Experimental Study On The Seismic Performance Of Low-ductility Reinforced Concrete Columns Strengthened With TRC

Reinforced concrete column(including bridge pier,frame column,etc.)is the most important anti-lateral force component in the seismic design of building structures.Part of the current concrete columns is designed according to the old standard components(Shear or anti-seismic measures are not perfect),can not meet the requirements of the new specifications,and in coastal areas or marine environment,its performance will degrade seriously due to corrosion.Thus,this kind of columns are easily destroyed under seismic action,and often lead to the local damage even collapse of the whole structure.In recent years,the frequent occurrence of earthquake disasters in China has caused great loss to the social economy and people’s lives and property.Therefore,it is imperative to carry out anti-seismic strengthening for such column members.Textile Reinforced Concrete(TRC)is a new type of fiber Reinforced composite material,consists of fabric mesh and fine aggregate concrete(or high performance mortar).It has been widely used in the field of strengthening and repairing of building structures,due to its advantages of high compactness and strength,crack resistance,and good durability.However,there are few studies on its application in structural seismic strengthening.Supported by the National Natural Science Fund Project " Research on the mechanical properties of composite life cycle of textile reinforced concrete template and composite beam slab(51478408)" and "Study on performance and damage mechanism of flexural-shear critical reinforced concrete columns including the effects of cyclic loading history(51508154)",This paper has carried out the seismic performance test of Reinforced Concrete Columns with Low-ductility Strengthened by Textile Reinforced Concrete.The main research contents and results were as follows:(1)The axial compression tests of 20 concrete short columns(including 4 control specimens and 16 strengthened specimens)were carried out to study the influence of the number of textile layers,the strength grade of concrete,stirrup rate and the short fibers on the effect of TRC confinement.The test results show that TRC reinforcement can obviously improve the failure mode of concrete columns and improve the bearing capacity and deformation capacity of concrete.The strengthening effect of TRC increased with the increase of the number of textile layers,and the load increased by 50% and the ductility performance increased by 57.68%.However,the effect of TRC reinforcement decreases with the increase of concrete strength.And the short fibers in TRC matrix can obviously improve the crack load of specimens,but have little effect on the ultimate load and ductility.(2)The load bearing capacity of TRC reinforced concrete column is analyzed,and the stress and strain calculation formula of TRC confined concrete and is established,and it can be used to calculate axial bearing capacity of concrete columns strengthened with TRC.According to the test load-displacement curve,a simplified stress-strain relation model of TRC constrained concrete is proposed.And it can be used for nonlinear analysis of load-deformation relationship of concrete columns strengthened with TRC.(3)Low cycle repeated tests were performed on 8 reinforced concrete columns(including 2 control specimen and 6 strengthened specimen),The failure pattern,bearing capacity,load displacement curve,stiffness degradation performance and energy dissipation capacity of each specimen are analyzed.The influence of the number of fabric mesh,shear span ratio,axial compression ratio and stirrup ratio on the seismic performance of TRC strengthened reinforced concrete columns is discussed.The results showed that the TRC can effective constraint concrete plastic hinge region,inhibiting crack propagation,improving the damage form,increasing the lateral stiffness and deformation capacity of the columns.Compared with the control specimen,the ultimate displacement,lateral bearing capacity and displacement ductility of TRC strengthened column was increased by 228.45%,33.81% and 111.6%.And the ductility and energy dissipation of the strengthened columns increase with the increase of the number of textile layers,and the stiffness degradation is slower.(4)The horizontal deformation(displacement)component and proportion of TRC reinforced columns were analyzed.The results show that,with the increase of the total displacement,the proportion of shear deformation gradually increase(keep in more than 20%),the proportion of bending deformation decreased first then increased,the proportion of slip deformation almost remain unchanged.The proportion of shear deformation of TRC strengthened columns is relatively stable(about 10% or less),and the variation trend of the proportion of bending deformation and slip deformation varies with the number of layers of fiber mesh shear-span ratio,and axial compression ratio.But overall,these two indexes are far greater than the proportion of shear deformation.Based on the results of low cycle repeated tests and combining with the previously proposed stress-strain model of concrete confined by TRC,the whole process analysis of TRC strengthened columns was carried out by using fiber model theory,and the load-deformation curve of reinforced concrete columns strengthened with TRC was calculated and compared with the experimental results.The comparison results show that the calculated curve is in good agreement with the test curve,and can be used to predict the skeleton curve of low ductile reinforced concrete columns strengthened with TRC.