采用块体-界面体系的砌体结构简化细观模型

基于ABAQUS装配式建模构架,提出了一种砌体结构的简化细观模型。该建模方法将块体砂浆界面及砂浆层统一采用块体间的界面来代替。界面属性包括法向和切向的力学参数,用来模拟砌体的剪压及受拉行为。界面的法向受拉采用粘性力学参数赋值,并通过与轴心受拉本构模型的等效,推导得出控制界面损伤演化速率的无量纲指数α的计算方程。剪压复合受力模型基于剪摩理论建立,通过粘性属性和库伦摩擦赋值。当剪压复合受力构件处于高轴压比时,通过块体的非线性属性实现了主压应力为主控的损伤阀值。按照该方法进行剪压相关性和砖墙剪切失效的试验仿真模拟,模拟得出的失效形态及力-位移曲线与试验结果基本相符。     

钢筋混凝土无腹筋细长梁剪切破坏机理模型研究综述

根据现有关于钢筋混凝土无腹筋细长梁剪切破坏机理问题的研究成果，介绍了基于修正压力场理论的抗剪模型、临界剪切裂缝理论、塑性理论、压力路径理论、劈裂破坏理论和基于截面应变分析的抗剪模型的基本假设、核心观点及受剪承载力计算方法，并给出总结、归纳及评析；另一方面，利用相关试验数据和ACI-DAfStb无腹筋细长梁剪切破坏数据库，分别对不同理论模型的受剪承载力计算公式进行了设计参数的影响评估和统计评估；并展望了无腹筋细长梁剪切破坏机理研究的发展方向。研究结果表明：不同理论模型的部分假设缺少直接的试验依据支持，梁腹混凝土的受拉（劈裂）或受剪（骨料咬合）以及受压区混凝土对抵抗剪力的贡献成为抗剪机制的主要分歧；不同受剪承载力计算公式对不同影响因素的考虑方式的合理性和计算结果的准确度均有待进一步提高。后续深入研究应综合考虑剪切破坏问题的随机性和物理属性，利用先进测试技术、应力演化分析方法，进一步揭示剪切破坏机理。     

酸雨环境下老旧砖砌体的抗压性能

为研究酸雨环境下老旧砌体抗压力学性能退化规律，实验室配置了PH值分别为1.5、2.5和3.5的3种硫酸和硝酸混合溶液来模拟酸雨环境，采用完全浸泡加速腐蚀的试验方法对砖、砂浆和砖柱进行不同程度的腐蚀，并测定其抗压强度。试验表明，随着腐蚀时间的增加，砂浆试块抗压强度先增大后降低；砖试块抗压强度随腐蚀时间的增加而降低；模拟酸雨溶液PH值越小，砂浆和砖试块抗压强度降低程度也愈大；砖柱极限承载力和弹性模量均随腐蚀时间的增加而降低，且模拟酸雨溶液PH值越小，降低程度愈大；随着腐蚀时间的增加，砖柱初始刚度逐渐减小，极限破坏位移增大；模拟酸雨溶液PH值越小，砖柱在达到峰值荷载时的变形值越小，脆性愈大；基于试验结果，建立了酸雨环境下砖柱应力应变曲线上升段统一数学表达式及酸雨侵蚀后普通烧结粘土砖砌体剩余抗压强度回归公式。     

污水环境对水泥土力学性能的影响试验研究

由于多数地下水泥土工程直接与地下腐蚀性介质环境接触,必将导致水泥土材料的逐步劣化甚至失效破坏。以某市区工地附近明渠排放的污水作为侵蚀性介质,制作了不同水泥掺量的水泥土试件,通过对比试验,研究了污水环境和清水环境下不同水泥掺量、不同龄期的水泥土抗压强度和抗剪强度。结果表明,在污水或清水环境下,相同水泥掺量水泥土30 d龄期的抗压强度几乎相等,随着龄期的增加其抗压强度均逐步增大,但污水环境下其抗压强度增长的幅度明显小于清水环境,90 d后清水环境的水泥土抗压强度不再增长,而污水环境的抗压强度开始降低;污水环境和清水环境下的水泥土内摩擦角和黏聚力随龄期、水泥掺量的增加均逐步增大,污水环境下龄期90 d后的内摩擦角和黏聚力均开始降低。     

异位发酵床垫料的直剪切及压缩试验研究

为研究不同含水率的条件下异位发酵床垫料：抗剪强度、黏聚力、内摩擦系数、压缩载荷的变化规律。本研究采用土壤力学试验方法,测定垫料五种不同含水率的相关参数。结果表明：当垫料含水率为29.22%~36.13%时,抗剪强度、内摩擦角系数会随着含水率的增大而增大;当含水率为45.55%~61.11%时,抗剪强度、内摩擦角系数会随着含水率的增大而减小。黏聚力不会因含水率的改变而出现明显变化;垫料的压缩载荷随加载时间增大而增大,递增幅度逐渐增大。     

高速铁路隧道基底软岩动力累积损伤特性

利用相似材料模拟高速铁路隧道基底软岩,采用荷载控制和非对称正弦波循环加载方式对软岩试件进行动三轴疲劳与损伤检测综合试验。通过试验结果分析,建立了软岩3参数多项式疲劳寿命计算模型和4参数多项式累积损伤参量计算模型,获得了软岩疲劳损伤特性,即：软岩疲劳破坏表现为端部拉-剪复合破坏和中部压-剪复合破坏两种模式;疲劳破坏全过程表现为初始微孔隙压密、裂纹发生与稳定扩展以及损伤裂纹加速发展3个发展阶段;软岩疲劳寿命主要取决于本身强度和动应力水平,强度愈高、动力应力水平愈低,其疲劳寿命就越长;当动应力水平相同时,软岩疲劳寿命与其弹性模量呈线性增长关系。     

高强钢绞线网加固混凝土粘结性能试验研究

通过高强钢绞线网聚合物砂浆加固层与混凝土结构的剥离破坏试验，对加固层与混凝土界面的剥离破坏特征进行了研究。探讨了单侧加固、植筋加固及U型加固等不同的加固方式对加固层抗剪承载力及抗剪强度的影响。试验结果表明，采用U型加固等增加粘结面积的方式能有效提高加固层粘结面抗剪承载力，但同时会削弱加固层的抗剪强度，而在界面上植入抗剪钢筋后，能同时提高聚合物砂浆加固层的抗剪承载力及抗剪强度。根据试验结果，提出了最小植筋率的建议值。     

重组竹的单轴与纯剪应力应变关系

重组竹是将竹丝束平行组坯、经高压胶合而成的一种生物质复合材料,是一种极具潜势的建筑结构材料。研究重组竹的基本力学性能和应力应变关系,是建立此类材料本构关系和进行重组竹结构非线性分析的基础。将重组竹理想化为横向各向同性复合材料,通过试验,给出了重组竹各主轴方向的单轴与各主平面的纯剪力学参数,建立了各种应力状态下的应力应变关系。结果表明,重组竹力学性能优于常用的结构用木材,且变异性较小。重组竹顺纹受拉强度约是顺纹受压强度的2倍;横纹受拉强度远远低于横纹受压强度;横切面内的剪切模量及强度远远低于另外两个方向,且横纹剪切强度是顺纹剪切强度的3倍。重组竹的应力应变关系和破坏模式与纤维参与受力程度密切相关。顺纹受拉时,拉应力完全由纤维承担,破坏表现为纤维的脆性拉断,强度最高,应力应变为完全线性关系;其他应力状态下,破坏均发生在基体或纤维-基体界面,若裂纹的扩展受到纤维限制,破坏呈渐进性,强度较低,应力应变曲线由早期的线性关系转入后期的非线性关系;当裂纹的扩展未受到纤维限制,破坏强度最低,应力应变呈线性关系。     

含水率和颗粒级配对稍密碎石土抗剪性能及地基承载力的影响

碎石土因特殊的工程特性而被科研人员关注，但对大粒径、粉质粘土填充、稍密状态下碎石土的力学性能涉足较少。根据该类型碎石土特点及大量勘察结果配置出两种比较典型级配的稍密碎石土，通过大型直剪试验仪测定了不同含水率状态下碎石土试样的抗剪强度，绘制剪应力与水平位移的关系图，通过一元回归得出稍密碎石的抗剪强度指标c、φ值，分析了不同含水率、不同级配对稍密碎石土抗剪性能的影响。结果表明：随着含水率的增大，碎石土粘聚力总体呈减小趋势，但变化趋势具有显著的阶段性且和粉质粘土的含量有关，含水率变化对碎石土内摩擦角的影响较小。用规范推荐方法计算了该类型碎石土地基承载力，并与地方规范经验取值和勘察工程实践取值进行了对比，结果表明：含水率对地基承载力影响较大，且与碎石土填充物的粉质粘土含量有关，粉质粘土含量越高，承载力影响越大。     

混凝土拉压强度尺寸效应的细观非均质机理

为了从材料细观非均质角度揭示混凝土强度尺寸效应机理,建立了混凝土细观单元等效非均质力学模型,开展了立方体抗拉、抗压强度尺寸效应细观数值模拟研究。研究结果表明：混凝土强度尺寸效应根源于材料细观非均质性,随着模型尺寸的增加,混凝土材料细观单元弹性模量变异系数增大,材料细观非均质性增强,大尺寸模型内部存在更多的低强度单元或缺陷,导致混凝土立方体抗拉、抗压强度降低,极限应变减小,脆性增大;混凝土损伤破坏由少量集中区域,发散扩展形成多条非贯通的裂纹带;数值模拟结果与尺寸效应实验数据相吻合。     

Seismic Shear Strength of Concrete Hollow Block Masonry

According to some problems existed in current Chinese codes for design of seismic shear strength of concrete hollow block masonry, the curve of shear strength of concrete hollow block masonry under shear-compression loading, including descent segment, was presented by theory of failure region and test results of 58 concrete block masonry walls under shear-compression loading. And the design seismic shear strength formula of concrete hollow block masonry, which has reliability guarantee, was deduced. Compared with current Chinese codes, the design seismic shear strength formula of concrete hollow block masonry not only can perfectly simulate the shear-friction, shear-compression and diagonal compression failure modes, but also avoid unreasonable and unsafe calculation of seismic shear strength of concrete hollow block masonry, which can be applied to design of tall reinforced concrete masonry structures.     

Experimental Study on Local Nonuniform Compression of Fired Shale Perforated Brick Masonry

In order to know the behavior of local nonuniform compression of fired shale perforated brick masonry with rectangular holes,the experimental study of 18 specimens with and without restriction at the end of beam under local compression was carried out.The failure modes and bearing mechanisms of specimens were researched and analyzed,the integrity coefficient of local compression stress figure was deduced,at last,the theoretical and testing values of local compression bearing capacity were compared and analyzed.The results indicate that the bearing performance at the end of wall section under local compression behaves better than that on the fringe,the vertical cracks throughout the specimen on the fringe caused by local nonuniform pressure weaken the advantageous function of 'unloading by the interior arch',the effective supporting length calculated according to code for design masonry structure is partial to safety.These results and suggestions can be used in the design of bearing perforated brick masonry for reference.     

钢结构仿古建筑双梁柱中节点的受力机理

为研究钢结构仿古建筑双梁柱中节点的抗震性能，对4个全焊双梁柱中节点进行了水平低周反复加载试验。通过观测试件在侧向力作用下的受力过程和破坏形态，分析双梁柱中节点的受力机理。根据梁截面形式的不同，将其分为箱型截面梁与工字型截面梁2类，依据仿古建筑独特的构造特点，将各试件节点核心区划分为上、中、下3个区域。通过量测各区域内的应变大小，分析该类结构节点核心区在侧向力作用下的受理机理及破坏模式，并建立双梁柱节点的斜压杆受力模型。试验结果表明：仿古建筑双梁柱节点的破坏形式主要为沿下核心区对角线的剪切破坏，并通过理论计算分析提出一种考虑轴压比与梁截面形式的双梁柱中节点抗剪承载力修正公式。     

Design Method of Reinforced Concrete Sandwich Beam column Joints

The experimental results of reinforced concrete sandwich beam column joints were studied intensively and finite element method simulation of such joints were performed for the sake of design method.Basic design criterion and computation contents were provided according to failure mode of specimens and other experimental results.And the limits of parameters were proposed based on the analysis of seismic behavior influence factors and comparison of traditional joints and sandwich joints.Hence, formulas of load resistant capacity were acquired by the results of load resistant capacity of specimens and nonlinear finite element method simulation.It is found that three measures should be taken for sandwich joints in order to reach demanded ductility and load resistant capability.Firstly, several parameters should be limited, including shear compression ratio, axial load ratio, ratio of beam concrete strength to column concrete strength, and minimal amount of transverse reinforcement of joint.Secondly, shear load resistant capacity and axial compressive load resistant capacity should be computed to ensure load resistant capability of joint, and essential strengthen measures could be applied if necessary.Thirdly, appropriate construction details should be taken to avoid reducing of beam bar anchorage capacity.     

Influence Factors Study of Bearing Capacity of T Shaped RC Steel Reinforced Concrete Short-pier Shell Wall

In order to ensure that the T shaped steel reinforced concrete short-pier shear wall ductile shear failure occurs, the failure mechanism on the basis of experimental research, using ANSYS finite element analysis software to simulate the failure mode. In the process of analysis considered the influence factors of horizontal steel reinforcement ratio, concrete strength, axial compression ratio and the content of steel. The results show: the level of reinforced volume reinforcement ratio, concrete strength and the content of steel can obviously change the the bearing capacity and ductility of components.     

Seismic performance of first floor corner joints of high-rise reinforced concrete frame structure

Crushing risk of corner column will increase substantially due to first floor corner joint shear failure of high-rise reinforced concrete frame structure under bi-directional loading and high axial compressive load caused by earthquake action. Therefore,     

圆钢管混凝土轴压长柱极限承载力的稳定系数法

为完善圆钢管混凝土轴压长柱极限承载力的计算理论，对比分析了中国国家标准GB 50936-2014和CECS 28：2012中轴压短柱极限承载力的N₀计算公式，并把GB 50936-2014中基于套箍系数的N₀计算公式改写成统一的形式，提出了基于正则长细比的轴压长柱的稳定系数计算式，并通过36个试件的对比，对计算式的精度和适用范围进行了分析。研究表明，现行国标GB 50936-2014中基于套箍系数的N₀计算公式更为精确，基于N₀计算公式和本文的稳定系数，可以计算得到更为精确的轴压长柱的极限承载力。     

Experiments on heat loss characteristics in a fully opened cylindrical cavity receiver

The climate has a great impact on highway bridge rubber bearings than on building rubber bearings. In order to study the change of the mechanical properties during the life of the plain chloroprene rubber bearings of highway bridge under freeze-thaw cycle condition, the plain chloroprene rubber bearings were processed 25, 50, 75, 100 times by freeze-thaw cycle in the standard freeze-thaw chamber, then the axial compression tests were carried. The changes of the performance indicators in the bearing capacity , the ultimate compressive strength, vertical stiffness, elastic modulus under different freeze-thaw cycles were analyzed comparatively. The results show that the plain chloroprene rubber bearings are more prone to brittle failure after the freeze-thaw cycle, and the failure phenomena of steel plate exposing or cracks is more serious than the phenomena of the standard specimen. With the increase of the number of freeze-thaw cycle, the ultimate bearing capacity, ultimate compressive strength and compressive elastic modulus of the plain chloroprene rubber bearings decrease. The attenuation formula and decay curve in 50 years of ultimate compressive strength and elastic modulus of compression are analyzed by least square method, the trends of change are both in line with the exponential function. The mechanical properties of plain chloroprene rubber bearings of highway bridge significantly decreased under freeze-thaw cycle condition. therefore, the temperature ranges of plain chloroprene rubber bearings of highway bridge should be strictly controlled, and some suggestions, such as increasing its minimum applicable temperature, usng the natural rubber bearings as much as possible in cold regions, have been given.     

Yield Displacement Calculation Method of High-Strength Concrete Shear Wall

It is assumed that concrete compressive stress of the cross-section compression zone is linear distribution when the cross-section of high-strength concrete shear wall reaches yield situation. Based on the plane section assumption, the yield curvature formula of shear wall section is obtained by using moment - curvature analysis method. The parameters affecting yield curvature of high-strength concrete shear wall are studied by using the yield curvature formula. The results show that longitudinal reinforcement yield strain is the most vital factor of the yield curvature in addition to axial load ratio. When axial load ratio is larger, both wing walls of shear wall section have larger impact. The yield curvature formula is presented, considering the impact of axial load ratio, boundary reinforcement yield stress and both ends of wing walls of shear wall section based on the regression analysis of calculation results. On this basis, the vertex yield displacement formula of high-strength concrete shear wall is proposed, and the calculation results of formula correspond well to the vertex yield displacement experimental values of the 12 high-strength concrete cantilever wall. The formula is also suited for the vertex yield displacement of comment concrete shear wall.