Experimental Study On Seismic Behavior Of High Ductile Hybrid Fiber Reinforced Concrete Cross-shaped Short Columns

The special-shaped column structural limb is the same thickness as the wall,which can avoid indoor column protruding from the wall.Due to the existence of the column limb,the special-shaped column is more likely to crack when it is stressed,and the brittleness characteristics is more obvious when it is damaged,the seismic performance of it is poor,compared with the ordinary rectangular column.So the application of special-shaped column structures is limited in high intensity and high-rise buildings.The inherent brittleness of concrete is root cause,which leads to the poor ductility of structural members.The researches show that high ductility hybrid fiber reinforced concrete has the characteristics of false strain hardening and multi-crack cracking,which improves the brittleness of concrete.This paper used the high ductility fiber reinforced concrete in special-shaped column structures to improve the seismic performance of special-shaped columns by taking advantage of its high crack control ability and ductility.The main study contents are as follows:(1)The hybrid high ductility fiber reinforced concrete material whose ultimate tensile strain can reach 0.5% above was prepared by using mixed Japanese PVA fibers and domestic PVA fiber,and the fine river sand with particle size range of 0.2 mm-0.4 mm.And use it to the cross-shaped short column.Five cross-shaped short columns were designed,including three high ductility hybrid fiber reinforced concrete cross-shaped short columns with different stirrup spacing,one high ductility hybrid fiber reinforced concrete/ordinary concrete composite cross-shaped short column and one ordinary reinforced concrete cross-shaped short column for comparision.And the low-cycle reversed loading test was carried out.(2)The crack propagation process,crack characteristics and failure pattern of all specimens were compared and analyzed,The results show that: the high ductility hybrid fiber reinforced concrete materials can effectively control the development of cracks,decrease the width of cracks,compared with the ordinary concrete;The the bottom section of the high ductility hybrid fiber reinforced concrete cross-shaped short columns remains intact without concrete peeling when they were failure,which effectively prevents the concrete collapse at the bottom of the column,The high ductility hybrid fiber reinforced concrete improved damage characteristics of cross-shaped short columns.(3)The hysteresis behavior,ductility,energy dissipation,stiffness degradation and the cumulative damage of all specimens were analyzed.The results show that: the high ductility hybrid fiber reinforced concrete materials can effectively control the development of cracks,decrease the width of cracks,improve the crumple spalling state at the bottom of the column,improve the ductility and energy dissipation capacity of the column,slow down the stiffness degradation,and the improvement of bearing capacity is not obvious;With the increase of volume-stirrup ratio,the deformation capacity and energy dissipation capacity of the high ductility hybrid fiber reinforced concrete cross-shaped short columns are improved;The seismic performance of the high ductility hybrid fiber reinforced concrete cross-shaped short column with the stirrup spacing of 60 mm are close to that of reinforced concrete cross-shaped short column with the stirrup spacing of 100 mm.Therefore,the high ductility hybrid fiber reinforced concrete materials can replace the role of some stirrups;The improvement of the seismic performance to the composite cross-shaped short column is nor much different form the cross-shaped short column with high ductility hybrid fiber reinforced concrete for all sections.(4)The restorative force model of the high ductility hybrid fiber reinforced concrete cross-shaped short column was established by analyzing and calculating the horizontal load-displacement curves which were measured by experiment.The calculation result of hysteretic curve is in good agreement with the test hysteresis curve,which can be used as a reference for the nonlinear analysis of the stress process that under earthquake action of this type of structure.