Heat-induced damage, surface scaling and cover cracking always occur ??? with different severity - in R/C members subjected to a fire. Hence, bar-concrete bond in general and cover integrity in particular are at risk in fire, with consequences that can span from the loss of anchoring ability and tension stiffening to cover spalling, followed by the exposure of the reinforcement to the flames. In this research project, concrete spalling and tension stiffening are addressed, the attention being focused on corner spalling in reinforced and unreinforced prismatic specimens in the former case, and on reinforced tension members in the latter case. An experimental procedure to assess concrete sensitivity to spalling is proposed as well. Though very different in their nature, concrete spalling and tension stiffening are investigated within the same project, because (a) the same prismatic specimens are firstly subjected to a rather severe temperature-time ramp to provoke spalling and later to sustained high temperature to induce a generalized damage in the concrete; and (b) the bars placed in the corners are the most exposed to the risk of spalling and to the loss of bond, to the detriment of tension stiffening. Twenty one prisms made of SCC (target strength fc = 50, 80 and 90 MPa) were put inside an electric furnace at 750°C to investigate spalling (9 unreinforced and 11 reinforced with a single bar totally embedded in the concrete). Later, the reinforced prisms were cleared of the concrete at their extremities, to allow the application of opposite tensile forces and to investigate tension stiffening. On the whole, the spalling tendency was rather weak, with 10% (20%) of the specimens exhibiting severe (light) spalling, while residual tension stiffening appeared to be still effective in only 50% of the reinforced specimens, where bond stiffness exhibited a roughly linear relationship with the residual compressive strength of the concrete.
SPALLING AND TENSION STIFFENING IN HEAT-EXPOSED MEMBERS MADE OF SELF-COMPACTING CONCRETE
LO MONTE, FRANCESCO
2013-01-01
Abstract
Heat-induced damage, surface scaling and cover cracking always occur ??? with different severity - in R/C members subjected to a fire. Hence, bar-concrete bond in general and cover integrity in particular are at risk in fire, with consequences that can span from the loss of anchoring ability and tension stiffening to cover spalling, followed by the exposure of the reinforcement to the flames. In this research project, concrete spalling and tension stiffening are addressed, the attention being focused on corner spalling in reinforced and unreinforced prismatic specimens in the former case, and on reinforced tension members in the latter case. An experimental procedure to assess concrete sensitivity to spalling is proposed as well. Though very different in their nature, concrete spalling and tension stiffening are investigated within the same project, because (a) the same prismatic specimens are firstly subjected to a rather severe temperature-time ramp to provoke spalling and later to sustained high temperature to induce a generalized damage in the concrete; and (b) the bars placed in the corners are the most exposed to the risk of spalling and to the loss of bond, to the detriment of tension stiffening. Twenty one prisms made of SCC (target strength fc = 50, 80 and 90 MPa) were put inside an electric furnace at 750°C to investigate spalling (9 unreinforced and 11 reinforced with a single bar totally embedded in the concrete). Later, the reinforced prisms were cleared of the concrete at their extremities, to allow the application of opposite tensile forces and to investigate tension stiffening. On the whole, the spalling tendency was rather weak, with 10% (20%) of the specimens exhibiting severe (light) spalling, while residual tension stiffening appeared to be still effective in only 50% of the reinforced specimens, where bond stiffness exhibited a roughly linear relationship with the residual compressive strength of the concrete.| File | Dimensione | Formato | |
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