Investigation of the flexural behavior of steel fiber reinforced concrete hollow beams exposed to elevated temperature

Hollow concrete beams, when adopted in structures, must meet the required structural safety at both conditions of ambient and high temperature. The behavior of this type of beam, with the influence of high temperature, has not been investigated by any previous study yet. This study aims to experimentally explore the behavior of concrete beams of circular hollow sections (80mm diameter) using conventional steel reinforcement and with or without steel fibers (SFs) under flexural loads prior to and after exposure to high temperatures. Besides, the investigation also included the mechanical characteristics (compressive strength and splitting tensile strength) of four mixtures were used to produce the beams specimens and studied their response to different inclusions of SFs (0, 0.5, 1, and 1.5% for each) under similar conditions of the beams test. A total of ten beams of square cross-section with similar external dimensions and lengths (150 × 150 × 950 mm) were prepared, eight of which were hollow, and two were solid. All these beams specimens were loaded until failure under four-point to assess and compare their behavior in terms of temperature evolution, load versus deflection at different stages of loading, ductility, failure mode, and cracks before and after being subjected to 550°C temperature. Based on the test findings, SFRC hollow beams exhibited a more ability to preserve load carrying capacity after heating than plain concrete beams. SFRC hollow beams can be a desirable structural solution and provides a reduction in weight and an increase in ductility without a significant reduction in flexural performance even after direct exposure to a source of intense heat.