Sagging behavior of precast NC beams with HPCs-filled wet joints incorporating pre-stressing technique

Precast segmental beams constructed with normal concrete (NC) are widely adopted in modern infrastructure because of their advantages in decreasing on-site labor, shortening construction time, and observing high-quality control. Such segmental beams might require using construction joint with superior characteristics. However, the presence of intermediate constriction joints introduces potential weaknesses, particularly under sagging loading, which may result in bond degradation, cracking, or interface failure. This investigation presents a comprehensive experimental and numerical investigation into the flexural performance of precast NC beams incorporating high-performance concrete (HPC)-filled wet joints of varying developed lengths (l d ), subjected to post-tensioning force. A total number of nine full-scale beams were experimented under flexural moments until failure. The considered parameters were: HPC type employed in the joint (ultra-high performance concrete (UHPC) and engineered cementitious composite (ECC)), the l d values (15, 20, and 25 times the bar diameter (D)), and the pressurising condition applied through of post-tensioning system. The results demonstrated that specific combinations of these parameters significantly enhanced cracking resistance, initial stiffness and energy absorption. Moreover, integrating a pre-stressing system with a UHPC-filled wet joint and a developed length of 25D led to an approximate 98 % increase in ultimate load. A nonlinear three-dimensional finite element model (FEM) was constructed and validated against the experimental outcomes, yielding high accuracy with discrepancies less than 4 %. Additionally, a novel predictive equation for the ultimate moment capacity of the studied beams was formulated, exhibiting a mean error margin of about 3 %.