| A concrete-filled steel tube surrounded by external concrete is a composite element known as a concrete-encased concrete-filled steel tube (CFST). This composite element is used in multi-story buildings, large-span constructions, bridges, and underground transit stations. This research examined the curvature behavior of fiber-reinforced concrete-encased CFST beams. Eight concrete-encased CFST beams and one conventional beam were subjected to four-point loads during testing. The factors examined were shear connection, section size, CFST ratio, outer concrete compressive strength, compressive strength of concrete inside the steel tube, steel fiber content, and unfilled steel tubes. Curvature is an important factor that determines the adequacy of reinforced concrete beams because it depends on the deflections, which are considered the major factor for accepting or rejecting the structural members in buildings. The test results showed that the conventional beam's ultimate moment is 141.9% greater than that of the concrete-encased CFST. Also, the curvature of the conventional beam is 30.4% lower than that of a reference beam constructed from concrete-encased CFST. Furthermore, increasing the CFST ratio from 2.7% to 5.4% resulted in a 62.4% enhancement in the ultimate moment, accompanied by an 11.3% reduction in beam curvature. Increasing the outer compressive strength of concrete from 25 MPa to 45 MPa resulted in a 13.8% rise in the ultimate moment and a 19.03% reduction in the beam's curvature. When the compressive strength of the concrete inside the inner steel tubes was raised from 35 MPa to 55 MPa, the ultimate moment went up by 6.7%, and the beam's curvature went down by 11.3% compared to the reference beam. The absence of steel fiber in concrete-encased CFST reduces the ultimate moment by 6.1% and diminishes the curvature by 22.3%. The unfilled steel tube inside concrete-encased CFST reduces the ultimate moment by 13.97%, while the curvature rises by 3.6%. The results show that section size, CFST ratio, outer concrete compressive strength, shear connection, and compressive strength of concrete inside the steel tube are the best results. In contrast, steel fiber content and unfilled steel tubes have the worst results compared to the reference beam. |
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