Experimental study and comparison of different fully transparent laminated glass beam designs

Laminated glass beams without metallic or polymeric reinforcements generally lack post-breakage strength and ductility. This paper aims to perform a comparative study by testing five different fully transparent laminated glass beam designs in order to see how parameters such as the number and thickness of glass sheets (3 x 10 mm or 5 x 6 mm), the interlayer material (PVB Clear or SentryGlas), and the thermal treatment of glass (annealed or heat-strengthened) affect the pre-breakage performance and post-breakage safety. A buckling analysis is also performed using a numerical model with ABAQUS CAE. The study includes a comparison between the results of different experimental mechanical tests on laminated glass beams, including the tests presented in this paper, as well as other tests found in the literature. All designs presented a linear elastic behaviour until initial breakage. The interlayer material mainly affected the crack shape of laminated glass beams. Beams with five sheets of annealed glass had a more progressive breakage, and therefore a safer behaviour, than beams with three sheets of annealed or heat-strengthened glass.

Evaluate equivalent-sectional shear modulus for laminated glass beams using in torsion tests and photogrammetry method

This paper proposes a concise concept for quantifying the shear/torsional stiffness of the laminated glass beams experimentally by introducing the Equivalent-Sectional Shear Modulus (ESSM), that is directly measured from the torque and sectional-rotation correlation with the torsion test and tailor-made photogrammetry technique. The advantage of this method is originated from the concept of measuring the overall rotation to torque response of a laminated glass beam altogether rather than the component individually. This eliminates the uncertainties of analytical approximations that are commonly adopted by most existing methods in which the composite shear/torsion stiffness is derived from its component mechanical properties. The photogrammetry technique increased the accuracy of the sectional rotation measurement by acquiring dense displacement sample points on the glass beam simultaneously. The accuracy of the photogrammetry setup and efficacy of the test design were proven by a micrometre and a monolithic glass beam test. One sample each for the polyvinyl butyral (PVB) and SentryGlas Plus (SGP) laminated glass beams were tested multiple times non-destructively to determine the ESSM. The result of the SGP laminated glass beam showed a closer agreement with the previous studies, however the result of the PVB laminated glass beam exhibited a larger difference from the previous studies. It also suggested that mechanical properties of the interlayer played an important role in the composite behaviour of the laminated glass beam. The experimental outcomes have demonstrated the proposed method is an accurate and effective technique for measuring the ESSM of laminated glass beams.

Post-tensioning of glass beams: Analytical determination of the allowable pre-load

The effectiveness of post-tensioning in enhancing the fracture resistance of glass beams depends on the level of compressive pre-stress introduced at the glass edge surface that will in service be exposed to tensile stresses induced by bending. Maximum pre-load that can be applied in a post-tensioned glass beam system, yielding maximum compressive pre-stress, is limited by various failure mechanisms which might occur during post-tensioning. In this paper, failure mechanisms are identified for a post-tensioned glass beam system with a flat stainless steel tendon adhesively bonded at the bottom glass edge, including the rupture of the tendon, glass failure in tension and adhesive/glass failure in the load introduction zone. Special attention is given to the load introduction failure given that the transparent nature of glass limits the use of vertical confinement usually applied in concrete. An analytical model for determination of the allowable pre-load in post-tensioned glass beams is proposed, based on the model applied for externally post-tensioned concrete beams. The model is verified with the results of a numerical model, showing good correlation, and applied in a parametric study to determine the influence of various beam parameters on the effectiveness of post-tensioning glass beams.

Finite Element Models and Numerical Analysis of a Structural Glass Beam Reinforced with Embedded Carbon Fibre Rod

Due to the its brittleness and unpredictable failure behaviour, the glass is considered a structurally unsafe material. The poor tensile strength and the occurrence of brittle failures prevent the possible use of structural glass elements (i.e. floors, beams and columns). The present study focuses on the numerical analysis of glass beams reinforced with composite material (Fiber Reinforced Polymer) and the numerical analysis of the behaviour of glass plates after being punched. In particular, the method of reinforcement analysed consists in embedding the Carbon FRP-rod in the interlayer of laminated structural glass beams with the aim to increase their failure strength, but also the post-failure strength and ductility. A numerical analysis on different specimens has been carried out to evaluate the effect of the reinforcement. The response of the reinforced and un-reinforced beams has been compared and the results have been discussed. The results provide an estimation of the expected performance in order to propose a reinforcement method for glass beams using FRP composites. This study includes the numerical analysis on laminated glass plates with wide holes at both ends, the latter made for technological reasons to connect the glass beam to the structure. The obtained results are compared with integer specimens.

Phase Field Simulation of Laminated Glass Beam

The complex failure mechanisms of glass laminates under in-plane loading conditions is modelled within the framework of phase-field strategy. Laminated glass is widely used for structural purposes due to its safe post-glass-breakage response. In fact, the combination of several glass plies bonded together with polymeric interlayers allows overcoming the brittleness of the glass and to reach a pseudo-ductile response. Moreover, the post-breakage behaviour of the laminate is strictly correlated by the mechanical properties of the constituents. Ruptures may appear as cracks within the layers or delamination of the bonding interface. The global response of a glass laminate, validated against experimental results taken from the literature, is carried out by investigating a simplified layup of two glass plies connected by cohesive interfaces through an interlayer. Delamination of the adhesive interface is described, and crack patterns within the materials are fully described. Finally, the proposed approach put the basis for future comparisons with results of experimental campaign and real-life applications.

The effect of openings on stress distribution in glass beams – Dependence on a hole to beam’s edge distance

The paper defines the behaviour of simply supported monolithic glass beam consisting of only one layer glass pane with discontinuities created by four holes positioned symmetrically on the beam. Similar glass panes can be found in real constructions where they act as a beam supporting glazing, roofs or decks of nowadays very popular transparent pedestrian bridges. The main aim of this paper is to provide both experimental and numerical analysis of stress distribution alongside the beam with a focus on areas where peak stresses may occur. The areas of interest are specifically speaking around openings, around supports and in the areas where the forces are introduced to the beam. As Eurocode standards for structural glass are still in the process of codifying and most of the nowadays literature only provides suggested axial distance of holes and hole to pane edge distance based on the thickness of the glass pane. This paper will provide the future designers of glass load-bearing structures with a closer look at stress distribution around the mentioned area. It was essential to do parametric study in software using FEM to investigate as much as possible axial distances of openings without a significant increment in the total cost of the experiment.

3D Adaptive Combined DE/FE Algorithm for Analyzing Impact Fracture of Laminated Glass

Laminated glass has been wildly employed in automobile windshields, modern buildings, etc. thanks to its security and durability performance. A novel 3D adaptive combined DE/FE algorithm is proposed to research its impact fracture mechanical properties if the fracture region is small relative to a specimen while the cracks are propagating at a random position. The proposed method can automatically convert the distorted finite elements into the spherical discrete elements during simulating the impact fracture of laminated glass. In this method a system is completely discretized into the finite elements at the initial moment without any discrete element existing until part of the finite elements becoming severely deformed. Subsequently each finite element, whose maximum tensile stress exceeds a user-specified conversion criterion, is converted into eight spherical discrete elements. At the same time the system is fragmented into two subdomains, the finite element (FE) and the discrete element (DE) subdomains. An extrinsic cohesive fracture model is adaptively adopted only in the DE subregion to capture the crack propagation when the normal stress between the DEs equals or exceeds the cohesive strength. The impact fracture of a glass beam is simulated by the adaptive algorithm and the discrete element method, respectively. Beside of the micro-cracks and cohesive zone, almost the same crack patterns are captured by both the numerical methods. Fortunately, the efficiency of the proposed method is much higher (10 times in this case) than that of the pure DEM. A satisfactory agreement of the simulation results certified the feasibility and effectiveness of such an adaptive algorithm. Finally, the impact fracture simulation is performed by the adaptive algorithm on a laminated glass beam which has the same size as the experimental specimens. Besides of the differences on the cracks occurrence and propagation angle, a similar agreement of the fracture patterns is observed as the experimental results. The common conclusions on the role of PVB interlayer can be obviously obtained by analyzing the simulation results, the same by analyzing the experimental ones. The proposed method is hopeful to be employed to analyze the impact fracture of an automobile windshield subjects to the head impact for the protection of pedestrians safety, the traffic accident reconstruction and the structural optimization of windshield.

Post-Cracking Capacity of Glass Beams Reinforced with Steel Fibers

A study concerning the flexural behavior of glass beams reinforced with steel fibers is presented in this paper. Two types of steel fibers were used for reinforcement, made of high strength and stainless steel. The coupling effect of the two materials was studied in terms of energy dissipation and failure loads, by comparing the elastic limits and the post-elastic behaviors of the reinforced glass beams. Results demonstrated that it is possible to increase the overall structural safety of a steel fiber reinforced glass beam. The relationship between the bending force and deflections was initially linear, however, following the opening of first cracks in the glass, the reinforcement steel material was able to withstand the tensile stresses, governing the overall post-elastic phase.