Influence of opening sizes on the flexural behavior of heat-damaged reinforced concrete slabs strengthened with CFRP ropes

This study investigated the flexural behavior of one-way RC slabs under different opening sizes and the CFRP ropes strengthening effect. Experimental testing was carried out on twenty-eight one-way slabs under the effect of square opening existence (with or without), heat levels (20, 200, 400, and 600) °C, opening size (100, 150, and 200) mm, and CFRP ropes strengthening (strengthened or unstrengthened). The opening was created on the maximum bending moment region at the slab's center between the two loading points. For comparison purposes, the tested slabs were divided into main groups based on the strengthening effect. It was found that the resulted improvement by applying the CFRP ropes is affected by the size of the created opening and the exposed temperature. Furthermore, results revealed an increasing linear relationship between the applied load and the deflection and between the longitudinal concrete strain and the steel reinforcement. In addition, strengthening with CFRP ropes reduces the reduction percentages in the slab's capacity by an average of 6 %. Moreover, increasing the opening ratio by twice increases the deflection value by an average value of 21 %, whereas strengthening the slab with CFRP ropes increases the percentages by 10 % on average. Moreover, initial stiffness is more affected by increasing the temperature values twice those recorded for the yielding stiffness. In contrast, the energy capability increases under different opening ratios. Besides, an increasingly linear relationship was found between the energy absorption and the opening ratio.