Assessment of Multispan Masonry Arch Bridges. II: Examples and Applications

Modern approaches to multispan masonry bridges are approximate in many ways: load distribution, masonry degradation, fill-to-barrel, span-to-span, and span-to-pier interaction are taken into account by means of approximate models or are neglected. At the end of the assessment procedure, the approximation to the load carrying capacity of the bridge cannot be easily quantified. In Part I of this paper, an extension of the classical approach to masonry arches was formulated taking into account the nonlinear response of masonry, a limit to compressive inelastic strains, and assuming simplifying but conservative assumptions. The procedure allows the analysis of multispan masonry bridges considering the nonlinear response of arches and barrels and the mutual interaction. The response of two- and three-span prototypes is compared to that of a single arch; then the procedure is applied to a six- 18.5-m span in-service viaduct. A detailed comparison with the single-span-bridge approach is discussed. Specific attention is paid to the evolution of the collapse mechanism and to the effect of load distribution, addressing the concentrated loads versus distributed equivalent loads problem and showing how the limit to compressive inelastic strains, i.e., to masonry ductility, may be of great importance to the structural analysis of masonry bridges.     

输送带用钢丝绳生产及技术进步

介绍输送带用钢丝绳的主要生产控制及使用要求。从捻制质量、结构选择、力学性能以及粘合力和镀层质量控制等方面介绍输送带用钢丝绳的生产工艺控制以及各生产工序质量控制的注意事项,指出钢丝绳弯曲疲劳、输送带张紧装置造成胶带张力过大和张力分布不均匀、外力过大、腐蚀、异物损伤以及接头抽丝是输送带用钢丝绳使用过程中断裂的主要原因,保证钢丝绳储存质量和改善钢丝绳接头工艺有助于减少输送带生产过程中的钢丝绳消耗。对输送带用钢丝绳的技术进步做了展望。     

Three-Dimensional Nonlinearly Varying Rectangular Loads on a Transversely Isotropic Half-Space

In engineering situations, loads applied to the four corners of a rectangle might have different values and might not be uniformly or linearly distributed. A configuration of linearly or nonlinearly varying loads with different contact pressures at each corner can be represented as a superposition of various loading types. The loading types include uniform, linearly varying in the x direction, linearly varying in the y direction, nonlinearly varying in the x direction, and nonlinearly varying in the y direction. This work newly presents the first and second loading solutions, and derives the others therefrom. These solutions are directly obtained by integrating the point load solutions in a transversely isotropic half-space. The presented solutions are concise and easy to use; they specify that the type and degree of material anisotropy, the dimensions of the loaded region, and the loading types decisively affect the displacements and stresses in a transversely isotropic half-space. The proposed solutions can simulate realistically the actual loading problem in many engineering situations.     

Load Transfer and Recovery Length in Parallel Wires of Suspension Bridge Cables

A new simplified contact model aimed at capturing the load transfer and recovery length in parallel steel wires, commonly used in main cables of suspension bridges, is presented. The approach is based on placing elastic–perfectly plastic spring elements at the contact region between the objects. These springs have varying stiffness (Model?I) or yielding (Model?II) depending on their proximity to the clamping loads. Their stiffness or yielding is highest when they are closer to this force, and it decays when they are farther away from the clamp. This decayed behavior is assigned according to Boussinesq’s well-known solution to a point load (applied on a half space). Both models converge quickly compared with a full contact model and recover Coulomb friction law on a two-dimensional (2D) benchmark problem. Moreover, when the same properties are chosen for all springs (disregarding Boussinesq solutions), the models reduce to the classical shear-lag model, which for high clamping (point) loads gives inaccurate results. The spring models are validated experimentally on a seven-wire tightened strand. In this case study, the outer wires are axially pulled, whereas the middle wire, slightly shorter than the outer wires, experiences no direct applied axial load. However, because the strand is radially fastened at several locations, the axial load is transferred to the inner wire by an interfriction mechanism between the wires. The strains at the center points of the outer and inner wires are measured via neutron diffraction for different clamping loads, showing that the inner wire is capable of recovering most of the load.     

非均布载荷下板材失稳判别试验装置

 失稳屈曲是板材失效的一种特殊方式,判断板材在不同分布载荷下是否失稳具有重要意义。目前虽然已对均布与非均布载荷下板材失稳屈曲问题进行了大量理论研究,但是缺少专门研究非均布载荷下板材失稳判别的试验设备。为此,专门设计了一套为板材施加非均布载荷的试验方案,当给定分布载荷的具体形式后,可由推导的公式计算压头与板材之间压块的高度分布,由此可以实现任意形式分布载荷的施加,具有结构简单及容易实现的优点,为板材失稳屈曲理论研究提供了一种简单易行的验证手段。     

Potential Improvement in Biofilter Design through the Use of Heterogeneous Packing and a Conical Biofilter Geometry

Due to the heterogeneous distribution of microbial activities in a biofilter, biomass accumulation and clogging often occurs in the inlet sections, leading to a considerable increase in the total pressure drop and shortening of the bed material life span. We propose two new design concepts to optimize biofilter performance and reduce pressure drop by distributing biomass or pressure drop more homogeneously. One concept involves using a heterogenous packing system where the biologically more active inlet sections have larger particles and the less active outlet sections have smaller particles. This provides a more even distribution of microbial activity and pollutant degradation, resulting in a considerable reduction in the total pressure drop. The other concept involves using a conical biofilter geometry instead of the conventional cylindrical form. The varying cross-sectional area counteracts an uneven distribution of microbial activities and thus achieves a more uniform pressure drop along a biofilter. Experimental and/or simulation results showed that heterogeneous packing and conical geometry could result in more cost-effective biofiltration.     

1000m~3高炉料车斜桥的静力分析

通过AutoCAD作图法对某钢厂1000m3高炉料车斜桥上料过程进行了静力学分析,计算得出了斜桥及卷扬机卷筒、绳轮、钢丝绳等设备和材料在空料车、正常装焦、正常装矿、过载装矿、料车卡住等各种工况下的受力,为结构专业进行计算提供了依据。     

Measuring Soil Pressure on a Buried Model Structure for the Validation of Quantitative Frameworks

The paper presents the methodologies and results of an experimental study aimed at measuring the soil contact pressures which develop on a buried structure as it interacts with the surrounding soil under load. The study has been based on measurements made on model structures tested in a pressure chamber filled with a fine uniform sand. The buried model structure was a very rigid right cylinder designed such that it could be fitted with roofs of different thicknesses. The structure bottom and roof were instrumented with newly designed and constructed soil pressure cells based on the null response concept. The device is unaffected by the issues that affect the use of traditional soil pressure cells. The development of pressure on the structure was measured as uniform pressure was applied to the soil surface. The results illustrate the effect of roof stiffness on the development of pressure at the roof center. The midroof pressure was seen to increase with roof stiffness, however the development of pressure was also seen to be dependent upon the actual deflection. In the case of a flexible roof it was seen that the development of contact pressure is a nonlinear function of the pressure applied at the soil surface and is highly dependent upon stress history. In contrast, it was seen that pressure on a stiff roof develops as a linear function of pressure applied at the soil surface and is less dependent of stress history. The results of the model tests together with soil stiffness data supplied in the paper will be useful in the calibration and validation of numerical and analytical frameworks.     

Coupling Behavior of Wire Ropes Subjected to Tensile Impulses

To determine the stress state of a wire rope is tedious although analytical solution of a simple rope subjected to static load is available. While facing the problems involving complex ropes, it is usual practice to take approximations based upon the concepts of an average stress state for the constitutive ropes or for every wire. For a statically loaded cable superimposed with a tensile impulse, practically in sudden lifting of a heavy weight, the coupled axial-shearing strain waves in the cable has rarely been studied and explored through analytical approaches. Based on Costello’s force-deformation relationship and elastic wave propagation theory, analysis procedures and results are presented in this paper. Time-dependent coupled axial-torsional displacements and axial-shearing strain waves in a simple straight wire rope, due to a longitudinal impact at one end, are obtained. At the instance of the strike, a pair of coupled primary axial-torsional waves is created and begins to travel in the cable independently with different speed. Meanwhile, a coupling induced secondary torsional wave and an axial wave were observed to travel with the primary axial wave and the primary torsional wave, respectively. Phenomenon such as the traveling, reflections from ends, and intersections of the primary waves as well as the secondary wave are presented. Information provided in this paper would be useful in the study of unexpected overstress and/or fatigue problems.     

In-Plane Nonlinear Buckling Analysis of Deep Circular Arches Incorporating Transverse Stresses

Large discrepancies exist among current classical theories for the in-plane buckling of arches that are subjected to a constant-directed radial load uniformly distributed around the arch axis. Discrepancies also exist between the classical solutions and nonlinear finite-element results. A new theory is developed in this paper for the nonlinear analysis of circular arches in which the nonlinear strain-displacement relationship is based on finite displacement theory. In the resulting variational equilibrium equation, the energy terms due to both nonlinear shear and transverse stresses are included. This paper also derives a set of linearized equations for the elastic in-plane buckling of arches, and presents a detailed analysis of the buckling of deep circular arches under constant-directed uniform radial loading including the effects of shear and transverse stresses, and of the prebuckling deformations. The solutions of the new theory agree very well with nonlinear finite-element results. Various assumptions often used by other researchers, in particular the assumption of inextensibility of the arch axis, are examined. The discrepancies among the current theories are clarified in the paper.     

Stresses at the meniscofemoral joint: elastostatic investigations on the applicability of interface elements

Stress distributions at the meniscofemoral joint were analysed and the applicability of nonlinear interface elements in a finite element model (FEM) were tested. Centred and 70% off-centre load cases with a complete, a partially removed or a totally removed medial meniscus were evaluated in two dimensions. Interface width was assumed to increase linearly from almost zero to 1 mm at the inner and outer border of the femoral condyles. Maximum interface forces were found at the centre of the condyles, decreasing to zero at the peripherical and intercondylar femoral border. Simulation data concerning a removed medial meniscus or medial 70% off-centre load with complete meniscus indicated higher medial contact forces in the first case. A decrease in the elastic modulus of the articular surface tissues caused two small force transfer peaks (femoral centre and intercondylar border), which were strongly influenced by the predefined gap width.     

多极边界元法及在轧制工程中的应用

 在多物体同时接触轧制工程问题中,对各物体抽象出来研究存在简化较多、计算精度低等缺点。开发了多物体弹塑性摩擦接触多极边界元法,对板带四辊轧制接触问题进行了数值模拟,获得了板带轧制压力和轧机轴承载荷分布规律。并通过对轴承载荷特性的实验,证明了多物体接触快速多级边界元法具有计算精度高、计算速度快等优点,是分析轧制工程中接触问题的最有效的数值工具之一。     

Conformable Tire Patch Loading for FRP Composite Bridge Deck

Fiber-reinforced polymer (FRP) composites are increasingly being used in bridge deck applications. However, there are currently only fledgling standards to design and characterize FRP deck systems. One area that should be addressed is the loading method for the FRP deck. It has been observed that the type of loading patch greatly influences the failure mode of a cellular FRP deck. The contact pressure distribution of a real truck loading is nonuniform with more concentration near the center of the contact area as a result of the conformable contact mechanics. Conversely, the conventional rectangular steel patch on a FRP deck act like a rigid flat punch and produces stress concentration near the edges. A proposed simulated tire patch has been examined for loading a cellular FRP deck with the load distribution characterized by a pressure sensitive film sensor and three-dimensional contact analysis using ANSYS. A loading profile is proposed as a design tool for analyzing FRP deck systems for strength and durability. Local top surface strains and displacements of the cellular FRP deck are found to be higher with proposed loading profile compared to those for the conventional uniformly distributed loading. Parametric studies on the deck geometry show that the global displacement criterion used for characterizing bridge deck is inadequate for a cellular FRP deck and that the local effects must be considered.     

Thermomechanical Postbuckling Analysis of Cross-Ply Laminated Cylindrical Shell Panels

The postbuckling analysis of symmetric and antisymmetric cross-ply laminated cylindrical shell panels subjected to thermomechanical loading is examined in this paper. The formulation is based on an extension of Reissner’s shallow shell simplifications and accounts for parabolic distribution of transverse shear strains. Adopting a multiterm Galerkin’s method, the governing nonlinear partial differential equations are reduced into a set of nonlinear algebraic equations. The nonlinear equilibrium paths through limit points are traced using the Newton–Raphson method in conjunction with Riks approach. Numerical results are presented for symmetric [?start0/90/0end?] and antisymmetric [?start0/90end?] cross-ply laminated cylindrical shell panels, that illustrate the influence of mechanical edge loads, lateral distributed load, initial imperfection, and temperature field on the limit loads and snap-through behavior.     

电气化铁路用铜合金接触线生产方法及特点

通过对电气化铁路用铜及铜合金接触线各种生产方法及其特点的比较,以及对不同生产方式对接触线组织性能的影响分析．得出上引连续挤压法具有显著的技术优势。该法克服了传统接触线制造方法的缺点．可获得目前国内品相和质量优异的无氧级、细晶粒金相组织的接触线产品。     

In-Plane Biaxial Crush Response of Polycarbonate Honeycombs

The crushing response of a polycarbonate circular cell honeycomb to inplane biaxial loading under displacement control is analyzed. The study involves a combination of experiment and numerical simulation. Experiments corresponding to several different biaxial loading conditions are carried out. In the first phase of the response, the material deforms in a uniform fashion. Next, a nonlinear phase caused by the progressive localization of deformation is characterized by the variation of overall (macroscopic) stiffness. The progressive localization causes the walls of each cell to contact. These periodic honeycomb materials show different collapsed modes under different biaxial loading histories. Experimental measurements indicate how the magnitude of the collapse load varies and how the load-displacement response changes as a function of load biaxiality. The experimental results are simulated through numerical analysis using the finite-element method.     

Nonlinear Analytical Solution for Cable Truss

In this technical note the nonlinear closed-form static solution of the suspended biconvex and biconcave cable trusses with unmovable, movable, or elastic yielding supports subjected to vertical distributed load applied over the entire span is presented. Irvine’s linearized forms of the deflection and the cable equations are modified because the effects of the nonlinear truss behavior needed to be incorporated in them. The concrete form of the system of two nonlinear cubic cable equations is derived and presented. From a solution of a nonlinear vertical equilibrium equation for a loaded cable truss, the additional vertical deflection is determined. The transformation analytical model serves to determine the response, i.e., horizontal components of cable forces and deflection of the geometrically nonlinear truss, due to the applied loading, considering effects of elastic deformations, temperature changes, and elastic supports. The deflection of asymmetric prestressed cable trusses has been compared with Irvine’s linear solution as well as the nonlinear finite element model results.     

Effect of Live Load Surcharge on Retaining Walls and Abutments

In the conventional design of retaining walls and bridge abutments, the lateral earth pressure due to live load surcharge is estimated by replacing the actual highway loads with a 600 mm layer of backfill. This original recommendation was made several decades ago when the highway truck loads were much lighter. A number of researchers have shown that the pressure exerted on the wall due to live load surcharge is greater near the surface and is diminished nonlinearly throughout the height of the wall. The heavier highway loads and the demonstrated nonlinear earth pressure distribution require a need for a more rational method for obtaining the equivalent height of backfill. This paper discusses theoretical background, an analytical approach to estimation of actual earth pressure, a number of innovative approaches to obtain a simplified pressure distribution, an extensive parametric study, calibration procedures for the traditional method, and recommendations.     

4100mm宽厚板轧机支承辊辊型曲线优化仿真分析

 辊间接触压力分布是影响宽厚板板形质量和轧辊使用寿命的重要因素,为了获得均匀的辊间压力分布,以4100mm宽厚板四辊轧机为对象,考虑轧件弹塑性变形和辊系弹性变形耦合作用,采用弹塑性热-力耦合非线性有限元方法,数值模拟分析了宽厚板轧制过程的辊间接触压力分布规律,并通过仿真分析,对支承辊辊型及其边部卸载曲线进行了选型和优化改进,获得了以二次曲线为辊凸度和抛物线为辊肩部卸载曲线的辊形,延长了轧辊的使用寿命,改善了宽厚板的板型质量。     

考虑端部摩擦的中心直裂纹巴西圆盘断裂参数解析解

运用权函数法推导出考虑加载端摩擦的四种形式分布载荷加载下,中心直裂纹巴西圆盘试样在任意I/II复合型断裂模式下I、II型应力强度因子及T应力的解析解,并探究了端部摩擦及载荷分布角度对断裂参数的影响。研究结果表明:（1）当中心裂纹相对长度β较小时,纯I型、纯II型断裂的Y_I、Y_II及T*（分别是量纲为一的I型、II型应力强度因子及T应力）均随摩擦系数及载荷分布角度增大而减小;但是,当β较大时,摩擦系数增大可使纯I型Y_I增大,而载荷分布角度增大可使纯II型T*增大。（2）接触载荷分布形式为常数函数时,载荷分布角度对断裂参数的影响最显著,而四次函数下其对断裂参数的影响相对最小。（3）当β较小时,纯II型加载角度随载荷分布角度增大而减小;当β较大时,其随载荷分布角度增大而增大;摩擦系数增大可使纯II型加载角度增大。