Study On Seismic Behavior Of Exterior Joints Of Scattering-filling Coarse Aggregate Concrete

In today's society,pumping concrete construction technology has been widely used in the construction industry due to its high degree of mechanization,stable quality,low noise and many other advantages.However,in order to meet its pumpability,compared with ordinary concrete,pumped concrete has the following significant characteristics:large slump(200±20mm),large sand ratio(40%~50%),large amount of cement(not less than300kg/m~3),and small diameter of coarse aggregate(not more than 1/4 of the inner diameter of pumped pipe).With the increase of cement content and the decrease of coarse aggregate size,the shrinkage value of concrete will increase correspondingly,which will lead to the phenomenon of early cracking.Moreover,the large amount of cement content does not conform to the concept of green concrete.The scattering-filling coarse aggregate concrete construction technology refers to a new construction technology,which first pumps the pumped concrete to the designated working face,then mixes a certain volume fraction of coarse aggregate through special equipment,and mixes it twice evenly,and finally carries out pouring and vibrating.Compared with pumping concrete,the content of cement in unit volume decreases and the content of coarse aggregate increases,which can effectively improve the serious phenomenon of early cracking,and has economic and environmental protection value.In order to study the seismic performance of scattering-filling coarse aggregate concrete,this paper studied the influence of post-mixing ratio,axial compression ratio and core area volume stirrup ratio on the seismic performance of scattering-filling coarse aggregate concrete frame exterior joints through the quasi-static loading test of 10 exterior joints.Moreover,based on the quasi-static test data,the restoring force model of the exterior joints of the scattering-filling coarse aggregate concrete frame was established by using the tri-linear restoring force model and regression analysis method.The results show that:(1)The failure process and failure mode of the exterior joint specimen with 20%post-mixing ratio are similar to those of the exterior joint specimen with 0%post-mixing ratio.(2)The energy dissipation capacity of specimens can be improved by appropriately increasing the axial compression ratio,but the ductility of specimens decreases with the increase of axial compression ratio.(3)Increasing the stirrup ratio of the core area can improve the seismic performance of the specimen,but the effect of stirrup ratio beyond a certain range is not obvious.(4)The displacement ductility coefficient of the specimens with 20%post-mixing ratio is between 3.75 and 4.68,and the equivalent viscous damping coefficient at failure point is between 0.234 and 0.283.Compared with the specimen with 0%post-mixing ratio,the energy dissipation capacity and ductility are reduced,however,the seismic performances do not degrade significantly.(5)The calculated skeleton curve of each specimen was obtained based on the skeleton curve model,and then according to the hysteresis rule,the calculated hysteresis curve of each specimen was drawn,the calculated curves are in good agreement with the test curves,and the established tri-linear restoring force model can provide a reference for the analysis of the elastoplastic seismic response of frame joints of the scattering-filling coarse aggregate concrete.