Numerical modeling of reinforcement pull-out and cover splitting in fire-exposed beam-end specimens

• FE analyses of beam-end specimens subjected to ISO 834 standard fire are performed.
• Different cover, fire exposure duration and exposure scenario are investigated.
• The importance of splitting as the main mode of bond failure is emphasized.
• Influence of concrete cover, heating rate, duration and scenario is investigated.
• An experimental program is planned to verify the findings of the numerical study.

The behavior of bond between reinforcement and concrete at high temperature is numerically investigated considering both pure bond failure and splitting of concrete. To this end, a transient three-dimensional thermo-mechanical model utilizing temperature dependent microplane model as the constitutive law for concrete is employed. Two heating types are considered to simulate the exposure conditions in a slab and in a beam, namely one-sided and three-sided heating, according to the ISO 834 standard fire curve. The results clearly show that for realistic concrete cover, confinement and fire exposure, the concrete splitting almost always governs the bond behavior. The common pull-out mechanism works only if the concrete cover is very high (largely exceeds the values used in the practice) and/or the temperature gradients are rather low. The results further indicate that the beam-end test specimen offers a suitable setup to investigate the pull-out behavior of reinforcement under high temperatures accounting for different influencing factors.