预应力UHPC-NC组合梁结合面徐变剪应力分析

在恒载应力作用下,预应力UHPC-NC组合梁因两种材料不同的徐变特性及加载龄期的差异导致结合面产生徐变剪应力,分别采用解析法和有限元法对结合面徐变剪应力进行分析。在解析法中,用三角级数表示UHPC-NC结合面的应力分布,基于结合面上的变形协调,利用最小余能原理推导出结合面徐变剪应力计算公式。在有限元法中,将组合梁UHPC层与NC层均划分成四边形平面应力单元,对结合面则采用等效杆单元模拟。以T形截面预应力UHPC-NC组合梁为例进行计算方法的验证,两种方法的计算结果吻合良好,且研究发现徐变剪应力最大值位于梁端;在此基础上对影响结合面徐变剪应力分布的UHPC层压应力、梁高、计算龄期、环境年平均相对湿度等参数进行分析,结果表明:结合面徐变剪应力最大值随着UHPC层压应力、计算龄期、环境年平均相对湿度的增大而增大,但基本不随梁高变化;结合面徐变剪应力最大值的位置随着梁高的增大而逐步向跨中靠近,其他因素不影响应力最大值的位置。研究结果可为UHPC-NC组合梁结合面的抗剪设计提供参考。

高性能防护网结合预应力锚杆在公路边坡高位崩塌落石综合整治中的应用

高性能防护网结合预应力锚杆具有较强的深层加固和局部块体的表层防护作用,在高位崩塌落石综合整治中具有明显优势。本文采用工程地质调绘、无人机测绘3D建模、病害调查和理论分析等方法对某高速公路隧道口9级路堑边坡的高位崩塌落石病害及其稳定性进行分析评价,经方案比选论证后采用高性能防护网结合预应力锚杆的措施对该病害边坡进行综合整治,消除了重大安全隐患,达到了预期效果,为各级公路边坡高位崩塌落石病害整治提供了可借鉴的工程经验。

表面工程中膜基结合应力的线法分析

首次导出了平面问题两种介质分界线为离散线的线法基本方程;三维问题离散线分布于界面内的技法基本方程;并采用线法对拉伸法试验中膜基最大剪切应力问题进行了计算,指出了原有结果中的不足.

后结合预应力组合梁桥的混凝土预应力实效测试与分析

为了研究后结合预应力法在组合结构连续梁桥中的应用效果,并与常规预应力组合梁的预应力实施情况进行比较,基于换算截面法分别推导了后结合和常规结合连续组合梁桥的中支点截面应力计算公式,结合国内首座大跨度后结合预应力组合连续梁桥开展实桥受力性能测试,测量负弯矩区中支点截面在各施工工况中的应力状态。测量结果表明:后结合预应力法不会在钢梁中产生压应力,有效提升了预应力在混凝土中的施加效率,后结合法产生在混凝土中的预压应力是常规预应力法的1.3倍。计算分析表明,采用后结合预应力法在跨径70 m以下连续组合梁中可以实现混凝土桥面板为全预应力状态,在跨径110 m以下连续组合梁中可以实现混凝土不开裂的A类预应力状态。

体外预应力钢-混结合梁桥温度效应分析

针对简支体外预应力钢-混结合梁,考虑钢梁与混凝土之间的相对滑移,温度沿混凝土截面线性分布,体外预应力筋直线布置,剪力钉所受到的剪力和钢梁与混凝土板的相对滑移呈线性关系,推导出结合梁及体外预应力筋由温度效应产生的内力计算公式。通过算例与有限元分析进行对比,并讨论了在日照温度效应下,各种因素对体外预应力钢-混结合梁温度应力的影响。结果表明:公式法和有限元法计算结果吻合;日照温度效应使简支结合梁的混凝土板受压,钢梁顶部受拉,底部受压,对体外预应力筋应力影响很小;当剪力钉刚度足够大时,温度应力不随剪力钉刚度变化而变化,剪力钉布置和桥梁跨度对体外预应力钢-混结合梁温度应力的影响不大。

矩形截面二次预应力组合梁结合面徐变应力分析

高速铁路桥梁对于徐变上拱度有着严格的限制。二次预应力组合梁结构既可以满足受力要求又可以减少徐变上拱,是一种值得推广应用的新型预应力结构。二次预应力组合梁由于施工工艺的原因,两期混凝土的恒载应力和龄期不同,徐变变形相互约束导致结合面上存在徐变引起的应力。用随龄期调整的弹性模量代替混凝土弹性模量,采用三角级数描述结合面应力,通过最小余能原理考虑结合面上的变形协调求得结合面徐变应力。由一个具体算例得到矩形截面二次预应力组合梁结合面徐变应力的分布形式,可为结合面抗剪设计提供参考。

Effect of consolidation parameters on mechanical properties of Cu-based bulk amorphous alloy consolidated by hot pressing

Cu50Zr40Ti10 bulk amorphous alloys were fabricated by hot pressing gas-atomized Cu50Zr40Ti10 amorphous powder under different consolidation conditions without vacuum and inert gas protection. The consolidation conditions of the Cu50Zr40Ti10 amorphous powder were investigated based on an L9（34） orthogonal design. The compression strength and strain limit of the Cu50Zr40Ti10 bulk amorphous alloys can reach up to 1090.4 MPa and 11.9 %, respectively. The consolidation pressure significantly influences the strain limit and compression strength of the compact. But the mechanical properties are not significantly influenced by the consolidation temperature. In addition, the preforming pressure significantly influences not the compression strength but the strain limit. The optimum consolidation condition for the Cu50Zr40Ti10 amorphous powder is first precompacted under the pressure of 150 MPa, and then consolidated under the pressure of 450 MPa and the temperature of 380 °C.

预应力结合梁收缩徐变行为的长期试验研究

针对某预应力钢—混凝土结合梁结构 ,设计制作了试验模型 ,对结合梁的应力重分布和变形性能进行了长期试验研究 。

Strength failure and crack coalescence behavior of sandstone containing single pre-cut fissure under coupled stress, fluid flow and changing chemical environment

In order to study the strength failure and crack coalescence characteristics of cracked rocks, uniaxial compression experiments were conducted on cylindrical sandstone specimens, sampled from Longyou Grottoes of Zhejiang Province, China, with a single pre-cut crack soaking in different chemical solutions. Based on the results of uniaxial compressive test under different chemical solutions and velocities of flow, the effect of strength and deformation characteristics and main modes of crack coalescence for cracked rocks under chemical corrosion were analyzed. The results show that the pH value and velocity of the chemical solutions both have great influence on the sandstone sample's uniaxial compressive strength and deformation characteristics. Cracked sandstone samples are tension-destructed under uniaxial compression, and the crack propagation directions are consistent with the loading direction. The phenomena of crack initiation, propagation and coalescence of sandstone are well observed. Four different crack types are identified based on the crack propagation mechanism by analyzing the ultimate failure modes of sandstone containing a single pre-cut fissure. The failure process of specimen in air is similar with the specimen under chemical solutions, however, the initial time of crack occuring in specimen under chemical solutions is generally earlier than that in the natural specimen, and the crack propagation and coalescence process of specimen under chemical solutions are longer than those of the natural specimen due to softening of structure of rock caused by hydro-chemical action. Immersion velocity of flow and chemical solutions does not have influence on the ultimate modes of crack coalescence.

Grain refinement and mechanical properties of pure aluminum processed by accumulative extrusion bonding

Ultrafine-grained aluminum processed by a new severe plastic deformation technique, accumulative extrusion bonding (AEB), was investigated. Microstructural characterization indicated good interfacial bonding and an average grain size of ~440 nm was obtained after six passes. Tensile testing revealed that the strength reached the maximum value of 195 MPa and the total elongation exceeded 16% after five passes. The hardness was also significantly improved and almost reached saturation after the first pass. SEM fractography of AEB-processed specimens after tensile test showed that failure mode was shear ductile fracture with elongated shallow dimples. Comparison with conventional accumulative roll bonding indicates that this new AEB technique is more effective in refining grain and improving mechanical properties of the specimens.

Research on replacement depth of black cotton soil based on cracking behavior of embankment

In order to analyze the influence of replacement depth of black cotton soil(BCS)foundation on the initial cracking depth of a highway embankment,the laboratory tests were performed to construct the constitutive relationship between state variables and stress variables of BCS,and the coupled consolidation theory for unsaturated soils was employed to simulate the change in the major principal stress of the subgrade soils caused by water loss shrinkage of BCS with the help of Abaqus 6.11 codes.The simulation results indicate that the water losing shrinkage of BCS causes tensile stress within the subgrade,which leads to embankment cracking.The crack depth decreases with the increase in the BCS replacement depth and the embankment height,and increases with the increase in the burial depth of BCS.In the distribution area of deep BCS,the key values of foundation replacement depth for controlling the crack depth of the embankment with the height of 1 to 4 m are 1.2 and 1.5 m.In the low filling section,when the buried depth of BCS is 2,3 and 4 m,the key values of the foundation replacement depth to control the crack depth of the embankment are 0.8 and 1.2 m.In order to control the embankment cracking induced by the water losing shrinkage of BCS,a reasonable replacement depth of the foundation should be selected while slope protection is carried out well.

非饱和土大气张力通用公式与地基压缩变形初探

提出了"土的压缩变形的变化只取决于有效应力的变化的观点是不成立的。自由水和孔隙气同样具有抗压能力,地基压缩变形应该用总应力计算。有效应力的实质是自由水和孔隙气没有抗剪能力。在抗剪极限状态,颗粒接触有效应力为法向压力,结合水膜和表面张力收缩膜贡献有效应力为法向拉力"。推出了非饱和土大气张力z方向时间应变率表达式。推出了抗剪极限状态非饱和土有效应力的大气张力通用公式。提出了渗流体的"等效压缩模量"的新概念。

Research on numerical welding experiment of a thick spherical shell structure

In this paper, in order to predict the residual deformation of thick spherical structure, a welding program is compiled in APDL language based on Ansys and a numerical welding experiment of a welding example is carried out. The temperature field of welding was simulated firstly, then a thermal-structure coupling analysis was carried out, and at last the residual stress and deformation after welding were got. After that, the numerical experiment result was compared with physical experiment one. The comparative analysis shows that the numerical simulation fits well with physical experiment. On the basis of that, a three-dimensional numerical experiment of a thick spherical shell structure was carried out to get the changing rule of stress and deformation of a thick spherical shell structure during welding. The research is of great value to the prediction of residual deformation and high precision machining.

框架结构加固的实际应用

工业厂房经常会出现因腐蚀或加载而导致结构的承载力不足,从而要对结构进行加固,同时由结构加固的原理引出一系列问题的思考。

Progressive failure analysis of composite structure based on micro- and macro-mechanics models

Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stress distribution of the composite structure is calculated by commercial finite element software. According to the macro-stress, the damaged point is found and the micro-stress distribution of representative volume element is calculated by finite-volume direct averaging micromechanics(FVDAM). Compared with the results calculated by failure criterion based on macro-stress field(the maximum stress criteria and Hashin criteria) and micro-stress field(Huang model), it is proven that the failure analysis based on macro- and micro-mechanics model is feasible and efficient.

Temperature Stress Analysis of Prestressed Concrete Box Girder with Corrugated Steel Webs

To figure out the distribution of temperature gradient along the girder height of steel-concrete composite box girder, combined with the mechanical characteristics of prestressed concrete composed box girder with corrugated steel webs, the calculation formulas of cross-sectional temperature stress along the span in a simply-supported beam bridge with composite section were derived under the conditions of static equilibrium and deformation compatibility of the beam element. The methods of calculating the maximum temperature stress value were discussed when the connectors are assumed rigid or flexible. Theoretical and numerical results indicate that the method proposed shows better precision for the calculation of temperature self-stress in both the top and the bottom surfaces of the box girder. Moreover, the regularity of temperature stress distribution at different locations along the girder span is that the largest axial force of the top or the bottom plate of the box girder is located in the midspan and spreads decreasingly until zero at both supported ends, and that the greatest longitudinal shear density in steel-concrete interface appears at both supported ends and then reduces gradually to zero in the midspan.

Determination Method on Initial Pretension of Cables in Steel Mega Frame and Prestressed Composite Bracing Structure

Determining initial pretension values of pre-stressed cables is one of the key problems for a steel mega frame and pre-stressed composite bracing structure.Through the mechanical analysis of the composite bracing under vertical loading,the critical factors deciding the initial pretention value were found.According to these factors,a rule for the initial pretension value was put forward.The determination equations were acquired based on the principle of force equilibrium at nodes.The numerical results indicate that the internal force disequilibrium in composite bracings resulted from symmetrical load can be eliminated only in a symmetrical way,so that initial pretention values are decided only by vertical loads.The influencing coefficient leveling method,taking into account interactions between story and story,is accurate and feasible.

Analysis of Cutout Fiber as Source of Delamination in Composites System Using FEM

Delamination in composite structures can be a serious threat to the safety of the structure. Delamination leads to loss of stiffness and strength of laminates under some conditions. This is particularly so in the case of compressively loaded structures as the loss of stiffness may lead to separation of layers, the consequences of which can be catastrophic. Causes of delamination are many. In aerospace applications, this includes manufacturing defects, as well as operationally induced defects such as bird strikes, hits due to runway debris and tool drops. In this work one of the main causes of delamination that is dealt with, is the one that redistribution of the stress state due to some defects all mostly like here is broken single fiber （cutout fiber） in composite system already initiated by one of the above causes. When a laminate is subjected to in-plane tension, the effects of delamination on the stiffness and strength may be characterized by analytical results concerning the onset of delamination growth and its subsequent development. Many of the analytical treatments deal with just free-edge delamination. In mean time the redistribution and the gradient of the stress state in composite system is playing an important role for causing delamination. The main task of this work is to analyze single fiber with and without cutout embedded in matrix. Different FE models were generated, from the results, the redistribution of the stress state around the defected fiber were presented and discussed. Finally concluded remarks were indicated.

SLM成形AlSi10Mg合金的变形行为与残余应力数值模拟

采用Simufact-additive 4.0软件对AlSi10Mg合金的选区激光熔化(SLM)成形过程进行数值模拟,研究了扫描速度、扫描间距、基板温度及激光功率对AlSi10Mg合金变形行为及制件与基板结合面残余应力的影响。结果表明:制件在x方向主要产生拉伸变形,在y方向和z方向则为收缩变形;随着基板温度(25~225℃)、激光功率(250~450 W)、扫描速度(900~1 300 mm/s)和扫描间距(40~80μm)的升高,结合面残余应力均呈先减小后增大的趋势。通过模拟得出最佳的打印参数分别为:基板温度180℃,扫描速度1 100 mm/s,激光功率450 W以及扫描间距70μm。

直驱风力发电机轴与轴套纯过盈配合校核计算方法

纯过盈配合是直驱风力发电机轴与轴套连接的一种常见形式,能够满足结构耐振、耐不均匀冲击和苛刻尺寸等要求,轴与轴套的配合公差是反映过盈量精准度的关键。提出一种传统经验法与有限元仿真相结合的过盈配合校核计算思路:首先,计算轴与轴套配合面传递荷载所需的过盈量,初步确定轴与轴套的配合公差;其次,校核配合公差达到最大过盈量时,轴与轴套配合面是否产生塑性变形;最后,基于ANSYS Workbench,进行有限元分析,在多种工况下对配合公差进行校核计算,并根据总体变形和综合应力仿真结果对配合公差进行修正。设计、生产的首批样机已经通过型式试验,与纯过盈配合相关的各项机械性能指标满足设计要求,且装机运行后保持运行状态良好,验证了该方法的准确性、实用性和可靠性。