Study On Bond-Slip Properties Of CFRP-Confined Section Steel Partially Encased Concrete

Since entering the 13 th Five-Year Plan,my country’s construction industry has experienced a rapid development,not only in the large number of high-rise and super highrise buildings,but also in the tremendous changes in building materials.As a load-bearing component,the column affects the overall safety of the building.In order to meet the needs of large-span,heavy-duty buildings,reasonable changes to the column are essential.As a new type of composite structural column,the section steel partially encased concrete column has a good development prospect in actual engineering due to its high load-bearing capacity and effective use of the properties of concrete and steel.The part of section steel encased with concrete through carbon fiber reinforced composite material(CFRP)-confined can further improve its bearing capacity and is suitable for harsh environments.Among them,the problem of bond slip is one of the most basic and key problem of combined member.In this paper,CFRP was used to confine the section steel partially encased concrete.Through standard introduction tests and the analysis of the test results and the ABAQUS finite element numerical simulation results,the bond-slip properties of CFRP-confined partially encased concrete was studied.The main work of this paper is as follows:(1)12 CFRP-confined section steel partially encased concrete push-out specimens were made with considering the influence factors of different section steel sections,CFRP encasing layers,concrete strength and section steel embedding length.By observing the entire test process,the stress situation of the test piece was analyzed and summarized: the unencased CFRP test piece was divided into 4 stress stages,and the CFRP encased test piece was divided into 6 stress stages.(2)The longitudinal strains of the section steel webs and flanges under various loads were measured by internally attached resistance strain gauges.By analyzing the test data,the strains of the section steel webs and flanges are exponentially distributed along the longitudinal direction of the embedding length of the section steel at the load rising stage was found;meanwhile,the relative slip of the loading end and the free end was recorded by displacement meter.Based on the force process,the 3 characteristic load values,characteristic slip values and 5 characteristic load values and characteristic slip values were defined,and the corresponding typical load-slip curve was obtained.(3)The relationship between four influencing factors and bond strength was analyzed.The results show that increasing the sections of section steel,the number of CFRP encasing layers and the strength of concrete will increase the bonding strength;increasing the embedded length of section steel will reduce the bonding strength.After sorting and summarizing the test data,the characteristic bond strength calculation formula under comprehensive factors were established.By comparing with the test value,the calculation formula was found to have higher accuracy;based on the analysis of the characteristic bond strength and characteristic slip value,a (?)-S constitutive model was established,and found that the fitting effect is better through comparison with the test curve.(4)Taking the contact area and the (?)-S constitutive model as the FD curve of the Spring 2 nonlinear spring element in ABAQUS.As well as,the finite element analysis of the bond slip of the push-out specimen was carried out,and the results of analysis and test were compared,it was found that the bonding degree was relatively high.