冻融循环下预应力CFRP板加固钢筋混凝土梁的耐久性研究

预应力CFRP加固混凝土结构技术由于具有显著优势,越来越多地被应用在桥梁加固中,本文针对冻融循环作用下预应力CFRP板加固钢筋混凝土梁的耐久性能进行了实验研究。通过12片加固梁试件的实验研究了不同次数冻融循环作用下预应力CFRP板加固梁的破坏形态和承载性能,分析了混凝土强度等级、冻融循环次数、CFRP初始应力水平等因素对加固梁耐久性能的影响。实验结果表明:经历冻融循环后试件的开裂荷载和极限承载能力都有了不同程度的下降,冻融侵蚀对CFRP加固混凝土结构产生了明显的不利影响;随着冻融循环次数的增加,加固试件的破坏模式逐渐由混凝土保护层剥离转变为界面剥离的破坏形态;冻融循环作用对预应力加固试件的整体不利影响要大于非预应力试件;混凝土强度为C60的预应力CFRP加固试件在冻融侵蚀作用下的退化要较强度为C30的加固试件显著。     

碳纤维布加固钢筋混凝土梁受力性能的试验研究

通过对8根矩形截面钢筋混凝土梁的静力加载试验,研究了抗弯和抗剪两种加固方式对钢筋混凝土梁的破坏形态和力学性能的影响,对比分析了碳纤维加固率、试验梁的状态、混凝土强度对加固效果的影响。结果表明：经碳纤维抗弯哥口抗剪加固后加圉梁相应的力学性能指标值明显提高;混凝土裂缝扩展得到了有效延缓,加固效果明显;抗弯加固后可显著提高混凝土梁的承载力和延性,但提高程度并不与加固率成正比;预裂粱抗弯加固后承载力和延性得到提高,但与其相同加固参数的梁相比,其承载力和延性有所降低;抗剪加固时混凝土强度越高,加固后混凝土梁的承载力和变形能力提高幅度越大,其中混凝土梁的变形能力受混凝土强度的影响较大。最后,对加固梁的极限承载力进行了理论分析与计算,建立了实用的理论计算公式,计算结果与试验结果吻合较好。     

Prediction of plane strain fracture of AHSS sheets with post-initiation softening

In this investigation, the three-parameter Modified Mohr–Coulomb (MMC) fracture model and the determination of the material parameters are briefly described. The formulation of the post-initiation behavior is proposed by defining both the explicit softening law and the incremental damage evolution law. As opposed to the existing attempts to simulate slant fracture with material weakening before crack formation, softening is assumed to occur only in the post-initiation range. The justification of this assumption can be provided by the interrupted fracture tests, for example, Spencer et al. (2002).Element deletion with a gradual loss of strength is used to simulate crack propagation after fracture initiation. The main emphasis of the paper is the numerical prediction of slant fracture which is almost always observed in thin sheets. For that purpose, VUMAT subroutines of ABAQUS are coded with post-initiation behavior for both shell elements and plane strain elements. Fracture of flat-grooved tensile specimens cut from advanced high strength steel (AHSS) sheets are simulated by 2D plane strain element and shell element models.     

A three-parameter elastic foundation model for interface stresses in curved beams externally strengthened by a thin FRP plate

Externally bonding of fiber reinforced polymer (FRP) plates or sheets has become a popular method for strengthening reinforced concrete structures. Stresses along the FRP–concrete interface are of great importance to the effectiveness of this type of strengthening because high stress concentration along the FRP–concrete interface can lead to the FRP debonding from the concrete beam. In this study, we develop an analytical solution of interface stresses in a curved structural beam bonded with a thin plate. A novel three-parameter elastic foundation model is used to describe the behavior of the adhesive layer. This adhesive layer model is an extension of the two-parameter elastic foundation commonly used in existing studies. It assumes that the shear stress in the adhesive layer is constant through the thickness, and the interface normal stresses along two concrete/adhesive and adhesive/FRP interfaces are different. Closed-form solutions are obtained for these two interfacial normal stresses, shear stress within the adhesive layer, and beam forces. The validation of these solutions is confirmed by finite element analysis.     

先张预应力CFL加固RC梁预应力损失的实验研究

由于预应力碳纤维增强复合材料(CFRP)加固钢筋混凝土(RC)结构技术能够充分发挥其优异的力学性能而备受关注。本文以预应力碳纤维薄板(CFL)加固RC桥梁结构为研究对象,研制了采用先张法对CFL施加预应力的实验装置,提出了先张预应力CFL加固RC梁的实验方法及其预应力损失的监测方法,并在3个预应力水平下对RC梁实施了预应力CFL加固,测试和分析了CFL的预应力损失演化规律。研究结果表明,本文提出的先张预应力CFL加固RC梁以及预应力损失测试的方法是可行和有效的。     

粘贴碳纤维布加固混凝土管道试验研究

首次通过对14个素混凝土和14个钢筋混凝土环状试件外粘碳纤维布加固性能进行试验，研究了碳纤维布加固混凝土内压圆管的破坏特征、受力性能和破坏机理。对不同加固方法及一次或二次受力的混凝土管在内压力作用下的极限承载力、荷载一应变关系等方面进行了研究。试验结果表明，用碳纤维布加固混凝土内压管可以显著地提高极限承载力，明显的改善了构件的延性，能够获得良好的力学性能。加固后试件的开裂承载力与未加固试件相比，提高幅度不大，加固试件二次受力与一次受力相比，开裂荷载有所降低，但极限承载力基本相同。用碳纤维布加固内压管是一个新课题，具有很好的应用前景，用本文提出的加固方法具有优良的加固性能，可为工程应用提供参考。     

Experimental study and analysis of RC beams strengthened with CFRP laminates under sustaining load

Six reinforced concrete beams strengthened in flexure using carbon fiber reinforced polymer (CFRP) laminates subjected to different sustaining loads were tested. The main goal of the test is to examine the effects of initial load and load history on the ultimate strength of strengthened reinforced concrete beams by externally bonded CFRP laminates. The main experimental parameters include different levels of sustaining load at the time of strengthening and load history. To explain the experimental results in quantitative terms, a theoretical model for flexural behavior of the strengthened reinforced concrete beam is also developed. Test results in the current study show that sustaining load levels at the time of strengthening have important influence on the ultimate strength of strengthened reinforced concrete beams. If the initial load is basically same, the ultimate strength of reinforced concrete beams strengthened with CFRP laminates is almost same regardless of load history at the time of strengthening.     

ESPI技术对外贴纤维混凝土加固承载的实验研究

采用电子散斑干涉技术,对外贴碳纤维加固混凝土梁的外贴材料位移的分布特征,进行了全场实时测量,通过实验获得的散斑干涉条纹图可以得到外贴材料与混凝土梁的粘结传力长度随粘结长度及初始载荷之间的关系;了解用于加固的碳纤维材料的应变分布特点和产生梁侧剥离破坏时的碳纤维表面位移(应变)的演化过程。实验还说明了电子散斑干涉技术不仅可用于位移的测量,而且也可用于结构安全监测和破坏预报。文中给出了对C20D、C25A和C60C侧贴碳纤维板加固在不同载荷作用直到构件破坏前的位移测试及对试件C60C轴线上的剪应力分析结果。     

An Experimental Method to Determine the Tensile Strength of Concrete at High Rates of Strain

In the present work, dynamic tensile strength of concrete is experimentally investigated by means of spalling tests. Based on extensive numerical simulations, the paper presents several advances to improve the processing of spalling tests. The striker is designed to get a more uniform tensile stress field in the specimen. Three methods proposed in the literature to deduce the dynamic strength of the specimen are discussed as well as the use of strain gauges and a laser extensometer. The experimental method is applied to process data of several tests performed on wet micro-concrete at strain rates varying from 30 to 150/s. A significant increase of the dynamic tensile strength with strain-rate is observed and compared with data of the literature. In addition, post-mortem studies of specimens are carried to improve the analysis of damage during spalling tests.     

骨料尺寸对混凝土层裂强度的影响

作为混凝土材料的主要组成部分,骨料对混凝土力学性能具有重要影响.但骨料尺寸对混凝土层裂强度的影响仍缺少研究.本文利用大直径Hopkinson杆对混凝土细长杆件进行层裂实验,通过放置在试件后方吸收杆上的波形测量混凝土层裂强度.对两种不同尺寸骨料的混凝土进行了不同冲击速度下的层裂实验研究.实验结果表明,在相同加载条件下,骨...     

桥梁空间分析中预应力效应分析方法研究

预应力技术在桥梁中的广泛使用,使得桥梁结构受力状况复杂,对预应力混凝土桥梁进行空间分析是必要的;但由于预应力筋数量庞大且形状复杂,对预应力空间效应的模拟是预应力混凝土桥梁空间分析的难点。从预应力筋的实际作用机理出发,提出在预应力张拉阶段用等效节点荷载来模拟预应力对结构的作用;而在预应力管道灌浆后,将预应力筋作为结构的一部分,用实体退化单元进行结构分析,并用两算例对本文的方法进行了验证。结果表明,该方法能真正模拟预应力的空间效应,可用于预应力混凝土桥的空间分析。     

Interfacial stresses in curved members bonded with a thin plate

The use of steel plates or externally bonded fibre-reinforced polymer laminates for flexural strengthening of concrete, masonry, timber or metallic structures is a technique that has become very popular. The effectiveness of this technique hinges heavily on the performance of the bond between the strengthening plate and the substrate, which has been the subject of many existing studies. In particular, the interfacial stresses between a beam and a soffit plate within the linear elastic range have been addressed by numerous analytical investigations. Surprisingly, none of these investigations has examined interfacial stresses in members with a curved soffit, despite that such members are often found in practice. This paper presents an analytical model for the interfacial stresses between a curved member of uniform section size and a thin plate bonded to its soffit. The governing differential equations for the interfacial shear and normal stresses are formulated and then solved with appropriate simplifying assumptions. Two numerical examples are presented to illustrate the effect of the curvature of the member on the interfacial stress distributions in a simply supported curved beam for the two cases of a point load and a uniformly distributed load. The analytical solution is verified by comparing its predictions with those from a finite element model.     

表层嵌贴CFRP板条-混凝土界面粘结应力模型的试验与理论研究

为研究寒冷地区饱和砂岩的冻融损伤机理,采用DMA450伺服压机,在静载100N、动载80N、波动频率5～200Hz、温度-40～40℃的条件下,进行了饱和砂岩在不同频率正弦波单轴载荷作用下杨氏模量随温度变化的实验研究,获得滞(粘)弹性的弛豫衰减,以及有衰减引起的砂岩样品微结构变化情况。结果表明：饱和砂岩的杨氏模量和弹性波速度随温度升高而降低,随频率提高而增大; -40～20℃温度范围是冻融损伤最严重的区域。同时,在三种低频条件下(1.6Hz、2.8Hz和5.0Hz)用共振法在0℃获得相变衰减峰,反映了饱和砂岩的冻胀融缩效应,其产生的应力导致了饱和砂岩的损伤。从机理来看,前者是微观缺陷的演变,长期积累会导致破坏;后者是一种物理风化作用造成的宏观损伤。本文结果可为研究寒冷地区饱和岩石冻融损伤的机理及规律提供一定的参考。     

巨型型钢混凝土柱双向偏心受压校核分析方法

利用ETABS截面设计器对某超高层建筑巨型型钢混凝土柱截面进行了双向偏心受压校核分析.首先由ETABS截面设计器得到构件截面相关曲线数据,通过编制的拟合及绘图程序采用空间相关曲面法对构件进行校核分析,针对空间相关曲面法的不足进一步提出了等效平面相关曲线法加以改进.等效平面相关曲线法基于映射原理将空间相关曲面转换成等效平面相关曲线,同时将空间内力点转换成等效内力点,方法直观简便,可在一个图形中给出各工况的校核结果,并且能定量地给出构件受力的安全程度.最后,以一个巨型型钢混凝土柱截面为例给出了等效平面相关曲线法的校核结果,对比了考虑型钢作用及不考虑型钢作用两种情况对巨型柱受力性能的影响.文中提出的方法可为类似工程和建筑结构设计软件的开发提供借鉴.     

混凝土楔入劈拉和三点弯曲断裂过程的细观数值模拟

基于离散元思想和Voronoi单元划分技术,利用混凝土细观刚体弹簧元模型,开展了混凝土楔入劈拉试件和三点弯曲切口梁的断裂过程数值仿真分析。从裂缝开展过程、试件破坏形态、荷载-张口位移曲线(P-CMOD)和断裂能等方面,将数值分析结果与已有的试验结果进行了对比。结果表明,细观刚体弹簧元法较准确地模拟了混凝土楔入劈拉试件和三点弯曲切口梁断裂过程。最后,分析了缝高比和骨料体积含量对混凝土断裂过程的影响规律,发现断裂能随骨料体积含量呈单调递增趋势。     

桥梁结构水下基础表观缺陷立体视觉检测试验

针对桥梁结构水下基础表观缺陷检测实际需求,提出立体视觉表观缺陷检测方法。采用SIFT算法完成表观缺陷图像特征提取与匹配,选用MATLAB编译立体视觉表观缺陷检测评定软件,集成桥梁结构水下基础表观缺陷立体视觉检测系统。使用该系统在实验室环境完成水及空气两种环境下混凝土剥落、裂缝及楔槽三种缺陷的检测对比试验,得到每种混凝土试块表观缺陷在不同环境下的检测结果。试验结果表明,立体视觉表观缺陷检测方法能准确评定表观缺陷几何尺寸,从而验证了该方法用于桥梁结构水下基础表观缺陷评定的实用性及可行性。     

THE MECHANISM OF EXPLOSIVE SPALLING OF HIGH STRENGTH AND HIGH PERFORMANCE CONCRETE EXPOSED TO ELEVATED TEMPERATURE

高强高性能混凝土已得到广泛应用,然而高温或火灾下的性能衰减与爆裂成为制约其应用的瓶颈问题,高温爆裂破坏机理尚不清楚. 该文对国内外高温或火灾下高强高性能混凝土爆裂机理的研究进行综述,阐述了蒸汽压、热应力、热开裂3 种热爆裂机理及其影响因素,分析了目前研究存在的困难与挑战. 提出建立一个以蒸汽压致爆机理为主,热应力和热开裂机理为辅的多因素耦合的爆裂模型来定量分析高强高性能混凝土的高温爆裂机理.     

混凝土楔入劈拉和三点弯曲断裂过程的细观数值模拟Mesoscale simulation on fracture process of wedge splitting and three-point bending of concrete

基于离散元思想和Voronoi单元划分技术,利用混凝土细观刚体弹簧元模型,开展了混凝土楔入劈拉试件和三点弯曲切口梁的断裂过程数值仿真分析。从裂缝开展过程、试件破坏形态、荷载-张口位移曲线(P-CMOD)和断裂能等方面,将数值分析结果与已有的试验结果进行了对比。结果表明,细观刚体弹簧元法较准确地模拟了混凝土楔入劈拉试件和三点弯曲切口梁断裂过程。最后,分析了缝高比和骨料体积含量对混凝土断裂过程的影响规律,发现断裂能随骨料体积含量呈单调递增趋势。     

CFRP索斜拉桥的索-浅拱模型及面内自由振动分析

本文针对斜拉桥的受力特点,基于索和浅拱的经典动力学运动方程,结合拉索与浅拱之间的耦合边界条件,并且考虑两者的几何非线性,建立了斜拉桥的多索-浅拱面内自由振动模型。将浅拱分段处理,结合索、浅拱连接处的动态平衡条件,应用分离变量法,建立多索-浅拱模型的面内自由振动理论。以双索浅拱模型为例,求解其特征值问题。同时,建立了相应的有限元模型,有限元计算结果与本文理论分析吻合良好。最后针对CFRP索斜拉桥的关键参数,基于本文的索-浅拱理论,对面内自由振动进一步研究。研究表明：浅拱的矢高在一定范围内变化,仅对某一阶频率产生影响,而其他各阶频率几乎没影响;CFRP拉索能显著改善索-浅拱组合结构的基本动力学特性。     

FRP约束钢管混凝土柱轴力-弯矩相关关系研究

为了建立FRP(Fiber Reinforced Polymer)约束钢管混凝土压弯构件轴力-弯矩相关关系曲线,分析组合结构中各组份对柱体压弯性能的影响,建立了FRP约束钢管混凝土截面分析计算模型,考虑不同FPR-钢复合约束程度和荷载偏心率对混凝土本构的影响。与现有CFRP(Carbon Fiber Reinforced Polymer)-钢管混凝土压弯试验结果对比,验证了模型的合理性。对模型开展参数分析,结果表明,FRP约束混凝土压弯性能主要受环向FRP影响,环向FRP层数的增加在提高柱体轴压承载力的同时可有效降低其界限偏心率,提高大偏心状态下柱体的轴压比;纵向FRP层数仅会影响柱体承载力,对其界限偏心率及大偏心受压状态下的轴压比影响不显著;随着环向FRP约束程度的提高,柱体对P-Δ效应的敏感性增强。