Performance of the laminated glass systems under static and blast pressure loading
Authors:   , Nawar Mahmoud 
Published: April 2021

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The increase of explosions threats toward civilian targets has raised concerns about a building's safety. Laminated glass (LG) is one of the widely used structural elements in building envelope where safety performance is highly required where the major threat of death and injuries comes from the flying glass fragments. Laminated glass can greatly reduce the hazard of flying shards by holding the fragments of the glass bonded to the polymeric interlayer which works as continuous membrane attached to the supporting frame and dissipates a great amount of cracking energy when the glass cracks due to blast loads. Recently, the blast-resistant glazing research has been improved broadly, but still few areas remain unexplored related to resistance function and blast response of the window system including new interlayer materials such as UVEKOL-S. This research develops finite element (FE) modeling using LS-DYNA software to study the response of LG windows and curtain walls to blast loads, the effect of the negative phase of the blast wave, and the dynamic reactions transmitted to the window frame and supporting structure. The dynamic response in terms of center deflection and dynamic reactions of the model were compared against those measured in blast testing and showed good agreement. But, after the point of glass failure, a difference in frequency response between the experimental results and LS-DYNA model were seen. This can be attributed to the random crack patterns and the lack of the exact dynamic properties of the post-cracked phase of the laminated glass panel. The static behavior of the polymer interlayer before and after breakage of the glass layers was investigated under quasi-static loading. Constitutive relations of virgin and extracted polyvinyl butyral (PVB) and UVEKOL-S extracted from laminated glass panels were evaluated, including the energy absorption capabilities for each material. Also, the post-breakage behavior of laminated glass was investigated. The experimental results of scored tensile samples carried out on UVEKOL-S glass laminates using different numbers of scores are presented, discussed, and compared with the results of the PVB glass laminates. The energy absorption of the PVB glass interlayer was found to be larger than that of the UVEKOL-S interlayer. From the scored tensile tests, it was concluded that the adhesion of PVB to glass panes is stronger compared with the adhesion of UVEKOL-S to glass panes. Conversely, it was found that this stronger bond led to premature tearing of the PVB interlayer when compared with UVEKOL-S, which allowed relative slip, leading to reduced tearing initiation. In this research, the dynamic constitutive behavior of virgin PVB and PVB and UVEKOL-S extracted from laminated glass panels were evaluated at an average strain rate of 30-40 s-1 using an impact drop-weight apparatus. A new technique was used to investigate the exact mechanical proprieties of PVB and UVEKOL-S before and after the breakage of the laminated glass, including the energy absorption capabilities for each material. The results show that both PVB and UVEKOL-S, at strain rates of 30-40 s-1 had an initial rise in strength, but after the maximum stress point both materials followed a noticeable difference in their response to failure. Comparing the high strain results with the static ones, they show that the dynamic loading significantly affects the material response and the energy absorption characteristics of the interlayer materials. Sufficient data was obtained from the tests to evaluate alternative approaches to modeling PVB and UVEKOL-S materials in a real blast event. In this research, experimental studies have been carried out to investigate the stress wave generation using a piston impact on fluid inside a tube attached to a fluid chamber to produce impulsive loads which are uniformly distributed over the test panels. Experimental shock wave simulation results for laminated glass panels validated the effectiveness of the system to produce a blast impulse with specific characteristics. Different blast wave and impulsive profiles were obtained using this blast simulator apparatus, which is neither expensive nor complex, to test small scale samples including laminated glass panels and aluminum cladding. Also this apparatus was used to investigate the initial speed of the glass splinters flying from the tested laminated glass samples using a high speed camera. Additionally, this research focuses on numerically and experimentally evaluating the resistance function of UVEKOL-S and PVB LG panes, including the structural glazing tape (SGT), silicon, or non-structural glazing tape (NSGT) as a glazing support to the surrounding frame. The resistance function must be obtained under uniform pressure (since the blast load is generally uniform). In this research, finite element program, LS-DYNA, was used to stablish and investigate the resistance function of cracked LG panes, which is contributed by the membrane resistance of the polymeric interlayer, which will be used in the SDOF idealization and dynamic analysis of window systems. A full-scale vacuum chamber and a small-scale water chamber were used to apply static uniform pressure on the LG panes to develop load-deformation failure relationships for LG panes. The results were used to improve the existing SDOF systems used for the design of blast resistant windows. The dynamic responses for two blast experiments using a shock tube were compared to the SDOF and WINGARD results to identify the accuracy of this method in designing LG window systems. Findings indicate that the SDOF results compared well with those obtained from the shock tube blast tests, and hence it can improve the abilities of engineers to better design LG panes under blast loads.