Test results of steel-ultra high performance concrete (UHPC) composite beams with welded steel shear keys (SSKs) under four-point bending are presented in this paper. The objective of the investigation is to reduce the self-weight and manufacturing cost of large-span structures. The study investigates the effects of strength of concrete slab, type, spacing and size of SSK, and concrete slab height and width on flexural behavior of composite beams. The experimental results demonstrate that enhancing concrete strength, reducing SSK spacing, increasing concrete slab size, and using large-size SSK can all significantly enhance the flexural performance. The composite beams with welded SSK exhibit a maximum relative slip of less than 4 mm, while the counterpart with welded bolts has a maximum relative slip greater than 4 mm. The study shows that the welded SSK is more effective than welded bolts in improving the interface shear performance of composite beams and improving the stiffness and load capacity. Additionally, the study defines four failure modes of steel-UHPC composite beams, and the formulae for flexural capacity is developed based on the reasonable basic assumptions. The calculated results fit well with the tested results. The research findings can be provided as a technical support for the design and application of steel-UHPC composite beams.

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