Shear Lag Analysis in Composite Beam Structures

Shear lag in composite beams refers to the non-uniform distribution of longitudinal stress across a flange or slab, arising from partial interaction between concrete and steel elements. This phenomenon leads to regions at the flange edges carrying less load than those adjacent to the web, reducing the effective flange width and affecting both strength and serviceability. Analytical approaches based on shear flow distribution and energy variational principles have evolved to capture the warping displacement and interfacial slip, while refined finite-element models integrate spatial and time-dependent effects such as creep and shrinkage. Modern research highlights the importance of accurate shear lag prediction for long-span bridges, box girders and building floors, showing that connector stiffness, flange geometry and time-dependent concrete behaviour significantly influence stress redistribution, deflection profiles and fatigue performance. Practical design codes increasingly adopt an effective width concept informed by these advanced models, ensuring safety and economy in the design of composite structures across civil, marine and aerospace applications.

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Recent work has produced a one-dimensional beam finite-element model that simultaneously accounts for interfacial slip, shear lag and concrete creep and shrinkage. This model employs a stepwise solution for time variables and validates long-term deflection and stress evolution against detailed numerical and experimental data, revealing that deflection at mid-span may increase by nearly half over three years, while shear-lag-induced warping intensifies appreciably at the slab and flange ends.

A theoretical analysis for thin-walled multicell box girders introduces modified longitudinal warping displacement functions to define the shear lag width and warping coefficients. Through the principle of minimum potential energy, governing differential equations are derived and solved under typical boundary and loading conditions. Validation against solid finite-element results confirms high accuracy, underscoring the method’s efficiency in predicting shear-lag effects in single- and multi-cell sections.

An analytical framework based on the shear flow distribution law establishes improved cubic-parabolic displacement functions for thin-walled box girders. Parameters of these functions are determined by continuity conditions, shear flow zero points and axial force equilibrium. The ensuing variational‐energy solution yields closed‐form expressions for shear lag coefficients under various boundary conditions, demonstrating that coefficients at different webs differ according to their distance from the shear flow null plane. Numerical comparison affirms the method’s simplicity and practical reliability.

Shear Lag Analysis in Composite Beam Structures publication trend

The graph below shows the total number of articles in shear lag analysis in composite beam structures across all publications each year (not limited to Nature Index journals).

Technical terms

Shear lag: Non-uniform longitudinal stress distribution across a flange or slab due to partial interaction between composite layers.

Composite beam: Structural element combining steel girders and concrete slabs, acting compositely under load.

Effective width: Simplified flange width that carries the same load as the actual non-uniform stress distribution.

Shear connectors: Elements (studs, bolts or plates) that transfer shear forces between steel and concrete, governing partial interaction.

Warping displacement: Out-of-plane longitudinal deformation of flanges induced by shear lag and bending.

Time-dependent effects: Creep and shrinkage phenomena in concrete that alter stress and deformation over service life.

References

1. Prediction of Shear Lag Effect in Thin‐Walled Single‐Box Multicell Box Girder Based on the Modified Warping Displacement Function. Advances in Civil Engineering (2020).
2. Analytical Method of the Shear Lag Effect in Thin-Walled Box Girders Based on the Shear Flow Distribution Law. Applied Sciences (2024).
3. A Beam Finite Element Model Considering the Slip, Shear Lag, and Time-Dependent Effects of Steel–Concrete Composite Box Beams. Buildings (2023).