The Effects of Cold Warping on Glass Stiffness

Abstract

Significant progress has been made during the past two decades to advance the use of cold warped glazing (glass that has been elastically twisted out of plane) to achieve architectural vision.  As with most new technologies, a full understanding of the mechanics of elastic cold warping has lagged its adoption and increasing specification for use in new construction.  As a contractor whose aim is to turn vision into reality, Enclos has been invested in research and development related to the structural and performance implications of cold warped glazing. One of the most recent discoveries from this work at Enclos has been to relate cold warping of glass to its effect on plate stiffness.  In particular, transverse stiffness to resist load may be negatively affected by the operation of cold warping glass supported by a perimeter frame.  This loss in stiffness has been observed in cold warped glass when compared to flat glass of equal size and thickness.  Recent work at Enclos indicates deflection due to transverse load increases with an increasing degree of warping.  This phenomenon is especially pronounced for thin plates that resist load through significant large-deformation, non-linear plate behavior.  As the degree of warp increases, the loss of stiffness becomes increasingly apparent, to the point at which the glass buckles. As a result of the warping operation, compressive membrane stresses are generated in the center region of the glass.  These compressive stresses counteract the tension that normally arises during large-deformation plate behavior and that contributes to its deflection performance.  As such, a membrane compression due to warping leads to the loss in stiffness when membrane effects appreciably contribute to overall bending stiffness (as they do in plates that fall within the large-deflection regime of bending).  An exploration of this phenomena using a series of finite element tests, coupled with observations from previous testing are the basis for these findings.