Flexural performance of partially encased steel-concrete composite beams with web opening

This paper is engaged in the study of a partially encased steel-concrete composite beam with web opening (PECBWO). PECBWO refers to a web opening in a wide flange H-beam or I-beam and then filling the web with concrete, with the concrete remaining equally cellular. This specimen is superior to conventional cellular beams and partially encased concrete beams (PECB), saving on casting formwork and structural self-weight. This test focuses on the flexural performance of the PECBWOs. The parameters of the PECBWOs studied are concrete strength, opening shape, opening ratio, and thickness of the bottom flange of the steel. For this purpose, seven PECBWOs were designed for flexural tests and one solid web partially encased beam (PEB) was used as a control group. The analysis of the damage pattern, load-deflection, strain distribution, bearing capacity and ductility of the eight specimens subjected to bending was carried out by obtaining load-displacement curves and strain data of the section steel through test practice. The results show that the PECBWO with 14.9 % opening ratio and circular openings have the excellent performance, with cracking load and flexural capacity similar to that of solid web PEB, and possess better seismic performance with 41.6 % increase in ductility. In addition the bottom flange of the steel is equivalent to the tensile reinforcement of the reinforced concrete beam, and the reduction of the thickness of the bottom flange significantly reduces the flexural capacity and ductility of the PECBWO. For the same case, the specimen with C50 has a higher crack load. An analytical model for flexural load bearing capacity was also provided.