Performance evaluation of demountable shear connectors with collar step at ambient and elevated temperatures

摘要

This paper presents the results of an experimental programme to investigate the performance of a new composite shear connector that can be used to build deconstructable composite floors. A total of 21 push-out tests were conducted to quantify the effects of different design parameters, including different nominal temperature levels (20 degrees C, 100 degrees C, 300 degrees C, 450 degrees C, 600 degrees C), with the steel decking perpendicular and parallel to the steel section, two different embedded shear stud lengths and two different grades of concrete (C40/50 and C20/25). The tests were mainly carried out under steady-state condition where the specimen temperatures were increased to the desired target and the load was then applied until failure of the specimen. A few transient tests were also carried out, in which a load equal to the load carrying capacity of the steady-state test at 600 degrees C was applied, followed by increasing the specimen temperature until failure. Three modes were observed: (i) concrete crushing with stud fracture, (U) stud fracture and (iii) concrete pull-out. Concrete pull-out occurred only on one specimen with concrete grade C20/25. It is found that the main failure mode at elevated temperatures not exceeding 400 degrees C was initiated by concrete crushing, concomitantly producing ductile stud damages. At elevated temperatures above 400 degrees C, the failure mode changed to shear stud fracture. The Eurocode 4 calculation equations were shown to produce shear connector resistances to be in reasonable agreement with the steady state results for the higher-grade concrete, even though the previous equations were developed for welded shear studs. The transient state tests failed at lower temperatures than the target temperature of 600 degrees C, indicating it may not be safe to use steady state tests for evaluation of shear connector resistance at high temperatures.