Delamination properties of laminated glass windows subject to blast loading

Delamination processes absorb significant amounts of energy in laminated glass windows when they are subjected to blast loads. Blast tests were performed previously and their results had been used to calculate the loads imposed on the support systems. In this research, the delamination process at realistic deformation rates was studied to understand the reaction force response obtained. Laboratory tensile tests were performed on pre-cracked laminated glass specimens to investigate their delamination behaviour. The experiments confirmed the presence of a plateau in the force-deflection graphs, suggesting that the delamination process absorbed significant energy. The experimental results were then employed to calibrate FEA models of the delamination process with the aim of estimating the delamination energy of the polyvinyl butyral (PVB) membrane and glass layers and its relationship with deformation speed. The delamination energies obtained through this research, if used with the appropriate PVB material model, are a valuable new tool new tool in the modelling and design of laminated glass façade structures

Blast resistance of laminated glass facades

The aim of this thesis is to improve the understanding of the behaviour of Polyvinyl Butyral (PVB) laminated annealed glass façade panels subjected to blast loading. A full scale blast test was performed. During this, deflection and strain data were collected employing digital image correlation techniques (DIC). Local reaction forces were measured using several pairs of strain gauges on the support. The full field deflection and strain data obtained were in line with those observed in historical tests. The strain gauge data available showed that the reaction forces varied along the edge, with higher values being reached at the quarter length gauge locations. The results from this test and from other historical experiments were used to calculate the reaction forces along the entire perimeter of the glass pane. The results showed that the forces reach an early peak before the glass failure, and then rise gradually approaching a plateau at high central deflections. To explain the specific form of this force time history, the detailed behaviour of the laminated material after the glass skins failed was studied. Existing experimental data was employed to fit a material model to the PVB material. Two Prony series models with different hyperelastic springs and a model employing a full finite deformation viscoelastic law derivation were employed. It was found that the finite deformation viscoelastic model could represent the material’s behaviour more accurately and fully include its rate dependency. One of the PVB models was employed to study the delamination between the glass and the membrane. Delamination energies were found for different speeds of deformation, and these parameters were employed to study the delamination of samples presenting different crack arrangements. The results showed that these had only a limited influence on the behaviour of the composite.Open Acces

Blast tests and FEA calibration

This document mostly reports on the efforts to determine whether the steel and sandwich structures were affected by the combined blast and fragment loading to the same extent as was seen for the RC structures. Of especial importance was to determine whether the impacts, besides transmitting significant momentum to the system, also affected its overall stiffness and capacity due to the localized damage. To achieve this, blast tests and quasi static tests were performed and modeled

Fixed supports and realistic blast studies

Real design scenarios are likely to differ in several respects from the analysed situations. One of these is the boundary condition. In the cases considered previously, the slabs were always simulated as simply supported, since this was the condition generally used during the tests. In realistic structures it is more likely that the concrete elements will have fixed boundary conditions, as these better represent the reinforcement ties generally included in design. Additionally, lower stand-offs and more concentrated fragment distributions are also likely to be required when design conditions are determined. Therefore, it was decided that the ability of modelling such different situations was an important parameter to assess the capability of the modelling method developed

Modeling of Combined Impact and Blast Loading on Reinforced Concrete Slabs

Explosive devices represent a significant threat to military and civilian structures. Specific design procedures have to be followed to account for this and ensure buildings will have the capacity to resist the imposed pressures. Shrapnel can also be produced during explosions and the resulting impacts can weaken the structure, reducing its capacity to resist the blast pressure wave and potentially causing failures to occur. Experiments were performed by the Defence Science and Technology Agency (DSTA) of Singapore to study this combined loading phenomenon. Slabs were placed on the ground and loaded with approximately 9 kg TNT charges at a standoff distance of 2.1 m. Spherical steel ball bearings were used to reproduce the shrapnel loading. Loading and damage characteristics were recorded from the experiments. A finite element analysis (FEA) model was then created which could simulate the effect of combined shrapnel impacts and blast pressure waves in reinforced concrete slabs, so that its results could be compared to experimental data from the blast tests. Quarter models of the experimental concrete slabs were built using LS-Dyna. Material models available in the software were employed to represent all the main components, taking into account projectile deformations. The penetration depth and damage areas measured were then compared to the experimental data and an analytical solution to validate the models.Published versio

Conversion of combined blast and fragment models for quasi static analysis

The residual capacity of structural elements after they are damaged by explosions or other catastrophic events is an important parameter in the design of structures. This is especially the case for key defensive elements, which need to be able to satisfy their original function though they might be targeted specifically

Impact tests and pre blast tests predictions

In this context, it was decided to consider the performance of steel vertical structures, composed of several steel universal beam (UB) sections welded together, with additional protective steel plates on each face. Additionally, a steel-concrete sandwich panel type was also included. It was decided that they would be included in the study to assess their performance with realistic charges. To fully consider the behaviour of these structures and to inform modelling techniques to be used to facilitate their design, it was decided to conduct a series of experiments, including both impact and blast tests. These would then be used to validate detailed numerical models, with a special attention to developing blast tests prediction capabilities

Literature review of CB&F and numerical study of basic scenario

Very low stand-off explosions of real ammunition can produce significant amounts of shrapnel, which will be propelled at high velocities onto structures. The impact of these fragments can represent a significant loading of structural elements, and its effects will be compounded to the damage caused by the blast shock wave. Therefore, designing structures to resist low stand-off blast loads requires an understanding of these combined phenomena to ensure that the proposed solutions will provide the desired level of protection in an efficient and cost effective manner

Mode I fracture characterisation of FRP-concrete interfaces under dynamic loading

Tensile (mode I) fracture between fibre reinforced polymer (FRP) and concrete is found in the FRP strengthened reinforced concrete (RC) structures, especially for structures under dynamic loads. However, currently, there is a lack of studies on the mode I fracture under dynamic loads. The present programme consisted of two sets of experiments to bridge this gap and to obtain the principal interfacial properties of such fracture. Direct tension tests and notched three-point bending tests were used to determine tensile bond strength and fracture energy of the FRP-concrete interface bond, respectively. Digital image correlation (DIC) measurements were used to characterise the fracture process. It was found that the two bond properties were close to those of plain concrete in the quasi-static regime and showed significant dynamic enhancing effect at a loading rate of 20 mm/s. Dynamic increase factor (DIF) equations for the two bond properties were provided to predict the interfacial response of FRP-concrete bond under dynamic loads. As an application example, the two bond properties were used in finite element simulations of the three-point bending tests.Defence Science and Technology Agency (DSTA)Accepted versionThe authors acknowledge the research scholarship given by Nanyang Technological University and the research grant of the project “Modelling of Fibre-Reinforced Polymer (FRP) Strengthened Reinforced Concrete Walls subject to Blast and Fragment Loadings” from the Defence Science and Technology Agency (DSTA), Singapore under the Project Agreement (PA) NO: DSTOOOEP016000821. The authors are grateful for their support in this research

Freely Hanging Multi-Layer Laminated Glass Subjected to Near-Field Blast

Laminated glass holds promise as a resilient building material with the potential for successful application under explosive conditions. This study investigates the dynamic response of freely hanging laminated glass to near-field blast loading. Experimental trials were conducted, examining two laminated glass configurations: a 5-layer setup and a 7-layer setup. Panels were designed using the sacrificial glass ply concept, comprising alternating layers of glass panels and polyvinyl butyral interlayers. The experimental methodology involved two types of explosives: Semtex 1A and granulated TNT. The samples were suspended on wire rope slings to eliminate support influences and allow comparison with numerical models. Samples were incrementally loaded with explosive weights to estimate the minimum impact energy required for glass failure. The overpressure from the blast was recorded and the response of the panels in terms of the acceleration, as well as crack formation and propagation, was studied. Accelerometers were affixed to each panel, whereas the crack development was examined after each test. The experimental results were compared to a numerical model. The study explores cracks based on numerous parameters like number of blasts and glass configuration. It also shows how different parameters impact panel velocity under blast and how damage affects their natural frequency. Comparison with numerical models shows that the setup accurately replicates the absence of supports