Analysis of tapered three-layered sandwich flexural members (Stobie poles) with partial shear interaction: Analytical model

This research paper presents an analytical model for predicting the load-deflection curves of three-layered sandwich (TLS) beams with interlayer slips, accounting for material nonlinearity in all three layers. An advanced 1D beam element with five degrees of freedom per node was developed to simulate the structural behaviour of TLS beams, with two additional degrees of freedom for slippage between adjacent layers. The Euler-Bernoulli kinematic assumptions were adopted, and the governing equations were derived based on equilibrium equations, followed by the derivation of the weak form equations. The finite element formulation was then developed, and the Newton-Raphson scheme was adopted for the solution of the nonlinear system of equations, with five-point Gaussian quadrature used for the integration over the length of the beam and trapezoidal integration used for the integration over the area of the cross section. The proposed model was applied to tapered steel-concrete-steel sandwich flexural elements known as Stobie poles. The model results were verified with full-scale experimental tests and numerical models, and the effects of slippage constitutive relationship, cross-section tapering, and mechanical properties of the core and skin layers were evaluated. The presented model provides a reliable tool for designing and analysing three-layered sandwich beams with partial shear interaction.