Theoretical study on the ultimate capacity of partially encased composite beams with web openings

Based on the failure mechanism of traditional steel-concrete composite vierendeel trusses, this study investigates the internal force conditions during failure of Partially Encased Composite Beams with web openings. By neglecting the contribution of concrete tension and steel compression to ultimate bearing capacity, four secondary moment equations were developed with axial force and bending moment as variables. Addressing the plastic hinge regions formed at the four corners of web openings in composite beams, a calculation method for the ultimate bearing capacity of Partially Encased Composite Beams with web openings is proposed. The calculation results demonstrate that: Filling concrete on both sides of I-shaped steel beams with web openings enhances their shear and flexural capacities; Opening dimensions are critical parameters influencing the ultimate bearing capacity of such composite beams. A half-symmetrical finite element model was established to verify the accuracy of the proposed calculation method.