Research On Axial Compression And Seismic Performance Of Solid-web GFRP-concrete-steel Tube Composite Column

With the revitalization in Northeast China,the reconstruction of adding storeys around the existing buildings has become a hot topic in civil engineering.Most existing buildings are low masonry buildings which were constructed for decades,and some can not be demolished and rebuilt for the special requirments.The bearing capacity of these buildings is lower,and it is impossible to add storeys directly around the original structures.Therefore,it became a key problem to realize the reconstruction of adding storeys around the existing buildings without interrupting their using function.Based on these problems,this paper proposes a novel assembled composite frame consisting of solid-web GFRP-concrete-steel tube?GCTC? columns and H-shaped honeycombed composite beams with rectangular concrete filled steel tube flanges.Both the columns and beams are connected together through integral joints.This kind of composite frame structure is suitable for reconstruction of adding storieys around the existing buildings.To investigate the axial compression performance of GCTC short columns,31 GCTC short columns are designed by considering the main parameters of slenderness ratio???,axial compression strength of core and sandwich concrete(f_ci,f_co),the diameter(D_frp),thickness(t_frp),fiber layers?n?and fiber winding angle???of GFRP and the tensile strength(f_yk),thickness?t_s? and diameter?D_s? of steel tube.The UMAT subroutine is programmed by FORTRAN language to define the properties of the anisotropic-fiber materials of GFRP tube,which was introduced into the finite element?FE?software ABAQUS to establish the FE model of GCTC specimens.The simulation analysis of 26 similar specimens is carried out,and load-axial displacement curves,the load-axial strain curves and hoop strain-axial strain curves of these are obtained.The rationality of the FE modeling method is verified by comparing with the existing experimental results.The further parameter analysis for 31 GCTC short columns is conducted and the influence of different parameters on the axial compression bearing capacity and ultimate displacement are investigated.The results show that the axial compression bearing capacity of GCTC short columns increases significantly by the increasing of D_frp,t_frp,f_cki and n.However,with the increasing of ?,the axial compression bearing capacity decreases gradually.The ultimate displacement of GCTC short columns increases significantly by the increasing of t_frp,? and n.However,with the increasing of D_frp,the ultimate displacement decreases gradually.All specimens show superior axial compression bearing capacity and convex expansion failure modes.Finally,by introducing the double combination constraint effect coefficient??_i,?_o?,the expression of axial compression bearing capacity of GCTC short columns is established by adopting statistical regression 1st Opt software.With the help of the reasonable FE model which been introduced above,23 GCTC composite columns are designed by considering the main parameters of axial compression ratio?n0?,axial compression strength of core and sandwich concrete(f_ci,f_co),the diameter(D_frp),thickness(t_frp),fiber layers?n? and fiber winding angle??? of GFRP and the tensile strength(f_yk),thickness?t_s? and diameter?D_s? of steel tube.The pseudo-static analysis was carried out and the load-displacement hysteresis curve and the overall failure model of GCTC columns were obtained.Based on the parameter range of this paper,the variation law of seismic performance indexes such as energy dissipation performance,stiffness degradation,resistance attenuation and skeleton curve of the GCTC specimens were analyzed.The results show that the equivalent damping viscosity coefficient is above 1.5,and the energy dissipation capacity is much better than that of reinforcment concrete composite columns,concrete filled single steel tube composite columns and concrete filled double steel tube composite columns.In view of the excellent axial compression and seismic performance of this newly composite column,it is suggested that the application in practical engineering should be popularized.