Adam Nizich

Effective Thickness – Informed Use in Laminated Glass Analysis

Effective thickness is a widely applied method for the simplified determination of laminated glass structural performance. Multiple effective thickness models published in glass standards (e.g., ASTM E1300 and the draft Eurocode CEN/TS 19100) and recently proposed in research are available to evaluate lite flexural stiffness, lite torsional stiffness, and ply surface stress. However, these models are not universally applicable to all section geometries, loading and boundary conditions, or consistently accurate for evaluation of stress.

Given each model’s limitations, it is necessary to be informed on the which method(s) are appropriate for evaluation of structural performance corresponding to a loading and boundary condition. Furthermore, application of multiple effective thickness values in a representative analysis is necessary for accurate evaluation of deflection, stress, and critical buckling. This can present a particular challenge with the use of shell elements based on a single effective stiffness for evaluation of critical buckling in glass fin designs.

In this paper, appropriate effective thickness methods for select loading and boundary conditions are identified, as proposed for a new ASTM effective thickness standard. Additionally, scaling of shell element properties corresponding to both effective flexural and torsional stiffness is evaluated for numerical analysis of a glass fin.

Application of Effective Thickness for Finite Element Analysis of Laminated Glass Fins

Laminated glass fins are a remarkably slender application of structural glass and are sensitive to lateral-torsional buckling from in-plane flexural forces. Development of flexural and torsional stiffness is critical to their flexural stability, and therefore, the accurate assessment of the partially composite stiffness is key to evaluation of their structural performance.

Effective thickness is an analytical method for the determination of equivalent monolithic section properties and is useful for evaluation of laminated glass structural performance using classic analysis methods. Multiple effective thickness values representing membrane, flexural, and torsional stiffness can be applied in hand calculations for basic design cases; however, representation of two or more effective thickness values in a finite element analysis (FEA) model presents a particular challenge for simplified numerical analysis. Furthermore, limited information is available on the evaluation of effective torsional properties of multilaminate sections with n-number of plies, commonly used in glass fins, presenting an additional limitation for simplified analysis of contemporary applications.

In this paper, Sandwich Theory effective thickness is applied to the evaluation of multilaminate glass fin stability for in-plane flexure. To address the challenge of processing membrane-, flexural-, and torsional-effective thicknesses in a simplified FEA model, an effective stiffness matrix for thin shell elements is proposed and benchmarked with detailed layered FEA models.

Company: Eckersley O’Callaghan, New York, USA

About the speaker:

Adam Nizich is a Senior Engineer with Eckersley O’Callaghan’s New York office. Adam applies a first principles approach to the design, engineering, and consulting on innovative facade and structural glass applications. He has collaborated on research for the development and application of effective thickness methods for laminated glass structural design and is currently leading the development of a new ASTM effective thickness standard.