Research on controlling long-term performance by tensioning post tendon of long-span continuous rigid-frame bridges

The problems like cracking of the girder in the mid-span and the ever-increasing vertical deflection appear during the long term usage of the long-span continuous rigid-flame bridge. Post-tension tendon with re- served duct can increase the pre-stress of the main beam effectively, and decrease the long term span deflection in order to improve the performance of the girder. At the same time, the proper tension position is very crucial to optimise the stress distribution of the bridge and control the deflection increase. Combining with practical en- gineering, the authors analyze the influence of different positions of post-tension tendon （ including top-, web- and bottom plate tendons） on the stress and deflection of the main beam, and find out the optimal position of post tendon.     

张力腿平台局部节点强度可靠度分析方法

局部节点可靠度分析对张力腿平台(TLP)整体安全性评估具有重要意义。提出了一个TLP平台局部节点可靠度的分析方法,首先对TLP平台整体进行分析,统计局部节点各种失效模式并得到典型失效模式及对应的典型荷载工况;然后应用改进的子模型技术对TLP平台局部节点进行极限承载能力分析,确定了局部节点在典型荷载工况下的极限承载力;对局部节点极限承载力及南海某区域的波浪荷载进行统计分析,得到其概率统计特性;在此基础上计算了TLP平台局部节点对应典型失效模式下的可靠度指标。通过算例分析表明,该TLP平台各节点可靠度指标值均大于3.1;立柱与浮箱连接节点在不同荷载工况下失效模式不同,而立柱与甲板连接节点易发生管交汇处剪切破坏。为TLP平台的安全性评估提供了一种有效的分析方法,具有一定的理论价值及实用价值。     

A finite element cable model and its applications based on the cubic spline curve

For accurate prediction of the deformation of cable in the towed system, a new finite element model is presented that provides a representation of both the bending and torsional effects. In this paper, the cubic spline interpolation function is applied as the trial solution. By using a weighted residual approach, the discretized motion equations for the new finite element model are developed. The model is calculated with the computation program complier by Matlab. Several numerical examples are presented to illustrate the numerical schemes. The results of numerical simulation are stable and valid, and consistent with the mechanical properties of the cable. The model can be applied to kinematics analysis and the design of ocean cable, such as mooring lines, towing, and ROV umbilical cables.     

Numerical models and ductile ultimate deformation response of post‐tensioned self‐centering moment connections

New steel moment‐resisting connections that incorporate post‐tensioning elements to provide a self‐centering capacity and devices to dissipate seismic input energy have recently been proposed and experimentally validated. Experimental studies have confirmed that these connections are capable of undergoing large lateral deformations with negligible residual drifts. To facilitate their implementation, accurate modeling of the behavior of systems incorporating post‐tensioned connections must be readily available to designers and researchers. A number of simplified models have been suggested in the literature by researchers trying to capture experimental results at the beam–column connections and thereby to predict the global response of structures incorporating such connections. To provide a clear set of guidelines for the modeling of post‐tensioned steel frames, for practicing engineers as well as researchers, in this paper three types of numerical models of increasing complexity are presented: (i) a sectional analysis procedure, (ii) a lumped plasticity spring frame leveled approach and (iii) a non‐linear solid finite element analysis to predict the response at ultimate deformation levels. The analytical results obtained from the numerical models predict well the structural behavior of these connections when compared with available experimental data. Even at the ultimate deformation level, analytical results are in good agreement with test results. Furthermore, detailing requirements are proposed to assure that flexural hinges form in the beams in order to improve the cyclic response of steel self‐centering connections when drifts exceeding the design drifts are imposed to the system. Experimental and analytical studies demonstrate that steel post‐tensioned self‐centering connections incorporating the proposed detailing in the beams develop an increased deformation capacity and thereby exhibit a ductile response while avoiding a sudden loss of their strength and stiffness. Copyright © 2008 John Wiley & Sons, Ltd.     

Interfacial tension measurements and wettability evaluation for geological CO2 storage

Interfacial interactions, namely interfacial tension, wettability, capillarity and interfacial mass transfer are known to govern fluid distribution and behavior in porous media. Therefore the interfacial interactions between CO₂, brine and oil and/or gas reservoirs have a significant influence on the effectiveness of any CO₂ storage operations. However, data and knowledge of interfacial properties in storage conditions are scarce. This issue becomes particularly true in the case of deep saline aquifers where limited, economically driven, data collection and archiving are available. In this paper, we present a complete set of brine–CO₂ interfacial tension data at pressure, temperature and salinity conditions, representative of a CO₂ storage operation. A semi-empirical correlation is proposed to calculate the interfacial tension from the experimental data. Wettability is studied at pore scale, using glass micromodels in order to track fluids distribution as a function of the thermodynamic properties and wettability conditions for water–CO₂ systems. With this approach, we show that, in strongly hydrophilic porous media, the CO₂ does not wet the solid surface whereas; if the porous media has less hydrophilic properties the CO₂ significantly wets the surface.     

Shaking table tests of steel frame with superelastic Cu–Al–Mn SMA tension braces

Shaking table tests are performed on a one‐bay one‐story steel frame with superelastic Cu–Al–Mn shape memory alloy (SMA) tension braces. The frame is subjected to a series of scaled ground motions recorded during the 1995 Kobe earthquake, Japan. The test results demonstrate that the SMA braces are effective to prevent residual deformations and pinching. It is also shown that the time history responses observed from the shaking table tests agree well with the numerical predictions using a rate‐independent piecewise‐linear constitutive model calibrated to the quasi‐static component tests of the SMA braces. This suggests that the loading rate dependence of Cu–Al–Mn SMAs as well as the modeling error due to the piecewise linear approximation can be neglected in capturing the global response of the steel frame. Numerical simulations under a suite of near‐fault ground motion records are further performed using the calibrated analytical models to demonstrate the effectiveness of the SMA braces when the variability of near‐fault ground motions is taken into account. A stopper, or a deformation restraining device, is also proposed to prevent premature fracture of SMA bars in unexpectedly large ground motions while keeping the self‐centering capability in moderate to large ground motions. The effectiveness of the stopper is also demonstrated in the quasi‐static component and shaking table tests. Copyright © 2015 John Wiley & Sons, Ltd.     

Dynamic properties analysis of a stay cable-damper system in consideration of design and construction factors

A numerical solution based on the Steffensen stable point iterative method is proposed to resolve the transcendental frequency equation of a stay cable-damper system. The frequency equation, which considers clamped supports and fl exural rigidity of the cable, is intended to investigate the infl uence of the parameters of the cable damper system on its dynamic characteristics. Two factors involved in the design and construction phases, the damping coeffi cient induced by external dampers and the cable tension, are the focus of this study. Their impact on modal frequencies and damping ratios in these two phases of cable-damper systems are investigated by resolving the equation with the proposed solution. It is shown that the damping coeffi cient and cable tension exert more noticeable effects on the modal damping ratios than on the modal frequencies of stay cable-damper systems, and the two factors can serve as design variables in the design phase and as adjustment factors in the construction phase. On the basis of the results, a roadmap for system-level optimal design of stay cable-damper systems that can achieve global optimal vibration suppression for the entire bridge is proposed and discussed.     

拉力分散型土层锚索工作机理与性状

通过简化理论计算及锚索原位拉拔试验实测抗拔承载力等多种方法分析阐明了土层锚索存在临界锚固长度及其确定方法。提出了拉力分散型锚索是工程实践中解决土层锚索中存在极限锚固段长度问题简单易行的方法,并对拉力分散型土层锚索的工作机理及性状进行了分析与说明。     

提高斜拉索索力估算精度的方法

振动法是测量实际索力的首选方法,但其测试精度会受到外界环境因素如温度、风和桥面对拉索作用等的影响。本文围绕如何将外界环境因素的影响降至最小,从测量时机的选取、数据处理方法的选择等方面,综合运用随机振动、风工程、非线性和误差分析理论,提出了提高拉索索力估算精度的实用改进方法,得出了一些有意义的结论。并通过哈尔滨松花江斜拉桥实例进行验证对比,结果表明,该方法具有较高的精度。     

考虑土体抗拉强度的边坡永久位移极限分析

通过野外观测与室内试验发现,边坡后缘往往存在拉应力区。拉应力区的存在会影响边坡的稳定性,而地震荷载的存在会放大这种影响。分析拉应力区对边坡稳定性的影响,当前主要采用的方式为:对强度准则中抗拉强度进行折减（即张拉截断）。文章通过极限分析上限原理和拟静力法,推导出边坡临界加速度计算方程。以边坡在不同参数组合下的位移系数为基础,输入实测地震波,采用改进的Newmark法对边坡进行位移分析。文章算例的结果表明:拉应力区的存在会大大降低边坡临界加速度,土体在完全张拉截断下的临界加速度对边坡可能会产生超过50%的折减。拉应力区的存在也可以使永久位移达到传统的摩尔库伦理论计算值的2倍之多。文中所有的结果皆以图表形式展示,非常便于理解以及读取数据。