Direct Displacement-Based Seismic Design Method Of High Performance Concrete Shear Walls

Performance/Displacement-based Seismic Design theory,which was put forward in 1990s,has been receiving considerable attentions,and it is regarded as the development direction of seismic design theory in the future.In the seismic fortification system of structure,shear walls are the prime lateral force-resisting elements and it is used as the first seismic fortification line generally.The seismic behavior of shear walls has a significant effect on the seismic behavior of the whole structure.In recent years,high performance concrete shear walls are used in tall buildings or super tall buildings widely, but the application scope of high performance shear walls is restricted because of the brittle character of high performance concrete and shear walls.Study on the displacement-based seismic design method of high performance concrete shear walls can improve the deformation capacity of high performance concrete shear walls to some extent,enlarge the application scope of high performance concrete shear walls,has important theoretical significance and practical value.In this paper,Performance-based Seismic Design(PBSD) methodology is briefly introduced.The basic methodology and corresponding design procedure of Direct Displacement-based Seismic Design(DDBSD) are emphasized.Based on previous research achievements,it manages to solve some problems in the process of DDBSD method of high performance concrete shear walls,and it will make this new design method more practical for shear-wall structures.The main content is presented as follows:(1) The performance objective of high performance concrete shear walls.Based on the tests of 5 high-performance concrete shear walls which shear span ratios are 1.5 and 1.0,the failure mode,failure mechanism and deformation capacity of medium-high and low-rise shear walls are studied.The new reinforcement method of several rings like a chain along boundary element in plastic hinge zone is verified to improve the deformation capacity of shear walls effectively,it shows that the deformation capacity design method of shear wall is reliable to a certain extent,and it indicates that the rotation of plastic hinge zone is related to the damage level of shear walls well.According to the damage level,the performance of shear wall structure is divided into three levels: "serviceability,life-safety and collapse-prevention",the storey drift ratio and the plastic hinge rotation are both used as the performance controlling indicators of shear wall structures,and the proposed values for each performance level are provided in this paper.(2) The macro model for high performance concrete shear walls' nonlinear analysis.The fiber wall element model in CANNY program is used to analyze the shear wall's non-linear performance.4 shear wall specimens' analysis results are very agreement with their test results,and it proves that the fiber wall element model is reasonable and efficient in the nonlinear analysis of shear walls.(3) Pushover analysis procedure considering higher mode effect.In the procedure of modal pushover analysis,the capacity spectrum theory is used to take the place of dynamic time-history analysis.Converting the acceleration response spectrum of current code into displacement response spectrum,the displacement response of ESDOF in each mode can be calculated by capacity spectrum method.Then the displacement response of MDOF can be obtained too,and it is used to compare with the objective displacement of each performance level,judging whether the structure satisfying its performance objective or not.(4) The reasonable elastic stiffness of shear walls.The structural target period in "serviceability" is deduced by its target displacement based on the displacement response spectrum."Target period" method that demands the natural periods should be smaller than or equal to corresponding target periods is used to select the section rigidity of shear walls.It can ensure that the capacity curve in elastic range is in agreement with the demand curve,and the seismic capacity equals to the seismic demand basically.(5) The design bearing capacity of shear walls.The bearing capacity demand of each performance level is determined by the target displacement and corresponding elasto-plastic displacement response spectrum,and the maximum is regarded as the structural bearing capacity demand.The over-strength coefficient of high performance concrete shear walls designed by Chinese code which is defined as the ratio of actual bearing capacity to design bearing capacity is discussed,and the bearing capacity demand divided by over-strength coefficient equals to the design beating capacity which ensures the structure meeting its performance objective in inelastic stage.(6) The calculation method for shear capacity of shear walls.Based on 313 test data of shear capacity of RC shear wall,the paper analyzes the reliability of calculation method for shear capacity of shear wall proposed by Chinese code,ACI code and truss-arch model.Some influencing factors of the shear capacity of RC shear wall are discussed,and the calculating equations of shear capacity of RC shear wall are rebuilt adopting mathematical statistics method.It provides a valuable thought to the modifying of current code.(7) The plastic hinge rotation-based design method of shear walls' deformation capacity.The relationship between plastic hinge rotation and cross section's curvature, axial load ratio and relative height of compression zone are deduced.The length of confined zone can be determined by plane-section assumption theory,and the transverse reinforcement characteristic value is determined by the stress-strain relationship of confined concrete.The length of confined zones and the transverse reinforcement characteristic values of boundary element in different seismic grades and axial load ratios are proposed.The paper illustrates the application of the proposed procedures above mentioned with an example and attempts to prove its feasibility.It provides a valuable thought to DDBSD method of high performance concrete shear wall structures.