Design of Slender Wall and Wall with Pilotis in Capacity Design of High-rise Residential Buildings

Abstract

As the risk of earthquake in Korea increases, interest in seismic design increases and application of related design standard is strengthened. It is difficult to predict seismic load accurately by seismic design method based on conventional elastic analysis. Therefore, capacity design method can be used for seismic design of high-rise residential building to evaluate seismic load more accurately and obtain optimal design result. However, in order to apply the capacity design method in design of Korean high-rise residential buildings, some precautions due to characteristics of structural system should be considered. Therefore, in this study, among the considerations for capacity design of high-rise residential building, the shear demand distribution for the slender shear wall system and the design of transfer zone in the pilotis-wall system were studied. First, the problem that occurred in the capacity design of slender shear wall system was that shear demand of actual case is considerably amplified compared to that of design case. If the amplified shear demand is not considered in design, structural members can be under-designed, resulting structural unsafety of the building. Therefore, amplification effect of shear demand was investigated and some design factors reflecting it in the capacity design process were proposed. By using Perform 3D, a nonlinear analysis program, nonlinear analysis modeling for each parameter were established and nonlinear dynamic analysis was carried out. Based on the analysis results, the factors affecting the shear demand amplification effect were analyzed and the base shear amplification factor for predicting the nonlinear shear demand was proposed. The proposed base shear amplification factor was determined by base over-strength factor and it can predict the nonlinear shear demand within the error range of 20%. Also, the story shear distribution model for nonlinear shear demand was suggested on the basis of average shear distribution of analysis results. The proposed story shear distribution model can predict the story shear demand more economically than conventional model which is suggested in Eurocode 8. The proposed base shear amplification factor and story shear distribution model can predict nonlinear shear demand of the wall more reasonably and secure the structural safety by preventing under-design. Next, the design consideration of the capacity design of the pilotis-wall system was an economical design method for the transfer zone in which the pilotis and wall are connected. A system in which the transfer girder was eliminated was proposed and a reasonable capacity design method for this system is proposed. To evaluate the structural performance of proposed system and verify the design method, cyclic loading tests and compression test were carried out. Based on principle of capacity design, the proposed pilotis-wall system without transfer girder was designed to prevent premature brittle failure in the transfer zone and pilotis and to induce ductile failure in the upper wall. Test results show that, in all the specimens, the premature brittle failure of the transfer zone and pilotis did not occurred, but in the upper wall, re-bars were yielded in the tensile side and concrete crushing occurred in the compressive side. The internal and external damage of the transfer zone and the pilotis were relatively limited. Through these results, it was confirmed that the preliminary design of the pilotis-wall system can be improved more economically without applying the special earthquake load and the presence of transfer girder.