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چکیده
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In a comprehensive investigation, the simultaneous effectiveness of the factors of temperature (five temperatures), volume ratio of steel fibers (three volume ratios), and concrete cover thickness over the rebar (three covers) on the compressive strength, tensile strength, and concrete-steel rebar bond behavior was evaluated. 180 specimens comprised of 45 cubic specimens for the compression test, 45 cylindrical specimens for the splitting tensile strength test, and 90 prismatic specimens for the pull-out test were made. The results demonstrated raising the temperature reduced the compressive strength such that the strength of the plain specimens after exposure to 800 ℃ declined by 71.6%, compared to that of the corresponding non-heated specimens. Moreover, at a given temperature, the presence of steel fibers improved the tensile strength. After exposure to 800 ℃, the tensile strength of specimens with 1% steel fibers in volume was 127.9% higher than that of similar specimens without fibers. At a given temperature, the use and content of steel fibers had an effective role in compensating for losses in the tensile strength and bond strength induced by applying heat. Furthermore, as the concrete cover over the rebar increased, the failure mode became more ductile. The effect of steel fibers on increasing the bond strength of the specimens with a thinner concrete cover heated at elevated temperature was greater and more noticeable. Also, the concrete cover over the rebar had an effective role in compensating for the heat-induced bond strength loss, such that increasing the concrete cover from 25 to 65 mm easily compensated for the concrete-rebar bond strength reduction for every 200 ℃ increment in the exposure temperature.
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