Study On Compressive Properties Of Concrete-filled Aluminum Tubular Medium Long Columns After High Temperature

Concrete filled aluminum tubular(CFAT)column is a new type of composite bearing member filled with concrete in aluminium tube.Compared with concrete filled steel tubular(CFST)columns,CFAT has better corrosion resistance and higher recycling efficiency and is an environmentally friendly building component in general.However,the research on mechanical properties and influencing factors of CFAT is not deep enough.Especially,the existing design theory of CFST columns is not clear about the feasibility of predicting the bearing capacity of CFAT columns after fire,which seriously affects the application of CFAT columns in the field of construction engineering.Therefore,based on theoretical analysis,tests and finite element simulation,the compressive Properties of CFAT medium long columns after high temperature is studied in this thesis.The main work and achievements of this thesis are as follows:A total of 24 CFAT stub columns were design for the push-out test after high temperature.The relative curves between relative slip(displacement)of outer aluminium tube and core concrete and axial load were obtained,and the distribution law of longitudinal strain on outer surface of aluminium tube under different load levels were also obtained.The ultimate bond strength,the slip values corresponding to the ultimate bond strength and the residual bond strength of specimen interfaces affected by heating(constant temperature),interfacial bond length and concrete strength were revealed.The model of bond-slip constitutive relationship of CFAT column after high temperature is proposed.The test and finite element analysis of twelve axially compressive circular CFAT medium long columns subjected to high temperature(normal temperature,constant temperature 300℃,constant temperature 500℃)were carried out.The failure mode,relative curves between test load and axial displacement,mid-span deflection,mid-span hoop strain and mid-span longitudinal strain of aluminium tube were obtained.The initial rigidity and ultimate bearing capacity of axially compressive CFAT medium long columns after high temperature affected by the heated(constant temperature)temperature,slenderness ratio of specimen,strength grade of core concrete,the wall thickness of aluminium tube and other factors were revealed.The results of finite element simulation show that the bond-slip model proposed in this thesis can be used to predict the compressive behavior of medium long CFAT columns.Based on the relative specifications of Chinese Code GB50936-2014,European Code EC4,American Code AISC 360-05 and Japanese Code AIJ-1997,respectively,the bearing capacity values of CFAT specimens in this thesis are predicted.The average value,standard deviation and dispersion coefficient of the ratio between the calculated values and the test values are obtained.The feasibility and accuracy of the current specifications for predicting the ultimate bearing capacity of CFAT medium-long columns after high temperature are compared and analyzed.The analysis results show that there is a certain gap between test values and theoretical calculation values of the four codes,with the average relative ratio in the range of0.610～0.764;The predicted values of EC4 are the closest of the four codes to the test values.On this basis,an improved method for calculating the ultimate bearing capacity of CFAT after high temperature is put forward.The corresponding ratio of predicted value to test value is0.959(at room temperature)and 0.875(after high temperature),which significantly improves the predicted accuracy compared with the existing specifications.This thesis has 77 pictures,24 tables and 117 references.