基于分形理论的CFRP布增强混凝土梁抗弯性能研究

在实验室模拟酸雨腐蚀环境,完成了普通混凝土梁与CFRP布增强混凝土梁的抗弯试验,得到了各级荷载作用下构件表面裂缝的分布与演化过程,验证了受腐蚀CFRP布增强混凝土梁表面裂缝分布的分形特征。基于分形理论分析了受腐蚀混凝土梁在弯曲荷载作用下的开裂及破坏过程,详细讨论了梁表面裂缝的分形维数与其抗弯性能参数(损伤深度、混凝土强度、一阶频率、极限承载力、跨中挠度、位移延性系数)之间的关系。研究表明裂缝分形维数随着损伤深度的增加而减小,CFRP布增强混凝土梁的分形维数大于普通混凝土梁,其分形维数变化率与构件承载力变化率之间存在线性关系;因此梁表面裂缝分布的分形特征可作为CFRP布增强混凝土受弯构件损伤程度的衡量指标的观点,可为今后对“在役混凝土结构承载力和寿命预测的研究”提供参考。     

预应力型钢超高强混凝土梁受剪承载力试验研究

基于12榀预应力型钢超高强混凝土简支梁和2榀预应力型钢普通强度混凝土简支梁的受剪试验,揭示了影响试验梁受剪性能的主要因素,探讨了剪跨比、箍筋间距、腹板厚度、混凝土强度和预应力度对试验梁的破坏形态、荷载-挠度曲线、斜截面开裂荷载和受剪承载力的影响规律。试验结果表明:预应力型钢超高强混凝土梁具有更好的受剪承载力和剪切延性,以及更大的刚度;基于试验结果建立了预应力型钢超高强混凝土梁的受剪承载力建议计算公式,计算结果与试验结果吻合较好,表明了该文提出的计算公式具有较高的精度。研究成果将为预应力型钢超高强混凝土梁的设计计算和工程应用提供理论依据。     

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。      

二次受力下自密实混凝土加固RC梁受弯性能研究

为模拟实际工程中加固构件的真实承载能力,实验在原混凝土构件持续受荷状态下,采用自密实混凝土对构件进行加固、养护。共进行了7根二次受力下自密实混凝土加固钢筋混凝土梁和2根对比梁的受弯性能试验,研究了不同初始受力水平、不同加固厚度及不同界面处理方式对加固钢筋混凝土梁抗弯承载力和截面刚度的影响。试验量测了构件裂缝分布形态、荷载-挠度曲线、钢筋应变发展规律等。结果表明:采用自密实混凝土加固钢筋混凝土梁,能有效地提高钢筋混凝土梁的抗弯承载力、截面刚度等性能;二次受力下自密实混凝土加固梁抗弯承载力随着初始受力水平的增大而降低。在试验结果的基础上,基于平截面假定,提出了二次受力下自密实混凝土加固梁钢筋滞后应变及抗弯承载力计算式,计算结果与试验结果吻合良好。     

锈蚀预应力混凝土梁承载力及破坏模式研究

随着服役时间增长,侵蚀环境下预应力混凝土梁因受力筋发生锈蚀而造成其延性与承载力降低,严重影响结构的安全使用。为分析侵蚀环境下预应力混凝土梁的承载性能,以集中荷载作用下锈蚀预应力混凝土梁为研究对象,分析混凝土梁锈蚀后各材料性能的劣化与预应力对其承载能力的影响,基于桁架-拱模型给出了桁架作用与拱作用的荷载分配系数,建立了预应力混凝土梁承载力计算模型及破坏模式判别方法,并通过76根预应力混凝土梁的试验数据对建议模型进行验证。研究结果表明:预应力混凝土梁承载力试验值与计算值之比的平均值为1.116,方差为0.033,吻合较好;基于建议分析模型对预应力混凝土梁破坏模式的预测判别与试验梁破坏模式符合程度较高,且该模型能反映预应力混凝土梁随着锈蚀程度增大其破坏模式发生演变这一特征。该文建议的理论模型可用于锈蚀预应力混凝土梁的承载力计算与破坏模式预测分析。     

Effect of damaged concrete cover on the behavior of corroded concrete beams repaired with CFRP sheets

Fiber reinforced polymer matrix composites are being increasingly considered for use in civil infrastructure. These materials have found the maximum current use as materials for rapid and cost-effective rehabilitation (retrofit, repair and strengthening) of deteriorating and under-strength structural concrete components. This paper presents the experimental results of damaged/repaired reinforced concrete (RC) beams. The experimental program consisted of RC rectangular beam specimens exposed to accelerated corrosion. The corrosion rate was varied from 5% to 15% which represents loss in cross-sectional area of the steel reinforcement in the tension side. Half of the damaged beams were repaired by bonding Carbon Fiber Reinforced Polymer (CFRP) sheets to the tension side to restore the strength loss due to corrosion. The other half of the beams was first cleaned by removing spalled concrete cover and rusted bars were thoroughly cleaned. A new layer of concrete was cast to replace the removed spalled concrete cover. Then the CFRP sheets were attached to the new concrete layer. Corroded beams showed lower stiffness and strength than control (uncorroded) beams. Strength of damaged beams due to corrosion was restored to the undamaged state when repaired with CFRP sheets for all repaired beams, but the stiffness was almost unchanged. However, the repaired beams with replaced concrete cover layer resisted higher loads on average of 13% compared to damaged beams repaired without replacing the concrete cover layer.     

模拟酸沉降环境混凝土梁承载性能研究

酸雨环境下钢筋混凝土梁力学性能的变化规律是揭示整个结构承载力和耐久性的前提和基础。参考我国典型城市酸雨的化学组成,分别配置PH1.5与PH2.5的硫酸、硝酸混合溶液来模拟不同酸度的酸雨;自行设计制作了人工降雨器模拟降雨;浇筑了11根120mm×200mm×1900mm的钢筋混凝土梁。分别采用完全浸泡、干湿交替、人工降雨等加速腐蚀试验方法,对10根钢筋混凝土梁进行加速腐蚀。对不同浓度溶液下经历不同腐蚀时间的钢筋混凝土梁,分别利用超声方法测试了混凝土损伤厚度和抗压强度,利用动力试验方法评价混凝土梁的整体特性,并对梁的抗弯性能进行了抗弯实验研究。得到了不同侵蚀状态混凝土梁混凝土损伤厚度、构件刚度、构件开裂荷载、极限承载等力学性能;对比分析了不同加速腐蚀条件下混凝土梁抗弯性能的退化规律,得到了混凝土强度、构件频率以及抗弯强度与混凝土梁损伤程度之间的定量关系。研究结果表明:人工降雨与干湿交替两种方法对混凝土梁抗弯性能的影响基本相似,较浸泡方法变化得到的混凝土梁抗弯性能的退化性能更为显著。     

免拆UHPC模板RC梁受弯性能试验及承载力分析

对4根免拆超高性能混凝土（UHPC）模板钢筋混凝土（RC）梁和2根RC梁进行了受弯性能试验,试件变化参数为配筋率和保护层厚度,重点研究免拆UHPC模板RC梁的受力性能以及模板与后浇混凝土的剥离情况。结果表明:从开始加载到峰值荷载点,免拆UHPC模板与后浇混凝土界面没有发生任何滑移及剥离;峰值荷载后至构件破坏时,预制UHPC模板与后浇混凝土界面出现轻微剥离;免拆UHPC模板RC梁的开裂荷载较普通RC梁提高了近50%,屈服荷载、极限荷载提高约为10%。基于截面平衡条件、平截面假定以及UHPC、混凝土、钢筋的本构关系,建立了免拆UHPC模板RC梁的受弯承载力计算公式,公式计算值与试验值吻合较好。     

Structural performance of corroded RC beams repaired with CFRP sheets

Corrosion of reinforcement is a serious problem and is the main cause of concrete structures deterioration costing millions of dollars even though the majority of such structures are at the early age of their expected service life. This paper presents the experimental results of damaged/repaired reinforced concrete beams. The experimental program consisted of reinforced concrete rectangular beam specimens exposed to accelerated corrosion. The corrosion rate was varied between 5% and 15% which represents loss in cross-sectional area of the steel reinforcement in the tension side. Corroded beams were repaired by bonding carbon fiber reinforced polymer (CFRP) sheets to the tension side to restore the strength loss due to corrosion. Different strengthening schemes were used to repair the damaged beams. Test results showed detrimental effect of corrosion on strength as well as the bond between steel reinforcement and the surrounding concrete. Corroded beams showed lower stiffness and strength than control (uncorroded) beams. However, strength of damaged beams due to corrosion was restored to the undamaged state when strengthened with CFRP sheets. On the other hand, the ultimate deflection of strengthened beams was less than ultimate deflection of un-strengthened beams.     

轻骨料无腹筋混凝土梁剪切破坏及尺寸效应:细观模拟

轻骨料混凝土具有轻质、高强及保温隔热性能好等优点,被广泛应用于工程结构中。采用细观数值模拟方法,将普通及轻骨料混凝土看作由骨料颗粒、砂浆基质及界面过渡区组成的三相复合材料,建立了无腹筋混凝土梁剪切破坏行为模拟的三维细观力学分析模型,研究了不同尺寸普通及轻骨料无腹筋混凝土悬臂梁在单调加载下的剪切破坏模式与失效机制,揭示了名义剪切强度的尺寸效应规律。此外,结合模拟结果对相关设计规范抗剪承载力计算公式的准确性和安全性进行了初步探讨。研究结果表明:区别于普通混凝土梁,轻骨料混凝土梁由于骨料强度较低而首先发生破坏;不同尺寸混凝土梁的剪切破坏模式基本一致,梁的名义剪切强度展现出明显的尺寸效应;相比于普通混凝土梁,轻骨料混凝土梁剪切破坏表现出具有更强的尺寸效应。     

形状记忆合金混凝土梁力学性能试验研究

将超弹性形状记忆合金(简称SMA)绞线作为主筋埋入到混凝土梁中,制成SMA混凝土梁。采用跨中单点加载试验对其进行力学性能测试,并利用同尺寸、同配筋率的钢筋混凝土梁作为参照,比较了各试验梁的承载力、残余变形和残余裂缝,分析了SMA的预应力及SMA与混凝土的粘结情况对试验梁力学性能的影响。结果表明,超弹性SMA绞线可以减小混凝土梁的残余变形和残余裂缝,提高混凝土梁的自修复能力。与普通钢筋混凝土梁相比,开裂后SMA混凝土梁的承载力增加的幅度更大,且粘结情况对梁的承载力有较大的影响。此外,对于无粘结SMA混凝土梁,对SMA绞线施加预应力可以提高混凝土梁的承载力和耗能能力。     

Influence of long-term chloride diffusion in concrete and the resulting corrosion of reinforcement on the serviceability of RC beams

This paper presents the chloride penetration and the effect of chloride ingress on the serviceability of reinforced concrete (RC) beams. A series of experimental studies were carried out on beams with various corroded ages up to 28 years. The chloride content in different locations were tested during various periods. Different states influencing the serviceability of the corroded beams were investigated, including the maximum width of the corrosion-induced cracks of the concrete cover, the mid-span deflection of the beams under the service load and their load-bearing capacity. Based on the results available from this programme, the service life of corroded beams was predicted by the corrosion process of the reinforcement. The results showed that the chloride corrosion could significantly deteriorate the serviceability of the beams. The current criteria concerning the chloride content at the level of the reinforcement of the concrete beams and the maximum width of the corrosion-induced cracks appear to be very conservative.     

外包钢板-高延性混凝土组合连梁抗震性能试验研究

为改善小跨高比连梁的抗震性能,采用高延性混凝土（HDC）代替混凝土,设计了2个外包钢板-HDC组合连梁、1个外包钢板-混凝土组合连梁和1个内置钢板-HDC组合连梁试件。通过拟静力试验,研究其破坏形态、变形能力及耗能能力。试验结果表明:采用HDC代替混凝土可提高外包钢板组合连梁的变形能力和耐损伤能力;HDC与钢腹板的协同工作性能较好,有利于钢腹板抗剪作用的发挥;外包钢板-HDC组合连梁的耗能能力明显高于外包钢板-混凝土组合连梁和内置钢板组合连梁;外包钢板-HDC组合连梁的剪压比设计值为0.65~0.70,其剪压比明显高于内置钢板组合连梁。因此,采用外包钢板-HDC组合连梁,可提高小跨高比连梁的剪压比限值,解决连梁设计中剪压比超限的问题。     

氯盐环境下锈蚀预应力混凝土梁抗弯性能试验

为探讨氯盐环境下锈蚀预应力混凝土梁的抗弯性能,制作了5根先张预应力混凝土梁,采用电化学法分别对其进行了0 d、7 d、14 d、28 d及42 d的快速腐蚀,随后进行了四点弯曲试验。研究了不同锈蚀程度对预应力混凝土梁自振频率、钢绞线滑移、结构变形、弯曲开裂、破坏模式及极限承载力等性能的影响。结果表明:氯盐环境下锈蚀对预应力混凝土梁高阶频率影响较小,导致一阶频率逐渐增大,28 d后锈蚀裂缝较大且局部混凝土脱落,一阶频率迅速减小;轻微腐蚀对预应力混凝土梁的抗弯性能影响较小,腐蚀程度增大,抗弯性能明显降低,腐蚀42 d后,极限挠度减小了18.7%,抗弯承载力减小了17.3%,延性降低了19%;锈蚀钢绞线与混凝土间滑移速率增大,极限滑移值由5 μm增加至11.4 μm;钢筋锈蚀对弯曲裂缝高度发展的影响不大,但促进了裂缝宽度的扩展,结构屈服后,底部裂缝开裂速率由0.0062 mm/kN增加至0.0252 mm/kN。在试验研究基础上,采用有限元软件ANSYS对各锈蚀梁的受载全过程进行了有限元模拟计算,极限荷载和钢绞线滑移量的模拟值与实测值误差分别小于5%和10%,吻合较好。      

再生混凝土梁挠度计算方法研究

对再生混凝土梁进行了正截面弯曲性能试验.结果表明,再生混凝土梁挠度随着纵向钢筋配筋率和混凝土强度的增加而减小,再生混凝土梁实测挠度较普通混凝土结构设计规范计算值大10%左右.依据普通混凝土受弯构件挠度计算理论,通过试验回归出再生混凝土梁刚度公式中的3个系数,从而建立了再生混凝土梁挠度计算方法.国内外有关试验数据验算表明...     

The shear fracture of concrete under impact loading using end confined beams

An investigation of the shear fracture of plain and steel fibre reinforced concrete (SFRC) under impact loading was carried out on both unconfined and confined beams. It was found that confinement played a significant role on the behaviour and properties of both plain and SFRC beams.A shear mode of failure could be obtained with increasing end confinement stresses. End confined concrete beams were stronger and tougher than unconfined ones, as indicated by the increase in both peak load and fracture energy. However, they were found to be less stress rate sensitive than unconfined concrete beams. This was due to the change in the failure mode from flexure to shear with sufficient end confinement. Using end confinement appears to be a promising method for the study of shear fracture in concrete.     

预制装配型钢混凝土梁受剪承载力试验与计算方法研究

为了深入研究预制装配型钢混凝土梁的受剪机理并提出可准确预测其受剪承载力的计算公式,该文完成了2个足尺预制装配型钢混凝土梁试件的静力剪切性能试验。通过分析试件的破坏过程、荷载-位移曲线和应变发展规律,对不同剪跨比下试件的破坏形态和承载能力进行了研究。基于变形协调桁架-拱模型和Nakamura模型建立了该种预制装配型钢混凝土梁及普通现浇型钢混凝土梁共同适用的受剪承载力计算模型。通过与75个发生剪切破坏的型钢混凝土梁试验结果对比可得:该文提出的计算方法可较好反映型钢混凝土梁的剪切破坏机理,试验值与计算值吻合良好;规范AISC 360-2010和JGJ 138-2016建议的受剪承载力计算公式较为保守。     

Strengthening of reinforced concrete beams in flexure by partial jacketing

This work investigates the structural behaviour of reinforced concrete beams strengthened in bending by the addition of concrete and steel on their tension sides using expansion bolts as shear connectors, technique here denominated partial jacketing. The experimental program comprised tests on eight full-scale reinforced concrete beams, simply supported, with rectangular cross section (150 mm × 400 mm) and 4,500 mm length. Five of these beams were strengthened in bending by partial jacketing, while the other three did not receive any strengthening and served as reference beams. The flexural reinforcement ratio in the beams varied between 0.49% and 2.33% and the beams target concrete strength was 35 MPa. On the basis of the obtained test results, the studied strengthening technique proven to be efficient in terms of increasing the resistance and stiffness of the beams. The used expansion bolts as shear connectors proven to be practical and added ease to the application of this technique.     

Flexural behavior of reinforced recycled aggregate concrete beams under short-term loading

Recycling of waste concrete is one of the sustainable solutions for the growing waste disposal crisis and depletion of natural aggregate sources. As a result, recycled concrete aggregate (RCA) is produced, and so far it has mostly been used in low-value applications such as for the pavement base. But, from the standpoint of promoting resource and energy savings and environmental preservation, it is essential to study whether a concrete made of recycled aggregates—recycled aggregate concrete (RAC) can be effectively used as a structural material. The experimental research presented in this paper is performed in order to investigate the flexural behavior of RAC beams when compared to the behavior of natural aggregate concrete (NAC) beams under short-term loading and consequently the possibility of using RAC in structural concrete elements. Three different percentages of coarse RCA in total mass of coarse aggregate in concrete mixtures (0 %—NAC, 50 %—RAC50, and 100 %—RAC100), and three different reinforcement ratios (0.28, 1.46, and 2.54 %) were the governing parameters in this investigation. Full-scale tests were performed on nine simply supported beams until the failure load had been reached. Comparison of load-deflection behavior, crack patterns, service deflections, failure modes and ultimate flexural capacity of NAC and RAC beams was made based on our own and other researchers’ test results. The results of conducted analysis showed that the flexural behavior of RAC beams is satisfactory comparing to the behavior of NAC beams, for both the service and ultimate loading. It is concluded that, within the limits of this research, the use of RAC in reinforced concrete beams is technically feasible.     

整体结构中两跨钢梁火灾变形性能的试验研究

为研究整体结构中钢梁的抗火性能,利用自行研制的试验炉和相关测试装置,对三层三跨足尺钢框架楼中三层顶一两跨连续梁进行受火试验研究,试验中钢梁受火,钢柱和节点不受火。试验量测了炉体内烟气温度、钢梁和混凝土楼板四等分点处截面沿厚度不同点的温度场、位于炉体外钢梁接点温度、钢梁和楼板四等分点处的竖向变形。结果表明:未进行防火保护的钢梁温度与烟气温度基本一致;升温阶段混凝土板温度滞后于钢梁的温度,停止升温后钢梁温度迅速降低,混凝土板温度仍会升高直至两者温度趋于一致。在整个试验过程中,沿混凝土板截面高度存在较大温度梯度;整体结构中未进行防火保护的钢梁具有很好的变形性能,可以考虑减少防火保护;不同位置的构件由于受到相临构件的约束程度不同,在火灾中的变形性能不同,在抗火设计时应进行区别对待;钢柱虽不受火,在整个试验过程中产生轴向膨胀。