In this research, pre-cracked concrete beams without reinforcement are exposed to direct effect of firing. These beams are divided into three groups. Each group is exposed to direct firing for certain period of firing time which is different than exposure firing time of each of the other two beam groups. This time dependent study on the effect of direct firing on the concrete beams surfaces is carried out to investigate the behavior of the cracked beams and concrete cracks firstly under only thermal stresses due to firing and then under mono-tonic loading in addition to the thermal stresses effect. These beams are tested under bending moment due to three point load test. The behavior of the cracking due to time dependent firing effect and then due to external static loading are well investigated. Cracking aspects are studied under the effect of thermal stresses and bending moments. Another group of concrete elements including random inclined cracks are studied. In this last group which is concrete prisms with thick dimensions, the effects of concrete size and thermal firing stresses on the inclined cracking process are studied. This research importance is for studying the concrete structures including cracks under the effect of the thermal stresses due to direct firing process. It is very important for protecting the structures and avoiding the sudden collapse of concrete structures due to high thermal stresses of firing effect.
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