混凝土结构耐久性与裂缝控制中值得探讨的几个问题(续)

耐久性与裂缝控制是目前土木工程界的主要研究前沿 ,本文就此方面研究中存在的问题进行了分析 ,并提出自己的看法。     

碱性环境下不同基体材料GFRP筋的拉伸性能试验研究

玻璃纤维增强聚合物(Glass Fiber Reinforced Polymer,简称"GFRP")筋作为一种替代钢筋的新型建筑材料已在混凝土结构中开始使用,研究在模拟混凝土的碱性溶液中,不同基体材料的GFRP筋在90 d浸泡周期内的腐蚀机理、破坏机理及拉伸强度、弹性模量等拉伸力学性能的变化规律。试验结果表明:两种基体材料GFRP筋的典型破坏形式大致相同,均为丝束状炸开的脆性破坏;基体材料为不饱和聚酯树脂基的GFRP筋的拉伸强度会不断降低,弹性模量前期稍有增长,后期也不断降低,最终浸泡周期达到90 d时,其拉伸强度和弹性模量的衰减均低于标准的最低要求;基体材料为乙烯基酯树脂的GFRP筋的拉伸强度会不断降低,但衰减速率要低于基体材料为不饱和聚酯树脂的GFRP筋,而弹性模量变化并不明显,最终浸泡周期达到90 d时,抗拉强度和弹性模量均满足标准规定的最低要求。     

玻璃纤维增强树脂基复合材料碾铆-粘接接头老化和腐蚀性能研究

主要对玻璃纤维增强树脂基复合材料碾铆-粘接接头进行了老化和腐蚀试验,通过静拉伸测试,分析了温度和腐蚀介质对混合连接接头力学性能的影响。结果表明:同温下,粘接层失效时的峰值载荷会随保温时间的增加而减小;同保温时间下,粘接层失效时的峰值载荷会随温度的增加而减小;在5%NaCl溶液中腐蚀时,连接件的抗拉伸性能受腐蚀时间延长的影响比较小;而在5%NaOH溶液和5%HNO_3溶液中腐蚀时,连接件的抗拉伸性能受到的影响比较大,样件的峰值载荷下降比较明显。试样的失效主要分为胶层失效和铆钉拉脱失效两个阶段。     

玻璃纤维布约束二次受力钢砼偏压柱加固效果的试验研究

对6根考虑二次受力的玻璃纤维布加固钢砼偏压柱的强度和变形特性进行了试验研究,探讨分析了二次受力的作用机理及其对加固柱加固效果的影响,指出滞后应变的大小是决定二次受力结构加固效果的关键因素,加固前应尽可能对结构进行卸载,但没有必要花费大量的人力、物力去完全卸载,只要卸载至原结构极限承载力的40%左右就能获得良好的加固效果。     

水泥杆中钢筋的电磁特性及其对周向定位的影响

钢筋是水泥杆的骨架,其健康状况直接影响水泥杆的强度。分析了电磁探伤的原理,设计出用于测试水泥杆中钢筋分布的标样和试验系统。标样由PVC管、端盖和钢筋构成,试验系统由传感器单元、信号采集器和分析软件组成。通过试验,对钢筋周向分布变化的电磁信号进行了采集,数据分析了钢筋的电磁特性及对周向定位的影响。研究表明,采用电磁法在适当精度内对钢筋定位的影响较小,可用于水泥杆的质量检测。     

The effect of homogenization temperature on the corrosion resistance of extruded 7050 Al-alloy bars

The homogenization time is decreased from 28 h to 6 h by using high-temperature homogenization heat treatment. With increasing of the holding time, the content of intergranular phase decreases quickly at first. When the holding time is more than 6 h, the content of intergranular phase keeps unchanged, and the area fraction of residual intergranular phase is 0.5%, lower than that (0.64%) of the two-step homogenization process. The mechanical properties of the extruded bars heat-treated by the high-temperature homogenization and the two-step homogenization heat treatment are almost the same. In the accelerated corrosion experiments, the maximum intergranular corrosion depth in the direction of perpendicular and parallel to the bar axis heat-treated by the high-temperature homogenization heat treatment are decreased by 43% and 60%, respectively, compared with that heat-treated by the two-step homogenization heat treatment.     

热轧带肋钢筋标准述评

在实际操作中,对带肋钢筋标准的“表面质量”和“反向弯曲试验”部分易引起的歧异提出有待进一步完善的可能性。     

Tensile tests and analyses of notched specimens fabricated from high strength steels using a generalized yield model

This article summarises the uniaxial tension tests for 20 notched bars fabricated from high strength steel Q345 specified in Chinese National Standards. The effects of the notch radius, r, and that of the notch depth ratio, d/D , on the ductility and fracture resistance of this high strength steel are examined. The experimental data are further analyzed using a generalized yield model together with an elliptical fracture stress envelope originally proposed by the first author. The experimental results demonstrate that cracks initiate at the notched section, with the fracture surface filled with many dimples and shearing marks. Specimens with a sharper notch radius (a smaller r) and a larger notch depth (a smaller d/D ratio) show poor ductility, but high fracture strength. The stress field computed from the numerical procedure including the generalized yield model indicates that the crack initiation occurs at the centre of the notched section which experiences the highest stress triaxiality ratio (σ_m/σ_seq) . As the stresses at the notched section reach the limiting values determined from the elliptical fracture criterion, macroscopic fracture failure in the notched bar occurs.     

嵌筋墙体抗剪破坏机理分析

嵌筋加固是一种新型后配筋砌体的墙体加固技术。根据高宽比为0.5和1.8的嵌筋加固墙体试验结果,对其破坏形式和破坏机理进行对比分析。结果表明,经嵌筋加固后,墙体的破坏形式不同于普通墙体。高宽比为1.8的具有斜压破坏特征;高宽比为0.5的初裂时具有剪压破坏特征,极限荷载时具有剪压和剪摩擦破坏特征。