EVA Interlayers in Hardened Facades

Explosions can result in very high loads of extremely short durations. Protective design to mitigate the effects of blast loading requires façade hardening, which includes special considerations for glazing. Hardened systems may require specialized design skills or the use of advanced design software to provide solutions that will be effective in protecting building occupants by ensuring catastrophic structural or component failures do not occur. Explosions are an extreme load, typically requiring glazing to be designed to accommodate permanent damage. The focus of design is to control costs while protecting building occupants. During an explosion, glass can shatter and send high velocity shards into occupied space. To mitigate this hazard, it is common to utilize laminated glazing panels, which consist of flexible interlayer(s) sandwiched between multiple layers of glass. The interlayer exhibits ductile response to blast loads, allowing displacement while retaining fragments. Polyvinyl butyral (PVB) is the most common film interlayer utilized for blast resistance. However, ethylene-vinyl acetate (EVA) is widely available and is a potential alternative to PVB.

This paper summarizes the basic protective design principles utilized for the selection of glazing layups and highlights a recently completed multiyear effort to assess the relative efficacy of EVA-laminated glazing panels to resist blast loads. This effort involved interlayer material characterization, shock tube testing and open-air blast testing of laminated glazing panels with EVA and PVB interlayers. Results indicated that the EVA films tested exhibited similar qualitative and quantitative responses under dynamic loading conditions. While EVA holds promise for inclusion in hardened facades, care must be taken in implementation to effectively harness its protective capabilities. Findings from this effort were used to derive recommendations for the inclusion of EVA in facades designed to resist blast loading. These recommendations, as well as possible extensions of this effort, are highlighted.