多点锚固体外无粘结CFRP预应力加固RC梁的抗弯性能

在梁侧或梁底用波形齿横向张拉CFRP片材并锚固的体外预应力加固混凝土结构技术,对3根完全相同的7 m跨T形截面梁进行加固：其中2根梁侧面加固;1根梁底部加固。试验表明：多点锚固体外无粘结CFRP预应力可以依据构件的弯矩来调整各段的加固量从而更有效的利用CFRP材料的高强性能;梁底与梁侧加固对提高构件的抗弯刚度差别不大;波形齿能彻底解决预应力CFRP片材的锚固问题。以该3根加固梁的试验结果为基础,提出了梁体极限状态下塑性绞区长度的体外无粘结预应力碳纤维加固受弯构件的抗弯承载力公式,以及考虑二次效应的有效惯性矩法的挠曲变形的计算公式,通过与试验值的对比分析可知,所提出的方法可供设计参考使用。     

预应力碳纤维布加固混凝土梁预应力长期损失的增量微分法

为深入了解预应力碳纤维布加固钢筋混凝土梁的预应力长期损失,采用随时间变化的换算弹性模量方法,建立了考虑混凝土收缩徐变、胶层徐变及钢筋混凝土梁与碳纤维布界面滑移的预应力长期损失增量微分模型,得到了给定边界条件和荷载形式下的预应力长期损失闭合解。为验证该方法的有效性,对相关学者的试验梁进行了长期预应力损失的计算。计算结果表明,所建立的微分增量模型可以用来预测预应力碳纤维布加固钢筋混凝土梁的预应力长期损失。     

RC加气混凝土砌块组合墙加固框架抗震性能试验研究

RC加气混凝土砌块组合墙（简称组合墙）是由混凝土梁柱网格与加气混凝土砌块组合形成的一种轻型网格式抗震墙,可用于框架结构的抗震加固。笔者进行了1/2比例空框架试件、组合墙试件和组合墙加固框架试件的低周反复荷载试验,分析了各试件的主要破坏过程,对比了组合墙加固框架前后试件承载能力、刚度等抗震性能变化。试验结果及分析表明：组合墙加固框架后承载力、抗侧刚度有较大幅度提高,中大震及大震阶段其承载力、等效刚度约为空框架和组合墙单独受力之和的0.9倍,两者具有良好的协同工作性能;加固试件的破坏过程基本上遵循填充砌块混凝土框格外框架的破坏顺序,能够发挥组合墙多重抗震防线的特点,采用RC加气混凝土砌块组合墙加固框架是一种较为经济实用的加固方法。     

T形板肋对预制带肋底板混凝土叠合板弯曲疲劳性能的影响

为研究T形板肋对预制带肋底板混凝土叠合板弯曲疲劳性能的影响,对3块T形肋底板叠合板和1块整浇板进行弯曲疲劳性能对比试验,主要考察T形板肋与疲劳荷载幅值对试件疲劳破坏形态及疲劳损伤程度的影响,得到了在不同疲劳循环加载次数下的跨中动位移、混凝土应变、预应力筋应变、残余变形等,分析了在不同疲劳循环加载次数下的刚度退化情况、荷载-应变分布规律、裂缝分布规律及剩余承载力等。研究结果表明,经历200万次疲劳循环加载后,T形肋底板叠合板无明显的刚度和强度退化,增设T形板肋的叠合板能达到与整浇板相同的弯曲疲劳性能;T形肋底板叠合板正截面弯曲疲劳强度计算可采用普通预应力混凝土受弯构件正截面疲劳应力验算的4个假定,最终以此建立了其正截面弯曲疲劳强度验算方法。     

基于内聚力模型的锈蚀砼梁抗弯刚度

粘结性能退化是导致锈蚀钢筋混凝土构件力学性能下降的主要因素之一，基于锈蚀构件粘结性能实验研究成果与内聚力模型，建立了有厚度的双线性内聚力单元与分离式钢筋混凝土梁分析模型，引入粘结界面层，研究了粘结性能退化对锈蚀钢筋混凝土梁抗弯刚度的影响。结果表明，双线性内聚力单元可以有效模拟钢筋与混凝土之间的粘结机制，而根据锈蚀深度确定的有厚度的粘结单元能合理描述锈蚀程度对粘结性能的影响。数值分析结果与实验及经验公式对比，表明了文中方法的有效性和合理性。     

HDPF加固钢筋混凝土柱抗震性能试验研究

为了研究高延性聚酯纤维加固钢筋混凝土柱的抗震性能，共进行了7根柱的低周反复试验，其中，3根在未加固状态下进行试验，4根柱粘贴高延性聚酯纤维加固后进行试验，针对位移延性系数、等效粘滞阻尼系数、总耗能、承载力和纤维带的应变进行了研究与分析。研究结果表明：未加固柱的承载力、耗能能力和延性都比较低，采用高延性聚酯纤维加固后的试件裂缝发展缓慢，加固后柱的承载能力、耗能能力、延性均有不同程度地提高；在塑性铰区域内增加局部配筋，能够提高纤维布的约束效果。     

多点锚固预应力CFRP带加固T梁的有限元分析

采用非线性有限元分析程序ABAQUS对无粘结体外预应力CFRP片材加固简支钢筋混凝土T形梁后进行数值模拟，该模拟梁共4根分别为3根梁侧对称加固，1根为梁底加固均为四点波形齿锚固预应力CFRP带。对比结果显示，数据模拟与试验结果在构件屈服以前的承载力、变形以及极限承载力吻合程度较好，构件屈服以后的变形差别较大，因此，可在一定程度上有效替代试验分析方法。依据吻合程度最好的TL3参数设计了“两点锚固”和“四点锚固”的模型进行模拟分析。通过对锚固点数及加固量改变的对比分析可知，依据加固构件的弯矩改变各段加固量及布置锚固点数的方法既可以保证加固效果不降低，又可以节约CFRP材料。     

Vector form intrinsic finite element analysis based on fine beam model

精细梁不同于Euler梁和Timoshenko梁,该模型在考虑剪切变形的同时还考虑了横向弯曲时截面转动产生的附加轴向位移及横向剪切变形影响截面抗弯刚度后产生的附加横向位移。推导了适用于向量式有限元分析的精细梁单元应变和内力表达式,采用FORTRAN自编了向量式有限元程序。对悬臂梁、两端固支梁和门式框架进行了算例分析,对比了采用不同梁单元模型下结构的竖向位移。结果表明：当高跨比较小时,3种梁单元的竖向位移相差不大;当高跨比较大时,精细梁单元的竖向位移较Euler梁和Timoshenko梁明显增大,表明剪切变形及刚度折减引起的附加轴向位移、附加横向位移不能忽略。精细梁单元模型对高跨比较大的梁进行分析可望得到更精确的结果。     

粘贴加固混凝土氯离子扩散的理论模型和数值模拟

基于物质非稳态扩散理论,采用现有研究对Fick第二定律的修正方法,并将粘贴加固考虑为对氯离子扩散方程边界条件的调整,提出可用于粘贴加固混凝土的氯离子扩散理论模型。利用ABAQUS、MATLAB PDE tool、MATLAB自编程3种方法均可对粘贴加固混凝土梁的氯离子扩散过程进行数值模拟。对比未加固与加固构件的氯离子扩散规律,发现粘贴加固可降低钢筋表面的氯离子浓度值,延缓氯离子浓度到达临界锈蚀浓度的时间,增加材料使用寿命,并且加固时间越早,增加寿命越长。     

表层嵌贴预应力CFRP板条加固钢筋混凝土梁的应力传递行为

表层嵌贴预应力FRP板条加固钢筋混凝土结构技术可充分发挥FRP材料强度，且不需设置永久锚具，具有较大的潜力。以试验得到的嵌贴FRP混凝土粘结滑移关系为基础，建立了嵌贴预应力CFRP板条与混凝土的粘结应力微分方程，并根据边界条件推导了方程的解析解，得到了嵌贴预应力CFRP板条放张后界面粘结应力、CFRP拉伸应力的分析模型。与试验结果的比较表明，该模型得出的界面粘结应力及CFRP拉伸应力与试验结果吻合较好。在此基础上，考虑放张后CFRP混凝土界面不出现剥离的条件，分析了粘结界面能抵抗的最大容许预应力。     

Effectiveness of U-Strips to Prevent CFRP Debonding in Strengthened RC Beams with Weak Interfaces

Weak interfaces may be induced during the process of substituting the damaged cover by corroded RC beams or strengthening directly with CFRP. The two possible causes are the combination between the new-old concrete and expansive cracks. In this study, nine strengthened beams were designed to investigate the effects of weak interface on CFRP debonding along with the effectiveness of conventional confinement provided by U-strips. The test results showed the structural integrity of strengthening system was impaired considerably by both types of weak interfaces. Furthermore, it easily led to CFRP debonding failure. Weaker the interface was, the less ability transfer shear forces are. Debonding failure could be effectively prevented by U-strips. Meanwhile, consequently flexural CFRP sheets performed mainly well. However, local cover delamination and premature rupture of flexural CFRP may still occur due to the effects of the weak interface. Therefore, the allowable tensile strain of flexural CFRP must be reduced, and stricter measures of confinement and anchorage must be taken in application.     

改性竹筋混凝土受弯构件力学性能试验研究

针对竹筋混凝土结构存在的问题,提出了多种对竹筋的改性方法。在此基础上,对12根采用不同配筋和不同改性方法的受弯构件(11根竹筋混凝土梁和1根钢筋混凝土梁)进行了试验研究,分析了不同改性方法和不同配筋率竹筋混凝土受弯构件的力学性能、破坏形态及其影响因素。研究结果表明：竹筋能有效提高混凝土受弯构件的承载能力;经过适当方法改性后的竹筋能确保竹筋和混凝土之间的有效粘结,其正截面强度计算可以采用平截面假定;竹筋混凝土受弯构件的破坏均为脆性破坏,其破坏形态与其截面配筋率有关。     

Calculation Method of Shear Behavior of Hybrid Fiber Reinforced High Performance Concrete Deep Beams

The static tests on hybrid fiber (steel fiber and polypropylene fiber) reinforced high performance concrete deep beams according to the orthogonal experimental design were conducted. The shear capacity and calculation method of deep beams were discussed as well. The contributory factors such as the characteristic parameters of steel fiber (types, volume fraction, aspect ratio), the volume fraction of polypropylene fiber, the ratio of web horizontal reinforcement and the ratio of web vertical reinforcement were analyzed. Results show that the shear failure mode of deep beams is changed with adding a reasonable volume of hybrid fibers, and hybrid fiber can greatly increase the diagonal cracking strength and shear strength of HPC deep beams. The diagonal cracking strength is increased by 45.2% averagely while the shear strength is increased by 25.6% averagely. A satisfied result is obtained when the plasticity theory is used to analyze shear behavior of hybrid fiber reinforced HPC deep beams. The contribution of web horizontal reinforcement and web vertical reinforcement to shear strength of deep beams is not obvious but the former plays a major role. After analyzing the strengthening mechanism of hybrid fiber, a formula to calculate the shear capacity of hybrid fiber reinforced HPC deep beams is presented based on spatial strut-and-tie mode and splitting failure.     

Experimental and Parametric Analysis of the Flexural Behavior of HRBF RC Beams

In order to investigate the flexural behavior of concrete beams reinforced with high strength hot rolled bars of fine grains, static bending test on four rectangle cross section HRBF400, HRBF500 RC beams was conducted. The results show that the experimental maximum crack width under short term load meets the requirement of current code while calculated value does not meet; mid span deflection of RC beams with HRBF400 under short term load still meets the requirement of current code while RC beams with HRBF500 does not meet. Bearing capacity calculating formula under conditions of crack/deflection control was proposed and conception of component's bearing capacity utilization coefficient (BCUC) was put forward. The influences of reinforcement strength, reinforcement diameter, concrete grade, reinforcement ratio, concrete cover thickness and high span ratio on BCUC were analyzed. Within the range of economic reinforcement ratio, ductility of HRBF RC beams meets the requirement. Energy dissipation capacity of HRBF RC beams is similar to that of normal RC beams at low reinforcement ratio but it decreases faster than normal RC beams with the increasing of reinforcement ratio. Energy dissipation capacity of HRBF RC beams is higher than that of normal RC concrete beams in elastic stage and it enhances with the increasing of reinforcement ratio.     

Experimental Study on Flexural Behavior of Reinforced Concrete Beams Strengthened With Ferrocement Mortar

Experimental research on flexural behavior of the different grade RC beams strengthened with ferrocement mortar through six RC beams is carried out. The matching of original component concrete to the composite mortar strength rank is studied and its influence on bending strength, the crack-resisting capacity and the bending stiffness of RC beams is analyzed. Based on plane cross-section assumption and the experimental results, the formulas of the theoretical ultimate strength capacity and stiffness are brought forward. The calculated results fit well with the experimental results, to provide a theoretical reference for actual engineering designs.     

Experimental analysis of strengthening effect of corroded reinforced concrete beams strengthened with bolted steel plates

In order to study the mechanical behavior of corroded reinforced concrete beams strengthened with bolted steel plates, this paper designed 12 reinforced concrete beams. These beams were corroded by using accelerated electrochemical corrosion method with a designed corrosion ratio of 10%. The pre-compression experiments were performed for all RC beams before strengthening and the maximum crack width was controlled as 0.2 mm. According to the thickness of concrete cover, the beams were divided into 3 groups. Each group was composed of one comparative beam and three tested beams strengthened by steel plates bolted with study according to the thickness of steel plates which were 3 mm, 4 mm and 5 mm, respectively. It was shown that the strain distributions along the height of the strengthened beams at middle-span were in good agreement with the plain section assumption basically. The serviceability performances of corroded RC beams were significantly improved and these ultimate bearing capacities increased obviously. The steel plate bolted with stud effectively reduced the crack width and the extension height of reinforced concrete beams. It was indicated that an increase of steel plates with 35 mm resulted in a decrease of deflection by 13%51% when beams had the same thickness of concrete cover and corrosion ratio. Influence of the thickness of concrete cover on the ultimate bearing capacity was not obvious.     

Simulation Analysis of Flexural Performance of Reinforced Concrete Beam in Salt-frost Environment

Considering the damage of concrete mechanical properties and bonding behavior between the steel bar and concrete after the freezing and thawing function in the numerical simulation, the nonlinear analysis on flexural performance of reinforced concrete beam which experiences different salt-frost cycles is conducted, and the evolution law of resistance performance of reinforced concrete beam is studied. It is shown that, in the salt-frost environment, the decrease of concrete mechanical properties is the main reason that causes the degeneration of RC beam on flexural performance, while the reduction of bonding property has an unobvious effect on the beam resistance performance. When the salt-frost cycles reach a certain level, the beam failure pattern would change from the under-reinforced failure to over-reinforced failure. The freeze-thaw damage of bonding property in the beam-ends anchorage zone has a certain effect on the beam resistance behavior, especially for the more serious freeze-thaw degree, the resistance performance of the beam reduces about 4% than the perfect anchor beam.