Study on the shear performance of hinged bolted connectors in steel-UHPC composite beams after elevated temperatures

• Published in: Structures (Oxford) Vol. 79; p. 109650
• Main Authors: Zuo, Kaiyuan, Yang, Yong, Chen, Xin, He, Jiuzhou, Hao, Ning
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2025
• Subjects: After elevated temperature; Hinged bolted connector; Push-out test; Random forest; Shear behavior; Shear connector; Shear connector; Shear behavior; Hinged bolted connector; Random forest; Push-out test; After elevated temperature
• ISSN: 2352-0124; 2352-0124
• DOI: 10.1016/j.istruc.2025.109650

Under fire conditions, the design of shear connectors is crucial for steel-UHPC composite beams. To enhance connection performance, hinged bolts are employed, enabling interference assembly and improving initial stiffness. This study investigates the mechanical properties of bolts at room and after elevated temperatures through tests on six push-out specimens, four of which were exposed to fire following the ISO-834. Concrete type and fire exposure duration were the variables. Post-fire phenomena, load-slip behavior, failure modes, shear capacity, and stiffness were analyzed. The results show that load-slip curves undergo three phases: elastic, plastic, and damage. As concrete strength increased and fire exposure duration shortened, the damage mode shifted from concrete slab crushing to bolt shear failure. All concrete slabs exposed to elevated temperatures developed thermal expansion cracks, along with concrete bursting and spalling. When concrete changes from C60 to UHPC improved shear capacity and stiffness by 14.5 % and 4.5 % at room temperature, and by 40.3 % and 46.3 % after elevated temperature, with a stronger effect at elevated temperatures. With longer fire exposure, the capacity after elevated temperature decreased by 49.8 % and 59.0 %, and the stiffness decreased by 87.2 % and 90.9 %, with C60 experiencing more severe reductions. Meanwhile, the initial fire exposure had more significant impact on capacity. Combined with the test results and the introduction of the discount factor, the formula for calculating the shear capacity of bolts is proposed. Predictions of load carrying capacity were made using a random forest algorithm to inform the design.