玄武岩纤维布约束高温损伤混凝土方柱轴压力学性能试验

对36个玄武岩纤维布增强聚合物基复合材料（BFRP）约束的高温损伤混凝土方柱和15个不同高温损伤的对比试件进行了轴压试验。试验表明,玄武岩纤维布横向约束能改变高温损伤后混凝土方柱的破坏形态,显著提高混凝土方柱的轴压强度和变形能力。其中三层玄武岩纤维布包裹的200℃、400℃、600℃和800℃高温损伤混凝土方柱轴压强度分别提高了48%、130%、206%和389%,轴向变形分别提高了433%、344%、319%和251%。采用典型的纤维增强聚合物基复合材料（FRP）约束常温未损伤混凝土轴压力学性能的设计模型预测FRP约束高温损伤混凝土的轴压强度和变形时存在较大的偏差。通过构建柱状膜结构静水压力平衡模型和约束混凝土方柱与FRP体积应变能平衡模型,分别改进了FRP约束混凝土方柱轴压极限应力和极限应变计算模型的基本形式。基于该基本形式和试验数据,分别确定了BFRP约束高温损伤混凝土方柱轴压极限应力和极限应变计算中与温度相关的参量,提出了适用于高温损伤混凝土方柱的轴压极限应力和极限应变的设计模型。      

高温后碳纤维布约束混凝土轴压力学性能试验

通过对20个经历四种不同高温后的素混凝土和无机胶粘贴碳纤维布加固混凝土圆柱体的轴压力学性能试验,研究了无机胶粘贴碳纤维布约束混凝土在经历不同高温后抗压强度、极限压应变和应力-应变关系的变化,得出所经历高温过程对其轴压力学性能的影响。结果表明:无机胶粘贴碳纤维布约束混凝土经历高温后的破坏形态与常温下基本相似;其抗压强度在经历100℃高温后,下降仅5%左右,在经历200℃、300℃和400℃高温后,约为常温试件的85%~90%;无机胶粘贴碳纤维布约束混凝土的极限压应变在100℃高温后略有减小,在200℃~400℃高温后则比常温下增大20%左右;碳纤维约束对核心混凝土抗压强度的提高作用,会随试件所经历温度的升高而逐渐增大;无机胶粘贴碳纤维布约束混凝土的应力-应变曲线在经历高温后会明显趋于扁平,并且多了一个呈上凹状的压密阶段。     

高性能PVA 纤维增强水泥基复合材料常规三轴受压本构模型

对PVA 纤维体积率从0%~2%的高性能水泥基复合材料(HPFRCC)圆柱体试件进行了6 种不同围压下的常规三轴受压试验,研究其三轴受压性能,测得了极限抗压强度、峰值应变、极限应变以及应力-应变曲线。根据试验结果得出HPFRCC 的极限抗压强度、峰值应变以及极限应变与侧向围压之间的关系。基于实测圆柱体应力-应变曲线的特点,提出了HPFRCC材料常规三轴受压本构模型。计算结果与试验数据的对比表明,根据该文模型所得的计算曲线与试验曲线吻合较好,研究成果可为HPFRCC结构非线性有限元分析提供依据。     

纤维增强聚合物复合材料-钢复合圆管约束混凝土轴压性能预测模型

纤维增强聚合物复合材料（FRP）-钢复合圆管约束混凝土由于具有很好的综合性能,近年来得到了广泛的研究,尚缺乏完整的应力-应变关系全曲线计算模型。本文在综合作者现有研究成果的基础上,广泛收集了96个FRP-钢复合圆管约束混凝土柱的轴心受压试验结果,系统分析了试件参数的影响规律,提出了FRP-钢复合圆管约束混凝土的应力-应变关系曲线的完整计算模型,包括峰值应力、峰值应变、极限应力和极限应变的计算方法,并建议了应力-应变关系全曲线预测模型,模型较好地预测了FRP-钢复合圆管约束混凝土的应力-应变关系曲线的特征,预测结果与试验结果吻合较好。建议模型具有较好的通用性和准确性。      

玄武岩格栅增强水泥基复合材料单轴拉伸力学性能试验及本构关系模型

考虑玄武岩纤维增强树脂合物基复合材料(BFRP)格栅层数和水泥基复合材料(ECC)配比等因素,对BFRP增强大掺量粉煤灰/矿粉ECC棒骨试件进行了静力单轴拉伸试验,研究掺加增强粉煤灰/矿粉ECC的抗拉力学性能。结合试验数据,基于Richard和Abbot的弹塑性应力-应变公式提出掺加增强ECC的应力-应变本构关系模型。试验结果表明:随着掺加层数的增加,格栅增强ECC的极限抗拉强度显著增大。同配合比掺矿粉制成的ECC抗压强度、开裂应变及应力高于掺粉煤灰制成的ECC。掺加增强掺矿粉ECC试件相对掺粉煤灰ECC试件具有较好的抗拉力学性能。计算结果表明,建立的单轴受拉本构关系模型可以有效地预测掺加增强ECC的应力-应变关系和极限抗拉强度。     

高强不锈钢绞线网/ECC约束高强混凝土受压本构模型

为将新型复合材料“高强不锈钢绞线网/ECC约束素混凝土”用于实际工程结构,基于高强不锈钢绞线网/ECC约束高强混凝土(简称HSME约束高强混凝土)复合材料轴心受压试验结果,分析ECC强度、核心混凝土强度以及横向钢绞线体积配网率等对其受压性能的影响规律。试验结果表明：HSME能够有效约束核心混凝土轴心受压,破坏模式具有明显的延性性能,根据试验数据绘出HSME约束高强混凝土复合材料受压应力-应变曲线,可以分为三个阶段：弹性阶段、弹塑性阶段和下降段。根据各阶段曲线的数学特征,建立HSME约束高强混凝土复合材料受压本构关系的全过程模型表达式。引入ECC特征值和横向钢绞线特征值,对本构模型的各参数进行分析,提出HSME约束高强混凝土复合材料的开裂压应变、峰值应力、峰值压应变和极限压应变等参数的表达式。将各参数代入所建立的受压本构关系绘出其应力-应变曲线,模型结果与试验所得应力-应变曲线吻合良好,开裂压应变与极限压应变的计算值与试验值对比范围分别为0.949～1.068和0.938～1.039。表明所提出的受压本构模型能够较好地反映HSME约束高强混凝土复合材料的应力-应变关系。     

FRP非均匀约束海水海砂混凝土方柱轴压性能

为扩大纤维增强树脂复合材料(FRP)-海水海砂混凝土(SSC)组合结构的应用范围,改善FRP约束海水海砂混凝土柱脆性破坏特性,对碳纤维增强树脂复合材料(CFRP)非均匀约束海水海砂混凝土方柱的轴压性能进行了研究。试验结果表明：由于CFRP非均匀约束试件中沿高度方向CFRP厚度并不相等,因而整个破坏过程具有明显的预兆,故脆性行为得到明显改善。相比于相同体积率下的全包裹和条带约束试件,其具有更优越的力学性能,尤其是在净距比较小的情况下。随着外部CFRP条带净距的下降和层数的增加,试件的极限强度和变形能力显著提高。具体而言,由于FRP条带净距的降低导致试件的极限强度增幅在5.4%～18.5%不等,而在净距比固定状态下,当外部条带层数增大1倍后,极限强度与应变的最大增幅分别为15.8%和21.8%。最后基于试验数据,对现有部分代表性应力-应变模型对于非均匀约束混凝土的适用性进行了讨论,并给出了所有模型对于试件极限状态的预测精度与误差大小。     

GFWRP管增强混凝土柱的轴压泊松比

为完善和发展GFWRP管增强混凝土柱的设计与计算理论,设计并制备了不同管径、壁厚及缠绕角的GWFRP管混凝土柱试件。进行了轴心压缩试验并对试验结果回归分析,得到GFWRP管混凝土柱轴心压缩过程中转折点及峰值点的泊松比变化方程和相应的应变预测公式,得到组合结构轴压全过程的泊松比变化预测方程。可由给定的组分材料性能预测组合构件的极限泊松比和极限应变,达到预测实际工程中GFWRP管混凝土柱抗力与变形性能的目的。通过试验及计算结果对GFWRP管混凝土与传统钢管混凝土的泊松比变化趋势进行了对比分析,发现两者变化规律完全不同。进一步探讨了GFWRP约束管的纤维缠绕角对组合结构轴压泊松比的影响。结果表明,纤维缠绕角与轴压泊松比近似成反比关系。为制定合理的GFWRP复合材料增强混凝土柱规范提供了理论依据。      

玄武岩纤维包裹混凝土圆形柱的抗冲击性能研究

对C30、C40、C50三种强度等级的素混凝土及1~4层玄武岩纤维(BFRP)包裹试件进行了SHPB冲击试验,分析了试件在冲击作用下的破坏现象,研究了应变率和约束比对应力应变曲线的影响,得到了BFRP约束混凝土的动态强度拟合公式。试验结果表明:BFRP包裹试件的抗打击能力和变形能力较未包裹试件有较大提高,具有良好的吸能能力;随着包裹层数的增加和应变率提高,试件抗冲击强度和变形能力提高明显,应力应变曲线下降段的下降速度开始变缓,说明纤维在试件中所起的作用增强。     

纤维增强树脂复合材料约束超高性能混凝土轴压性能的细观数值模拟

利用LS-DYNA有限元分析软件建立纤维增强树脂(FRP)复合材料约束超高性能混凝土(UHPC)圆柱细观有限元模型,以研究其单轴受压性能。通过已有试验数据验证了模型的有效性,并建立了能准确反映FRP复合材料约束作用的K&C模型的剪切膨胀参数预测公式。在此基础上进行参数分析,研究FRP复合材料厚度、纤维缠绕角度和钢纤维掺量的影响。结果表明,本文模型不仅能模拟随机分布钢纤维对试件应力分布的影响,且能较准确反映FRP复合材料约束作用对核心UHPC强度和延性的提高效果。模型在轴压作用下的破坏模式和应力-应变曲线与试验结果基本一致。参数分析表明,随FRP复合材料厚度或纤维缠绕角度的增大,试件极限承载力和延性均增大,而增大钢纤维掺量虽可限制核心UHPC斜裂缝的开展,但对试件强度和延性影响较小。      

Behavior in compression of concrete cylinders externally wrapped with basalt fibers

This paper gives additional information on the use of new class of composites constituted by Basalt Fiber Reinforced Polymer (BFRP) bonded with epoxy resin to concrete specimens as an alternative confinement material for compressed concrete members with respect to carbon or glass fibers. From the experimental point of view, concrete cylinders are wrapped with continuous fibers, in the form of sheets, applying both full and partial discrete wrapping with BFRP straps, and then tested in compression. For comparison, few other concrete cylinders are wrapped with Carbon Fiber Reinforced Polymer (CFRP) sheets and tested in compression. The number and type of plies (full or partial wrapping), the type of loading (monotonic and cyclic actions) and the type of fiber (basalt and carbon) are the main variables investigated. The experimental results obtained from the compressive tests in terms of both stress–strain curves and failure modes show the possibility of reducing the brittleness of unconfined concrete, resulting significantly increased both the post-peak resistance and the axial strain of confined concrete corresponding to BFRP failure. Form the analytical standpoint, a review of the available models given in the literature is made and verified against the experimental data. Finally, a proposal for analytical expressions aimed at the calculation of the compressive strength and corresponding strain of confined concrete is provided also including the strain at BFRP failure.     

网格箍筋约束混凝土柱轴压受力性能试验研究

为研究使用网格箍筋强度不同、素混凝土轴心抗压强度不同的约束混凝土的轴压受力性能,完成了39个网格箍筋约束混凝土方柱的轴心受压试验。混凝土设计强度等级为C20、C30、C40、C50,箍筋分别选用HRB335、HRB400、HRB500、HRB600钢筋,体积配箍率范围为1.0%～2.2%。试验结果表明：约束混凝土压应力达到峰值时,受压试件的约束箍筋屈服;随着配箍特征值增大,网格箍筋约束混凝土峰值压应力和峰值压应变提高幅度增大,受压应力-应变曲线下降段变缓。根据试验结果,通过回归分析获得了网格箍筋约束混凝土峰值压应力、峰值压应变的计算公式;建立了相应的轴心受压应力-应变模型,与几种具有代表性的箍筋约束混凝土应力-应变模型的对比表明,建立的模型与试验结果吻合较好;提出了约束混凝土极限压应变计算方法。     

CFRP约束高温后混凝土力学性能试验研究

以混凝土经历的最高温度和CFRP布层数为参数进行了CFRP约束高温后混凝土力学性能试验研究。通过实测应力-应变曲线,研究温度和CFRP布层数对CFRP约束高温后混凝土抗压强度、极限应变和初始刚度等力学性能指标的影响规律。试验结果表明,CFRP约束显著影响了高温后混凝土受压破坏形态,并大幅度提高了高温后混凝土强度,说明CFRP约束可作为火灾后混凝土结构的一种有效的抢修与加固措施。同时,综合分析温度软化效应和CFRP约束强化效应对混凝土抗压强度的影响,CFRP约束强化效应处于主导地位。此外,在现有模型的基础上,提出了评估CFRP约束高温后混凝土力学性能的简化模型,经试验结果验证,该简化模型具有良好的精确性与实用性。     

Behavior and modeling of confined concrete cylinders in axial compression using FRP rings

This study suggests a secondary dense lateral reinforcement for reinforced concrete (RC) columns that are located between the primary lateral reinforcement and concrete surface, which are used to delay the buckling of longitudinal reinforcement and increase the ductility of RC columns. ‘Dense’ means that the spacing of the lateral reinforcement is smaller than the maximum gravel size. This study conducted axial compressive tests on concrete cylinders confined by dense reinforcement in order to improve the effectiveness of the dense lateral reinforcement. FRP (Fiber Reinforced Polymer) rings were used for the reinforcement since they are corrosion resistant. The dense reinforcing method with FRP rings can successfully increase the peak strength of the concrete and the failure strain. The stress–strain curves of the confined concrete became almost bilinear with hardening behavior, which were similar to that of the concrete confined by the jackets of FRP sheets. This study also provides models of stress–strain in an axial direction and lateral strain. Based on the models, this study analyzes the confining effectiveness of the FRP rings on concrete.     

Influence of concrete strength and confinement method on axial compressive behavior of FRP confined high- and ultra high-strength concrete

This paper presents an experimental investigation on the effect of concrete compressive strength and confinement method on confined high and ultra high-strength concrete (HSC and UHSC) specimens. A total of 55 fiber reinforced polymer (FRP) confined concrete specimens were tested under monotonic axial compression. All specimens were cylinders with 152 mm diameter and 305 mm height and confined by carbon FRP (CFRP). Three different concrete mixes were examined, with average compressive strengths of 35, 65 and 100 MPa. The effect of the confinement method was also examined with FRP-wrapped specimens compared to FRP tube-encased specimens. Axial and lateral behavior was recorded to observe the axial stress–strain relationship and lateral strain behavior for concentric compression. Ultimate axial and lateral conditions are tabulated and the complete stress–strain curves have been provided. The experimental results presented in this paper provide a performance comparison between FRP-confined conventional normal-strength concrete (NSC) and the lesser understood area of FRP-confined HSC and UHSC. The results of this experimental study clearly indicate that above a certain confinement threshold, FRP-confined HSC and UHSC exhibits highly ductile behavior, however for the same normalized confinement pressures, axial performance of FRP-confined concrete reduces as concrete strength increases. The results also indicate that ultimate conditions of FRP-wrapped specimens are similar to those confined by FRP tubes, however a performance difference is evident at the transition region. The performance of 10 existing stress–strain models were assessed against the experimental datasets and the performance of these models discussed. The results of this model assessment revealed the need for further development for stress–strain models developed specifically for FRP-confined HSC or UHSC.     

新型复合材料“高强钢绞线网/ECC约束素混凝土”受压性能试验研究

考虑混凝土强度、工程水泥基复合材料(ECC)强度和横向高强钢绞线配筋率等因素，研究新型复合材料“高强钢绞线网/ECC约束素混凝土”(以下简称HSE约束素混凝土)的受压性能。HSE约束素混凝土轴心受压试验显示，达到最大荷载的30%左右时，约束层ECC出现约为0.01 mm的竖向裂缝；约为最大荷载的85%时，表面最大裂缝宽度约为0.07 mm；达到最大荷载时，最大裂缝宽度仅为0.20 mm；说明该新型复合材料具有很好的裂缝分散和控制能力。之后荷载缓慢下降至最大荷载75%左右，第一根横向钢绞线断裂；达到破坏时裂而不碎，约束层和核心混凝土未发生黏结破坏，完整性良好。HSE约束素混凝土与素混凝土相比，其开裂应力提高了88%~116%；轴心抗压强度提高了21%~49%、轴心压应变增加了约45%；极限压应变提高了106%~175%。ECC强度和混凝土强度及横向钢绞线配筋率的提高，均增大其开裂和最大荷载及极限压应变。      

武器间接命中条件下FRP约束混凝土抗多次打击能力

在3种约束比下FRP约束混凝土圆柱体试件准静载和快速加载试验的基础上,进行多次打击试验及多次打击后的准静载试验 。结果表明:FRP约束混凝土是一种抗多次打击能力较好的抗压复合材料,经每次打击后的刚度虽逐渐衰减,但有收敛趋势,其残余刚度随约束比ξ及最大应力比η的增加而减小。经受多次打击后的FRP约束混凝土与未经受多次打击的试件相比,其准静载下的初始弹性模量降低,强度基本不变,极限应变提高,其中弱约束混凝土延性提高得尤其显著,强约束混凝土应力-应变曲线中线性强化段的斜率随刚度衰减程度的增加而增加,最终FRP强约束混凝土有变成线弹性材料的趋势,为进一步研究FRP约束混凝土在防护结构中的应用提供条件。      

FRP tube encased rubberized concrete cylinders

In this study, FRP tube encased waste tire rubber modified concrete cylinders were investigated. Four batches of confined and unconfined concrete cylinders with a diameter of 101.6 mm and a height of 304.8 mm were prepared. Each batch contained three confined cylinders and three unconfined cylinders. The total number of effective cylinders prepared was 24. Batches 1–3 were made of rubberized concrete. In Batch 1, 15% by volume of coarse aggregate was replaced by waste tire fibers or stripes; in Batches 2 and 3, 15% by volume of sand and 30% by volume of sand were replaced by crumb rubbers, respectively. Batch 4 was a control batch with conventional plain concrete. Uniaxial compression tests were conducted on all the cylinders per ASTM C39. Strain gages were installed on the encased rubberized concrete cylinders to obtain local strain distributions. The compressive strength and strain at the peak load were compared with the predictions by available design-oriented confinement models. It is found that the FRP tube encased rubberized concrete cylinders have higher confinement effectiveness, ductility, and elastic regions than FRP tube encased conventional concrete cylinders. Waste tire fiber modified concrete performs better than crumb rubber modified concrete with a lower cost. Instead of volume contraction, FRP encased rubberized concrete cylinders experience volumetric expansion. The current design-oriented confinement models cannot consistently predict the compressive strength and strain of the encased cylinders. An 1-D coupon test cannot uniquely determine the hoop tensile strength of the FRP tubes which are subjected to a 2-D stress condition.