预应力碳纤维板加固钢筋混凝土梁的受弯性能

为研究预应力碳纤维板加固钢筋混凝土梁的受弯性能,进行3根碳纤维板加固钢筋混凝土梁和1根对比梁的试验研究。研究预应力以及梁底锚固方式对混凝土梁的受弯承载力、刚度、裂缝发展情况、碳纤维板利用率的影响。试验结果表明:预应力碳纤维板加固可明显提高试件的受弯承载力,提高碳纤维板的利用率,减小裂缝宽度,其延性有所下降,在加固构件设计时需特别关注;两种锚固方式均满足正常使用要求,综合考虑无需开槽的MJ-2锚具适用性更强。     

预应力碳纤维布材加固混凝土梁受弯性能非线性分析

根据平截面变形假定,考虑材料的非线性性质,用分级加应变的方法计算预应力碳纤维布加固的混凝土梁的荷载-挠度关系,得到的5根预应力碳纤维加固混凝土梁和4根非预应力加固混凝土梁的荷载-挠度曲线与试验结果吻合较好。并在此力学模型的基础上对预应力碳纤维布加固的受弯构件的二次受力性能进行了非线性分析,研究了碳纤维初始应变、截面高度、预应力大小对被加固梁受弯性能的影响。分析结果表明：预应力可有效发挥碳纤维高强性能,二次受力条件下预应力碳纤维布材的加固效果远好于非预应力碳纤维布材加固,可有效解决构件二次受力应力应变滞后问题。     

Environmental efficiency of strengthening schemes for concrete beams with externally bonded fibre reinforced plastic composites

Externally bonded fibre reinforced plastic (FRP) is one of the most widely used methods in engineering practice to strengthen in-service reinforced concrete (RC) structures. Although some specifications, such as GB50367-2013 (China) and ACI440-2008 (U.S.A), have been issued to guide the design of strengthening schemes, few researches were conducted to evaluate environmental impacts of the strengthening schemes. This study aims to explore the environmental impact of FRP strengthened RC beam considering the structural safety and uncertainty, and to establish sustainable design criteria. Environmental impact and improvement of structural safety of two strengthening schemes designed according to the specifications of China (GB50367-2013) and U.S.A. (ACI440-2008) were evaluated by Life Cycle Assessment (LCA) method and reliability method, respectively. An environmental-efficiency index was introduced by taking an increment of safety as a functional unit in the LCA method. Furthermore, the allowable environmental impact was assumed and uncertainties involved in the LCA method were considered. The exceedance probability, denoting the possibility that environmental impact of a design scheme exceeds a presumed allowable value, is presented and calculated. It can be found that the environmental-efficiency indices of two schemes are close to each other. Moreover, the exceedance probability depends on the allowable environmental impact, thus it should be determined cautiously.     

体外预应力混凝土梁受剪承载力计算方法研究

为研究体外预应力对混凝土梁受剪承载力提高的作用机理和体外预应力混凝土梁受剪承载力计算方法,分析钢筋混凝土梁和体外预应力混凝土梁微元体受力特点的区别,探讨体外预应力对受剪性能影响的机理,求解体外预应力对混凝土和箍筋抗剪贡献的提高系数,得到体外预应力混凝土梁受剪承载力理论计算式。采用已有体外预应力混凝土梁剪切破坏的试验数据对理论计算式进行验证,并与各国规范计算结果进行对比。结果表明,理论计算式得到的受剪承载力计算值与试验值的比值均值为0.950,标准差为0.125,提出的计算式可较好地预测体外预应力混凝土梁的受剪承载力,并可以考虑梁的几何尺寸、剪跨比、预应力筋弯起角度、纵筋率、配箍率、纵筋及腹筋屈服强度、混凝土强度等影响因素。     

AFRP筋体外预应力混凝土梁的自振频率分析

分析了考虑应力增量时AFRP筋体外预应力梁的自振频率计算方法，并根据自编的MathCAD程序，对AFRP筋与高强钢丝分别作为体外筋材时梁的自振频率理论计算值进行了对比。     

预应力CFRP板加固钢筋混凝土梁的延性设计方法

在4根预应力CFRP板加固混凝土梁试验研究的基础上,通过平截面假定以及材料应力应变本构关系进行推导,提出根据确定的目标延性系数反算CFRP板加固面积或初始张拉控制应力的计算方法.计算结果与试验结果比较,计算方法具有良好的适用性,可为实际工程中进行预应力CFRP板加固混凝土梁设计提供参考.     

体外预应力梁受力性能研究

本文作者根据四根体外预应力简支梁的试验,得出了体外预应力梁在非线性状态下的反应,并利用大变形条件下的杆件结构变形推导了包括几何非线性和材料非线性的单元刚度矩阵,同时编制了非线性有限元程序进行验证。     

预应力碳纤维布加固混凝土梁有限元分析

利用碳纤维布(CFRP)加固钢筋混凝土构件是一种先进的工程加固技术,已经在土木工程中得到了较为广泛的应用。本文应用ANSYS软件对碳纤维加固预应力和非预应力梁体受弯进行仿真,来分析和研究碳纤维加固混凝土梁的受力机理和加固效果,并给出了相应的荷载挠度曲线。结果表明应用预应力碳纤维的梁体明显优于普通碳纤维布加固的受损梁,不仅提高了结构各阶段的承载力而且降低了梁破坏时的挠度。     

碳纤维布加固梁的计算

通过对预应力碳纤维布加固钢筋混凝土梁的受力过程进行分析,结合我国现行规范,假定加固梁的截面应变符合平截面假定,通过截面极限状态分析,分别提出了界限破坏、受压破坏和受拉破坏模式下受弯承载力的理论计算公式。     

体外预应力混凝土连续梁弯曲性能试验研究

为了研究体外预应力混凝土连续梁的弯曲性能、极限受力状态及内力重分布规律,以施工方法和体内外预应力筋配比为参数,对1根整体式(体内外配筋)和2根节段式(体内外配筋和全体外配筋)体外预应力混凝土连续梁进行了模型试验。通过试验数据分析,得到了模型梁挠度、混凝土应变、体外预应力筋应力与有效高度随荷载变化规律,以及混凝土裂缝发展与分布情况。结果表明:整体式梁的混凝土极限压应变和挠度最大、延性较好但体外预应力筋有效高度减少最大,节段式体内外预应力梁的体外预应力筋极限应力最大,节段式全体外预应力梁的混凝土极限压应变和挠度最小、延性较差、体外预应力筋极限应力及有效高度减少也最小。节段式梁的裂缝主要集中在接缝位置、无斜裂缝,接缝位置的塑性变形使内力重分布更充分。整体式梁内力重分布的区域集中而节段式全体外预应力梁的范围较大,各梁控制截面弯矩增、减幅值不超过10%。     

体外预应力混凝土简支梁剪切性能试验研究

为了研究节段式体外预应力混凝土梁的剪切性能,采用剪跨比、配箍率、接缝类型、体内外预应力筋配比等参数进行了13根整体式和14根节段式(胶接缝和干接缝)体外预应力混凝土简支模型梁试验。描述了模型梁箍筋应力、体外预应力筋应力、挠度随荷载变化规律,以及破坏裂缝形成过程和破坏形态;分析了剪跨比、体内外预应力筋配比、接缝位置和数量及类型对梁剪切性能的影响。研究表明,节段式体外预应力混凝土梁的剪切性能和整体式梁有很大差异,接缝决定着剪切破坏形态与破坏裂缝的形成、较大削弱了梁的抗剪承载力、明显增大了破坏裂缝的宽度和梁体破坏时的变形;配置体内预应力筋能有效改善体外预应力混凝土梁的剪切性能;整体式体外预应力混凝土梁的剪切性能和一般预应力混凝土梁也有一些差异。     

无粘结预应力混凝土梁的ABAQUS有限元模拟

在ABAQUS有限元软件中,由于无粘结预应力混凝土中的预应力筋与混凝土的接触关系难以按有粘结混凝土那样的常规方法建立,因此采用ABAQUS软件建立有粘结预应力混凝土模型较为普遍,而建立无粘结预应力混凝土模型则比较少。基于此原因,提出一种处理无粘结筋与混凝土接触关系的改进方法——引入局部坐标的Coupling方法,通过已有的一个实例——抛物线布筋的无粘结预应力筋混凝土简支梁,介绍基于ABAQUS建模的全过程,并进行计算值与试验值的验证。结果表明该模拟方法的准确性和可行性。     

Structural performances of short steel-fiber reinforced concrete beams with externally bonded FRP sheets

The application of externally bonding FRP sheets to concrete structures has become a popular strengthening procedure. However, such FRP strengthening effect sometimes could not be well achieved due to the premature interfacial debonding along FRP–concrete bond interface. In FRP-reinforced plain concrete members, the rapid propagation of localized flexural cracks in concrete is one of the primary reasons that cause the concentration of interfacial shear stress around where concrete crack happens, thus resulting in the debonding initiation. Therefore, an effective control of crack localization and propagation in concrete might be a solution to avoid or delay the debonding. This article presents an approach to improve the FRP strengthening performance to concrete beams by mixing short steel-fibers into the concrete matrix. To investigate the enhancement of FRP strengthening effect, a series of experiments are carried out, which include a standard JIS test of short four-point bending beams without FRP strengthening and a test of three-point bending FRP-strengthened concrete beams with different volume fractions of mixed short steel-fibers. The control of crack propagation and the increase of concrete toughness through mixing short steel-fibers are achieved. In the experiment of three-point bending, FRP-strengthened concrete beams increasing steel-fiber volume fraction, leads to a smeared crack distribution in the concrete. The ultimate failure mode also changes from peeling-induced debonding to FRP rupture so that the FRP sheet can exert its strengthening effect sufficiently. In addition, a finite element analysis is performed to compare the experimental results, in which the increase of concrete toughness is described by fracture energy. The simulation basically reproduces the experiments. The validity of the proposed approach is demonstrated.     

体外预应力3跨变截面连续梁裂缝行为分析

根据4片体外预应力高强混凝土3跨变截面连续梁静力加载试验,对其裂缝发生、发展及卸载后闭合的行为,进行了较为深入的研究.     

体外预应力混凝土简支梁抗剪承载力计算方法

将已进行的13根整体式和14根节段式(胶接缝和干接缝)体外预应力混凝土简支模型梁剪切性能模型试验成果,作为建立抗剪承载力简化计算方法的基础资料。根据模型梁剪切性能试验的研究结果,以施工方法(整体式和节段式)、剪跨比、配箍率、接缝类型、体内外预应力筋配比等为参数建立斜截面抗剪承载力的回归计算公式,基于混凝土双轴强度理论和接缝截面极限平衡条件推导接缝截面抗剪承载力计算公式,利用试验数据对计算公式进行验证。按照我国公路桥梁设计可靠度水平和现行规范的要求对计算公式进行修正,提出可用于体外预应力混凝土梁截面抗剪承载力设计的简化计算方法。研究表明,简化计算方法能有效反映体外预应力混凝土梁剪切破坏特点和各主要因素对抗剪承载力的影响规律。     

Torsional behavior of steel fiber reinforced concrete beams

Torsion of structural members and the behavior of steel fiber reinforced concrete became the area of interest of many researchers in the past and it is still newsworthy. In this study, 12 reinforced concrete (R/C) beams with Steel Fiber Reinforced Concrete (SFRC) were tested to observe the failure under torsional moments. The volumetric steel fiber content, fiber aspect ratio, and the longitudinal reinforcement were the variables of the investigation. Unit torsional angle of twist versus torsional moment (torque) response of each specimen was monitored during the experiments, and the effect of above variables on this response was critically investigated. It was observed that not only the torque capacity of R/C beam is modified by the addition of Steel Fiber Reinforcement (SFR) but also the energy absorption capacity is significantly affected by the SFR addition. Besides, an empirical equation relating the torque to twist for SFRC beams is proposed and tested against the test data.     

预应力型钢混凝土简支梁受弯性能试验研究

预应力型钢混凝土梁是在普通型钢混凝土梁的基础上采用预应力技术的一种新型组合构件。基于13根预应力及普通型钢混凝土梁的受弯性能试验,分析了其受力过程、破坏形态、裂缝的开展与分布规律、刚度变化规律等。试验结果表明,预应力型钢混凝土梁比普通型钢混凝土梁具有更好的刚度和抗裂性能,裂缝开展得到较好的控制。基于改进综合内力法,建立了预应力型钢混凝土梁正截面受弯承载力及裂缝宽度计算公式,公式计算值与试验结果吻合良好。     

碳纤维筋体外预应力混凝土梁的研究

对碳纤维筋的定义及优缺点进行了阐述,对体外预应力混凝土桥梁的性能及特点进行了介绍,对碳纤维筋作为体外预应力筋在桥梁中的应用做了总结和展望,以推广碳纤维筋的应用。     

预应力碳纤维布加固损伤混凝土梁非线性有限元分析

采用ANSYS有限元分析软件,对不卸载时预应力碳纤维布加固钢筋混凝土梁的受力变形性能进行了计算分析。计算中采用升温法来施加预应力,利用单位的生与死来实现不卸载时的加固。通过与试验结果进行对比可知,数值计算结果与试验分析结果吻合较好。在此基础上,对不同初始损伤量及CFRP加固量进行了扩展计算可知,初始损伤梁对混凝土梁承载能力几乎无影响,通过增加CFRP加固层数能有效提高混凝土梁的承载能力。