Influence of cross section loss on the stress-strain characteristics of corroded quenched and self-tempered reinforcing bars
Severin Haefliger, Walter Kaufmann
Abstract
Many ageing reinforced concrete structures are affected by severe damage of reinforcing bars due to corrosion. Accurate knowledge of the stress-strain characteristics of the installed reinforcing bars is an indispensable prerequisite for the realistic assessment of the structural safety of such structures. The reduction in cross section does not only reduce the load bearing capacity of the reinforcing bars, but in case of hot-rolled, quenched and self-tempered (QST, process branded as “Tempcore®” or “Termex®”) reinforcing bars also changes their structural characteristics. Since these bars exhibit three distinct microstructures in core, transition zone and outer annulus, each with different mechanical characteristics, the overall stress-strain behaviour of a corroded QST reinforcing bar depends on the composition of its residual area, which varies significantly with ongoing corrosion. As QST reinforcement is widely used in concrete structures worldwide, this effect is of high importance for any structural safety assessment of structures affected by corrosion. This study investigates the influence of microstructure on strength and ductility of QST reinforcing bars subjected to axisymmetric cross section loss. In a comprehensive experimental campaign, 31 tensile tests on QST reinforcing bars with continuously reduced diameters were conducted, exploring the contribution of the concentric layers of the cylindrical cross section to the overall behaviour. Experimental results indicate a pronounced variation of strength and ductility over the cross section. Based on these observations, a simplified model was developed for the relationship between loss of cross section and mechanical characteristics. A validation shows excellent agreement between model and experimental data.