Shear lag effect in continuous rigid frame bridges with single box and single cell during construction

The shear lag effect in bridges can cause uneven cross-sectional stress distribution, compromising load-bearing capacity and structural performance, particularly in continuous rigid-frame bridges. This study integrates energy variation method, finite element modeling, and construction monitoring data to analyze shear lag effects in a single-cell continuous rigidframe box girder bridge during construction. The energy variation method was employed to establish fifth-degree polynomial analytical formulas for calculating shear lag coefficients under various loading conditions. Finite element analysis indicates that prestressing load primarily dominates the transverse shear lag distribution, while optimal tendon placement significantly reduces the maximum shear lag coefficient. During cantilever construction with suspended scaffolding, the shear lag coefficients at the top slab-rib junction follow the sequence <i>&#955;</i>₃ > <i>&#955;</i>₂ > <i>&#955;</i>₁ > <i>&#955;</i>₅ > <i>&#955;</i>₄ across five stages: segment n tensioning (<i>&#955;</i>₁), subsequent hanging basket installation (<i>&#955;</i>₂), segment (n+1) concrete pouring (<i>&#955;</i>₃), segment (n+1) tensioning <i>&#955;</i>₄) and hanging basket movement (<i>&#955;</i>₅). Monitoring data indicate that in the early stages of cantilever construction, the shear lag coefficients and average normal stresses are high in the top and bottom slabs, whereas subsequent segments exhibit decreasing shear lag coefficients and increasing average normal stresses. The findings provide essential guidance for improving bridge design and construction.