The Conjugate Beam Effective Thickness Method

Abstract

The structural performance of laminated glass is strongly dependent on the shear coupling offered by the interlayer between the bounding layered and monolithic limits of the glass plies. The most common simplified design approach consists of defining the effective thickness, i.e., the thickness of a monolithic section with equivalent flexural section properties. The Enhanced Effective Thickness (EET) method has been verified to estimate deflection in laminated glass for a range of load and boundary conditions for two-, three-, and multi-ply beams; however, for some static schemes, the EET method is less accurate for predicting stress. The recently proposed Conjugate Beam Effective Thickness (CBET) method, initially developed for cantilevered laminated glass balustrade applications, accounts for the relative displacement of glass plies across the interlayer for a range of loads and statically determinate boundary conditions. In this paper, the CBET method is extended to the evaluation of two-ply simply supported beams under concentrated, uniformly, and tapered distributed out-of-plane loads. Predicted deflection- and stress-effective thickness obtained from effective thickness methods is compared with finite element model results in illustrative examples, demonstrating improved accuracy. Closed-form formulas are summarized in tables to facilitate the practical application of the CBET method in the design practice.