Facade Wind Loading

Wind induced pressure is a major design consideration for building facades. However, the effects of facade geometry and urban terrain on wind loading are often difficult to quantify without costly and time-consuming wind tunnel testing. Accurate 3-dimensional data, covering most major cities, is becoming increasingly accessible, and such models are ideal to support numerical modeling of environmental effects on the built environment, especially if such modeling attempts to capture the geometric effects of the cityscape.

This paper describes a new methodology to assess the effects of wind loads on the structural strength of glass using transient, geometrically non-linear analyses and improved glass failure prediction models. A description is provided for both the calculation of wind-induced facade loads, and the development and employment of a finite element (FE) solver to model facade performance.

A Reynolds Averaged Navier-Stokes (RANS) solver for incompressible turbulent flow with the standard k-ε turbulence model is used to calculate air flow velocities and pressure loads for the model. The RANS approach predicts the mean flow field in the domain and can be applied to achieve analysis results in a computationally cost-effective manner. Facade response is calculated using a FE solver that represents the structural mullions as Timoshenko-type beam elements while glass lites, interlayers, and IGU spacers are modeled with reduced-integration shell elements. Constant stress solid elements are used to represent the IGU air gaps and structural silicone. Using this mixed element approach, a design-level fidelity is achievable, facilitated through the use of user-defined constitutive models for glass, PVB, and silicone. Glass material behavior is characterized with a material model with an embedded flaw-based probabilistic failure criterion consistent with ASTM E1300 Standard Practice for Determining Load Resistance of Glass in Buildings. In addition to glass material behavior, hyper-elastic material models that incorporate dynamic strength increases associated with both strain and strain-rate are also used to characterize the material behavior of PVB and silicone.