Experimental research on physical and mechanical performance of steel rebars in Chinese modern reinforced concrete buildings built during the Republic of China era from 1912 to 1949

摘要

In order to study the physical and mechanical performance of rebars in Chinese modern reinforced concrete buildings built in the Republic of China era from 1912 to 1949, 66 rebars including 36 rectangular rebars and 30 round rebars were collected from the different Chinese modern concrete buildings. Surface geometries, mechanical properties, chemical composition and metallographic microstructures of these rebars were tested and analyzed. The test results show that the rib heights of rectangular rebars meet the requirements of current standards, but the rib spaces, the sums of gaps between the ribs, and the relative rib areas do not. For the rectangular rebars, the average yield strength is 278.60 MPa, the average tensile strength is 375.86 MPa, the average ratio of tensile strength and yield strength is 1.35 and the average elongation is 32.25 %. For the round rebars, the average yield strength is 350.65 MPa, the average tensile strength is 464.37 MPa, the average ratio of tensile strength and yield strength is 1.32 and the average elongation is 25.08 %. These two kinds of rebars are all low-carbon and hot-rolled steel bars. According to the test results above, the physical and mechanical performance of rebars in Chinese modern concrete buildings obviously differs from that of the current rebars. Finally, the relationship formulas between strength and Leeb hardness of these two kinds of rebars are presented respectively. These results can be applied to analysis of the bearing capacity and the structural safety assessment of Chinese modern reinforced concrete buildings, which provide calculation basis of the conservation design of these buildings