is not significant;Finally,based on the assumptions of plane section and beam-column model.Finally,based on the assumption of plane section and the tension rod model,the horizontal bearing capacity calculation formula of frame structure with new partial shear wall given in this paper,the calculated value fits well with the simulated value.