非线性弹性模量对波速影响的实验研究

在循环应力作用下，对砂岩和石英砂两种结构较松散的样品进行了实验研究。对非线性模量与应变的关系作了非线性拟合，用非线性模量代替弹性模量，对弹性介质中的波速公式作了修正。将波速与应力的多值函 数关系转化成波速作为应变（或密度）的单值函数。同时考虑了水饱和对非线性模量和波速的影响，得出了速度与应变的拟合关系曲线。实验数据和理论曲线有较好的一致性。     

反复荷载下碳纤维布加固钢筋混凝土框架梁的试验研究

通过2个碳纤维布加固钢筋混凝土框架梁和1个未加固框架梁的对比试验，分析了低周反复荷载作用下碳纤维布加固框架梁的加固效果，提出了加固梁的正截面承载力计算方法。     

Hysteretic model development and seismic response of unbonded post‐tensioned precast CFT segmental bridge columns

The study investigated the cyclic behavior of unbonded, post‐tensioned, precast concrete‐filled tube segmental bridge columns by loading each specimen twice. Moreover, a stiffness‐degrading flag‐shaped (SDFS) hysteretic model was developed based on self‐centering and stiffness‐degrading behaviors. The proposed model overcomes the deficiency of cyclic behavior prediction using a FS model, which self‐centers with fixed elastic and inelastic stiffnesses. Experimental and analytical results showed that (1) deformation capabilities of the column under the first and second cyclic tests were similar; however, energy dissipation capacities significantly differed from each other, and (2) the SDFS model predicted the cyclic response of the column better than the FS model. Inelastic time‐history analyses were performed to demonstrate the dynamic response variability of a single‐degree‐of‐freedom (SDOF) system using both models. A parametric study, performed on SDOF systems subjected to eight historical earthquakes, showed that increased displacement ductility demand was significant for structures with a low period and low‐to‐medium yield strength ratio and reduced displacement ductility demand in these systems was effectively attained by increasing energy dissipation capacity. Copyright © 2008 John Wiley & Sons, Ltd.     

An improved method of evaluating liquefaction potential with the velocity of shear-waves

According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic shear modulus, which shows the relation of G _max (kPa) with (σ_d/2)^1/2(kPa)^1/2. When applied to soils from different sites, the correlation can be normalized in reference to its minimum void ratio (e _min). Accordingly, an improved method is established to evaluate the liquefaction potential with shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the maximum acceleration during earthquakes, which can be used to explain the phenomenon that the possibility of liquefaction decreases with the increment of the depth. Compared with previous methods this method turns out simple and effective, which is also verified by the results of cyclic triaxial tests. Foundation item: State Natural Science Foundation (59678020) and Natural Science Foundation of Zhejiang Province (RC9609).     

地电阻率年变化与气象因素及水位的关系

为了消除d_s 观测资料中的年周期变化,对宝坻、塘沽地震台的地电阻率观测资料与台站附近地区的气压、气温、相对湿度、水位及海水水位的同期资料进行了相关处理分析, 并对地电阻率年周期变化产生的原因进行了分析,认为产生地电阻率与气象要素年周期变化的外因是同一源场作用的结果。 而地电阻率变化的内因,则是基于地下咸水层厚度的改变及地壳应力场的变化。 采用最小二乘法由气象参量和水位变化拟合出地电阻率模型值, 并计算出观测值与拟合值的残差,以消除电阻率观测资料中的年周期变化。结果表明, 近年来华北地区发生的 6级左右地震前,在宝坻、塘沽地震台的观测资料中均存在明显的短期前兆异常。     

在二维应力状态下地震触发砂土液化动应力条件

在二维应力状态下,地震在土体中不仅产生动水平剪应力τｈｄ,而且也引起在一般情况下不可忽略的竖向与水平动正应力关「σｖｄ－σｈｄ」／２,二者定义为动偏应力之二分量,均应是评估土体或土工结构物变形及其稳定性的主要因素。本文给出了在地震动偏应力二分量共同作用下,土单元中最大往返剪切作用面及其上最大动剪应力比「τｄ／σｓ」ｍａｘ的确定方法。据此,提出了地震触发砂土液化的应力条件及液化判别准则。     

沿深度强度增加软土中吸力锚循环承载力模型试验

采用分层底部真空预压技术,在模型试验箱内制备强度沿深度增加的模型试验土层;进而利用自行开发的电动伺服加载装置,在荷载控制方式下,针对水平破坏模式,进行两种直径的吸力锚在最佳系泊点受倾斜方向静荷载与循环荷载共同作用下的承载力模型试验。试验结果表明,循环荷载作用过程中锚的循环变形没有明显增加,导致锚破坏的是循环累积变形。强度沿深度增加软土和均一强度软土中吸力锚循环承载力的相对变化规律一致,当循环破坏次数为100时,循环承载力是静承载力的90%左右;当循环破坏次数增加至2 000时,循环承载力减小至静承载力的70%左右。锚径的变化只影响循环承载力的大小,不影响其相对变化。强度沿深度增加土层中的吸力锚,其循环荷载下竖向阻力弱化程度大于水平阻力弱化程度,这与均一强度土层中吸力锚受循环荷载作用时的性态一致。     

A regularized fiber element model for reinforced concrete shear walls

Reinforced concrete shear walls are used because they provide high lateral stiffness and resistance to extreme seismic loads. However, with the increase in building height, these walls have become slenderer and hence responsible of carrying larger axial and shear loads. Because 2D/3D finite element inelastic models for walls are still complex and computationally demanding, simplified but accurate and efficient fiber element models are necessary to quickly assess the expected seismic performance of these buildings. A classic fiber element model is modified herein to produce objective results under particular loading conditions of the walls, that is, high axial loads, low axial loads, and nearly constant bending moment. To make it more widely applicable, a shear model based on the modified compression field theory was added to this fiber element. Consequently, this paper shows the formulation of the proposed element and its validation with different experimental results of cyclic tests reported in the literature. It was found that in order to get objective responses in the element, the regularization techniques based on fracture energy had to be modified, and nonlinearities because of buckling and fracture of steel bars, concrete crushing, and strain penetration effects were needed to replicate the experimental cyclic behavior. Thus, even under the assumption of plane sections, which makes the element simple and computationally efficient, the proposed element was able to reproduce the experimental data, and therefore, it can be used to estimate the seismic performance of walls in reinforced concrete buildings. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation of the seismic response of high‐rise buildings supported on tension‐resistant elastomeric isolation bearings

In many applications of seismic isolation, such as in high‐rise construction, lightweight construction, and structures with large height‐to‐width aspect ratios, significant tension forces can develop in bearings, raising concerns about the possible rupture of elastomeric bearings and the uplift of sliding bearings. In this paper, a novel tension‐resistant lead plug rubber bearing (TLRB) with improved tension‐resisting capabilities is developed and experimentally and numerically assessed. This TLRB consists of a common lead plug rubber bearing (LRB) and several helical springs. After describing the theory underlying the behavior of the TLRB, the mechanical properties of reduced‐scale prototype bearings are investigated through extensive horizontal and vertical loading tests. The test results indicate that TLRBs can improve the shear stiffness and tension resistance capacity even under significant tensile loads. A series of shaking table tests on scaled models of high‐rise buildings with different aspect ratios were conducted to investigate the dynamic performance of the TLRB and the seismic responses of base‐isolated high‐rise buildings. Three different cases were considered in the shaking table tests: a fixed base condition and the use of TLRB and LRB isolation systems. The results of the shaking table test show that (a) base‐isolated systems are effective in reducing the structural responses of high‐rise buildings; (b) an isolated structure's aspect ratio is an important factor influencing its dynamic response; (c) TLRBs can endure large tensile stresses and avoid rupture on rubber bearings under strong earthquakes; and (d) the experimental and numerical results of the responses of the models show good agreement. Copyright © 2016 John Wiley & Sons, Ltd.     

单、双向动三轴试验条件下饱和砂动力特性对比

在饱和砂土地震液化评估中,多用单向动三轴试验代替双向动三轴试验获得土体的抗液化强度。由于单向激振和双向激振产生的应力路径不同,土的动力特性受应力路径影响,其合理性尚待证明。本文利用双向振动三轴仪分别采用单、双向振动形式进行饱和砂土振动液化试验,对比了相同动剪应力作用下累积孔压和动强度,分析了较大循环振次作用下单、双向振动方式使试样动力响应产生差异的原因,提出了利用单向三轴试验代替双向振动模拟地震循环剪应力获得砂土动力特性的室内试验方法的适用条件。