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Study on the Shear Lag Calculation Method for Damaged Box Girder

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Publicado en:Buildings vol. 15, no. 11 (2025), p. 1901
Autor principal: Zhang, Yulong
Otros Autores: Wang Junguang, Wu, Xiaoguang, Yin Jiahao, Shi Yuanxu
Publicado:
MDPI AG
Materias:
Finite element method
Shear lag
Closed form solutions
Stiffness
Influence lines
Damage
Localization
Bending stresses
Stress analysis
Crack geometry
Crack propagation
Deflection
Box girder bridges
Prestressed concrete
Load tests
Iterative methods
Exact solutions
Mechanical analysis
Methods
Normal stress
Deformation
Scale models
Embedding
Acceso en línea:Citation/Abstract
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Resumen:Shear lag stresses increase significantly in cracked concrete box girders; however, most existing models assume intact sections and are, therefore, unsuitable for rapid field diagnosis. This study integrates a stepped stiffness model with deflection influence lines to accurately capture the mechanical response of damaged, simply supported box girders. Regions containing flexural cracks are assigned a reduced bending stiffness <inline-formula>EI′</inline-formula>, whereas intact zones retain the original stiffness <inline-formula>EI</inline-formula>. A closed-form stiffness-reduction coefficient <inline-formula>φ=EI′/EI</inline-formula> is obtained from crack geometry and, independently, from the second derivative of the deflection influence line. Embedding <inline-formula>φ</inline-formula> in a variational shear lag formulation yields explicit expressions for flange displacement and normal stress without numerical iteration. This approach is validated by finite element simulations of a plexiglass scale model with four preset damage levels and by a load test on a 30 m prestressed concrete box girder bridge. Field measurements show that midspan stiffness decreased to 81% of the as-built value; the proposed method reproduces this value with a deviation of 3%. Predicted upper-flange stresses differ from measured values by 5.7–13.6% and from finite element results by less than 10% for damage ratios up to 40%. The second derivative of the influence line difference exhibits a distinct peak at the cracked region, accurately localizing the damage. Compared with classical formulas, the proposed model (i) is fully closed-form, (ii) links global deflection data to local shear lag stresses, and (iii) delivers conservative estimates suitable for routine bridge assessment.
ISSN:2075-5309
DOI:10.3390/buildings15111901
Fuente:Engineering Database