Seismic response analysis of structures with velocity-dependent dampers

This paper is concerned with seismic response analysis of structures with velocity-dependent passive energy dissipation devices, such as viscous and viscoelastic dampers. The modeling of a damper-brace component composed of a viscous or viscoelastic damper connecting with braces in series is presented. Several key parameters influencing the energy dissipation efficiency of such dampers in the damper-brace component are investigated and the relationships of the parameters and efficiency of the dampers are established. An equivalent model for the passive energy dissipation system is developed, which can significantly simplify the dynamic analysis of structures with the velocity-dependent dampers. The seismic responses of a single-story structure and a multi-story structure with the viscous and viscoelastic dampers are analyzed to verify the effectiveness of the passive energy dissipation devices for suppression of dynamic responses of structures and the reliability of the proposed simplified computational methods.     

Seismic response control of high arch dams including contraction joint using nonlinear super-elastic SMA damper

In this study, the shape memory alloy (SMA) restrainer bars utilized to reduce the seismic response of arch dams with vertical contraction joints were investigated. The SMA damper model and the nonlinear behavior of arch dams affected by contraction joint opening/closing during earthquakes were simulated in ANSYS. Moreover, the nonlinear damping control principle and method were discussed. The effectivity of the SMA restrainer bars in arch dams was assessed through comparing with a traditional measure of reinforced steel across contraction joints. The SMA restrainer bars were effective in limiting the relative openings of the contraction joints and reducing the seismic acceleration. In addition, the new SMA vibration damper devices of arch dams are simple and easy to install.     

Seismic response of base isolating systems with U-shaped hysteretic dampers

This paper proposes a base isolating system to reduce the seismic demands of low- or medium-rise structures and experimentally investigates its seismic response using shake-table tests. The base isolating system considered in this study consists of laminated-rubber bearings and U-shaped hysteretic (UH) dampers which are made of high toughness steel (HTS) and are machined with slotted holes to increase their deformation capacities. A base isolated 2-story specimen for shake-table tests was first designed and cyclic tests of laminated-rubber bearings and UH dampers implemented in the base isolating systems were then carried out. The component test for the laminated-rubber bearings shows typically low lateral stiffness with enough vertical stiffness to carry gravity loads. The test results for the UH dampers demonstrate that the use of HTS material and the introduction of the slotted holes details increase deformation capacities by inducing uniform stress distribution along a UH damper. Finally, shake-table tests were performed using specimens shaken with increasing ground acceleration records. The shake-table tests show that the proposed base isolating system with UH dampers limits the seismic demands of a base isolated structure by lengthening its structural period, concentrating displacement demands on the base isolating floor and adding seismic energy dissipation from the UH dampers.     

Seismic response control of asymmetric buildings using tuned mass dampers

The aim of the present study is to investigate the efficiency of the torsional tuned mass dampers (T‐TMDs) in response control of asymmetric buildings under bidirectional earthquake ground excitations. The efficiency of the T‐TMDs is compared with bidirectional tuned mass dampers (BTMDs). The T‐TMDs are oriented to the rotation of the structures about vertical axis with a single torsional mass attached to spring–dashpot elements, whereas the BTMD connects a single mass to two orthogonal sets of spring–dashpot elements oriented to principal axes of the building. The buildings are idealized three‐dimensional models with two translational and one torsional degrees of freedom for each floor. Three different configurations (cruciform‐shaped, L‐shaped, and T‐shaped) of multistory buildings are considered. The 5‐, 15‐, and 20‐story buildings with and without the tuned mass damper schemes are subjected to bidirectional earthquake ground excitation. In order to evaluate the effectiveness of the T‐TMDs and BTMD, the rotation, displacement, acceleration, and base shear force responses are computed. Parametric studies are conducted for all the configurations installed with the T‐TMDs and BTMD by varying their mass ratio, damping ratio, and ground motions. It is concluded that the T‐TMDs are more effective in mitigating the torsional response of asymmetric buildings as compared with the BTMD.     

弱连体结构地震反应分析

采用随机振动、时程分析及振型分解反应谱方法,分别对多种隔震支座刚度情况下的高位隔震大跨连体结构地震响应进行分析,从而得出连体结构在不同频率比(塔楼基频/隔震装置固有频率)下的地震响应关系曲线;通过对曲线进行分析,得出当塔楼基频与隔震装置的固有频率比大于1.2~1.4时,连接体桁架地震响应就可产生减震效果的结论。通过对比三种方法计算结果发现,反应谱法计算出来的连体桁架位移与其他两种方法相比有明显误差,当隔震支座刚度较小时尤为明显。     

软硬交互横向不均匀场地地震反应分析

软硬交互横向不均匀场地十分常见,其在强震作用下的地震反应对工程结构的安全有着重要影响,然而目前还很少有针对该场地地震反应分析的研究。基于精确动力刚度矩阵和均布荷载动力格林函数的间接边界元方法,经快速傅里叶逆变换,在时域内求解了层状半空间中软硬交互横向不均匀场地的地震反应问题。求解中将模型分解为含较硬介质的层状半空间域和较软介质域,同时将总波场分解为自由波场和散射波场两部分,通过在相应边界上施加斜线和水平线虚拟均布荷载,进而求解动力格林函数以模拟散射波场,自由波场可由直接刚度法方便求得。验证了方法的正确性,检验了求解模型的收敛性,进而开展了相应的数值计算分析,着重讨论了介质参数和软硬交界面倾角对场地地震反应的影响。研究表明:软硬交互场地中,较大的地表地震动响应发生在较软介质侧;软硬交界面的存在使得场地地表加速度响应发生突变,突变程度受介质参数和交界面倾角的影响显著;随着介质参数差异和交界面倾角的增大,地表加速度峰值增大,反应谱曲线显示短周期成分变得更为丰富,对基岩地震动的放大作用增强;软硬交界面对场地地表地震反应的影响主要在交界面外的两倍介质层厚度范围。     

Seismic response analysis of skew bridges with pounding deck-abutment joints

In this paper the seismic response of short skew bridges with deck-abutment pounding joints is revisited. The permanent deck rotations and transverse displacements of such bridges after the recent earthquake in Chile created an incentive to revisit their non-conventional behaviour. A novel non-smooth rigid body approach is proposed to analyze the seismic response of pounding skew bridges which involves oblique frictional multi-contact phenomena. The coupling of the response, due to contact, is analysed in depth. It is shown that the tendency of skew bridges to exhibit transverse displacements and/or rotate (and hence unseat) after deck-abutment collisions is not a factor of the skew angle alone, but rather of the plan geometry plus friction. This is expressed with proposed dimensionless criteria. The study also unveils that the coupling is more pronounced in the low range of the frequency spectrum (short-period excitations/flexible structures) and presents novel dimensionless response spectra for the transverse displacements and rotations, triggered by oblique contact in a skew bridge subsystem. Despite the complexity of the response, the proposed spectra highlight a clear pattern. The dimensionless rotations, arising from contact, decline as the ratio of the structural versus excitation frequency increases and become practically negligible in the upper range of the frequency spectrum. Finally, a pilot application to a typical skew bridge is presented.     

Seismic response of self‐centering precast concrete frames with hysteretic dampers

With the rapid development of cities and the invasion of major natural disasters such as earthquakes, the resilience city as a new design concept has been paid more and more attention. As an important branch of self‐centering seismic resisting system, self‐centering concrete frame system has been studied by many scholars. These studies prove that self‐centering concrete frame structure has excellent self‐centering ability but poor energy dissipation capacity. Adhering to the working principle of self‐centering structure and considering the development concepts of building industrialization and modularization, this paper proposed a kind of self‐centering precast concrete frame with hysteretic damper (SCPCHD). In order to verify its energy dissipation capacity and seismic performance, elaborate finite element models were established and elastoplastic dynamic time history analyses were carried out. The results showed that the SCPCHD frame has a similar interstory displacement response to the reinforced concrete (RC) frame and the energy dissipation performance of its joint is obviously superior to the RC frame under rare earthquake because the SCPCHD frame has low damage characteristics and excellent damping device. In summary, this paper proves the feasibility and superiority of the SCPCHD frame, providing reliable support for further research.     

Seismic performance of steel structures with slit dampers

During the Northridge and Kobe Earthquakes, many steel moment resisting frames suffered damage at the beam-to-column connections. In order to solve this problem, an innovative structural system with slit dampers was developed in this study, which could not only provide good seismic performance but could also be easily repaired after a heavy earthquake. In the proposed structural system, a mechanical joint is adopted that is equipped with a metallic damper as the beam-to-column connection. The main feature of this system is that plastic deformation is limited to the slit dampers at the bottom flange. The seismic performance of the proposed connection was verified through cyclic tests of three full-scale steel structures that had slit dampers and of one specimen that had a conventional welded moment resisting frame. Test results indicated that the proposed connection showed an excellent hysteretic behavior. In addition, the energy dissipation and plastic deformation in this system were concentrated only at the slit dampers, while the inelastic behavior of the beams and columns is prevented through appropriate capacity design.     

带RC耗能器-限位斜撑框架抗震性能研究

通过两榀设置钢筋混凝土耗能器框架的伪静力试验,对比了设有限位斜撑及未设限位斜撑两种方案下结构的抗震性能,得到了两种情况下各构件的破坏过程、破坏形态和框架的滞回特性等。通过计算分析探讨了耗能器、限位斜撑分别对结构承载力和刚度的贡献。结果表明,耗能器屈服可以先期消耗部分地震能量,改善了框架整体的延性,而限位斜撑则大幅提高了结构后期的承载能力,充分体现了设置多道抗震防线的思想。