Residual behavior of steel rebars and R/C sections after a fire

The mechanical properties of various steel bars exposed to high temperature (“residual” properties) are experimentally investigated up to 850 °C, with reference to a number of steel and bar types (carbon and stainless steel; quenched and self-tempered bars; hot-rolled and cold-worked bars; smooth and deformed bars). The aim is to clarify to what extent the thermal sensitivity of the different bars affects the ultimate capacity of a typical R/C section subjected to an eccentric axial force, past a fire (“residual” capacity). As usual in the design of R/C sections under combined bending and axial loading, the ultimate behavior is represented through the “M–N envelopes”, where the materials strength decay due to high temperature is taken into account. The results show that quenched and self-tempered bars (QST), very popular in Europe, are more temperature-sensitive above 600 °C than the carbon-steel bars extensively used in the States and nowadays rarely used in Europe. Furthermore, the best response is exhibited by the stainless-steel bars, provided that they are hot rolled, as it is generally the case for medium- and large-diameter bars. Similar conclusions can be drawn for the sections reinforced with the different bar types.