Reinforced concrete is one of the most widely used structural components about which much scientific research has been conducted; however, some of its characteristics still require further research. The main focus of this study is the effect of direct fire on the shear transfer strength of concrete. It was investigated under several parameters including concrete strength, number of stirrup legs (the steel area across the shear plane), and fire duration. The experimental program involved the testing of two sets (groups) of specimens (12 specimens each) with different concrete strengths. Each set contained specimens of two or four stirrup legs exposed to direct fire from one side (the fire was in an open area to simulate a real-life event) for a duration of one, two, and three hours. The results of the comparison showed the importance of using high-performance concrete (instead of increasing the number of stirrup legs) to resist shear stress for the purpose of safety. A significant reduction in shear strength occurred due to the deterioration of the concrete cover after three hours of direct fire exposure.

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Recent developments in the production of ecologically friendly building composites have led to a renewed interest in the use of vegetable fibers as a reinforcement element. Traditional pure Plaster of Paris (POP) can suffer from the development of micro-cracks due to thermal expansion. Therefore, sisal fiber was studied for its potential as an ecological element to restrict and delay the development of micro-cracks in POP. Different sisal proportions of 0, 2, 4, 6, 8 and 10 wt. % of POP were used to characterize the physical and mechanical properties of POP at the ambient temperature. Then, the effects of temperatures of 25, 100, 200, 300, 400 and 500  were investigated. Results proved that the composite of 10% sisal fiber had the best mechanical properties. Also, when the fiber content was increased, the composite’s performance was enhanced, becoming better able to resist elevated temperatures. However, raising the temperature to 300 or above had a negative effect on the mechanical properties, which were significantly decreased due to the degradation of the sisal fiber.

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Concrete filled steel tube (CFST) truss girder usually consists of CFST chords and hollow braces. The performance of steel tube truss girders filled with self-compacting concrete was investigated in this study. A total of eight CFST truss girders (Warren-vertical truss) specimens were tested. The main parameters were the concrete compressive strength and adding a reinforced bar in the concrete core of the bottom chord. Two of specimens without reinforcement were suggested as reference specimens. This study shows the load-deflection curves at the midspan, overall deflections, ultimate loads, flexural strength and failure modes of the tested specimens. The Proposed design equation found in the literature was used to predict the flexural strength of CFST trusses. The failure mode includes: weld fracture and shredding around joints and local buckling of the diagonal braces. Results show that the increase of concrete compressive strength caused a slight increase of the CFST truss strength by about (2.8%-10.34%), also the results showed that the best addition to the core concrete of the bottom chord was the circular steel tube compared with the addition of the steel bars.