Experimental Research On Bond Interface Damage Properties Of Concrete Filled Steel Tube Columns

The bond strength and bond-slip relationship have important influence on the mechanicalproperties of concrete filled steel tubes(CFST). The study on the bond-slip behaviors at theinterface of CFST has profound theoretical significance and practical value, and it is furtherconcerned by construction engineers.The interface between Steel and concrete will have the inevitable initial imperfections,when under external loads, these initial defects continue to accumulate and develop, resultingin interface bonding performance degradation, bond stress reduction, structural capacitydecline. Therefore, we must explore the initial damage of the impact on material properties,identify ways to reduce and prevent the occurrence and the development of the initial defects.In this paper, we deeply study the CFST interface bond performance both inexperimental and theoretical. This test is divided in two parts, firstly, the axis push-out testdesigned with the parameters of debond ratio was carried out. Subsequently, the push-out testdesigned with basic parameters of the number of fatigue load and stress ratio was carried out.The research work is summarized as follows:1. To probe the mechanical properties affected by interface debond, the test that7specimens designed with the parameters of initial debond ratio was carried out, examiningCFST interface bond performance.2. To explore the mechanical properties affected by fatigue loading, the test that7specimens designed with the parameters of fatigue loading and stress ratio was carried out,examining CFST interface bond performance.3. Based on the test result, the working mechanism about CFST push-out test wasrevealed deeply. At first, three CFST interface states were described, the basic concepts aboutultimate bond strength and the average bond strength were defined clearly. Through thecalculation of bond strength, which was obtained in debond. Then, we investigate thecomposition of the bond strength, deduce the size of the bond strength, obtaining therelationship between bond strength and debond.4. Based on the damage consideration, through the study of the damage model of CFST，damage variable was defined by bond strength and secant modulus; and we probe therelationship between the two damage and the damage variables, revealing the damageevolution law. The influential mechanism considered in this test was analyzed.