POST-LAMINATION RESPONSE OF WARM-BENT LAMINATED GLASS
Warm-bent laminated glass is obtained by elastically curving glass plies against a constraining negative mould and by performing, in this condition, the lamination process in autoclave. After removing the constraints, the laminate holds its curved geometry because of the shear coupling from the polymeric interlayer. So curved panels are called “warm bent” to distinguish them from “cold-bent” ones, where flat glass is bent on site and restrained by a frame. An analytical study is presented to describe how, after removal of the constraints, the laminate maintains the curvature only partially, suffering an initial spring-back followed by a long-term relaxation. The model problem considered here is that of two Euler-Bernoulli beams coupled by a thin viscoelastic adhesive layer. Within a variational approach, we analytically describe the relationship between the initial constrained shape and the shape of the curved beam, which is time-dependent due to viscosity of the interlayer. Localized contacts and stress concentrations may occur, depending upon the type of profile that is initially imposed. Comparison of the cases of instantaneous or gradual release of the contact with the mould evidences a remarkable reduction of the transient state of stress in the second case.
IS CURRENT SIZING OF FLOAT GLASS STRUCTURES TOO MUCH CONSERVATIVE?
Structural design of float glass is performed with the semi-probabilistic approach by defining partial factors for glass strength, calibrated with full probabilistic methods on paradigmatic case-studies. Although the most used statistics for float-glass strength is the 2-parameter Weibull’s (2PW), we show that it fails to interpret the extreme tail of the population of experimental data, associated with small failure probabilities. The tails govern the calibration of partial factors, since the target values for failure probability admitted for a construction work are very small; hence, this statistics leads to very conservative design. Contrariwise, from experiments a lower bound for float-glass strength, attributable to modern factory production controls, is recognizable. Moreover, through a micro-mechanically-motivated interpretation, we show that corrosion/abrasion do not imply the decay of strength below a certain limit, inducing instead a lower dispersion in the data. Therefore, we propose to use generalized Weibull statistics, among which the left-truncated Weibull distribution, to better interpret the tail of the population. Partial material factors calibrated with the novel approach are considerably lower than with the 2PW statistics. Enormous saving could be achieved with this more refined statistical approach to interpret float-glass strength.
- Company:University of Parma, Italy
- Short Bio:Gabriele Pisano, born in 1989, studied civil engineering from 2007 to 2013 at the University of Salerno. He is a Ph.D. candidate at the University of Parma, where he collaborates with Prof. Royer Carfagni. His studies are focused on the statistical characterization of brittle material strength and on the correlation of the micro- and the macro-mechanical behavior.
- 30/06/2017, 09:50 GPD Finland 2017
- 29/06/2017, 16:35 GPD Finland 2017