新的kho-法计算双筋梁

介绍一新的钢筋混凝土双筋梁的计算方法和算例,该法是在单筋梁的计算公式基础上推导而得.受压区混凝土压应力分布仍然采用矩形加抛物线.计算公式形式与单筋梁的相同,简洁明了.在计算钢筋面积时,无须将弯矩分解成两部分,即混凝土受压合力与对应的钢筋拉力组成的力偶矩和受压钢筋与对应的受拉钢筋组成的另一个力偶矩.受拉钢筋总面积可直接求得.在事先制成的计算表格中已自动排除了超筋,即无须验算受压区的最大高度,受拉和受压钢筋的应变均能大于其屈服应变.     

新的k_(h0)-法计算单筋梁

介绍一新的钢筋混凝土单筋梁的配筋计算方法和算例,该法在混凝土受压区采用矩形加抛物线的应力分布,在计算中求解的未知量是混凝土边缘压应变或受拉钢筋应变,而不是"等效矩形应力"法中的受压区高度。该法是欧洲规范Eurocode2中采用的方法,计算过程简便,求得配筋后,无须在验算受压区高度;此外,还可用于弯压或弯拉构件的配筋计算。计算结果中除了含有计算钢筋面积的钢筋系数外,还有混凝土受压区边缘应变、受拉钢筋应变、受压区高度及内力臂系数等,结果一目了然。     

HRB500/HRB600钢筋作纵筋的混凝土框架梁端弯矩调幅试验研究

为研究HRB500钢筋和HRB600钢筋作纵筋的混凝土框架梁端弯矩调幅规律,完成了12榀单层两跨混凝土框架静力加载试验。试验结果表明:由于受拉纵筋屈服强度提高,一方面梁端塑性铰出现推迟,塑性铰形成前会发生一定的弯矩调幅;另一方面锚固于节点内的梁端受拉纵筋应变渗透引起较大的梁端附加转角,加大了弯矩调幅能力。将试验框架梁端弯矩调幅分塑性铰形成前后两阶段进行考察,第一阶段弯矩调幅幅度为10.35%~33.42%,第二阶段弯矩调幅幅度为3.39%~30.5%。基于试验结果,建立了与梁端控制截面相对受压区高度呈幂函数减小趋势、与受拉纵筋屈服强度和受拉纵筋屈服时刻应变渗透引起的梁端附加转角呈线性增长趋势的第一阶段弯矩调幅系数计算公式;建立了与总塑性转角（塑性铰区范围内的塑性转角与应变渗透引起的梁端附加塑性转角之和）呈幂函数增长趋势、与受拉纵筋屈服强度呈线性减小趋势的第二阶段弯矩调幅系数计算公式。     

一新的混凝土配筋计算方法:无量纲图表法

该文介绍作者推导的一新的主要用于混凝土梁配筋计算的无量纲通用图表法,该图表法的"新"和"通用"分别在于推导时没有用传统的"等效矩形应力"换算以及一表可适用于不同钢筋级别和不同混凝土等级(C15―C50)的配筋计算。该法扩展了《混凝土结构设计规范》的混凝土应力-应变关系的运用范围,至今只用到了混凝土的极限应变。该法计算过程简便,求得配筋后,无须再验算受压区高度,同时还可用于弯压或弯拉构件的配筋计算。计算结果中除了含有计算钢筋面积所需的内力臂系数外,还有混凝土受压区边缘应变、受拉和受压钢筋应变、混凝土受压区高度等,结果直观和一目了然,并为混凝土构件的设计提供了一新的更为精确的设计方法。     

混合配筋钢纤维增强混凝土梁受弯承载力试验及理论计算

为研究玻璃纤维增强聚合物复合材料(GFRP)筋与普通钢筋混合配筋钢纤维增强混凝土(SF/混凝土)梁的受弯性能及其受弯承载力计算方法,在考虑受拉区混凝土抗拉强度的基础上,给出混合配筋SF/混凝土梁的界限配筋率及受弯承载力计算公式;在此基础上设计制作了三种配筋方式的SF/混凝土梁,重点探讨了混合配筋率及筋材面积比(A_f/A_s)对试验梁失效模式和受弯承载力的影响;同时,借助已有相关试验结果,对比分析了混凝土强度对混合配筋SF/混凝土梁受弯性能的影响。试验和对比分析结果表明:混合配筋SF/混凝土梁正截面应变仍符合平截面假定;相同配筋形式下,混合配筋SF/混凝土梁的受弯承载力和跨中挠度随筋材面积比A_f/A_s的增加而增大;单层配筋梁的受弯承载力比双层配筋梁大;合理提高混凝土强度可在充分发挥GFRP筋抗拉作用的同时进一步提高混合配筋SF/混凝土梁的受弯承载力;采用本文给出的界限配筋率公式能有效预测混合配筋SF/混凝土梁的失效模式;梁受弯承载力建议公式的预测值与试验值吻合较好,具有良好的适用性。      

钢筋混凝土桥墩的延性抗震分析

本文采用理论推导的方法，分两种最终极限状态即受压区混凝土达到极限应变时的极限状态和受拉区钢筋达到单向拉伸流幅区域的上限时和要限状态，得到了延性系数的公式，通过对一些算例的比较发现，采用本文的计算公式得出的计算结构和欧洲、新西兰及日本规范的计算结果接近。     

受压区局部约束塑钢纤维轻骨料混凝土梁的抗弯性能

为提高塑钢纤维轻骨料混凝土梁的受弯性能,采用矩形箍约束局部受压区的方式,设计了六根受压区增强塑钢纤维轻骨料混凝土梁,分析了纵筋配筋率和混凝土强度对塑钢纤维轻骨料混凝土梁受弯力学性能的影响,并对其进行有限元分析.结果表明:采用箍筋约束受压区混凝土后,局部受压区极限压应变增大,试件的承载力和延性有显著提高;随着配筋率增加,试件的承载力有明显提高,且高配筋率梁的超筋破坏现象得到明显改善;随着约束区混凝土强度的增大,梁的承载力变大,而延性降低.有限元分析结果表明,在受压区局部配置箍筋约束后,受压区混凝土极限压应力变大,极大地改善了梁跨中受压区的应力集中现象,从而抑制了梁受压区边缘混凝土的压碎破坏,提高了梁的承载力和延性.     

正常使用状态下RUHTCC梁的弯曲变形预测

该文以有效截面惯性矩为参数,提出了正常使用状态下钢筋增强超高韧性水泥基复合材料(RUHTCC)梁的挠度简化计算方法。与钢筋混凝土梁不同,RUHTCC梁需要考虑受拉区UHTCC在弯曲开裂后的承载能力,理论分析表明基于拉压区面积矩平衡与基于内力平衡且假定压应力线性分布所得的中和轴高度计算公式不同,而后者符合中和轴的物理意义。采用UHTCC的非线性拉、压本构模型以及受压区边缘压应变对应的割线模量,得到基于内力平衡的RUHTCC梁完全开裂截面的中和轴高度以及惯性矩公式。其次,有效惯性矩公式中的常系数m修正为随配筋率变化的函数,得到适用于RUHTCC梁的有效惯性矩公式。采用该文提出的挠度简化计算方法,对比预测与实测的屈服前荷载-挠度曲线,两者基本一致。     

FRP筋混凝土梁正截面抗弯承载力设计研究

基于本课题组9根、国内外其他学者102根FRP筋混凝土梁的试验结果以及本课题组完成的38根FRP筋混凝土梁的有限元参数分析结果,对FRP筋混凝土梁的正截面抗弯承载力进行了较系统的研究.研究表明FRP筋混凝土梁的破坏模式有受拉破坏、平衡破坏和受压破坏三种.确定了FRP筋混凝土梁的最小配筋率以及配筋率与破坏模式的关系;给出了FRP筋"名义屈服强度"的计算公式,并较系统地提出了FRP筋混凝土梁正截面抗弯承载力的设计建议.与ACI 440.1R-01中的设计方法相比,基于该文设计建议的计算值与试验结果更为接近.     

钢筋活性粉末混凝土简支梁受弯力学性能试验与计算

活性粉末混凝土（RPC）与普通混凝土（OC）相比，具有超高的强度、高韧性和优异的耐久性，其构件承载力与刚度计算方法必然不同于普通混凝土构件。该文对4根钢筋活性粉末混凝土简支梁开展受弯性能足尺试验，获得了梁的开裂弯矩、极限弯矩及荷载-跨中位移曲线，揭示了RPC简支梁受弯变形特征与破坏模式，推导了钢筋RPC简支梁的开裂弯矩与正截面受弯承载力计算公式。结果表明:钢纤维RPC极限压应变为4394 με~5200 με，开裂应变为690 με~820 με，均远大于普通混凝土；由于添加了钢纤维，公式推导时必须考虑RPC拉区拉应力的影响，推导所得开裂弯矩、正截面受弯承载力及刚度公式计算值与试验值吻合较好，计算公式具有较高的精度，可用于钢筋RPC梁的设计计算。     

Flexural strength of reinforced concrete T-beams with steel fibers

The ultimate strength of reinforced concrete T-beams reinforced with conventional steel bars and short discontinuous steel fibers are studied. It is found that the presence of steel fibers reduced effectively the deflection, width of cracks and also improved the ductility and flexural rigidity of the concrete beams. Hence, an appreciable increase to the ultimate compressive strain is observed as well as the increase in the ultimate compressive strength. These are reflected by an increase in the value of the compressive block parameters. In addition, an increase in tensile strength is achieved and a rectangular tensile stress distribution is proposed. It was found that a negligible difference in moment capacity between overreinforced and underreinforced concrete beams. Therefore, it may be economical to use more amount of tension reinforcement than that allowed by the codes. Theoretical equations are developed to calculate the ultimate strength of reinforced concrete T-beams taking into account the effect of amount of compression reinforcement and amount of steel fibers. Theoretical equations show good agreement when compared with experimental results.     

水泥基复合材料加固小偏心受压钢筋混凝土柱承载力

通过对工程水泥基复合材料(ECC)加固钢筋混凝土(RC)柱和未加固RC柱进行小偏心受压试验,研究ECC加固RC柱小偏心受压性能。试验结果表明,ECC加固层能有效约束核心混凝土;与未加固柱相比,加固柱的裂缝细而密,达到峰值荷载时受压区ECC尚未被压碎,破坏过程比较平缓,有较好的完整性,并表现出一定的延性特征;相对偏心距相同时,加固柱的开裂荷载、峰值荷载及延性相比未加固柱分别提高了107%～236%、45%～159%、37.4%～41.3%。依据试验结果,绘制出各加固柱跨中荷载-挠度曲线,可分为4个阶段：弹性阶段、裂缝稳定扩展阶段、最大荷载阶段及下降段。随着加固层厚度的增大,相同荷载下ECC竖向应变及钢筋应变越小;随着相对偏心距的增大,相同荷载下ECC竖向应变及钢筋应变越大。基于混凝土结构理论及力学原理,分析ECC加固层对核心混凝土柱的约束机制,提出ECC约束混凝土抗压强度和峰值应变的表达式,推导出加固柱受压承载力计算公式,承载力计算值与试验值相对误差在10%以内,二者吻合良好,为ECC加固混凝土柱在实际工程中的应用提供理论参考。     

钢筋混凝土双向受弯梁次生扭矩的分析研究

探讨了次生扭矩对钢筋混凝土双向受弯梁抗剪承载力的影响。提出逐级加载、待定系数的方法计算钢筋混凝土双向受弯梁的次生扭矩,编制了钢筋混凝土双向受弯梁次生扭矩的全过程分析计算机程序。计算值与试验结果的对比分析表明,该方法合理可行。通过对次生扭矩影响抗剪承载力的主要因素的分析,获得一些有参考价值的结论,并提出在工程实践中,计算承受集中荷载的有腹筋双向受弯梁的抗剪强度时,次生扭矩影响应予以考虑。     

Mechanical behaviour of corroded reinforced concrete beams—Part 1: Experimental study of corroded beams

Steel corrosion in reinforced concrete leads to crack occurrence along the reinforcement (secondary cracks), to a reduction in bond strength and a reduction in steel cross section. The purpose of this study is to determine the effect of these deteriorations on the global behaviour of reinforced concrete structural elements in their service and ultimate states. Mechanical experimentation was carried out on fourteen-year-old reinforced concrete beams, on two control elements and two corroded beams. A comparative analysis of the results obtained on the beams showed that concrete cracking in the compressive area had no significant influence on the behaviour in service of the corroded elements. However, significant modifications of service behaviour were observed, due to the degradations in the tensile zone, namely: loss of bending stiffness, dissymmetrical behaviour. Finally, the measure of the residual steel cross-section of the corroded re-bars showed that the loss of bending stiffnes due to steel corrosion cannot be merely explained in terms of steel cross-section reduction. Concerning the ultimate behaviour, the loss of steel cross-section is the main parameter which leads to a reduction of bearing capacity and ductility. Another part will explain the separate and coupling effects of bond strength and steel cross-section loss on the mechanical behaviour of corroded beams.     

Evaluation of size dependent design shear strength of reinforced concrete beams without web reinforcement

Analytical studies on the effect of depth of beam and several parameters on the shear strength of reinforced concrete beams are reported. A large data base available has been segregated and a nonlinear regression analysis (NLRA) has been performed for developing the refined design models for both, the cracking and the ultimate shear strengths of reinforced concrete (RC) beams without web reinforcement. The shear strength of RC beams is size dependent, which needs to be evaluated and incorporated in the appropriate size effect models. The proposed models are functions of compressive strength of concrete, percentage of flexural reinforcement and depth of beam. The structural brittleness of large size beams seems to be severe compared with highly ductile small size beams at a given quantity of flexural reinforcement. The proposed models have been validated with the existing popular models as well as with the design code provisions.     

Experimental behaviour of reinforced concrete elements repaired with polymer-modified cementicious mortar

This paper presents the results of experimental tests on flexural behaviour of reinforced concrete beams repaired by polymer-modified mortar. Tests were repeated varying repair thickness, which included or did not include the steel reinforcement. Also the position of repair mortar was varied, as it was carried out either in the tension or compression region. Finally, the reinforcement ratios of beam sections were also varied. Results were compared with those from control beams, which were tested in non-damaged, non-repaired conditions. Thick repairs that include the longitudinal reinforcement can restore the load-bearing capacity and ductility of non-damaged control beams, whether they are applied in the tension or in the compression region. Thin repairs in tension, which substitute the concrete cover, but do not include the reinforcement, can even decrease the load bearing capacity and ductility of the beam, whereas thin repairs in compression are more effective than those in tension.     

Flexural strength of palm oil clinker concrete beams

This paper presents an experimental program on the flexural behaviour of reinforced concrete beams produced from palm oil clinker (POC) aggregates. POC is obtained from by-product of palm oil milling. Utilisation of POC in concrete production not only solves the problem of disposal of this solid waste but also helps to conserve natural resources. An experimental work was conducted involving eight under-reinforced beams with varying reinforcement ratios (0.34–2.21%) which were fabricated and tested. The data presented include the deflection characteristics, cracking behaviour and ductility indices. It was found that although palm oil clinker concrete (POCC) has a low modulus of elasticity, the test results revealed that the deflection of singly reinforced POCC beams, with reinforcement ratio less than 0.524, under the design service load is acceptable as the span-deflection ratios range between 250 and 257 and these values are within the allowable limit provided by BS 8110. In addition, the results reported in this paper indicate that the BS8110 based design equations can be used for the prediction of the flexural capacity of POCC beams with reinforcement ratio up to 2.23%.