Seismic Performances And The Corresponding Size Effect Of RC Columns

In recent years,with great progresses of large-scale reinforced concrete structures,the increases on the size,height and span of the engineering structures and the diversification of the structural types,result the bearing capacity of the reinforced concrete(RC)members larger and larger,and the mechanical system more and more complicated.The size effect behavior of reinforced concrete poses a new challenge to the safety design of concrete structures.At present,many scholars at home and abroad have done a lot of studies of size effect on mechanical properties of RC components(including beams,columns,and beam-column connections).However,due to the limitation of experimental conditions,very few scholars have studies the size effect on the seismic behavior of RC members.Therefore,with the improvement of test conditions,it is necessary to study the size effect on seismic performance of RC members,so as to verify whether the related conclusions based on small-size specimens are suitable for various size components.In view of the above condition,this paper around the seismic behavior and size effect of different sizes,especially large-size reinforced columns to carry out the following main tasks:(1)The compression shear/flexural compressive failure tests of reinforced concrete short/long columns under the action of earthquake were designed and carried out.A total of 18 specimens were designed in the tests.The section sizes were 300 mm × 300 mm,500mm × 500 mm and 700 mm × 700 mm.The shear span ratio were 2 and 4,and the axial load ratio were 0.4 and 0.6.The influences of cross-sectional size on seismic performance index,like failure modes,shear/flexural bearing capacity,ductility,energy dissipation capacity and stiffness degradation of short/long colums under monotonic/cyclic loadings,were analysis.(2)From the mesoscopic view,combining with the micro-mesoscopic structure character of concrete,considering the nonlinear binding-slip behavior between steel bar and concrete,the three dimensional meso-scale numerical model of reinforced concrete columns was set up.Based on verifying the feasibility of the numerical model,the effects of axial compression ratio and shear span ratio on the seismic performances of RC columns with different structure sizes,especially large size columns were studied.By comparing the results with the classical Size Effect Law(SLE)proposed by Ba?ant,it can be found that the size effect law of RC columns under both compression and bending loadings was in good agreement with the Ba?ant size effect law.(3)Based on the Ba?ant size effect law,a modified formula is proposed by means of experimental and numerical data,to reflect the size effect on the shear capacity of reinforced concrete short columns.The calculated values of the formula are in good agreement with the test values,and the formula can provide a reference for engineering design and specification revision.