Behavior Of GFRP Tube Confined Seawater And Sea-sand Recycled Block Concrete Columns And Laminated Columns Under Axial Compression

GFRP pipe constrained seawater sea-sand recycled block concrete composite column is a new type of composite component,which is formed by placing GFRP pipe constrained seawater sea-sand recycled block concrete precast segments inside circular steel pipes and pouring self compacting concrete into the interlayer.The internal GFRP pipe can be used to constrain the seawater sea-sand recycled block concrete segments,which can be mass-produced by the factory using prefabricated assembly technology.The construction site no longer involves the placement of recycled blocks,which can ensure construction quality and improve construction efficiency.In addition,the use of seawater sea-sand and recycled blocks in prefabricated segments is conducive to alleviating the problem of traditional building resource shortage and facilitating the recycling of waste concrete.This article conducts axial compression tests on GFRP tube confined seawater sea-sand recycled block concrete columns and GFRP tube confined seawater sea-sand recycled block concrete composite columns,and conducts theoretical analysis and derivation.The main work and conclusions are as follows:(1)Fifteen sets of restrained columns were subjected to axial compression tests to investigate the effects of recycled block replacement rate,strength grade difference between new and old concrete,GFRP pipe wall thickness,and specimen size on the axial compression performance of these specimens.The results show that the replacement rate of recycled blocks has a significant impact on the bearing capacity and ductility performance of the specimen.When the replacement rate increases in a small range,the ultimate bearing capacity of the specimen increases significantly.When it exceeds a certain range,it shows a downward trend,and the ultimate strain shows a decreasing trend.Finally,based on the limit equilibrium theory,a formula for calculating the axial compression bearing capacity of this type of component is proposed,and compared with the experimental results,it is found that it has good prediction accuracy.(2)Axial compression tests were conducted on 17 laminated columns to investigate the effects of recycled block replacement rate,core concrete strength grade,GFRP pipe model,steel pipe thickness,number of prefabricated sections,and slenderness ratio on the axial compression performance of these specimens.The results show that the failure modes of laminated columns are divided into local buckling shear failure and local buckling waist drum failure,both exhibiting good ductility performance;The bearing capacity of the specimen increases with the increase of the replacement rate of recycled blocks,but the growth rate decreases;The ultimate bearing capacity and ultimate displacement of the specimen increase with the increase of the number of prefabricated segments;When the number of prefabricated segments is the same,the ultimate bearing capacity and ultimate displacement of the specimen increase with the increase of the thickness of the steel pipe and GFRP pipe,as well as the increase of the mixed strength of new and old concrete.However,as the diameter of GFRP pipe increases,the ultimate bearing capacity increases,while the ultimate displacement decreases significantly.(3)Conduct a full process stress analysis of the composite column,and based on the limit equilibrium theory and unified theory,analyze the axial compression bearing capacity of the GFRP pipe constrained seawater sea sand recycled block concrete composite column.Derive a formula for calculating the axial compression bearing capacity of this type of composite column,and compare the results of experiments in this article and other literature to find that the calculated values of the formula derived by both methods are in good agreement with the experimental values.This article contains 38 drawings,12 tables,and 84 references.