Shaking table tests of tunnel linings in progressive states of damage

Tunnels have long been assumed to be able to withstand earthquakes and suffer little damage. However, investigations of tunnels after the Wenchuan earthquake in China revealed that over 30 tunnel linings were cracked. Different types of cracks were found in almost all the tunnel linings. In this study, a series of shaking table tests were conducted on scaled tunnel models under seismic excitations with increasing intensities. White noise sweep tests were interlaced with the seismic excitations to identify the damage in the tunnel linings. The accelerations and strains of the tunnel lining were measured. The test results are discussed based on the dominant frequencies, amplification factor, and lining strains. Furthermore, this paper presents the results of damage identification for various states of damage using the white noise sweep method. The dominant frequencies decreased with an increase of the input peak ground acceleration (PGA), which also reflected the damage of the tunnel lining. The dominant frequencies decreased by approximately 32% for an input PGA intensity of approximately 0.6 g, but the first cracks could still be visually detected. The cracks gradually propagate with the PGA increasing from 0.6 to 0.8 g. The effect of lining damage on the seismic performance of tunnel linings should be considered in the seismic design of tunnels.     

超长混凝土基础隔震结构温度应力分析

温度应力一直是超长结构中需要解决的主要问题。本文采用大型有限元分析软件SAP2000对超长混凝土结构隔震与非隔震下的温度应力进行分析比较,研究了基础隔震超长结构在温度应力下的受力特点,提出了超长结构温度应力控制的新思路,为以后工程设计人员提供了一些可供借鉴的理论和方法。     

含有屈曲约束支撑框架的振动台试验研究

通过对含有屈曲约束支撑的框架进行振动台试验,研究了屈曲约束支撑对结构地震反应的减震效果。选用3条天然波和1条人工波进行加载,记录了模型的加速度反应,分析了BRB在试验中的力学性能,并与理论计算值进行了对比,研究了台面输入加速度为0.6g和1.0g时框架底层BRB的滞回曲线。探讨了不同台面输入下输入能量在模型中的分布情况。试验及研究结果表明,当台面输入加速度小于0.6g时,屈曲约束支撑可以为结构提供稳定的侧向刚度;当台面输入加速度大于0.6g时,屈曲约束支撑通过自身塑性变形来吸收能量;当台面输入加速度为1.0g时,屈曲约束支撑可以吸收台面输入的20%~40%的能量。     

The use of the diagonal compression test to identify the shear mechanical parameters of masonry

In this paper, the mechanical meaning, the experimental evaluation and the proper use of the mechanical parameters, which the most diffused simplified models for the prediction for the Diagonal Cracking failure mode in masonry piers are based on, are analysed. Moreover, a procedure to obtain a “mean” evaluation of the cohesion and the friction coefficient of mortar joints of masonry through the diagonal compression test is proposed. In order to assess the reliability of the procedure, a set of non-linear numerical simulations have been performed.     

Shear response of brick masonry small assemblages strengthened with bonded FRP laminates for in-plane reinforcement

Modern composite materials are receiving increasing attention as reinforcing solutions applicable to the repair and strengthening of concrete and masonry structures. Aiming towards a better characterization of the possibilities offered by these materials, the research work reported here investigates the shear response of small masonry assemblages strengthened externally with sheets made of glass and aramid fiber reinforced polymer laminates. An alternative strengthening approach provided by microlaminated wood is also investigated.The assemblages, consisting of masonry couplets, were subjected to combined shear and axial loading and were laid to failure through monotonic and cyclic loading processes. The efficiency of the different strengthening materials is investigated by comparison with measures obtained for unreinforced assemblages subjected to similar load conditions. The research is aimed at characterizing the contribution of the different strengthening materials and arrangements to increase both the peak shear strength and the residual (post-peak) shear strength. An attempt is made to analytically describe the strengthening effect of reinforcement. For this purpose, two different effects provided by the reinforcing laminates – the increase of friction at the brick–mortar interface and the shear strength of the laminate itself – are considered.     

Assessment of modal pushover analysis and conventional nonlinear static procedure with load distributions of federal emergency management agency for high‐rise buildings

The nonlinear static pushover analysis technique is mostly used in the performance‐based design of structures. However, the pushover analysis with load distributions of Federal Emergency Management Agency (FEMA) loses its accuracy in estimating the seismic responses of long‐period structures where higher mode effects are important. Recently, modal pushover analysis (MPA) has been proposed to consider these effects. Hence, FEMA load patterns and MPA are evaluated in the current study and compared with inelastic response history analysis. These approximate procedures are applied to medium‐rise (10 and 15 stories) and high‐rise (20 and 30 stories) buildings; advantages and limitations of them are elaborated. It is shown that MPA procedure presents significant advantage over FEMA load distributions in predicting story drifts. MPA is able to compute hinge plastic rotations better than FEMA load distributions at upper floor levels of high‐rise buildings due to considering higher mode effects by this procedure, but both are unsuccessful in predicting hinge plastic rotations with acceptable accuracy. Copyright © 2008 John Wiley & Sons, Ltd.     

NGA衰减关系应用于重大水电工程抗震设计的可行性探讨

选择大震近场条件的实际基岩记录、我国地震安评工作常用衰减关系和现行水工规范谱与NGA衰减关系进行比较,研究考虑近断层特性的NGA衰减关系用于描述近场、大震条件下地震动的优势,论证NGA衰减关系在我国水电工程抗震设计中应用的可行性,并指出大震近场条件下规范谱的缺陷和修订方向。     

Space–time SUPG finite element computation of shallow-water flows with moving shorelines

We show that combination of the Deforming-Spatial-Domain/Stabilized Space–Time and the Streamline-Upwind/Petrov–Galerkin formulations can be used quite effectively for computation of shallow-water flows with moving shorelines. The combined formulation is supplemented with a stabilization parameter that was originally introduced for compressible flows, a compressible-flow shock-capturing parameter adapted for shallow-water flows, and remeshing based on using a background mesh. We present a number of test computations and provide comparisons to theoretical results, experimental data and results computed with nonmoving meshes.     

On the seismic response of shallow-buried rectangular structures

Compared to bridges, underground structures are inappropriately regarded as less crucial components of road infrastructure in view of their supposedly low seismic vulnerability. The literature indicates, however, that shallow-buried rectangular structures, such as box culverts or rectangular tunnels, can be affected by shaking failure. To avoid the complexity of a fully non-linear soil–structure interaction analysis, a number of simplified methods have been proposed in recent years, which have gained popularity among designers. The aim of this paper is to investigate the applicability limits of such simplified analyses. The study compares the results obtained using simplified approaches with those emerging from non-linear static soil–structure interaction analyses, accounting for the following effects: the frictional behavior of the soil–structure interface, the geometry of the box structure, the overburden depth, the maximum PGA, and the increasing soil stiffness with increasing depth. The outcomes of the analysis indicate that shallow-buried rectangular structures are strongly affected by non-linear frictional effects at the soil–structure interface. The soil–structure interaction under seismic condition is shown to change smoothly from the condition of deep burial to the condition of “null overburden depth”. For a given aspect ratio, stiff, shallow-buried rectangular structures prove to be affected more deeply by sliding at the soil–structure interface than flexible structures and, for low aspect ratios, these structures may undergo a rigid rotation (rocking) that may even involve a partialization of the base foundation. For a reliable evaluation of member forces from racking distortions, rocking must be carefully taken into account.