Prediction of failure of a cantilever–wall connection using post-installed rebars under thermal loading

Polymer based mortars allow post-installing rebars into pre-existing concrete structures by bonding the steel to the concrete in a few hours. This type of steel–polymer–concrete bond may show similar performances to classic rebar–concrete connections at ambient temperature but, due to the adhesive layer, it tends to lose rapidly its load bearing capacity at higher temperatures which raises the issue of fire safety for these types of structural connections. This paper presents a simple model for estimating the time before collapse in a structure subjected to fire according to ISO 834-1 heating. Entry data for the ultimate load calculation is obtained through pull-out tests performed at different temperatures on small size samples made out of concrete cylinders in order to obtain an ultimate bond stress–temperature relationship. Model predictions are then compared to data from a full scale test made out of a wall–cantilever connection using post-installed rebars. The connection is thermally loaded in a gas furnace up to collapse of the cantilever due to the slip of the chemically bonded rebar. Temperature and displacement measurements during the test are analyzed in order to evaluate the accuracy of this method in safely estimating the ultimate temperature and stress distribution along the bond just before failure.