Experimental and Numerical Analysis on the Thermo-Mechanical Stresses Triggering the Onset of Fire-Induced Concrete Spalling

Fire-induced spalling of concrete is a fundamental problem in the design of concrete structures when subjected to fire loading. Among several factors known to influence the occurrence of spalling, there is general consensus that the internal rate of heating is a governing factor. This article describes an experimental and numerical analysis to study the spalling behaviour of high-strength concrete under heating conditions replicating the heating of concrete during a temperature–time Standard and Hydrocarbon curve. Six prismatic concrete samples embedded with thermocouples were cast and heated using an H-TRIS (Heat-Transfer Rate Inducing System) experimental test setup controlling incident heat-flux at the heated surface of each sample tested. In-depth temperature distribution was measured and used for comparing the heating conditions triggering the onset of concrete spalling during fire testing. To complement the experimental work, a numerical model was developed to perform the thermo-mechanical analysis at the moment of spalling. Stress distribution along the thickness of specimens was compared for the two heating conditions. An additional numerical study conducted shows the influence of sustained external loads (uniaxial or biaxial) during heating of concrete.