Analysis of live load distribution factors in prestressed concrete girder-bridges with asymmetric losses in prestressing strands

Asymmetric loss of prestressing strands in concrete bridge girders presents a critical yet underrecognized threat to structural integrity, particularly in exterior girders subjected to impact or localized deterioration. This form of localized and unbalanced damage leads to eccentric reductions in prestressing force, rotation of the principal axis, and diminished flexural capacity, effects not explicitly addressed in current design standards such as the AASHTO LRFD Bridge Design Specifications. This study presents a comprehensive numerical investigation into the structural implications of such asymmetric damage, focusing on its effect on live load distribution factors (LLDFs) across prestressed girder bridges. A parametric study of 2160 bridge configurations was conducted, considering variations in span length, number of girders, girder spacing, lane-loading scenarios, and progressive levels of asymmetric strand loss. Biaxial sectional analysis was first employed to quantify reductions in flexural capacity and principal-axis rotation caused by asymmetric damage. A simplified closed-form expression for residual capacity estimation was then developed and validated, showing agreement within 8 % of detailed biaxial analysis for moderate damage levels. The degraded girder stiffness was subsequently implemented into grillage-based finite element bridge models to evaluate damage-induced live load redistribution. Results demonstrate that a 16 % asymmetric strand loss can reduce flexural capacity by 18 %, while severe cases involving 75 % loss lead to capacity reductions approaching 80 %. Under a 50 % stiffness reduction in an exterior girder, adjacent interior girder LLDFs increased by 20–27 % under one-lane loading. Although computed LLDFs remained within AASHTO LRFD limits, several short-span and closely spaced configurations exhibited significantly reduced safety margins.