Study On The Seismic Behavior Of Reinforced Concrete Columns Strengthed With TRC Under Chloride Dry-wet Cycle And Load Action

Chloride ion erosion in marine engineering is an important reason causing the series of durability problems,such as corrosion of steel bars,cracking and spalling of protective layer.At the same time,the dry-wet cycles of the ocean splash area and tidal zone is the most unfavorable environmental condition for the coastal reinforced concrete(RC)structures,and the deterioration of the concrete performance always relates to the dry-wet cycles.Therefore,a large amount of cost is spent every year on reparing and reinforcement to ensure these structures can meet the design life span.Textile reinforced concrete(TRC),as a new type of cement-based reinforcement material,has the advantages of high corrosion resistance and high bearing capacity.Therefore,scholars has carried out a series of research at home and abroad.In addition,China is a country with many earthquakes and structural aseismic has become an important part in the design of building structures.However,there are few studies on the seismic performance of TRC reinforced RC elements under the corrosive conditions and it is necessary to further study the effect of the chloride corrosive condition on the seismic performance of the RC structures strengthened by TRC.In this paper,there were senveteen RC columns.Five unreinforced columns were the control,and the others were strengthened with TRC.The seismic performance of the RC columns strengthened by TRC were explored,considering the different volume content of PVA short cut fibers added in the TRC matrix,dry-wet cycles,and the coupling of dry-wet cycles and sustained load.In addition,based on the existing theories and experimental results,a restoring force model of TRC reinforced RC columns is established,which considered the dry-wet cycle times and coupling of dry-wet cycles and sustained load.The main conclusions as following:1)TRC could limit the development of cracks,increase the initial stiffness of the component,reduce the rate of stiffness degradation after the yield and improve the failure form of the specimens.In addition,TRC could improve the deformation and energy dissipation capacity so that enhance the seismic performance of the specimens.When the PVA fiber is in a certain range,the mechanical properties of TRC improved,and the reinforcement effect of TRC enhanced.However,the excessive dosage could cause adverse effects on TRC.Based on the experimental results,the reasonable volume of PVA fiber is about 0.5%.2)Compared with the unreinforced columns,TRC can effectively improve the cracking load,yield load and peak load of the reinforced component,and increase the initial stiffness of the component.It could also reduce the rate of stiffness degradation after the yield and improve the failure form of the reinforced component.In addition,TRC can improve the deformation and energy dissipation capacity.The dry-wet cycles have little effect on the cracking load of the reinforced specimens.However,with the increase of dry-wet cycles,the yield load and peak load of the specimen reduced and the energy dissipation capacity reduced.The displacement ductility coefficient of the specimen increases first,then decreases and then increase.The variation of the stiffness degradation rate is the same as the displacement ductility coefficient before and after the specimen yielded.However,in the late stage of displacement loading,there is no obvious effect on the stiffness degradation of specimens.3)With the increase of sustained stress ratio,the phenomenon of "kneading" in the hysteresis curves of the specimens is more and more obvious and the area of the hysteresis loop decreases so that the energy dissipation capacity of the specimen reduced.In addition,the ductility coefficient of the specimen increases first,then decreases and then increases,but it has little effect on the stiffness degradation of specimens.Under the same chloride corrosive conditions,the peak load of specimen decreases gradually along with the increase of sustained stress ratio,but the variation law of peak load is not obvious in the negative direction.A reasonable proportion of vertical load could improve the seismic capacity of unreinforced specimen under chloride corrosion.In addition,the seismic performance of TRC strengthened columns is better than that of unreinforced columns under the same sustained stress ratio.4)The restoring force model of the RC columns strengthened by TRC is established,considered the dry-wet cycles and coupling of chloride corrosive condition and sustained load.Based on the existing theories and experimental results,the hysteretic rule simplified by using the three linear skeleton curve model of stiffness degradation.The results show that the model proposed in this paper is good in agreement with the experimental results.