玄武岩纤维布增强树脂基复合材料约束高温损伤混凝土轴压力学性能

对36个玄武岩纤维布增强树脂基复合材料（BFRP）约束加固的高温损伤混凝土圆柱体和15个不同高温损伤的对比试件进行了轴压试验。试验表明,BFRP侧向约束能显著改变混凝土圆柱体的破坏形态,提高混凝土圆柱体的轴压强度和变形能力。其中二层BFRP包裹的200℃、400℃、600℃和800℃高温损伤混凝土圆柱体的轴压强度分别提高了56%、82%、234%和250%,轴向变形分别提高了328%、198%、232%和136%。采用典型的纤维增强复合材料约束常温未损伤混凝土轴压强度和变形计算模型预测纤维增强复合材料约束高温损伤混凝土轴压极限强度和极限变形时存在较大的偏差。基于本文试验数据,确定了BFRP约束高温损伤混凝土极限应力和极限应变计算模型中与温度相关的参量,建议了适用于预测纤维增强复合材料约束高温损伤混凝土的极限应力计算模型和极限应变计算模型。     

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。     

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。     

FRP增强重组竹梁受弯性能数值模拟

通过有限元软件ABAQUS对纤维增强聚合物基复合材料（FRP）增强重组竹梁受弯性能进行了分析,有限元模拟结果与试验结果相一致,两者荷载-位移曲线相吻合,跨中截面应变发展过程基本一致,70 kN荷载时,截面应变误差在13.96%内,承载力预测具有很好的精度,预测最大误差为9.04%,FRP的增强使竹梁截面的应力重新分布,受压区竹材得到更加充分的利用;进一步参数化分析了截面宽高比、FRP层数、FRP种类对FRP增强重组竹梁受弯性能的影响。发现:FRP层数的增加对重组竹梁极限承载力和截面刚度提升作用显著;相同层数、相同种类FRP增强重组竹梁时,截面高度减小,极限承载力和截面刚度提高幅度增加;相同截面宽高比和FRP层数时,碳纤维增强聚合物基复合材料（CFRP）增强效果优于玄武岩纤维增强聚合物基复合材料（BFRP）增强效果。      

基于广义回归神经网络的纤维增强聚合物复合材料约束损伤混凝土强度预测

纤维增强聚合物复合材料(FRP)约束损伤混凝土抗压强度模型对于混凝土柱类构件的修复和加固具有重要指导意义.现有FRP修复混凝土的强度模型适用条件有限,同一模型不能同时应用于不同强弱约束、不同强度混凝土、不同倒角混凝土的强度预测.本文根据广义回归神经网络(GRNN)的特点,基于46个FRP强约束损伤混凝土方柱、210个F...     

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。      

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。     

碱、盐环境下不同应力水平FRP筋抗压强度试验与理论研究

为了研究温度、应力水平等因素对纤维增强聚合物(Fiber Reinforced Polymer,FRP)筋在碱、盐环境下抗压强度衰减规律的影响,将FRP筋分别置于60℃和25℃的碱、盐溶液进行加速腐蚀试验,然后测定其抗压强度衰减规律。60℃下FRP筋的压应力水平分别为0%、20%和40%,腐蚀时间分别为10d、21d、42d;25℃下FRP筋压应力水平为0%,腐蚀时间分别为36d、64d、100d。通过观察腐蚀前后FRP筋表面形貌的变化,可以得出:FRP筋表面侵蚀程度随腐蚀时间的增加而增加;同条件下,碱溶液对FRP筋的表面侵蚀程度大于盐溶液。对腐蚀后的FRP筋进行抗压强度试验,结果表明:应力和温度的提高加速了FRP筋抗压强度的退化,在60℃碱溶液中腐蚀42d后,应力水平为0%和40%的玻璃纤维增强聚合物(GFRP)筋、玄武岩纤维增强聚合物(BFRP)筋和碳纤维增强聚合物(CFRP)筋抗压强度分别下降了31.8%、43.6%、51.5%和44.2%、54.8%、57.1%,60℃盐溶液中腐蚀42d后,应力水平为0%和40%的GFRP、BFRP和CFRP筋抗压强度分别下降了22.2%、31.8%、18.1%和29.0%、37.2%、23.5%。基于Fick定律,提出了考虑应力水平、温度和腐蚀时间的FRP筋抗压强度预测模型,该模型可用于预测FRP筋在实际工况下抗压强度衰减规律。     

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。      

FRP约束混凝土关键问题综述

本文从国内外文献中选取了29个纤维布(FRP)约束混凝土峰值应力模型和19个峰值应变模型，并依据诸多同行研究结果中的相关实测数据，对上述模型的精度进行了验证。结果表明，这些模型对强约束构件的预测精度不足，在此基础上，我们通过分段拟合得到了精度较优且较为简洁的峰值应力及应变模型。同时，基于文献数据，我们对影响环向约束力的FRP弹性模量及撕裂应变这两个因素进行了探讨。我们认为：(1)相较于低弹性模量，高弹性模量FRP可延缓混凝土损伤，进而提高核心区混凝土的力学性能；(2)导致FRP撕裂应变降低的原因包括施工扰动、受力差异及材质非均质性；(3)对于碳纤维增强复合材料(CFRP)、玻璃纤维增强复合材料(GFRP)和芳纶纤维增强复合材料(AFRG),撕裂应变有效系数分别取0.723、0.774和0.774。本文旨在为FRP约束拓展运用提供参考。     

Compressive behavior of large-scale square reinforced concrete columns confined with carbon fiber reinforced polymer jackets

Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. The data available for square/rectangular columns are still limited. This paper reports the results of an experimental research program on the performance of large-scale square RC columns wrapped with carbon fiber reinforced polymer (CFRP) sheets. Attention is focused on the investigation of the total effect of longitudinal and transverse reinforcement and FRP jackets on the behavior of concentrically loaded columns. A total of 20 large-scale RC columns were fabricated and tested to failure under axial loading in the structural laboratory. Three types of columns were primarily considered: unwrapped; fully wrapped; and partially wrapped. Based on the test results of RC columns, existing experimental data and procedures in the literature are also evaluated. Furthermore, stress–strain curves of the columns are successfully predicted by the analytical approach previously proposed for FRP-confined concrete.     

Performance of externally FRP reinforced columns for changes in angle and thickness of the wrap and concrete strength

In this study, the performance of axially loaded, small-scale, and fiber-reinforced polymer (FRP) wrapped concrete columns with various wrap angle configurations, wrap thicknesses, and concrete strengths was investigated through nonlinear finite element analysis. Three different wrap thicknesses, wrap ply angle configurations of 0°, ±15°, and 0°/±15°/0° with respect to the circumferential direction, and concrete strength values ranging from 3 ksi to 6 ksi were considered. An existing experimental study on FRP-confined circular columns in the literature was utilized to validate numerical analysis models. The finite element analysis results showed substantial increase in the axial compressive strength and ductility of the FRP-confined concrete cylinders as compared to the unconfined cylinders. The increase in wrap thickness also resulted in enhancement of axial strength and ductility of the concrete columns. The gain in axial compressive strength in FRP-wrapped concrete columns was observed to be higher for lower strength concrete and the highest in the columns wrapped with the 0° ply angle configuration.     

Strength and durability performance of concrete axially loaded members confined with AFRP composite sheets

The performance of concrete columns externally wrapped with aramid fiber reinforced polymer composite sheets is presented in this paper. The confined and unconfined (control) specimens were loaded in uniaxial compression. Axial load and axial and hoop strains were measured in order to evaluate stress–strain behavior, ultimate strength, stiffness, and ductility of the wrapped specimens. Results show that external confinement of concrete by fiber reinforced polymer (FRP) composite sheets can significantly enhance strength, ductility and energy absorption capacity. An analytical model developed earlier by the author to predict the entire stress–strain response of concrete specimens wrapped with FRP composite sheets was applied. Comparison between the experimental and analytical results indicates that the model provides satisfactory predictions of the stress–strain response. The paper also presents the performance of the wrapped concrete specimens subjected to severe environmental conditions such as wet–dry and freeze–thaw cycles. The specimens were exposed to 300 cycles of wetting and drying using salt water. Results show that specimens wrapped with aramid fibers experienced no reduction in strength due to wet/dry exposure, but some reduction was observed due to freeze/thaw exposure.     

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.     

Evaluating and proposing models of circular concrete columns confined with different FRP composites

Commonly used fiber-reinforced polymer (FRP) includes Carbon, Glass, and Aramid FRP composites. Meanwhile, some new FRPs such as PBO (Polypara-phenylene-Benzo-bis-Oxazole), PET (Polyethylene Terephthalate/Polyester), Dyneema, and Basalt have been gradually applied in recent years. Over the past 20 years, there has been extensive research on modeling of stress–strain response of confined concrete using the common types of FRP. In this study, most popular and recent models are investigated to evaluate their general practical application in predicting the response of FRP-confined concrete with strain-hardening performance without any restriction on the fiber used. The aim of the study is twofold. In case of different types of FRP composites, providing equivalent confinement modulus (lateral stiffness), five models are employed to find the FRP-confined concrete stress–strain relationship of three scale-model circular columns. Second ascending part (second stiffness) of the stress–strain relationship of FRP-confined concrete with strain-hardening performance is evaluated in the light of available database from the existing literature using these analytical models. The results showed that the examined models do not satisfy the fact that the slope of the second ascending branch of the stress–strain curve of FRP-confined concrete is independent of its types, provided the design confinement modulus is the same. A comparison of predicted values of the second stiffness with the collected test results of 257 cylinder specimens confined with the common types of FRP composites revealed the necessity for a more accurate model. Based on the discussion of the features and accuracy of these models, a model considering the effect of FRP lateral stiffness is proposed. Because of the variability observed in the test data, however, it appears impossible to develop simple empirical models based on the current database with less than approximately 27% mean absolute error for the second stiffness, and 16% mean absolute error for ultimate strength.     

地震荷载作用下FRP加固钢筋混凝土圆柱变形能力计算方法研究

基于性能的抗震设计要求对结构的变形能力能够进行计算,以确保不同的性能目标要求得以满足。该文研究地震荷载作用下纤维增强复合材料(FRP)加固钢筋混凝土(RC)圆柱截面曲率延性和柱顶侧向位移角计算方法。根据数值计算结果,得到了截面屈服曲率计算方法,由试验结果得到了FRP加固RC圆柱截面极限曲率计算方法。试验结果表明加固柱塑性铰长度和FRP用量密切相关,通过对29个大比例柱试验结果进行回归,得到了加固柱塑性铰长度计算方法,并分析了高FRP用量导致加固柱塑性铰长度减小的原因。经参数分析,探讨了FRP用量、轴压比与加固柱顶侧向变形能力的关系,提出了具有理想加固效率的FRP用量上限范围。     

基于基因表达式编程的FRP约束混凝土极限轴向应变预测

纤维增强树脂复合材料(FRP)以其质量轻、强度高、耐腐蚀和施工方便等优势被广泛应用于混凝土结构性能提升和受损构件加固中。FRP约束混凝土的极限条件是选择FRP种类、选择FRP厚度及确定包裹层数等必须要考虑的因素,现有极限应力模型的预测结果能够较好反地映真实情况,而现有极限轴向应变模型的预测精度偏低,故本文对极限轴向应变进行了研究。由于影响FRP约束混凝土极限轴向应变的因素较多,许多研究人员提出的模型在输入参数的选择上存在较大差异,故本文在通过基因表达式编程建立极限轴向应变模型的同时还探讨了不同输入形式对模型预测精度的影响。采用决定系数及平均绝对误差等5种统计指标对模型预测结果进行评价,并将其与现有模型进行对比分析。研究结果表明:原始数据和新数据组合的输入形式对应的模型具有最高的预测精度,因此在模型输入参数的选择上不能仅考虑原始数据或者新数据;与其他研究人员所提模型相比,本文所提模型预测精度更高,其决定系数为0.893,平均绝对误差等指标均在0.35以下。      

Behavior of square and rectangular ultra high-strength concrete-filled FRP tubes under axial compression

This paper presents results of an experimental program undertaken to investigate the behavior of square and rectangular ultra high-strength concrete (UHSC)-filled fiber reinforced polymer (FRP) tubes (UHSCFFTs) under axial compression. The effects of the amount of confinement, cross-sectional aspect ratio and corner radius were investigated experimentally through the tests of 24 concrete-filled FRP tubes (CFFTs) that were manufactured using unidirectional carbon fiber sheets and UHSC with 108 MPa average compressive strength. As the first experimental investigation on the axial compressive behavior of square and rectangular UHSCFFTs, the results of the study reported in this paper allows a number of significant conclusions to be drawn. Of primary importance, test results indicate that sufficiently confined square and rectangular UHSCFFTs can exhibit highly ductile behavior. The results also indicate that confinement effectiveness of FRP tubes increases with an increase in corner radius and as sectional aspect ratio approaches unity. It is found that UHSCFFTs having tubes of low confinement effectiveness may experience significant strength loss along the initial portions of the second branches on their stress–strain curves. Furthermore, it is observed that the behavior of UHSCFFTs at this region differs from their normal-strength concrete counterparts and is more sensitive to the effectiveness of confining tube. The second half of the paper presents the performance assessment of the existing FRP-confined concrete models in predicting the ultimate conditions of the HSC and UHSCFFTs. The results of this assessment demonstrate that the existing models provide unconservative estimates for specimens with higher concrete strengths. To address this, a new model that was developed on the basis of a comprehensive experimental test database and is applicable to both NSC and HSC of strengths up to 120 MPa is proposed. The model comparisons demonstrate that the proposed model provides significantly improved predictions of the ultimate conditions of FRP-confined HSC compared to the existing models.     

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.