论文部分内容阅读
卓越的抗震性能一直是高层建筑结构设计不断追求的目标,而抗侧力体系则是实现该性能目标的关键因素.伸臂桁架体系作为目前最常见的抗侧力结构体系之一,广泛应用于各地标高层建筑中.然而,伸臂桁架体系的力学性能受桁架布设位置、拓扑形式、施工工序等因素影响,同时还存在整体结构竖向刚度不规则问题,因此,其实际抗震性能和优化途径值得关注.梯式连梁体系是一种较为新颖的抗侧力结构体系,每一层均设置水平连梁连接核心筒与巨柱,与伸臂桁架体系在某些楼层处形成集中刚度相比,其抗侧刚度分布更加均匀.为了对比上述两种抗侧力结构体系的抗震性能,以一栋80层的建筑模型作为研究对象,利用ETABS有限元程序建立其数值模型,并采用基于性能的抗震设计方法开展计算分析.按沿高度方向共设置4榀伸臂桁架进行设计,综合考虑结构自重、基底弯矩、基底剪力、层间侧移、筒体弯矩等多种因素,明确了伸臂桁架布设位置,分别是17～18层、32～33层、46～47层和62～63层.此外,建立了4种用钢量相同但几何拓扑形式不同的伸臂桁架模型,通过对比整体结构的自振周期以及在多遇地震和设防烈度地震作用下的基底剪力、弯矩和层间位移等地震响应,选取了最优的拓扑形式.在此基础上,利用等效刚度原则建立了梯式连梁体系数值模型,明确了连梁的截面形式和设计参数,确保其与伸臂桁架体系模型具有相同的整体抗侧刚度.采用FEMA 365指南中的构件性能曲线特征值以及性能水准判别准则,选取7组天然地震动和2组人工地震动记录作为输入参数,考虑三向地震作用,分别对伸臂桁架体系模型、梯式连梁体系模型和纯筒体体系模型开展了不同地震烈度下的非线性动力时程分析.计算结果显示:1)在位移响应方面,与纯筒体体系相比,伸臂桁架体系和梯式桁架体系在多遇地震作用下的最大层间位移分别减小了60％和47％,此时两种体系的修正系数R均为1,表明结构处于弹性阶段时伸臂桁架体系更加有效;在设防烈度地震作用下的最大层间位移分别减小了55％和69％,而在罕遇地震作用下则分别减小了56％和70％,此时两种体系的修正系数R分别为3和6,表明梯式连梁体系在结构处于弹塑性阶段时具有更好的延性和地震耗能特性,同时二者的顶点位移响应亦反映出同样的结构变形性能规律.2)在结构内力响应方面,伸臂桁架体系在多遇地震作用下能更加地有效降低核心筒的弯矩,而在设防烈度地震和罕遇地震作用下,梯式连梁体系对核心筒弯矩的降低作用则更为显著,表明在高烈度地震作用下梯式连梁体系能够更为有效地实现整体结构共同受力.3)在结构损伤状态方面,伸臂桁架体系和梯式连梁体系在多遇地震作用下各构件均处于立即使用(IO)性能水准,整体结构处于弹性状态;而在罕遇地震作用下,伸臂桁架体系中部分连梁构件达到生命安全(LS)和防止倒塌(CP)性能水准,相比而言,梯式连梁体系中达到防止倒塌(CP)性能水准的连梁数量显著增加,同时,两种体系中剪力墙构件的损伤状态均以防止倒塌(CP)性能水准为主,且梯式连梁体系中随高度增加,损伤程度稍加严重,但整体塑性损伤分布模式差别不大.由此可见,刚度等效原则更适用于结构在多遇地震作用下的计算分析,而在高烈度地震作用下该方法会导致耗能计算及损伤分布出现偏差,其适用范围具有一定局限性.“,”Excellent seismic performance of high-rise building is a continuous destination in structural engineering, that highly relies on the lateral load resisting system. As one of the most common lateral load resisting systems, the outrigger system is widely applied to skyscrapers. However, its mechanical properties are affected by the truss location, the topological form as well as construction process, in addition, the irregular vertical stiffness of the entire building occurs. Therefore, the actual seismic behavior and optimization methods are worthy paying attention to. The ladder system is a novel lateral load resisting system, in which the horizontal beams are set to connect the mega columns at each floor, resulting in a more uniform vertical stiffness compared with the outrigger system.In order to compare the seismic performance between the above two systems, the numerical models of 80-story building were established by means of the finite element program ETABS, and the performance-based seismic design method is adopted to carry out calculation and analysis. For the outrigger system, four levels of steel outrigger trusses were set along the height, and the specific locations that floor 17-18, floor 32-33, floor 46-47, and floor 62-63, respectively, were determined by considering the multiple factors including structural weight, base moment, base shear, inter-story drift, and core moment. In addition, the optimum topology of the outrigger truss was selected out of four different trusses\' topologies with the same steel consumption according to the favorable natural period and the global response of the structure, such as base shear, bending moment and inter-story drift under the action of frequent and moderate earthquakes. Subsequently, the ladder system was generated based on the principle of the equivalent lateral stiffness with the outrigger model, and the cross section as well as the design parameters were presented. Nonlinear dynamic time history analysis was carried out to compare the global and components\' performance between the outrigger, ladder, and stand-alone core systems under the FEMA356 guidelines requirements, where 7 sets of natural ground motions and 2 sets of artificial ground motions for different intensities were selected as a seismic input. The results showed that:1) comparing with the stand-alone core system, the inter-story drift under the frequent earthquake level was reduced by 60％ and 47％ in outrigger and ladder systems, respectively. While the modification factors of both systems equal to 1, denoting that outrigger system is more efficient in the elastic stage. However, under the rare earthquake, the inter-story drift reduction was 56％ and 70％ for outrigger and ladder systems, respectively. While the modification factors of two systems equal to 3 and 6, indicating that the ladder system has better ductility and energy dissipating performance in the elastoplastic stage. Besides, the top displacement response of both systems reflect the same structural deformation feature. This indicates that the outrigger system is more effective in the elastic stage, while the ladder system is more ductile in the elastoplastic stage dissipating more input energy. 2) The same trend was for the internal forces, where the outrigger system reduced the core bending moment under the frequent earthquake level, while the ladder system showed a superiority under the moderate and rare earthquake evaluation. 3) In terms of the damage state evaluation, all the structural components in both outrigger and ladder systems were under Immediate Occupancy ( IO) performance level for the frequent earthquake;while for the rare earthquake, most of the coupling beams reached the Collapse Prevention ( CP) performance level in the ladder system, while only some of them reached the Life Safety ( LS) and CP performance levels in the outrigger system. At the same time, the damage state of the shear walls was CP in both systems under the rare earthquake, and the damage state grew severer from lower to higher floors in the ladder system, however, the global plastic damage distribution has similarity between two systems. It can be concluded that the principle of the equivalent stiffness is more adequate under the frequent earthquake evaluation than the high earthquake intensity, where the calculation errors on energy dissipating and damage distribution would occur.