Abstract

In order to realize multi-objective seismic rehabilitation of existing reinforced concrete structures based on displacement performance requirements,this paper studied the seismic behavior of reinforced concrete columns confined with fiber reinforced polymer(FRP).The failure process of reinforced concrete(RC)column confined by FRP under lowcycle repeated lateral forces was simulated by using the finite element software.The concrete damaged plasticity(CDP)material model was adopted in the finite element model.The numerical specimens failure modes and load-displacement curve were verified by the tested results.After that,the influences of the number of FRP layers,the axial compression ratio and the shear-to-span ratio of columns on the failure mechanism and the mechanical behavior of the confined columns were studied.Especially,the relation of the plastic hinge length of the RC columns was carefully analyzed.

Fiber reinforced polymer is widely used in strengthening concrete structure.FRP-confinement significantly improves the seismic strength and ductility of concrete columns[1].Especially,the deformation ability can be significantly improved.It was reported that the number of reinforcement layers[2],the concrete strength of the component,the axial compression ratio and the loading history in the experiments[3]had significant ef fects on the deformation capacity of the constrained column.In this paper,the seismic behavior of confined RC columns with different parameters was studied by finite element method.

If selected two typical tested columns from Li's experiments[4]and established model for simulation.One was a control and the other was a strengthened column.The compressive strength of 150 mm×150 mm×150mm cubes was 20.1 MPa.The yield strength of the longitudinal bars and transverse bars was 400 MPa and 300 MPa,respectively.The elastic modulus of the CFRP laminate is 210 GPa,and its nominal thickness was 0.111 mm.The three-dimensional finite model setup by ABAQUS[5]was shown in Figure 1.The solid element was used for concrete,the truss element was employed for all the longitudinal and transverse reinforcement bars,and the membrane element was chosen for CFRP.The CDP model was selected for concrete material.The accuracy of the model was verified by the test fact,then the parameter numerical study was done.

Figure 1　The detail of numerical column(unit:mm)

The fifteen columns of different parameters including axial compression ratio,CFRP layers and shear span ratio were numerical analyzed.The load displacement skeleton curves were all shown in Figure 2.

Then further analysis about the length of column plastic hinge was done,which was defined by two ways including the yielded rebar zone as Lsy and the crushed concrete zone as Lcs[6]in Figure 3.

Figure 2　Load versus displacement skeleton curves

Figure 3　The definitions of columns plastic hinge