Analysis of crack development law and calculation of crack width in the negative moment zone of externally inverted U‐shaped steel concrete composite beams

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Abstract
In order to study the factors that affect the crack width, cracking mechanism, and development laws of the U‐shaped steel concrete composite (USCC) beam, and to propose a crack width calculation formula suitable for this new type of composite beam, cracking tests were conducted on four simply supported beam specimens. These specimens, which featured different steel beam forms, shear connectors, and longitudinal reinforcement arrangements, were all subjected to negative bending moments. Research has shown that USCC beams and H‐shaped steel concrete composite (HSCC) beams exhibited basically consistent crack width‐load relationships. In the early stage of the experiment, the crack width of the specimen exhibits an approximately linear relationship with the load, while in the late stage of the experiment, the crack width rapidly increases. In addition, the crack width of the USCC beam specimen developed faster than that of the HSCC beam. The experimental phenomenon shows that whether it is an USCC beam or a HSCC beam, the distribution of crack width along the concrete slab width is uneven, and this non‐uniformity is more obvious outside the beam width range. The centralized arrangement of longitudinal bars will exacerbate the non‐uniformity of crack width distribution, and the overall crack width is greater than that of specimens with uniformly arranged longitudinal bars. In addition, the effectiveness of channel shear connectors in controlling crack propagation is better than that of shear studs, and the slip at the interface between the concrete slab and the steel beam of the specimen using shear studs is greater than that of the specimen using channel shear connectors when the load is large. Based on the experimental results and formulas in the “Design Standards for Steel Structures” and the “Design Specifications for Concrete Structures,” a formula for calculating the crack width of USCC beams is proposed, and the coefficients in the current specifications have been corrected. The calculated crack width is in good agreement with the experimental value, which can provide a reference for calculating the crack width of this type of composite beam.

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