Strengthening concrete box girder bridges using K-Brace Track Combination Truss: experimental and theoretical performance analysis under wet joint damage conditions

To address the insufficient transverse connectivity of concrete box girder bridges due to wet-joint degradation, this study investigates an improved K-Brace Track Combination Truss (K-BTCT) with bolted connections as a strengthening scheme. Compared with conventional welded trusses, the bolted K-BTCT offers advantages in prefabrication, onsite assembly and force transfer efficiency. The performance was evaluated through experimental and finite element studies on two groups of specimens under five levels of equivalent wet-joint damage (0–50%). Results indicate that K-BTCT significantly enhances structural performance. At 0% and 50% damage rates, ultimate load-bearing capacities increased by 60.19% and 58.68%, respectively. The scheme effectively reduced maximum deflection and strain, while promoting transverse load redistribution. Furthermore, a modified transverse load distribution method is proposed by converting K-BTCT stiffness into an equivalent increment of the deck moment of inertia to revise the dimensionless stiffness parameter β. A damage sensitivity coefficient k is introduced to account for wet-joint deterioration. Comparisons show that the traditional rigid-joined beam method underestimates load concentration with a 19.52% error, whereas the proposed method reduces this error to 1.42%, providing accurate predictions for bridges under coupled damage–strengthening conditions.