冲击载荷下CFRP及GFRP层板断裂韧性的研究

利用Hopkinson杆加载装置, 对带有单边切口的炭纤维增强复合材料(CFRP)及玻璃纤维增强复合材料(GFRP)层板试件进行冲击拉伸加载实验。根据一维应力波理论求得作用于试件上的载荷P(t)和试件加载点的位移δ(t)。 根据试样中应力随时间的变化历史σ(t), 并基于断裂韧性测试原理, 建立了动态应力强度因子K_Ⅰ (t)响应曲线。利用柔度变化率方法确定起裂时间, 分别得到在两种加载速率下CFRP、 GFRP层板的动态断裂韧性。结果表明, 随着加载速率的提高, 这两种复合材料的断裂韧性降低。      

Y形偏心支撑钢框架的地震反应折减系数和超强系数

该文采用静力推覆和能力谱方法分析了基于我国抗震规范设计的12 个Y 形偏心支撑钢框架的地震反应折减系数R和超强系数Ω及赘余度超强系数Ω₃, 分析了结构层数、楼层高跨比对各系数的影响。研究结果表明:Y 形偏心支撑钢框架的设计地震作用可在我国现行抗震规范的基础上降低20%左右。     

LiCl改性尼龙6的结晶行为及受限机制

为了扩宽尼龙6(PA6)的工程应用领域,首先,通过熔融挤出制备了LiCl/PA6复合材料;然后,利用XRD、DSC、流变仪及电子拉伸试验机等研究了LiCl含量对PA6结晶行为和力学性能的影响及结晶的受限机制。结果表明:随LiCl含量的增加, LiCl/PA6复合体系的成核温度、晶体生长温度及熔融温度均向低温方向移动;成核密度和速率均逐渐减小,导致结晶能力下降,结晶度由原来的36.5%降低为5.6%;γ晶结晶度逐渐降低,而α晶结晶度先增大后减小, γ晶与α晶发生转变。此外, LiCl/PA6复合材料的拉伸强度和冲击强度均先增大后减小;当LiCl含量为6.0wt%时,冲击强度达到最大值7.9 kJ/m2,是纯PA6的冲击强度(5.5 J/m2)的1.44倍。      

1-3型水泥基压电复合材料的制备及性能

采用切割-浇注法, 以硫铝酸盐水泥为基体, 制备了1-3型水泥基压电复合材料。详细阐述了1-3型水泥基压电复合材料的制备过程; 研究了0.375Pb(Mg_1/3Nb_2/3)O₃-0.375PbTiO₃-0.25PbZrO₃压电陶瓷柱的宽厚比w/t对1-3型水泥基压电复合材料的压电性能、 介电性能和声阻抗的影响。结果表明: 压电陶瓷柱的宽厚比w/t对1-3型水泥基压电复合材料性能有很大影响, 随着w/t的增加, 其压电应变常数d₃₃、 机电耦合系数K_p与K_t、 机械品质因数Q_m、 介电常数ε_r和介电损耗tanδ均随着w/t的增加而减小, 而压电电压常数g₃₃值几乎不受w/t的影响。在压电陶瓷体积分数仅为22.72%的条件下, 调节压电陶瓷柱的宽厚比w/t至0.130, 可使复合材料的声阻抗与混凝土的声阻抗十分接近, 从而有效地解决了智能材料在土木工程中的声阻抗相容性问题。      

聚合物基复合材料的湿扩散参数研究

通过系统地研究几种国产复合材料的吸湿行为,获得了描述湿气在其中扩散的基本参数,如平衡湿含量M_m,M_m与相对湿度φ关系中的常数a和b,沿板材厚度方向上的一维湿扩散系数D_x以及D_x与温度关系中的常数ΔE(湿扩散活化能)和D₀等。      

纤维增强复合材料横向弹性常数

本文提出了一个计算单向纤维增强复合材料横向弹性模量和泊松系数的边界元计算模型.泊松系数ν₁₂、ν₃₂、ν₁₃和ν₂₃的计算结果与实验结果吻合得很好.碳纤维增强复合材料横向模量E₂和E₃的计算值也和实验结果完全吻合,而玻璃纤维/环氧横向模量E₂、E₃的计算值却比实测值偏小约10%～25%.予计这是由于本文计算模型未考虑界面层的性能,它对材料的宏观性能产生了较明显的影响.      

玻璃微珠表面处理对LDPE 复合材料拉伸性能的影响

应用Inst ron 材料试验机, 于室温下考察了玻璃微珠含量及其表面处理对填充低密度聚乙烯复合物拉伸性能的影响。结果表明, 复合材料的弹性模量(E_c) 随着微珠体积分数的增加而增大, 屈服强度(R_yR ) 变化不大, 而断裂强度(R_bR )、断裂应变(E_bR ) 和断裂能(E _bR ) 则减小; 在相同的实验条件下, 微珠表面经硅烷偶联剂预处理的填充体系的E c、R_yR 和R_bR 稍高于未作表面预处理的复合材料; 对于E_bR 和E _bR , 两体系之间的差异甚微。      

亚健康简支T梁桥限载指标评估及验证

为更合理评价亚健康桥梁剩余承载力,该文提出通过截面折减反馈计算法对亚健康简支T梁桥的应变进行控制,从而确定桥梁临界使用承载力和限载指标行之有效的评估方法。通过旧桥荷载试验实测数据与有限元模型计算结果的比值,推算其刚度折减系数,再算出亚健康桥梁折减抗弯惯性矩以及质心位置,修正有限元计算模型,进行反馈计算。通过控制应变,以折减设计荷载的方式求出桥梁内力,进而确定旧桥的限载指标。通过旧桥检测实例,验证该限载措施的有效性和该评估方法的可行性。     

深受弯构件抗剪影响参数显著性分析

为合理量化不同规范中深受弯构件抗剪影响参数的显著性,结合691组受剪试验数据,通过相关分析系统地研究了单因素、组合因素对其抗剪能力影响的显著性,采用Kendall相关系数、Spearman相关系数和偏相关系数进行量化评估,并利用主成分分析法给出四项综合指标,分析各指标对实际受剪承载力的影响比重。研究表明:单因素条件下,混凝土强度等级f_c'对受剪承载力影响较为显著,截面尺寸b和h₀,剪跨比a/h₀次之;组合因素下,f_c'、bh₀、ab、a/h₀对受剪承载力影响较显著。同时,由主成因素分析得到的四项综合指标对深受弯构件受剪能力贡献比重依次为31%、16%、13%、9%,为深受弯构件的抗剪设计提供理论参考。     

丙烷-氧气预混气体的火焰传播及点火特性

采用有机玻璃管装置,研究了丙烷-氧气预混气体在管道中的火焰传播特性及最小点火能。研究表明:3种惰性气体(CO₂、N₂、Ar)均明显降低了预混气体火焰在管道中的加速进程;其中,CO₂抑制效果最为显著,其次是N₂和Ar。点火敏感电极间距为2 mm。最小点火能（E）随混合气体初始压力的增大而减小,初始压力为100 kPa时,0.16 mJ＜E ＜0.32 mJ;当压力降至30 kPa时,2.00 mJ＜E ＜3.00 mJ。     

Efficacy of CFRP-based techniques for the flexural and shear strengthening of concrete beams

Near surface mounted (NSM) and externally bonded reinforcement (EBR) strengthening techniques are based on the use of carbon fiber reinforced polymer (CFRP) materials and have been used for the structural rehabilitation of concrete structures. In the present work, the efficacies of the NSM and EBR techniques for the flexural and shear strengthening of reinforced concrete beams are compared carrying out two experimental groups of tests. For the flexural strengthening, the efficacy of applying CFRP laminates according to NSM is compared to those resulting from applying CFRP laminates and wet lay-up CFRP sheets according to EBR technique. The influences of the equivalent reinforcement ratio (steel and laminates) and spacing of the laminates on the efficiency of the NSM technique for the flexural strengthening is also investigated. A numerical strategy is implemented to analyze the applicability of the FRP effective strain concept, proposed by ACI and fib in the design of FRP systems for the flexural strengthening. To assess the efficacy of the NSM technique for the shear strengthening of concrete beams, four beam series of distinct depth and longitudinal tensile steel reinforcement ratio are tested. Each series is composed of one beam without any shear reinforcement and one beam using the following shear reinforcing systems: conventional steel stirrups; strips of wet lay-up CFRP sheet of U configuration applied according to EBR technique; and laminates of CFRP embedded into vertical or inclined (45°) pre-cut slits on the concrete cover of the beam lateral faces, according to the NSM technique. Using the obtained experimental results, the performance of the analytical formulations proposed by ACI, fib and Italian guidelines is appraised.     

锈蚀钢筋混凝土结构可靠度评估

钢筋锈蚀是混凝土结构破坏最主要的原因之一,目前钢筋混凝土结构可靠度研究大多数没有考虑锈蚀的影响。提出了锈蚀钢筋混凝土结构可靠度评估方法。首先分析大气环境下和氯离子环境下钢筋锈蚀的模型,然后考虑钢筋面积和粘结强度的降低,建立锈蚀钢筋混凝土结构抗力的随机模型,最后采用一次二阶矩实用分析法计算可靠度指标,以评估大气环境下和氯离子环境下混凝土结构可靠度。两个算例表明,该方法可用于锈蚀钢筋混凝土结构可靠度评估。     

预应力CFRP加固钢筋混凝土受弯构件的抗力概率模型研究

预应力CFRP 加固混凝土结构技术因其在材料性能利用方面的优越性能已成为CFRP 加固的热点方向,其中预应力CFRP 加固结构的可靠性是这一方向研究的重要内容。该文分析了影响预应力CFRP 板加固钢筋混凝土受弯构件承载力的主要变量的概率特征,考虑CFRP 板尺寸效应和应力分布的影响,采用Weibull 分布推导了CFRP 板的极限强度概率分布函数,根据预应力CFRP 张拉工艺,分析了预应力损失随机变量,建立了在不同失效模式(破坏形态)下的受弯构件抗力概率模型,并开展了参数敏感性分析,获得各个失效模式下抗力概率模型的主要影响因素。研究结果表明:抗力概率模型是预应力CFRP 加固结构的失效概率计算与可靠度校准的重要内容之一,各参数的影响规律与各失效模式的破坏形式密切相关。     

模拟不中断交通状况下粘贴碳纤维布加固钢筋混凝土梁试验研究

为了调查动荷载作用下碳纤维布与钢筋混凝土梁的粘贴性能及加固效果,进行了5根模拟交通荷载(等幅正弦波形动荷载)作用下粘贴碳纤维布加固钢筋混凝土梁和1根保持荷载下粘贴碳纤维布加固钢筋混凝土梁以及2根对比梁的试验研究。试验中考虑了混凝土等级、配筋率、有无锚固条、粘贴长度、荷载幅值5个变化参数。试验结果表明,在模拟交通荷载的作用下,碳纤维布加固的钢筋混凝土梁粘贴性能满足要求,粘贴效果良好。在模拟交通荷载后的静载作用下,试验梁的抗弯承载力提高较多,加固效果明显,进一步验证了粘贴效果。     

Tests of continuous concrete slabs reinforced with carbon fibre reinforced polymer bars

Although several research studies have been conducted on simply supported concrete elements reinforced with fibre reinforced polymer (FRP) bars, there is little reported work on the behaviour of continuous elements. This paper reports the testing of four continuously supported concrete slabs reinforced with carbon fibre reinforced polymer (CFRP) bars. Different arrangements of CFRP reinforcement at mid-span and over the middle support were considered. Two simply supported concrete slabs reinforced with under and over CFRP reinforcement and a continuous concrete slab reinforced with steel bars were also tested for comparison purposes. All continuous CFRP reinforced concrete slabs exhibited a combined shear–flexure failure mode. It was also shown that increasing the bottom mid-span CFRP reinforcement of continuous slabs is more effective than the top over middle support CFRP reinforcement in improving the load capacity and reducing mid-span deflections. The ACI 440.1R–06 formulas overestimated the experimental moment at failure but better predicted the load capacity of continuous CFRP reinforced concrete slabs tested. The ACI 440.1R–06, ISIS–M03–07 and CSA S806-06 design code equations reasonably predicted the deflections of the CFRP continuously supported slabs having under reinforcement at the bottom layer but underestimated deflections of continuous slabs with over-reinforcement at the bottom layer.     

CFRP筋增强ECC梁弯曲性能试验研究

为研究碳纤维增强树脂复合材料(Carbon fiber reinforced polymer,CFRP)筋/超高韧性纤维增强水泥基复合材料(Engineered cementitious composite,ECC)梁的抗弯性能,对3根CFRP筋/ECC梁、1根玻璃纤维增强树脂复合材料(Glass fiber reinforced polymer,GFRP)筋/梁和1根CFRP筋混凝土梁进行了四点弯曲试验,分析了配筋率、纤维增强树脂复合材料(Fiber reinforced polymer,FRP)筋类型和基体类型对梁抗弯性能的影响。试验结果表明:CFRP筋/ECC梁与GFRP筋/ECC梁和CFRP筋混凝土梁类似,均经历了弹性阶段、带裂缝工作阶段和破坏阶段;配筋率对CFRP筋/ECC梁的受弯性能影响较大。随着配筋率的增加,CFRP筋/ECC梁的承载能力不断提高,延性性能逐渐减弱;ECC材料优异的应变硬化能力和受压延性,使得CFRP筋/ECC梁的极限承载能力和变形能力均优于CFRP筋混凝土梁;由于ECC材料多裂缝开裂能力,CFRP筋/ECC梁开裂后,纵筋表面应变分布比CFRP筋混凝土梁更均匀; 由于聚乙烯醇(Polyvinyl alcohol,PVA)纤维的桥联作用,CFRP筋/ECC梁破坏时,其表面出现了大量的细密裂缝,且能保持较好的完整性和自复位能力;正常使用阶段,CFRP筋/ECC梁的最大弯曲裂缝宽度均小于CFRP筋混凝土梁。最后,根据试验结果,建立了基于等效应力图的CFRP筋/ECC梁弯曲承载力简化计算模型,确定模型中的相关系数。由简化模型计算的极限承载力与试验结果具有较好的相关性。      

Flexural response predictions of reinforced concrete beams strengthened with prestressed CFRP plates

Existing experimental studies showed that the reinforced concrete (RC) beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates had three possible flexural failure modes (including the compression failure, tension failure and debonding failure) according to the CFRP reinforcement ratio. Theoretical formulas based on the compatibility of strains and equilibrium of forces were presented to predict the nominal flexural strength of strengthened beams under the three failure modes, respectively, and a limitation on the tensile strain level developed in the prestressed CFRP plate was proposed as the debonding failure occurred. In addition, the calculation methods for cracking moment, crack width and deflection of strengthened beams were provided with taking into account the contribution of prestressed CFRP plates. Experimental studies on five RC beams strengthened with prestressed CFRP plates and a nonlinear finite element parametric analysis were carried out to verify the proposed theoretical formulas. The available test results conducted by other researchers were also compared with the predicted values.     

Response of steel fiber reinforced high strength concrete beams: Experiments and code predictions

The shear-flexure response of steel fiber reinforced concrete (SFRC) beams was investigated.Thirty-six reinforced concrete beams with and without conventional shear reinforcement (stirrups) were tested under a four-point bending configuration to study the effectiveness of steel fibers on shear and flexural strengths, failure mechanisms, crack control, and ductility.The major factors considered were compressive strength (normal strength and high strength concrete up to 100 MPa), shear span-effective depth ratio (a/d = 1.5, 2.5, 3.5), and web reinforcement (none, stirrups and/or steel fibers).The response of RC beams was evaluated based on the results of crack patterns, load at first cracking, ultimate shear capacity, and failure modes.The experimental evidence showed that the addition of steel fibers improves the mechanical response, i.e., flexural and shear strengths and the ductility of the flexural members.Finally, the most recent code-based shear resistance predictions for SFRC beams were considered to discuss their reliability with respect to the experimental findings. The crack pattern predictions are also reviewed based on the major factors that affect the results.     

Shear strengthening of reinforced concrete beams using different configurations of externally bonded carbon fibre reinforced plates

This paper deals with research undertaken at Oxford Brookes University into shear strengthening of reinforced concrete beams using externally bonded carbon fibre reinforced plastic plates (CFRP). Thirty-eight reinforced concrete beams of 1.8 m length were constructed and tested and are described in this paper. The relative performance of a group of sixteen beams with the same steel reinforcement but with different amounts of shear strengthening is discussed. All the beams were designed to fail in shear using a spreadsheet program. The spreadsheets were designed to ensure that the beams' flexural capacity exceeded the shear capacity after strengthening. The variables were: main reinforcement ratio, spacing between links in the shear span and different configurations of CFRP plates on shear spans. The concrete had an average compressive strength of 61.76 N/mm². The majority of the beams tested showed a significant improvement in shear strength by the addition of CFRP plates, with increases of between 19–122% over the control beams.     

CFRP布加固方案对RC梁剪切性能及尺寸效应影响分析EI北大核心CSCD

采用同时考虑混凝土材料非均质性、钢筋与混凝土之间的相互作用以及CFRP布与混凝土之间的相互作用影响的三维细观数值模拟方法,建立了CFRP布加固RC梁剪切破坏力学分析模型。在验证了细观数值方法合理性的基础上,设计并建立了12根CFRP布加固RC梁细观模型,探究相同CFRP配纤率(用布量)前提下,不同CFRP布加固方案对单调荷载作用下RC梁的剪切性能及尺寸效应的影响。结果表明:CFRP布应变分布与裂缝位置紧密相关,越靠近裂缝位置的CFRP布应变越大,提供的抗剪贡献越多;在CFRP配纤率一致的前提下,CFRP布宽度大厚度小的加固方案优于CFRP布厚度大宽度小的加固方案;CFRP布U型加固RC梁剪切强度存在尺寸效应现象,但相同CFRP配纤率下,不同CFRP布加固方案对名义抗剪强度尺寸效应的影响较小,可以忽略。