摘要
500MPa钢筋是一种强度高,延性好的新型钢筋。在国外高强钢筋已经得到了广泛的应用,然而在我国由于500MPa钢筋的研究起步较晚并且缺乏相应钢筋混凝土构件试验资料,而尚未列入我国《混凝土结构设计规范》(GB 50010-2002)中,因此为了与国际接轨,推广和应用500MPa钢筋,有必要补充相关试验对其性能进行研究。然而应用500MPa钢筋作为受力主筋,提高结构可靠度,减少了用钢量,但是可能会导致结构或构件在高应力作用下出现过大的裂缝而不能满足结构的适用性和耐久性的要求。因此,研究高强钢筋混凝土结构的工作性能具有重要的理论和工程实际意义。
对配置500MPa钢筋的混凝土梁受弯、受剪性能进行了系统的试验研究,分析了高强钢筋混凝土梁的开裂荷载、极限承载力、裂缝分布形态以及影响裂缝宽度的因素。同时应用500MPa钢筋作为受力主筋,可能会导致构件在高应力状态下出现过宽裂缝,试验设计了六组配有蒙皮钢筋的梁进行承载力、变形及裂缝宽度的对比研究。结果表明,配置500MPa钢筋的混凝土梁与普通钢筋混凝土梁具有相同受力特征,可按照《混凝土结构设计规范》相关公式计算其受弯承载力、受剪承载力、挠度及垂直裂缝宽度,但应对裂缝宽度计算值进行适当修正。同时,蒙皮钢筋的配置能够有效地减小试验梁的整体变形,限制裂缝的开展宽度,使得梁在正常使用阶段能够满足裂缝宽度限值要求。在试验的基础上,根据混凝土基本理论和计算方法,推导了配有蒙皮钢筋的混凝土梁的受弯承载力和挠度计算公式,公式的计算结果偏于安全。
基于混凝土梁表面裂缝分布特征,采用分形理论对钢筋混凝土梁开裂和破坏过程进行了定量化描述,提出混凝土梁在破坏状态以及各荷载水平下构件表面裂缝分布可以用构件表面裂缝的分维数来表征。同时建立了混凝土梁表面分维数与损伤变量的量化关系,为钢筋混凝土梁的开裂和破坏过程定量化研究提供一种新的思路。
通过理论分析,建立合理的计算模型,推导了钢筋混凝土梁斜裂缝宽度的计算公式。试验结果对比表明,采用本文提出的计算公式可以定量的计算钢筋混凝土梁受剪斜裂缝宽度,其计算结果是安全可靠的。
500MPa steel bars is a new type steel bar which has high-strength and strong ductility. This kind of steel bar has been widely used in foreign countries. But it hasn't been taken in by Code for design of concrete structures (GB 20010-2002). In order to take the internationalization into reality as soon as possible and popularize this new kind of steel bar in engineering area of our country, the experiment researches should be done on the characteristic of reinforced concrete members with such steel bars. However, such concrete beams, applying higher tensile steel as reinforcement, may appear oversized cracks which cannot satisfy the requirement for applicability and durability. Therefore, the research on the performance of such high strength reinforced concrete beams is meaningful.
Based on the experimental research on reinforced concrete beams with 500MPa steel bars, the development of crack and the different factors which affect the crack width are discussed. Moreover, six groups of members with welded wire fabric near the concrete surface have been designed and compared with bending capacity, deformation and crack width. From the test results, it is indicated that this kind of members with 500MPa steel bars can work well as the common RC flexural members and the formula in Code for Design of Concrete Structures can be used to calculate bending capacity, deflection and crack width, but the calculated crack width should be calibrated. Furthermore, welded wire fabric can not only be used to control the development of crack but also make the beams to meet the limit of maximum crack width. On basis of the experimental results, using the basic calculated principle and method of concrete, a formula which can be used to calculate the bending capacity and deflection of the concrete beams with welded wire fabric safely has been given out.
Further, according to the distribution character of the surface cracks of reinforced concrete beams, it is shown that the expansion process of concrete beams under load can be described with such nonlinear theories as fractal geometry. Therefore, fissure dimensions on the surface of concrete beams can be used to describe the state of cracking damage under the influence of various stresses. Moreover, a relationship has been established between the fissure dimensions and the damage variable. Therefore, fractal geometry theory can provide a new thought and method for the study of the cracking and breakage of concrete structures.
Based on reasonable theoretical models and the experimental results, a formula which can be used to calculate the diagonal crack width of reinforced concrete beams has been given out. It is shown that the calculated results are feasible and safe by comparing the results between experiment and calculation.
引文
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