Comparative study on the performance of composite beams with detachable bolts and studs under negative moment

This study investigates the flexural performance of prefabricated composite beams under negative moment, utilizing detachable bolt connectors and ultra-high performance concrete (UHPC). Experimental results demonstrate that the UHPC-bolt synergy significantly enhances structural behavior: UHPC increases the cracking load by nearly 50% compared with the normal concrete specimen (N-SD) and promotes micro-cracking, while bolt interface slip releases tensile stress, reducing crack density and width. Bolt-connected specimens exhibit unique stiffness self-restoration and improved ductility due to a bearing-type load transfer mechanism. The effective width and a required pre-tightening force to ensure slip-before-cracking were determined. Post-test deconstruction confirmed excellent demountability. Theoretical models for cracking and ultimate loads show good agreement with test data, supporting this system as a superior solution for crack-resistant and serviceable prefabricated composite bridges.