Post-tensioned coupling beams: Mechanics, cyclic response, and damage evaluation

This study investigates the influence of axial load ratio, initial prestressing ratio, and aspect ratio on the cyclic performance of post-tensioned coupling beams. An analytical solution was derived and verified against experimental studies conducted on post-tensioned beams and a comprehensive numerical parametric analysis was conducted, examining fifty-one scenarios with varying design parameters. These scenarios incorporated three key parameters: the beams' aspect ratio (span to height), ranging from 1.5 to 3.5; the axial load ratio, ranging from 0.04 to 0.175; and the initial prestressing ratio, ranging from 0.35 to 0.65. Increasing the axial load ratio led to more severe damage, while higher aspect and initial prestressing ratios reduced damage. The axial load ratio had the greatest effect on damage severity, while the aspect ratio mainly influenced the size and length of crushed regions at the beam corners. Deeper post-tensioned coupling beams (aspect ratio <2.5) showed higher coupling shear forces. Increasing the axial load ratio significantly boosted shear capacity, while a higher initial prestressing ratio slightly reduced it. Additionally, both a higher axial load ratio and aspect ratio increased ultimate beam chord rotation, whereas higher initial prestressing ratios decrease it. The estimated stiffness factor, ranging from 0.04 to 0.4, decreased with smaller aspect ratios. Both axial load and initial prestressing ratios had a similar influence on the stiffness factor. A smaller axial load ratio reduced beam-wall interaction and lowered the stiffness ratio, while increasing the initial prestressing ratio raised compressive stress at beam corners, leading to higher initial stiffness and a larger effective moment of inertia. These estimated stiffness factors were then used to derive a relation for the design of post-tensioned coupling beams.