Study On Load-bearing Axis Properties Of Steel Column Encased By Concrete Cover

With the application of properties of steel column encased by concrete cover has been more and more widely in recent years, which solves the problem of fire and corrosion protection of steel structures, and improves the overall and local stability of steel columns. However, the calculation process and construction requirements (such as nailing stud and strengthening column base) of this reinforcement method is not involved in the Chinese steel structure reinforcement specification.There are four kinds of calculation methods of bearing capacity for normal section of steel reinforced concrete in specifications around the world:empirical formulas based on the results of calculate values, regard steel as reinforcement, calculated in accordance with bearing capacity calculation model reinforcement concrete columns, regard reinforcement as steel, calculated in accordance with the bearing capacity calculation model of pure steel column and the theory based on superposition theory. Intensity superposition theory is simple and safe, which is in accordance with design practices of Chinese designers. In addition, this paper compared the thickness of concrete cover for steel core and bars, the clear spacing between the steel core and longitudinal reinforcing, minimum steel core ratio, diameter and spacing of steel bars and lateral ties, the minimum reinforcement ratio for longitudinal reinforcing and lateral ties, width-thickness ratio of flange, height-thickness ratio of web, the design of beam-column joints in EC4, AISC-360-10, ACI-10,CH3-78, JGJ138-2001 and AIJ YB9082-97, which can provide recommendations for the new Chinese steel structure reinforcement specification.Study on axis load-bearing properties of steel column encased by concrete cover,the force transmission of laminated column and the stress distribution of section were analyzed based on the test data in this paper. Stress redistribution does not occur immediately on post-pouring concrete, but the additional loads are shared by the whole steel reinforced concrete laminated columns. In the second loading process, the strain of post-pouring concrete lags behind original steel column, which accumulated strain is always higher than the steel reinforced concrete. When the limit state of steel is achieved, the strain of post-pouring concrete is still low, which strength should be reduced. Whether the post-pouring concrete and internal steel column can work cooperatively depends on configuration treatment and construction methods of interface, such as the increase of welding studs.The simulation analysis of laminated column after reinforcement was performed in AB AQUS using the plastic-damage constitutive of concrete and isotropic hardening constitutive of steel. The steel bars were embedded into concrete. The bond-slip constitutive relation between shape steel and reinforced concrete proposed by Zhao and Yang was applied in the finite element analysis. The secondary loading was simulated accurately by using birth-death elements, which results were in good agreement with test results. The initial stress, which has a big influence on bearing capacity, makes the load-displacement curve move backward, and the axial loads are mainly borne by internal steel column.Finally, the calculation formula of bearing capacity of steel columns with enclosed reinforced concrete based on the superposition principle was proposed, which results matched the test results well.