7.Interfacial bonding properties of ultra-high performanceconcrete-filled square steel tube

Abstract:

In order to study the interface bond-slip performance between square steel tube and ultra-high performance concrete ( UH-PC) ，18 UHPC filled square steel tube specimens were designed and manufactured for static push-out test considering the research pa-rameters such as the width-to-thickness ratio of steel tube，length-to-width ratio of specimens and the compressive strength of UHPC．The interface bond-slip mechanism and failure mode，load-slip curves，bond strength and interface bond stress distribution of the UHPCfilled square steel tube were studied，and the influences of various parameters on the bond-slip mechanical properties of the UHPCfilled square steel tube were revealed． The experimental results show that the steel tube and the core UHPC were basically separatedfrom each other after loading，the steel tubes were not buckled，and the longitudinal strains of the steel tube were basically in the elas-tic range． The width-to-thickness ratio of the steel tube is the controlling factor affecting the shape of the load-slip curves and the bondstrength of the UHPC filled square steel tube，the test specimens with different width-to-thickness ratios have two typical load-slipcurves with obvious peak points and no obvious peak points． The length-width ratio and compressive strength of UHPC only affect the value of the bond strength，further whose influence degree is related to the width-thickness ratio of the steel tube． Comparing the exper-imental results with the calculation results of the existing bond strength model，it can be seen that the calculation results of the existingbond strength formula have a large error compared with the experimental values． It is necessary to further increase the test sample datato improve the calculation theory of bond strength between UHPC and square steel tube．

Keywords: Ultra-high Performance Concrete ( UHPC) ; push-out test; bonding strength; load-slip curves