Dispersions for the pushover‐based risk assessment of reinforced concrete frames and cantilever walls

The paper presents the results of an investigation into the dispersion values, expressed in terms of limit‐state spectral accelerations, which could be used for the pushover‐based risk assessment of low‐height to mid‐height reinforced concrete frames and cantilever walls. The results of an extensive parametric study of a portfolio of test structures indicated that the dispersion values due to record‐to‐record variability and modelling uncertainty (β_LS,RU) are within the range from 0.3 to 0.55 for the near collapse limit state, and between 0.35 and 0.60 for the collapse limit state. The dispersions β_LS,RU proposed for the code‐conforming and the majority of old (non code‐conforming) frames are in between these values. On the other hand, the dispersions proposed for the old frames with a soft storey and an invariant plastic mechanism, and for the code‐conforming cantilever walls, are at the lower and upper bounds of the presented values, respectively. The structural parameters that influence these dispersions were identified, and the influence of different ground motion sets, and of the models used for the calculation of the rotation capacities of the columns, on the calculated fragility parameters was examined and quantified. The proposed dispersion values were employed in a practice‐oriented pushover‐based method for the estimation of failure probability for eight selected examples. The pushover‐based risk assessment method, although extremely simple and economical when compared with more rigorous probabilistic methods, was able to predict seismic risk with reasonable accuracy, thus showing it to be a practical tool for engineers. Copyright © 2016 John Wiley & Sons, Ltd.     

地震波CT在混凝土防渗墙质量检测中的应用

本文给出了一个地震波CT技术检测混凝土防渗墙质量的实例,其检测结果和部分墙体的钻孔取芯、土工试验和注水试验进行了对比,结果表明地震波CT技术在检测混凝土防渗墙质量时快速无损,准确可靠,在防渗墙质量无损检测中有广阔的应用前景。      

Seismic pressures on rigid cantilever walls retaining elastic continuously non-homogeneous soil: An exact solution

The dynamic response of an elastic continuously nonhomogeneous soil layer over bedrock retained by a pair of rigid cantilever walls to a horizontal seismic motion and the associated seismic pressure acting on these walls are determined analytically–numerically. The soil non-homogeneity is described by a shear modulus increasing nonlinearly with depth. The problem is solved in the frequency domain under conditions of plane strain and its exact solution is obtained analytically. This is accomplished with the aid of Fourier series along the horizontal direction and solution of the resulting system of two ordinary differential equations with variable coefficients by the method of Frobenius in power series. Due to the complexity of the various analytical expressions, the final results are determined numerically. These results include seismic pressures, resultant horizontal forces and bending moments acting on the walls. The solution of the problem involving a single retaining wall can be obtained as a special case by assuming the distance between the two walls to be very large. Results are presented in terms of numerical values and graphs using suitable dimensionless quantities. The effect of soil non-homogeneity on the system response is assessed through comparisons for typical sets of the parameters involved.     

Centrifuge modelling of flexible retaining walls subjected to dynamic loading

This paper outlines the results of an experimental program carried out on centrifuge models of cantilevered and propped retaining walls embedded in saturated sand. The main aim of the paper is to investigate the dynamic response of these structures when the foundation soil is saturated by measuring the accelerations and pore pressures in the soil, displacements and bending moment of the walls. A comparison among tests with different geometrical configurations and relative density of the soil is presented. The centrifuge models were subjected to dynamic loading in the form of sinusoidal accelerations applied at the base of the models. This paper also presents data from pressure sensors used to measure total earth pressure on the walls. Furthermore, these results are compared with previous dynamic centrifuge tests on flexible retaining walls in dry sand.     

Seismic behavior and modeling of steel reinforced concrete (SRC) walls

The steel reinforced concrete (SRC) wall consists of structural steel embedded at the boundary elements of a reinforced concrete (RC) wall. The use of SRC walls has gained popularity in the construction of high‐rise buildings because of their superior performance over conventional RC walls. This paper presents a series of quasi‐static tests used to examine the behavior of SRC walls subjected to high axial force and lateral cyclic loading. The SRC wall specimens showed increased flexural strength and deformation capacity relative to their RC wall counterpart. The flexural strength of SRC walls was found to increase with increasing area ratio of embedded structural steel, while the section type of embedded steel did not affect the wall's strength. The SRC walls under high axial force ratio had an ultimate lateral drift ratio of approximately 1.4%. In addition, a multi‐layer shell element model was developed for the SRC walls and was implemented in the OpenSees program. The numerical model was validated through comparison with the test data. The model was able to predict the lateral stiffness, strength and deformation capacities of SRC walls with a reasonable level of accuracy. Finally, a number of issues for the design of SRC walls are discussed, along with a collection and analysis of the test data, including (1) evaluation of flexural strength, (2) calculation of effective flexural stiffness, and (3) inelastic deformation capacity of SRC walls. Copyright © 2014 John Wiley & Sons, Ltd.     

偏心水平荷载下内藏钢桁架混凝土核心筒抗震试验研究

对两个1／6缩尺的核心筒结构模型进行了偏心水平荷载作用下的低周反复荷载试验研究,其中包括一个普通混凝土核心筒和一个内藏钢桁架混凝土组合核心筒。在试验的基础上,分析了两个试件的承载力、刚度、延性、滞回特性、耗能能力、破坏特征以及抗震机理。试验研究表明：偏心水平荷载作用下,内藏钢桁架混凝土组合核心筒比普通混凝土核心筒抗震能力显著提高。     

部分反射直墙前二维物体的绕射和辐射问题

基于映像理论将部分反射直墙前物体的散射问题,等效于开敞水域中原物体的散射和关于直墙映像体散射的线性叠加进行求解。采用高阶边界元方法建立了部分反射直墙前二维任意形状物体波浪绕射和辐射问题的数值分析模型,通过与已发表的海底方箱和淹没圆柱结果的对比验证了数值模型的准确性。应用该模型研究了直墙反射系数幅值及相位、方箱与墙间距离等参数对水面方箱上波浪激振力、附加质量和辐射阻尼的影响。结果表明：直墙反射系数幅值越大,波浪激振力、附加质量和辐射阻尼的波动越大,附加质量在一些频率下出现负值;相位角的变化会改变波浪激振力、附加质量和辐射阻尼曲线的偏移,在低频区对升沉附加质量有显著影响;方箱距离直墙越远,方箱上的波浪激振力、附加质量和辐射阻尼随波数振荡的频率越快,峰值频率向低频侧移动。     

基于悬臂梁模型的管道矫直理论及有限元分析

海底管道的卷管铺设过程涉及多次正向和反向弯曲,并会产生较大的塑性变形。在铺设入水前,管道必须进行矫直处理,因此如何准确预测矫直过程中管道的力学响应以及如何对矫直器进行合理的设置具有重要意义。针对中国首艘卷管式铺管船“深达号”的矫直装置设计与典型工况,建立了一种基于悬臂梁的力学理论模型。该模型综合考虑了铺设过程中退卷和矫直的加载历程、管道材料的弹塑性特性以及校准器和上、下矫直器的相对位置关系。模型能实现对反弯半径及矫直器姿态等关键参数的计算。建立有限元分析模型,对理论模型进行验证并对管道矫直过程进行数值分析。结果表明理论模型可以准确预测管道矫直所需反弯半径、矫直器侧向行程以及倾角等参数。在管道矫直过程中,上矫直器处的作用载荷远大于下矫直器处。所提出的矫直理论模型可适用于不同尺寸管道的矫直分析,矫直后残余曲率满足DNV规范要求,预期可为“深达号”的实际矫直工艺设计提供指导。     

Piezoelectric Energy Analysis on Diverse Buoy Coupling with Hydrodynamic Parameters

This paper mainly describes the influence factors of the captured energy power by huge wave energy harvesters, in which the vertical motion of buoy can transform ocean’s potential energy into piezoelectric energy power by undulating waves. Firstly, related environmental coefficients are analyzed by means of the incident wave theory. Besides, the geometric structural parameters are also analyzed and compared under optimal environmental coefficients with semi-analytical solutions. Thirdly, the numerical results also show the impact trend of hydrodynamic parameters and geometric volume on motion, voltage and power with qualitative agreement. The numerical simulation confirms that the improved structure parameters could markedly deliver sufficient power under the same conditions with long-time stability.     

建筑墙体热性能动态分析和保温厚度优化

为研究动态热条件下不同结构材料的建筑墙体热性能和保温厚度优化问题,针对大庆地区冬季气候特征,建立墙体非稳态传热模型,分析分别采用Concrete、Briquette、Brick、Blokbims、AAC等5种结构材料和挤塑聚苯乙烯EPS、泡沫聚苯乙烯XPS等2种保温材料的建筑墙体热性能,计算大庆地区1月典型日的室外综合温度并进行各种墙体传热分析和保温厚度优化.结果表明:冬季最大温度波动和峰值负载发生在Concrete结构材料墙体中,其次是Briquette、Brick、Blokbims和AAC结构材料墙体中,且在相同情况下AAC结构材料墙体的保温效果明显优于其他结构材料墙体;综合考虑影响保温层经济厚度的主要因素,通过经济分析计算,得出在相同经济条件下、大庆地区采用5种不同结构材料240mm厚度墙体保温时的最优保温厚度,为建筑墙体工程应用提供指导.