Time-Dependent Analysis of Steel–Concrete Composite Beams Considering Shear Deformation and Interface Slip

A time-dependent analytical model that incorporates both shear deformation of the constituent layers and interfacial slip was developed in this study to predict the long-term behavior of steel–concrete composite beams. Within the finite-element (FE) framework, the discrete shear connectors are idealized via a continuous bond-slip model, and the steel and concrete layers are modeled using Timoshenko theory. The interface permits slip but not uplift, leading to shared transverse displacements yet independent rotations between the layers. The creep and shrinkage effects of concrete are considered by an age-dependent linear-viscoelastic model. The time domain is discretized into increments to formulate a time-stepping constitutive relation for concrete, whereas the steel is treated as linear elastic. By integrating the equilibrium, kinematic, and constitutive equations, governing equations with interfacial forces as primary variables are derived and solved at each time step, yielding closed-form solutions for displacements and internal forces. The exact stiffness matrix and equivalent nodal force vector of the composite beam element are derived using the direct stiffness method. Numerical case studies demonstrate the validity and effectiveness of the proposed approach in simulating the long-term response of composite beams, including the combined influence of shear deformation and interlayer slip.