膨胀性黄土隧道钢拱架–格栅联合支护力学特性研究

为了研究膨胀性黄土隧道围岩与支护结构作用机制,解决膨胀力作用下的隧道支护难题,利用弹性薄壳理论建立了联合支护的力学分析模型,引入等效截面法和膨胀力参数得到了改进的围岩–支护特征曲线。基于上述模型和方法,对该黄土隧道初期支护的力学特性进行分析,提出适用于膨胀性黄土隧道的"格栅拱架+钢拱架+喷射混凝土"联合支护方式。结果表明:所建立的模型和方法对膨胀围岩条件下初期支护的力学特性分析具有较好的适用性,从理论角度解释该隧道原始初期支护发生破坏的原因;与"钢拱架+喷射混凝土"和"格栅+喷射混凝土"支护方式相比,提出的联合支护方式在膨胀性黄土隧道中更具优势,充分发挥了不同材料的承载特性,保证了隧道的稳定性。     

网状扁壳与带肋扁壳组合结构的拟三层壳分析法

本文对网状扁壳与带肋扁壳共同工作的组合结构(可简称组合网状扁壳),采用连续化的拟三层壳的计算模型,按弹性小挠度薄壳理论进行分析计算,推导建立了混合法的基本方程式。由于这种构造上的拟三层壳在一般情况下不存在中面,因而壳体的薄膜内力、弯矩与薄膜应变,弯曲应变是耦合的,存在一个耦合矩阵,使得基本方程式比单层光面的符氏扁壳方程要复杂得多。对于周边简支的组合网状扁壳可求得基本方程式的解析解。文中对三向、四向组合网状扁壳进行了详细讨论,并指出了在特定条件下,可退化为一个当量的各向同性单层扁壳。对于一般网状扁壳的拟壳分析法及带肋扁壳的拟壳分析法分别属于本文的两种特殊情况。文中附有计算例题。     

A new method for the structural design of flexible liners for gravity pipes of egg-shaped cross section: Theoretical considerations and formulation of the problem

The majority of gravity pipes with a non-circular cross section have an egg-shaped profile and an inner surface that can be geometrically delineated by three interconnecting circles on each side of a vertical axis of symmetry. Renovation of these pipes can be undertaken at low cost and with minimal surface disruption by installation of a close-fitting polymeric liner, most commonly by the ‘cured-in-place pipe’ technique.There are two pre-existing methodologies for the structural design of such liners. Although these procedures have served the international wastewater industry well over an extended period, detailed consideration of both methods suggests that an improved methodology which is straightforward to apply and addresses all relevant issues in a consistent manner would be both technically and financially beneficial. Accordingly a new design method is here proposed, which is based on an assumed displacement distribution in a manner consistent with previous work on close-fitting liners of circular cross section. The new design procedure addresses all the relevant issues in a rational manner, and is readily implemented as a small computer software simulation mountable on any current generation personal computer.     

管棚受力和变形的分析预测方法及工程应用

采用管棚预先对浅埋软弱围岩进行支护时,对管棚力学响应的精确预测是保证管棚结构设计合理性的重要依据.在管棚的弹性地基梁分析模型基础上,考虑掌子面失稳段对管棚约束的弱化,建立基于Pasternak弹性地基梁理论的管棚分析模型来预测预支护段开挖时管棚的受力和变形.利用Euler-Bernoulli梁的控制方程以及Paster...     

Neural network for the estimation of the inelastic buckling pressure of loosely fitted liners used for rigid pipe rehabilitation

One of the structural design aspects of most of the liners is to check their stability under external uniform pressures. This requires the definition of the critical pressure at which the liner destabilizes. A neural network based on the results of a previous parametric study using the Finite Element Method (FEM) is developed. The neural network provides an estimate for the critical pressure of an elasto-plastic loosely fitted liner. The inputs for the network are the liner’s thickness-to-radius, gap-to-radius, and the equivalent yield stress-to-Young’s modulus ratios. The network results are checked against the FE results and compared to Jacobsen solution. The results of the neural network show excellent agreement with the FE results and Jacobsen solution for thick liners. This network provides a new tool that can be used in the structural design of loosely fitted liners.     

圆柱形网壳的塑性极限分析

本探讨了圆柱形网壳结构的塑性极限分析，在分析过程中，采用拟壳法将圆柱形网壳结构等效为连续的夹层壳，然后对等效夹层壳进行塑性极限分析，由于夹层壳结构的极限条件是线性的，因而在求解时问题得到了大的简化，鉴于有矩理论的复杂性，本在作极限分析时，采用了无矩理论和半无矩理论的平衡方程分别作为中短壳和长壳的平衡方程。     

一边固支三边简支预制矩形肋底板混凝土双向叠合板的简化弹性计算方法

结合预制矩形肋底板混凝土双向叠合板(简称双向叠合板)的受力特点,分析了当前实际工程设计中存在的问题。针对双向叠合板的正交构造异性特征影响,采用荷载叠加法和正交构造异性板理论求解了均布荷载下一边固支三边简支双向叠合板挠度及弯矩的解。通过对解作形式变换和引入等效跨度比,将双向叠合板等效为各向同性双向板进行计算,提出了简化弹性计算方法。编程计算得到了双向叠合板强、弱方向刚度比为0.5和2.0,以及等效跨度比在0.5~1.0时的弹性系数。介绍了按照等效跨度比查找各向同性双向板弹性系数的线性插值法,并与编程计算结果进行对比。结果表明:采用简化弹性计算方法得到的结果与编程计算结果吻合良好,完全能够满足工程设计要求,该方法准确可行。     

Wind loading and its effects on single-layer reticulated cylindrical shells

In this paper, the wind load distribution as well as its effects on single-layer reticulated cylindrical shells, which are widely used in practice, is investigated. At first, wind pressure distributions on three rigid cylindrical shell models considering different shape ratios are measured simultaneously in a wind tunnel. Some special characteristics of the measured wind pressure, especially its fluctuating component, are discussed. Then, considering the special structural mechanical behaviors, the effects of wind load, especially the fluctuating component, on the limit load-carrying capacity and the stability of the shells are investigated by both equivalent static analysis and dynamic analysis. Suitable methods to get a reasonable estimation of wind load effects in estimating the equivalent static wind load distribution for such shells are investigated. Finally, with comparison analyses using different methods mentioned in this paper, the efficiency of the method in estimating the effective wind load distribution presented by the authors previously for single-layer reticulated spherical shells is demonstrated, and some advices for estimating the wind load distribution on single-layer reticulated cylindrical shells is given for wind-resistant design in practice.     

框架中钢-混凝土组合梁等效弯曲刚度分析

框架体系中钢-混凝土组合梁在竖向荷载作用下的弯矩分布与其端部受到的转动约束条件密切相关,而在不同方向的弯矩作用下钢-混凝土组合梁截面的抗弯刚度又差异显著,要准确计算竖向荷载作用下组合梁的等效弯曲刚度必须充分考虑与其相连的梁柱变形对其端部产生的转动约束刚度。为此,采用分段刚度建立了框架中组合梁在竖向荷载作用下的等效刚度理论模型,以考虑不同梁端转动约束刚度和楼板开裂前后截面特性差异对组合梁等效刚度的影响。基于该理论模型进行大量参数分析,识别了影响组合梁等效弯曲刚度的两个关键参数：转动约束刚度与组合梁开裂后截面线刚度比和梁开裂前后截面刚度比,得到了随梁端转动约束刚度变化的组合梁在竖向荷载作用下等效弯曲刚度的计算式,在框架设计时可方便地用于组合梁的变形和内力计算。对比讨论了建议算式和现有公式的计算精度,并通过结构体系的非线性全过程分析对建议算式的合理性做了进一步的验证。理论分析和设计方法表明,组合梁在竖向均布荷载作用下的负弯矩区长度和等效弯曲刚度随梁端转动约束刚度变化显著,必须在设计中准确考虑。     

Probabilistic analysis for design assessment of continuous steel-concrete composite girders

In the design of continuous steel-concrete composite girders, cross section plastic resistance can be exploited in the sagging regions, where the compressed flange of the steel beam is connected to the reinforced concrete slab. However, elastic verification of cross sections is normally adopted in the hogging regions, where the compressed portion of the steel beam is unrestrained by the concrete slab and more prone to buckling. In a combined design approach, which uses the cross section plastic resistance in the sagging regions and the cross section elastic resistance in the hogging regions, the design must satisfy the condition that the sagging plastic moment can develop while the hogging bending moment remains below the elastic limit. The objectives of this work are to present a framework for simplified probabilistic nonlinear analysis of steel-concrete composite bridges and to assess, through such framework, the combined elastic-plastic design as applied to a realistic three-span continuous steel-concrete composite road bridge. The methodology presented here is based on the First-Order Second-Moment (FOSM) approximation, adopted to compute the first- and second-order statistical moments (means, variances and covariances) of structural response quantities. Deterministic and probabilistic numerical results for the benchmark problem are illustrated and discussed.     

Compression–shear strength criterion of coal–rock combination model considering interface effect

Surrounding rocks around coal tunnel in western mining area of China are typical composite structures composed of weakly cemented soft rock and hard coal, and the tunnel stability is closely related to the overall mechanical behavior of the combination body. The equivalent homogeneous model of coal–rock combination body and its stress state expressions were firstly established based on the strain energy equivalency principle. Then, the general compression–shear failure criterion of the equivalent model which takes into account the cohesive strength of the interface between coal and soft rock was derived by assuming that the yielded mediums all met Mohr–Coulomb criterion. Furthermore, accuracy of the proposed analytical model was verified by carrying out laboratory test for coal-mudstone specimen, and it found that the theoretical results were in good agreement with the test values. Strength of the combination body lies between the strong body and weak body. Finally, the effects of interface cohesion strength, rock thickness and stress level on the failure behavior of combination model were analyzed based on the analytical model. Results show that the proposed model not only contains the classical sliding failure theory for two-dimensional weak plane presented by Jaeger, but also reflect strength behavior of a more complex composite model composed of different rock mediums and structural plane. Thus, the analytical model provides theoretical basis for further studying the mechanical behavior of coal–rock combination model.     

挥发性有机化合物在复合衬里中的一维扩散解

土工膜和粘土衬里组成的复合衬里已广泛用于填埋场的防渗。有机挥发性化合物在复合衬里中迁移时,其主要的机理是分子扩散作用。本文建立了有机挥发性化合物在复合衬里中的一维扩散模型,并得到了解析解。将该解析解和以往给出的数值解法作了比较,发现两者得到的结果较为接近,从而验证了本文解的可靠性。基于本文计算模型,分析了三种常用复合衬里对挥发性有机化合物的防渗性能。研究发现对于挥发性有机化合物甲苯,土工膜和GCL组成的复合衬里的浸出液总量要比土工膜和较厚粘土衬里组成的复合衬里大好几个量级。     

U形预制截面预应力混凝土叠合梁正截面抗裂验算

提出一种新型叠合梁结构--U形预制截面预应力混凝土叠合梁,探讨了其结构特点;介绍了国内外对预应力混凝土叠合梁抗裂度的研究概况;对U形预制梁制作、运输吊装阶段和叠合梁使用阶段开裂前的截面应力应变关系分别进行分析,在此基础上推导出相应阶段的正截面抗裂验算方法.     

Unified calculation method and its application in determining the uniaxial mechanical properties of concrete

This paper presents a unified calculation method and its application in determining the uniaxial mechanical properties of concrete with concrete strengths ranging from 10 to 140 MPa. By analyzing a large collection of test results of the uniaxial mechanical properties of normal-strength, high-strength and super high-strength concrete in China and performing a regression analysis, unified calculation formulas for the mechanical indexes of concrete are proposed that can be applied to various grades of concrete for determining the size coefficient, uniaxial compressive strength, uniaxial tensile strength, elastic modulus, and strain at peak uniaxial compression and tension. Optimized mathematical equations for the nonlinear stress-strain relationship of concrete, including the ascending and descending branches under uniaxial stress, are also established. The elastic modulus is almost constant throughout the elastic stage for the ascending branches of the stress-strain relationship for concrete. The proposed stress-strain relationship of concrete was applied to the nonlinear finite element analysis of both a steel-concrete composite beam and a concrete-filled steel tubular stub column. The analytical results are in good agreement with the experiment results, indicating that the proposed stress-strain relationship of concrete is applicable. The achievements presented in this paper can be used as references for the design and nonlinear finite element analysis of concrete structures.     

Simulation of partially encased composite steel-concrete columns with steel columns

This paper presents a method for simulating composite steel-concrete columns of double-symmetrical, partially encased cross-sections, as equivalent steel columns of fictitious cross-section, for the purposes of linear elastic analysis. The latter consist of the actual steel cross-section and two additional pairs of plates, one perpendicular to the web at mid-height and one perpendicular to the flanges at mid-width. Plate dimensions are chosen to match the compression resistance and principal bending stiffness of the composite section. Section equivalence results in three algebraic equations for the dimensions of the additional plates, in terms of the geometry of the actual section and the material properties of steel, concrete, and reinforcement bars. These equations are solved in closed form by neglecting a small contribution to major-axis stiffness. The proposed method combines accuracy, efficiency, and convenience; it takes advantage of widely available software for linear elastic steel structure analysis and obviates the need for finite-element simulation.     

火荷载下沉管隧道结构的热-力耦合分析

以上海外环线越江沉管隧道为背景,用有限元程序模拟火荷载作用下沉管隧道结构温度场及应力场,并将计算结果与试验数据对比分析,从而确定最佳的分析模型和边界条件,为该领域的研究提供参考依据。根据沉管隧道的结构形式及其特点建立有限元分析模型;参考隧道火灾的试验资料和研究成果确定模型边界条件;通过分析选取合理的混凝土和周围土体的本构模型;分析时还考虑到混凝土热工参数随温度的变化。通过对火灾时沉管隧道不同温度量级的稳态温度场和瞬态温度场分析,得出温度随空间和时间的变化规律,并把分析结果与试验结果进行对比分析。分别进行常温下和火灾时沉管隧道的热-力耦合分析,从而更直观地了解温度场对应力场的影响,得出沉管隧道各个部位在火灾发生时的应力分布情况以及随着不同温度量级的变化规律,以便更有效地为优化设计和防火救灾提供理论指导。最后根据计算结果,结合大量的隧道火灾资料总结火灾时隧道内部的温度场及应力场的危险区域。     

钢拱架应力反分析隧道初期支护力学性能的研究

适时分析软弱破碎围岩段衬砌结构的内力状态是隧道动态施工中的关键性问题之一,对判断隧道施工安全状态和评价支护结构稳定性具有重要意义。考虑钢拱架已作为软弱围岩段公路隧道初期支护的重要形式,现通过分析隧道施工现场钢拱架支护的自身特点和受力特性,建立含有钢拱架和喷射混凝土的隧道复合初期支护的地基曲梁力学模型。然后运用地基曲梁相关理论,通过现场监测的钢拱架应力推求出隧道复合初期支护内力解析式,从而迅速得到隧道支护结构的应力集中部位。最后,经由台阶法施工的隧道工程实例运用表明,基于实测钢拱架应力求解隧道初期支护内力的解析研究是分析软弱破碎围岩段隧道支护力学性能的一种新方式,并能及时有效地为隧道现场施工安全提供直观、可靠的力学依据和技术支持。     

Numerical experiment-artificial intelligence approach to develop empirical equations for predicting leakage rates through GM/GCL composite liners

The aim of this study is to develop empirical equations to predict the liquid leakage rate through a composite liner comprising a geomembrane and a geosynthetic clay liner (GM/GCL) underlain by a free draining boundary and having a circular or a longitudinal defect in the geomembrane. For this purpose, an intensive numerical experimental program was conducted where different defect geometries and flow transport characteristics were studied to simulate most of the conditions likely to exist in practice in such type of composite liners. The results are presented in a dimensionless form to generalize the observed behaviour and to give more insight on the factors that control the leakage behaviour. Furthermore, the results are also used to develop empirical equations for predicting the rate of leakage. An artificial intelligent approach referred to as General Method of Data Handling (GMDH) was used for this purpose. The main advantage of the proposed leakage equations is their validity for different flow patterns as the effect of defects geometry and flow characteristics of the composite liner components are already embedded in the development of the equations. However, their validity is limited to the ranges of the dimensionless parameters that were used to develop them.     

浅埋暗挖隧道管棚变形监测及受力机制分析

在土江冲隧道进口段采用应变计对管棚纵向变形进行监测，根据现场测试结果分析管棚在隧道开挖过程中的受力特性，讨论管棚的作用机制。对管棚的刚性固定端Winkler弹性地基梁模型进行改进，建立浅埋暗挖隧道管棚受力的弹性固定端双参数弹性地基梁模型，推导出管棚的扰度方程及应力、应变计算公式，提出求解方法。将弹性固定端双参数弹性地基梁模型应用于土江冲隧道管棚作用机制的分析，计算结果与实测结果吻合较好，说明采用弹性固定端双参数弹性地基梁模型分析管棚受力特征是可行的。     

含衬砌圆形压力隧洞弹塑性新解

 研究含衬砌圆形压力隧洞的弹塑性问题。考虑地应力的释放和衬砌安装的时序，提出合理模拟隧洞修筑过程的力学模型。运用Muskhelishvili复势理论的级数展开技术，构造合适的复应力函数，利用边界上位移和力的连续性条件，通过等式两边同次幂指数的系数比较，将问题转化为线性方程组的求解，得到围岩和衬砌内的复应力函数表达式。基于Mohr-Coulomb屈服准则，且考虑衬砌内、外边界以及弹塑性区交界面上的边界条件，得到弹塑性交界面位于衬砌内，屈服条件中的第一主应力分别为径向应力和环向应力时的解答，经典的Fenner公式和Savin解答等许多已往解答，可以作为其特殊情况退化得到。