Influence of the column-to-beam flexural strength ratio on the failure mode of beam-column connections in RC frames

The column-to-beam flexural strength ratio(CBFSR)has been used in many seismic codes to achieve the strong column-weak beam(SCWB)failure mode in reinforced concrete(RC)frames,in which plastic hinges appear earlier in beams than in columns.However,seismic investigations show that the required limit of CBFSR in seismic codes usually cannot achieve the SCWB failure mode under strong earthquakes.This study investigates the failure modes of RC frames with different CBFSRs.Nine typical three-story RC frame models with different CBFSRs are designed in accordance with Chinese seismic codes.The seismic responses and failure modes of the frames are investigated through time-history analyses using 100 ground motion records.The results show that the required limit of the CBFSR that guarantees the SCWB failure mode depends on the beam-column connection type and the seismic intensity,and different types of beam-column connections exhibit different failure modes even though they are designed with the same CBFSR.Recommended CBFSRs are proposed for achieving the designed SCWB failure mode for different types of connections in RC frames under different seismic intensities.These results may provide some reference for further revisions of the SCWB design criterion in Chinese seismic codes.

Flexural fatigue strength of steel fibrous concrete containing mixed steel fibres

This paper reports investigation conducted to study the fatigue performance of steel fibre reinforced concrete (SFRC) containing fibres of mixed aspect ratio. An extensive experimental program was conducted in which 90 flexural fatigue tests were carried out at different stress levels on size 500 mm×100 mm×100 mm SFRC specimens respectively containing 1.0%, 1.5% and 2.0% volume fraction of fibres. About 36 static flexural tests were also conducted to determine the static flexural strength prior to fatigue testing. Each volume fraction of fibres incorporated corrugated mixed steel fibres of size 0.6 mm×2.0 mm×25 mm and 0.6 mm×2.0 mm×50 mm in ratio 50:50 by weight. The results are presented both as S-N relationships, with the maximum fatigue stress expressed as a percentage of the strength under static loading, and as relationships between actually applied fatigue stress and number of loading cycles to failure. Two-million-cycle fatigue strengths of SFRC containing different volume fractions of mixed fibres were obtained and compared with plain concrete.

A Parametric Approach to the Evaluation of Flexural Strength of Advanced Ceramic or Glass Like Cylindrical Rods at Ambient Temperature

This critical review presents a parametric approach to the evaluation of flexural strength of advanced ceramic or glass like cylindrical rods at ambient temperature.The parameters governing the measurement and evaluation of flexure strengths of glasses and ceramics are detailed with references.The scope for improvement in the existing ASTM STM C-1684 standard is described with a logical rationale and the parameters that need to be addressed are listed and explained.

Effect of Fiber Weight Ratio and Fiber Modification on Flexural Properties of Posidonia-Polyester Composites

The main objective of this research is to study the effect of fiber weight ratio and chemical fiber modification on flexural properties of composites reinforced with Posidonia fiber. An unsaturated polyester matrix reinforced with untreated and treated Posidonia fibers was fabricated under various fiber weight ratios. Results showed that the combined chemical treatment provided better mechanical properties of composites in comparison with untreated fiber. The fiber weight ratio influenced the flexural properties of composites. Indeed, a maximum value of flexural modulus was observed for 10% fiber weight ratio for composites reinforced with treated fibers. SEM photographs revealed a different fracture surface between Posidonia fibers reinforced polyester composites.

Research on Flexural Behavior of Coral Aggregate Reinforced Concrete Beams

Through the flexural behavior test of coral aggregate reinforced concrete beams(CARCB) and ordinary Portland reinforced concrete beams(OPRCB), and based on the parameters of concrete types, concrete strength grades and reinforcement ratios, the crack development, failure mode, midspan deflection and flexural capacity were studied, the relationships of bending moment-midspan deflection, load-longitudinal tensile reinforcement strain, load-maximum crack width were established, and a calculation model for the flexural capacity of CARCB was suggested. The results showed that with the increase in the reinforcement ratio and concrete strength grade, the crack bending moment(Mcr)and ultimate bending moment(Mu) of CARCB gradually increased. The characteristics of CARCB and OPRCB are basically the same. Furthermore, through increasing the concrete strength grade and reinforcement ratio, Mcr/Mu could be increased to delay the cracking of CARCB. As the load increased, crack width(w) would also increase. At the beginning of the loading, w increased slowly. And then it increased rapidly when the load reached to the ultimate load, which then led to beam failure. Meanwhile, with a comprehensive consideration of the effects of steel corrosion on the loss of steel section and the decrease of steel yield strength, a more reasonable calculation model for the flexural capacity of CARCB was proposed.

煤矸石机制砂C20混凝土力学性能研究

为探究煤矸石机制砂对低强度等级C20混凝土力学性能的影响,调控煤矸石机制砂掺量和水灰比浇筑混凝土试块,开展抗压和抗折强度试验。结果表明:相同水灰比下,随煤矸石机制砂掺量增加,混凝土的抗压强度先增强后降低;相同取代率下,混凝土的抗压和抗折强度随水灰比增大而降低。相较于煤矸石机制砂取代率,水灰比对混凝土抗折强度的影响更大。取代率不超过30%时,对混凝土的抗压和抗折强度均有利,水灰比为0.55、取代率为25%时,混凝土抗压和抗折强度提高最多。

两类三元胶凝体系的构建及配比优化

为了保证混凝土材料性能,同时实现低碳、绿色化发展,本文以矿渣粉(GS)、粉煤灰(FA)和石灰石粉(LS)等辅助胶凝材料(SCMs)替代55%(质量分数)水泥(C)制备了两种三元胶凝体系,即粉煤灰-矿渣粉-水泥体系(FGC)和石灰石粉-矿渣粉-水泥体系(LGC),研究了体系中FA-GS、LS-GS比例变化对三元胶凝材料粉料堆积密实度、工作性和强度的影响,并结合微观结构分析确定了三元胶凝体系的最佳配比。结果表明,随着两种三元胶凝体系中GS占比的增大,试样密实度和流动性略微减小,试样抗压、抗折强度以及环境效益逐渐增大。在FA-GS和LS-GS质量比均为3∶8时,两种胶凝体系制备的胶砂试样中后期强度均能接近甚至超过纯水泥试样。

AlN/YAlO_(3)复合陶瓷的抗热震性能

AlN陶瓷硬度高、脆性大,难以烧结致密,作为熔炼容器时会因高温变形或被温度变化引起热冲击破坏。将YAlO_(3)作为颗粒增强相加入AlN中,通过无压烧结方法制备AlN/YAlO_(3)复合陶瓷,研究不同温度下AlN/YAlO_(3)复合陶瓷的抗热震性能,分析热震前后AlN/YAlO_(3)复合陶瓷的物相结构、断口形貌和表面形貌,并阐明热震损伤机理。结果表明,在AlN陶瓷中加入YAlO_(3)能够促进AlN陶瓷的烧结,将致密度提升至98.37%,同时细化晶粒,提高AlN/YAlO_(3)复合陶瓷的抗弯强度和抗热震性能。在温度较高的热震试验中,当热震温度升高至600℃后,AlN/YAlO_(3)复合陶瓷的抗弯强度和残余强度保持率显著高于AlN陶瓷,表明添加YAlO_(3)能够有效提高AlN陶瓷的抗热震性能,这主要归因于微裂纹增韧及裂纹的偏折、分叉等机制的协同作用减缓了AlN/YAlO_(3)复合陶瓷抗弯强度的降低速度。此外,当热震温度达到1 000℃时,AlN发生氧化生成Al_(2)O_(3),导致AlN/YAlO_(3)复合陶瓷抗弯强度降低。

冷补植物沥青混合料制备及应用

采用植物沥青替代石油沥青制备冷补植物沥青混合料,计算了不同油石比下冷补植物沥青混合料的贯入度(高温下)、低温弯拉强度、渗水系数及冻融劈裂抗拉强度比,得出最佳油石比。采用油石比6.5%制备冷补植物沥青混合料,对寒区无砟轨道防水保护层粉化进行整治,并检测其整治效果。结果表明:随着油石比增大,冷补植物沥青混合料的贯入度逐渐增加但增幅不大,低温弯拉强度先增大后减小,渗水系数逐渐减小,冻融劈裂抗拉强度比逐渐增大;油石比为6.5%时,冷补植物沥青混合料高温抗变形、低温抗开裂、防渗及水稳定性的综合性能最佳;整治后,沥青混合料防水保护层平整密实,横向和纵向排水坡度满足要求,排水通畅。冷补植物沥青混合料具有良好应用效果。

秸秆灰对砂浆力学性能的影响和微观分析

秸秆灰含有大量的活性SiO2,具有一定的火山灰活性,可以作为水泥掺合料使用。为了探究秸秆灰对水泥砂浆强度的影响,采用秸秆灰作为掺合料制备砂浆进行了试验分析。使用3种不同活化处理方法以提高活性,将秸秆灰按水泥质量的百分比(10%、20%和30%)等量取代水泥掺入到水泥砂浆中,分别对不同龄期砂浆进行抗压、抗折强度试验、X射线衍射(X-ray diffraction, XRD)和扫描电子显微镜(Scanning electron microscope, SEM)检测,对其力学性能和微观形貌进行了分析。结果发现,在养护前期秸秆灰会抑制砂浆强度的发展,各组砂浆强度都有不同程度的下降;在养护后期,秸秆灰砂浆强度增长速率提高,其中经过研磨、400℃高温灼烧,并水洗处理后的秸秆灰在掺量为10%时,砂浆强度效果影响明显,60 d龄期时抗压强度高于基准组,达到75 MPa,抗折强度与基准组持平,达到10.4 MPa,会略微降低砂浆的韧性。

全再生混凝土力学性能及导热性能研究

采用再生粗骨料(RCA)、再生细骨料(RFA)及再生微粉(RCP)制备全再生混凝土,通过正交试验研究了水胶比、RCA取代率、RFA取代率、RCP取代率和AOS引气剂掺量对全再生混凝土性能的影响。结果表明:AOS引气剂掺量对全再生混凝土抗压强度、抗折强度、折压比及比热容的影响最大,强度总体上随AOS引气剂掺量的增加先降低后提高。RCA取代率对导热系数影响最大,RCA取代率为50%时,导热系数最小。最优配合比为:水胶比0.43、RCA、RFA、RCP取代率分别为75%、50%、15%、不掺AOS引气剂,制得的全再生混凝土抗压、抗折强度分别为45.8、4.6 MPa、导热系数为0.9844 W/(m·K)、比热容为0.8807 MJ/(m^(3)·K)。

钢纤维掺量及长径比对无筋管片混凝土力学性能的影响

为提高钢纤维无筋盾构混凝土管片的力学性能,研究了钢纤维掺量(30 kg/m^(3)、40 kg/m^(3)、50 kg/m^(3))和长径比(0.8、0.7、0.6)对管片混凝土抗压强度、抗弯强度的影响。结果表明:在本文研究掺量范围内,管片混凝土抗压强度、抗弯强度均随钢纤维掺量的增加而提高;无筋盾构管片用C50混凝土的钢纤维推荐掺量为30~40 kg/m^(3),推荐长径比为0.8。

界面处理对硫铝酸盐水泥修补砂浆黏结性能的影响

基于水灰比对硫铝酸盐水泥(SAC)修补砂浆界面弯拉强度的影响,确定了SAC修补砂浆最佳配合比,并研究了增大粗糙度、不同溶液浸润的界面处理方式对SAC修补砂浆新旧界面弯拉强度的影响。结果表明:SAC修补砂浆的3 d界面弯拉强度随着水灰比的减小逐渐增大,当水灰比为0.35时,SAC修补砂浆界面弯拉强度达到最高,为3.82 MPa;对界面进行粗糙处理可显著提高SAC修补砂浆1、3、28 d新旧界面弯拉强度,相较于界面未进行处理组分别提高了1.03、1.08、0.64 MPa;与粗糙处理方式相比,对界面进行水浸润或碱溶液浸润处理均对SAC修补砂浆的新旧界面弯拉强度不利。

玄武岩纤维增强赤泥基混凝土力学性能研究

为了提升赤泥综合利用率,改善赤泥基混凝土(RMC)力学性能,以20%赤泥粉体替代水泥,研究了不同玄武岩纤维(BF)掺量(0.1%、0.2%和0.3%)和长度(12 mm、18 mm和24 mm)对RMC流动性、立方体抗压强度和抗折强度的影响规律,并通过多元回归分析建立了强度预测模型。结果表明,掺入BF降低了RMC流动性;适量BF对RMC抗压强度具有一定提升作用,其最优掺量范围为0.1%~0.2%;BF长度对RMC抗压性能表现出不同的影响规律,B4试样28 d抗压强度达到最大值46.6 MPa。随着BF掺量的增加,RMC抗折强度明显升高,但提升效果随长度的增加而减弱,B3试样28 d抗折强度达到最大值5.5 MPa,较RMC提升31.0%;同时,随着BF掺量增大,BFRMC折压比呈上升趋势,韧性改善效果越明显。强度预测模型结果表明28 d抗压和抗折强度预测值与试验值最大误差分别为3.29%和2.86%,与试验结果吻合较好,抗压强度模型预测的最优组合为纤维长度16 mm和掺量0.12%,最高抗压强度为46.0 MPa。

基于响应面法的透水混凝土配合比优化设计

为了研究基于响应面法Box-Behnken的水胶比、骨料级配和粉煤灰掺量对透水混凝土性能的影响,建立了抗压强度、抗折强度、透水系数与上述3个因素的回归模型,得出了优化的配合比参数.结果表明,对抗压强度和抗折强度影响的显著性排序为:骨料级配大于水胶比大于粉煤灰掺量,对透水系数影响的显著性排序为:水胶比大于粉煤灰掺量大于骨料级配,水胶比和粉煤灰掺量的交互作用对抗压强度和抗折强度影响显著,所有因素之间的交互作用对透水系数的影响均较为显著.

不同煤矸石粗骨料替代率下混凝土的低温力学性能研究

为研究煤矸石粗骨料对C40混凝土低温力学性能的影响,制作4种替代率下煤矸石粗骨料试件,以全替代率为基础,对比设计强度为C30,C50煤矸石粗骨料混凝土,在低温下恒温4 h,分别测试在20,-10,-20,-30℃下的抗压强度、劈裂抗拉强度、抗折强度和相对动弹性模量.结果表明,在低温条件下,煤矸石骨料混凝土的强度和动弹性模量均提高,且温度越低,其抗压强度、劈裂抗拉强度、抗折强度以及动弹性模量提升幅度越大.

钢结构用界面处理砂浆的制备及影响因素研究

研究了水胶比、胶砂比、胶粉及憎水剂掺量对界面处理砂浆性能的影响,以拉伸粘结强度、压折比作为衡量指标,制备了与钢结构表面粘结性能优异的界面处理砂浆。试验结果表明:界面处理砂浆水胶比为0.5、胶砂比为1∶2.5、胶粉掺量为10%,憎水剂掺量为1.5%时,界面处理砂浆与钢构件的标准、耐水、耐热、热湿循环、耐冻融拉伸粘结强度分别为1.35、0.78、1.09、0.65、0.70 MPa,压折比为2.5。

水灰比与减水剂对全再生粗骨料混凝土力学性能的影响

定量分析了全再生混凝土水灰比及聚羧酸减水剂掺量改变时,全再生粗骨料混凝土抗压强度与抗折强度的变化趋势,得出合理的水灰比和适宜的减水剂掺量。试验结果表明:随着水灰比增大,全再生粗骨料混凝土抗压强度先增大后减小,抗折强度缓慢减小,水灰比为0.36时,立方体试块抗压性能最佳,强度达到最大值42.3 MPa,通过试验数据分析全再生混凝土试件的抗压强度与抗折强度力学指标关系,得出合理的全再生混凝土水灰比应控制在0.36。水灰比一定,掺入聚羧酸减水剂,抗压强度先增大后减小,抗折强度先缓慢增大后趋于稳定,抗压强度为41.4 MPa与抗折强度4.62 MPa均为最大时,此时聚羧酸减水剂掺入量0.60%,因此,适宜的聚羧酸减水剂掺量范围为0.60%。

面膜膜布用聚乳酸纤维针刺法非织造布的制备及其性能评价

采用针刺法将2种线密度的聚乳酸(PLA)纤维与黏胶纤维加工成不同的非织造布以制备面膜膜布,观察其表观形貌,并进一步测试其力学性能、吸液性能、失液性能、透气性能、透湿性能、柔软性能及贴肤性能。结果表明:针刺法可作为面膜膜布的一种加工方法;在黏胶纤维中混合一定比例的PLA纤维,所得产品在悬垂性和黏附强力方面有更优的表现;提出的面膜膜布黏附强力测试方法可为面膜贴肤性能的评价提供参考。

砂胶比对纤维增强砂浆韧性及收缩性能的影响

文中采用四点弯曲试验、三点抗折试验以及抗压试验,研究不同砂胶比对纤维增强砂浆韧性和力学强度的影响,并进行30d的收缩量监测,研究砂胶比对砂浆总收缩量的影响规律。结果表明:增大砂胶比会导致纤维分散不均匀、减小包裹纤维的浆体的厚度,进而降低了抗弯强度、弯曲韧性以及峰值位移;增大砂胶比提高了早期抗折强但后期抗折强度下降;砂胶比大于0.5,会减小浆体体积,增加砂浆内部的空隙和缺陷,进而降低抗压强度;增大砂胶比减小了单位体积内胶凝材料的含量并增强了砂粒对水泥基胶凝材料收缩的阻碍作用,有利于降低收缩值。