预制混凝土框架梁底部纵向钢筋锚固性能试验研究

通过20个预制混凝土框架梁底部纵向钢筋锚固节点实体构件钢筋拉拔试验,对钢筋端部焊接钢筋锚固件的锚固性能及锚固抗拉承载力进行了研究,分析了预制装配式混凝土框架结构梁柱节点受力及破坏机制。试验结果表明,提出的“预制整浇装配式混凝土框架结构”体系可实现预制装配式混凝土框架结构连接节点强锚固、强连接、弱构件、易安装,节点整体安全性能等同现浇框架结构的特点。在此基础上,提出预制框架梁的底部纵向钢筋在框架柱内锚固抗拉承载力计算公式。

UHPC接缝单根钢筋锚固性能拉拔试验研究

为验证UHPC接缝单根钢筋的锚固性能,本文选取了UHPC等级、钢筋直径、加载方式和埋置深度四个试验参数,开展了UHPC接缝单根钢筋拉拔试验,分析了试件的荷载破坏模式和受力性能。结果表明:所有试件均出现钢筋屈服和拉断的现象,UHPC表面形成一定区域的劈裂裂缝和环形破坏面;UHPC接缝单根钢筋受拉荷载-位移曲线呈现弹性、屈服和强化三个阶段;其极限承载力随UHPC强度、埋置深度和UHPC表面约束程度增加而增加;当钢筋直径较大时,搭接范围内钢筋拉应变较大,内部埋置钢筋对增大钢筋锚固作用有一定的影响。

预制混凝土构件U型连接筋的单肢锚固性能试验研究

通过U型连接筋拉拔试件单肢受拉锚固性能试验,研究了拉拔钢筋直径、拉拔钢筋的弯弧内半径、弯后水平段长度、单侧保护层厚度等参数对锚固性能的影响,并对比分析了基于中国、美国、欧洲规范计算的理论锚固强度值。结果表明:当弯弧内半径和水平段长度与L型连接筋的相关构造相同时,两者的锚固性能基本相当;按中国规范进行设计是偏于安全的;单侧保护层厚度对U型连接筋锚固性能的影响较大;U型连接筋水平段末端弯弧段及相应侧的竖直段对锚固性能的强化作用不明显;研究结果揭示了U型连接筋的受力机理,可为建立相关设计方法提供参考。

铸坯裂纹造成钢材缺陷的特征及控制措施

采用金相显微镜(OM)及扫描电子显微镜(SEM)等仪器对铸坯裂纹造成钢材缺陷的特征及成因进行分析。结果表明:钢筋拉拔断裂、钢板表面结疤及麻坑缺陷均是由铸坯裂纹遗传至轧制过程所导致的。由铸坯裂纹引起的缺陷往往在缺陷处可观测到一薄层高温氧化铁,附近分布着大量细小高温氧化圆点,且在中高碳钢材中缺陷处往往伴随有脱碳迹象。为改善钢材品质,全面分析了铸坯裂纹的形成原因,并针对相关原因提出了相应的改进措施。

Bond strength improvement of GFRP rebars with different rib geometries

Based on the Canadian Standards Association (CSA) criteria,105 pullout specimens were tested to investigate the effect of different rib geometries on bond strength of glass fiber reinforced polymer (GFRP) rebars embedded in concrete. Two kinds of conventional reinforcing rebars were also studied for comparison. Each rebar was embedded in a 150 mm concrete cube,with the embedded length being four times the rebar diameter. The experimental parameters were the rebar type,rebar component,rebar diameter,rebar surface texture,rib height,rib spacing and rib width. Theoretical analysis was also carried out to explain the experimental phenomena and results. The experimental and theoretical results indicated that the bond strength of GFRP rebars was about 13%～35% lower than that of steel rebars. The bond strength and bond-slip behavior of the specially machined rebars varied with the rebar type,rebar diameter,rebar surface texture,rib height,rib spacing and rib width. Using the results,design recom-mendations were made concerning optimum rib geometries of GFRP ribbed rebars with superior bond-slip characteristics,which concluded that the optimal rib spacing of ribbed rebars is the same as the rebar diameter,and that the optimal rib height is 6% of the rebar diameter.

Bond Strength of Bamboo Reinforcement in Light Weight Concrete

Bamboo reinforced concrete as a building material is expected to be an alternative to steel reinforced concrete. Due to the fact that steel is not renewable and polluting steel mills are fairly high. The bond strength is a major concern for the natural fiber used as reinforcement in structural composites. This paper reports study on the bond strength of bamboo reinforcement in concrete, to determine the adhesion reinforcement in concrete often do by the pull-out test. The research objective was bond strength of lightweight concrete and bamboo reinforcement. The test used light weight concrete with foam additives klerak. Bamboo slats were coated with paint and sprinkled with sand. The results obtained showed that the bond strength bamboo 60% of the bond strength steel.

防护专用高强无机聚合物混凝土材料研究

高强钢筋混凝土结构是军用防护工程建设中使用的主要材料。本文采用无机聚合物混凝土成功研制出工作性能良好、抗压强度接近100MPa、对钢筋粘结力强的高性能混凝土。为无机聚合物混凝土的防护工程应用提供实验依据。