Shear capacity calculation of precast U-shaped UHPC composite beams using a truss-arch model

To investigate the shear performance of precast U-shaped ultra-high performance concrete (UHPC)- normal concrete (NC) composite beams, shear-span ratio, stirrup ratio, and NC strength grade were selected as test parameters. Shear tests were conducted on eight precast U-shaped UHPC-NC composite beams and one conventional reinforced concrete (RC) beam. Based on the truss-arch model theory, the composite beams were analyzed. A calculation formula for the shear capacity of precast U-shaped UHPC-NC composite beams was proposed, and the parameters within the formula were discussed. Considering the softening effects of both UHPC and NC, applicable methods for determining the softening coefficients of UHPC and NC were proposed. Building upon the simplified section method for precast U-shaped UHPC permanent formwork, a simplified calculation formula for the shear capacity of precast U-shaped UHPC-NC composite beams was developed. Validation using the proposed simplified formula was performed against a dataset of 18 composite beams from collected shear tests. The results indicate that the calculated values show close agreement with the experimental values, exhibiting a statistically significant correlation with a low coefficient of variation. The precast U-shaped UHPC-NC composite beams demonstrate excellent shear performance and hold significant application potential in prefabricated structures.