Outrigger system analysis and design under time‐dependent actions for super‐tall steel buildings

The outrigger system has been widely adopted as an efficient structural lateral‐load resisting system for super‐tall buildings in recent years. Although the outrigger system has many structural advantages, it has a significant defect due to differential shortening, which cannot be neglected. Due to the shrinkage and creep of concrete, as well as the differential settlement of foundation, the shortening of the structural member is an important time‐dependent issue, which leads to additional forces in the outriggers after the lock‐in of the outriggers. As a result, it will increase the size of the structural member cross section in the design. In a real project, engineers can delay the lock‐in time of the outrigger system to release the additional forces caused by the differential shortening during the construction phase. The time‐dependent actions, such as the column shortening and the differential settlement of the foundation, were estimated. A mega frame steel structure was employed to illustrate the analysis and design of the outrigger under the time‐dependent actions. Furthermore, a simple optimal method, considering the structural stability and overall stiffness, was proposed to optimize the construction sequence of the outrigger system.     

山东平安金融中心塔楼结构设计

山东平安金融中心塔楼建筑高度360m,地上结构采用型钢混凝土框架柱-钢框架梁和钢筋混凝土核心筒组成的双重抗侧力体系,并布置3道加强层。塔楼中区外框柱均倾斜布置以满足建筑外立面的变化。塔楼为超高、超限结构,风荷载按照《建筑结构荷载规范》(GB 50009—2012)及风洞试验结果包络设计。采用ETABS和YJK两种软件对主塔楼结构进行弹性分析,并采用LS-DYNA软件进行动力弹塑性分析。塔楼各项分析结果均满足规范及超限审查要求,并满足设定的抗震性能目标,塔楼整体结构安全可靠。     

Energy dissipation and performance assessment of double damped outriggers in tall buildings under strong earthquakes

The use of a single set of outriggers equipped with oil viscous dampers increases the damping ratio of tall buildings in about 6–10%, depending on the loading conditions. However, could this ratio be further increased by the addition of another set of outriggers? Should this additional set include dampers too? To answer these questions, several double damped outrigger configurations for tall buildings are investigated and compared with an optimally designed single damped outrigger, located at elevation 0.7 of the total building's height (h). Using free vibration, double outrigger configurations increasing damping up to a ratio equal to the single‐based optimal are identified. Next, selected configurations are subjected to several levels of eight ground motions to compare their capability for avoiding damage under critical excitations. Last, a simplified economic analysis highlights the advantages of each optimal configuration in terms of cost savings. The results show that, within the boundaries of this study, combining a damped outrigger at 0.5h with a conventional outrigger at 0.7h is more effective in reducing hysteretic energy ratios and economically viable if compared with a single damped outrigger solution. Moreover, double damped outrigger configurations for tall buildings exhibit broader display of optimal combinations, which offer flexibility of design to the high‐rise architecture.     

带伸臂超高层结构最优伸臂道数及位置确定的灵敏度向量法

以最大层间位移角为优化目标,提出一种简单有效的向量积算法,可以快速确定最优的伸臂桁架设置数目及位置。以上海中心大厦为例,给出了该算法的应用方法及过程,并结合分析结果对带伸臂超高层结构的最优伸臂道数及位置的设置规律进行了分析。对于典型的100层以上的超高层建筑,向量积算法的效率比常规的穷举法提高约28倍。分析表明,最优的伸臂桁架设置方案与桁架设置的数目和位置均有关系,且伸臂桁架设置方案的最优性并非随着伸臂桁架数目的增加而增加。     

Strength demand of dual‐purpose outrigger system for reducing lateral displacement and differential axial shortening in a tall building

Certain maximum lateral displacement (LAT) and differential axial shortening (DAS) values can lead to the deterioration of the serviceability of a structure. Previous studies indicated that an outrigger system can be used to control both the DAS and the LAT in a tall building. In order to enhance the applicability of the dual‐purpose outrigger system, the amount of stress developed on the outrigger due to the reductions of the LAT and DAS should be determined. Therefore, in this study, the stresses due to the LAT and DAS were analyzed in terms of the reduction ratio of the LAT and DAS, and the absolute sum of stresses, which was the strength demand of the outrigger, was evaluated as well. To identify the parameters affecting the additional stress of the outrigger, analytic equations were proposed to predict the additional shear force acting on the outrigger due to DAS reduction. A finite‐element analysis was performed to quantitatively identify the reduction ratio of the LAT and DAS as well as the resulting stress by changing four parameters: the stiffness, location, number, and connection time of outriggers. The results demonstrated that the stress of the dual‐purpose outrigger can be minimized by adjusting the design parameters.     

Simultaneous size and topology optimization of 3D outrigger‐braced tall buildings with inclined belt truss using genetic algorithm

To investigate the optimum location of the outrigger system, a metaheuristic‐based size and topology optimization of the outrigger‐braced tall buildings is carried out by various three‐dimensional structural frames with different shapes of belt trusses. By considering the elastic behavior, the whole elements of the structural models such as beams, columns, core, and trusses are optimized simultaneously in conjunction with the location of the outrigger. Furthermore, to reach more optimality, several novel types of belt truss are proposed having inclined and inverse‐inclined belt trusses with better structural and architectural features and optimum performance in comparison with the horizontal one. Different models with 25 to 40 stories having various span numbers are optimized using the genetic algorithm, and the results are compared with each other. In the modeling process, the exact wind load distribution is applied to the structure based on the ASCE7‐16 rather than the uniform or triangular ones. According to the results, the optimum cross‐sectional size and outrigger locations of different models are obtained, and it is indicated that the proposed novel belt trusses are optimal solution for the problem.     

平安金融中心结构设计研究综述

平安金融中心塔楼采用巨型空间斜撑框架-劲性钢筋混凝土核心筒-外伸臂结构体系,有效满足了该超高层结构的设计要求。通过合理地配置内筒、外框结构的刚度及其连接构件,形成多重抗侧力结构体系,充分发挥了结构构件的效用,保证了结构的安全性。对结构进行了深入细致的计算分析,并展开各项试验研究,以保证工程的安全性和合理性。     

兰州红楼时代广场超限高层性能化抗震设计

兰州红楼时代广场屋顶结构标高245.60m,是目前西北地区第一高楼,地处兰州市中心,设防烈度为8度(0.20g),地震安全性评价的设防烈度接近8度(0.30g)。项目除高度超限外,还存在其他多项超限内容,如利用避难层设置2道加强层,裙楼局部利用转换桁架实现抽柱转换,塔楼顶部和裙楼入口处形成斜切面,核心筒剪力墙从层55开始内收等。进行了基于性能的抗震设计,根据构件的重要性分别提出不同的性能设计目标,并采取相应抗震加强措施。通过不同程序分别进行了中震弹性和不屈服计算、以及大震弹塑性分析。分析表明,所提出的各种性能化目标均得到实现,性能化抗震设计和采用的抗震措施能满足结构"小震不坏、中震可修、大震不倒"的抗震设防要求。     

超高层建筑结构环带桁架的研究与设计

框架-核心筒结构是超高层建筑中最常用的结构体系之一.当结构抗侧刚度不足时,在设备层设置水平伸臂桁架可以显著增大结构的抗侧刚度,减小结构位移,降低水平荷载作用下核心筒的倾覆力矩.但是传统的伸臂桁架设置会带来一系列问题,例如容易引起结构刚度、结构内力的突变,产生较大的附加内力,连接节点复杂,施工周期长等.而环带桁架加强层可...     

汽车起重机支腿反力简化计算方法与实验验证

在汽车起重机支腿反力计算中,提出了必须同时考虑车架大梁扭转变形和支腿弯曲变形的观点,并据此建立了起重机支腿反力计算模型。通过实验验证,表明文中给出的计算模型能较好地反映支反力的幅值与变化规律,为后续的实验和结构优化提供了理论依据。