Study On Seismic Behavior And Torsional Failure Mechanism Of ECC Composite Columns

ECC,known as engineered cementitious composites,is a kind of Engineering cement-based composite material,which is composed of cement,water,fiber,fly ash and other materials.This composite material has ultra-high toughness.Under uniaxial tension,the material shows the characteristics of multi crack cracking and strain hardening.The ultimate tensile strain can reach 3%,which is more than 200 times of that of ordinary concrete.Due to its excellent mechanical properties,ECC in building seismicThe field has great application value.In the investigation of earthquake disaster,it is found that the torsional failure of vertical members is one of the important factors leading to the damage of buildings,but in the actual project,there are almost no single torsional members,and many structural members are in the state of compression bending shear torsional composite stress.Therefore,this paper studies the failure mechanism and seismic performance of steel reinforced ECC columns in the state of composite torsional,which is the actual stress of ECC columns To provide technical support.The main research contents are as follows:(1)In this paper,six ECC columns and one ordinary concrete column were tested under the combined stress of compression,bending,shear and torsion.The failure process of each specimen was recorded in detail,and the development rule of the cracks of the specimens under the combined stress was summarized.The results showed that the failure process of ECC columns showed obvious ductility characteristics.Because of the existence of fibers,there were many and dense cracks on each surface,and fibers The maximum crack width is less than 2 mm even when the specimen reaches the ultimate load.During the whole loading process,there is no phenomenon of concrete falling off.When the loading displacement is zero,the crack can be closed..(2)Based on the study of hysteretic curve,skeleton curve,stiffness degradation curve,strength degradation curve and equivalent viscous damping coefficient,the effects of stirrup ratio,longitudinal reinforcement ratio,base material and fiber content on the seismic performance of the specimen are analyzed.The results show that the seismic performance of ECC is much better than that of ordinary concrete columns,and the increase of stirrup ratio and fiber content can improve the seismic performance of ECC.(3)The failure mechanism of the specimen is analyzed through the stress analysis and test phenomenon,and the calculation formula of ECC column composite torsional bearing capacity is put forward.The calculated value is in good agreement with the measured value.