THE RESEARCH FOR DAMAGE BEHAVIOR OF REINFORCED CONCRETE COLUMN UNDER BI-DERECTION LATERAL LOAD REVERSALS

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Using cantilever type column specimen to model a central column of the first floor of RC frames for medium rise buildings, the seismic behavior of RC columns subjected to one direction and two direction input motions was investigated. 10 specimens of common type RC column and 14 specimens of precast-shell RC columns were used. The common type are those cast in-situ and are called RC-columns and the precast-shell are those which have a prefabricated external shell with only the core concrete cast in place. This last type are denominated PCa columns. In total 24 specimens were tested. Also, normal and high strength concrete was used. In the case of normal concrete the cross section of the specimens was 40cm*40cm with a shear span ratio of 2.5 and for high strength concrete the cross section was of 35cm*35cm with a shear span ratio of 3.0.For normal concrete columns, 12-D16 bars of SD35 steel were used as main reinforcement and the nominal strength of the concrete was 240kg/cm2. For high … More strength concrete column, 12-D19 bars of SD50 steel were used as main reinforcement with a nominal strength for concrete of 600kg/cm2. In the case of PCa specimes, the nominal strength of the concrete for the prefabricated shell was of 600kg/cm2 when concrete for core was of normal strength and 800kg/cm2 when concrete for core was high strength concrete. The parameters taken into account in this research were the loading path (one direction and two direction), transverse reinforcement ratio (pw=0.29,0.57,0.6,0.97,1.2%), transverse reinforcement arrangement (simple stirrup and double stirrup, spiral), axial force ratio (N/BDFc=0.25,0.4,0.5), and material strength.The strain distribution measured experimentally was compared with that obtained analytically using the fiber model analysis and shown good agreement. As conclusion, was observed that for small transverse reinforcement the maximum strength of the column or the maximum load is smaller when the specimen were subjected to two directional loal that when were subjected to one directional load. For large amount of transverse reinforcement that difference in the maximum load in not appreciable. However, in all cases, when the specimens were subjected to two directional loads the strain distribution shown a lager strain that when the specimens are under uniaxial loads. This shows that the two direction loading gives more serious damage than the one direction loading. Comparing the analytical results with experimental results it can be stated that the fiber model can be used to simulate the seismic behavior of the RC column. Less