Modeling of bonding between steel rebar and concrete at elevated temperatures

A mechanical model of bonding between steel rebar and concrete at elevated temperatures is proposed based on the smear crack theory and the thick-wall cylinder in its partially cracked elastic stage. The relationship between the splitting bond strength and the inner crack radius of the concrete is established by taking into account the variation of the material properties with temperature and the differential thermal expansion of the rebar and the concrete. The model is validated by using previous experimental results on the bond strength. Parametric studies are conducted to investigate the effect of the variation of compressive strength of concrete, concrete cover and temperature on the bond strength degradation. It has been found that the estimate of bond strength based on the previous studies may be unconservative if the concrete cover is relatively small compared with the rebar diameter in which case the concrete cover is more susceptible to splitting failure.

► A mechanical model of bonding at elevated temperatures is proposed.
► The relationship between the bond strength and the crack radius is established.
► Parametric studies are conducted and compared with the previous studies.
► If the concrete cover is small, the strength of the previous studies may be unconservative.
► The computed strength degradation can be used as a guideline for bond design under fire.