The resistance of laminated glass to blast pressure loading and the coefficients for single degree of freedom analysis of laminated glass

For terrorist explosions or accidental explosions in urban areas, the greatest threat of death and serious injury comes from the effects of glass fragments. Laminated glazing has been proven by trials and experience of actual events to eliminate the risk of significant fragment injury to people behind the glazing, and also to provide substantial protection from blast injury effects, provided that after cracking it remains as a continuous membrane substantially attached to the supporting frame. However, design of laminated glazing is currently based on extrapolation from testing, with limited understanding of the material behaviour that underlies the behaviour under blast loading. This thesis presents an investigation into the application of a simplified method of dynamic analysis for laminated glass, the development of parameters derived from the properties of the materials in laminated glass and the behaviour of laminated glass systems that can be applied to the design of laminated glazing to resist blast loading. The development of the single degree of freedom method for analysis of dynamic response is reviewed from its inception use for analysis of glazing, through its adaptation for reinforced concrete analysis, to its modern use for analysis of glazing. Although the principles of the method are widely applicable, some procedures established for elastic-plastic reinforced concrete analysis in the 1950s are not appropriate for glazing, and should be treated with care. Coefficients for analysis of reinforced concrete date from approximate analyses in the 1950s and 60s and are not accurate. New calculations using advanced yield line models and finite element analysis have been used to provide alternative coefficients for rectangular panels supported on four edges. The elastic analyses for reinforced concrete are linear because they are based on small-deflection theory. Deflections of most uncracked glass panes exceed the limits of this theory. The development of practical non-linear large-deflection analyses in the 1980s was dependent on numerical methods and computer analysis, but they have previously only been applied to resistance and cracking. New non-linear finite element analyses refine the existing resistance data, and data from the same calculations has been used to derive large deflection single degree of freedom parameters for dynamic analysis and to assess the reaction distribution. The cracking of glass arises from small flaws in its surface, and can be very variable in its onset. In addition, the strength is sensitive to the loading rate. Statistical approaches have been based on quasi-static tests, either assuming a normal distribution, or using a more complex Weibull distribution. However, statistical refinement gains little, as strengths then need to be increased for the faster loading under blast. Back-analysis of extensive blast tests had been used to establish deterministic lower bound design cracking strengths for different types of glass. These have been applied in this thesis for design, and back-analysis of blast trials indicates that the design cracking strengths are lower bound. Formulae for a monolithic pane with equivalent behaviour to a laminated glass pane are proposed that would allow the large deflection analysis to be applied to laminated glass up to cracking of the final ply. The results of some blast trials of uncracked laminated glass are reported which are consistent with an equivalent monolithic analysis. They indicate that laminated glass under blast can be taken as fully composite to temperatures approaching 20ºC, but that it is not fully composite at 29ºC or above. Unfortunately, there is currently no data to indicate the performance in the critical temperature range between. After laminated glass cracks, the resistance is provided by an interlayer of the viscoelastic polymer, Polyvinyl Butyral. Though research is ongoing, non-linear viscoelastic material models for finite element analyses have not yet been developed to the point that they can reproduce the full range of behaviour observed in the tensile tests over the range of temperatures and elongation rates which are reported in the thesis. Instead, the results of the tensile tests are fitted to a simple bilinear material model by back-analysis of the tensile tests to give three stiffness and strength parameters that vary with temperature and strain rate. Non-linear finite element analyses of PVB membranes corresponding to two series of laminated glass blast trials are used to produce single degree of freedom parameters for membrane response. The blast trials are reported, and back-analysis of the deflection histories is used to estimate the ratio of the PVB material strain rates and the observed laminated glass strain rates for the best-fit calculated response. This ratio, found to have a mean value of 3.8, is expected to reflect the stiffening of PVB by attached glass fragments, together with other factors. However, the scatter in the data is large, so the reliability of this figure should be viewed with this in mind. Laminated glass providing blast protection is normally maintained close to room temperature, so a design based on a room temperature of 23ºC is proposed, using single degree of freedom data that is a composite of the uncracked data up to cracking and the membrane data after that point. For normal laminated glazing where the observed strain rate is expected to be about 10 /s, design membrane properties based on a PVB strain rate of 40 /s are proposed, but this may need to be modified for other cases. Typical design cases for marginal behaviour are analysed on this basis, and also for material properties at temperatures 6ºC higher and lower than 23ºC, to assess the sensitivity of the design to likely temperature variations. These indicate that a margin of 16-21% may be needed on deflection limits to allow for temperature increases, but that the calculated deflections would still be below the maximum deflections observed in the trials without PVB failure. The analyses indicate that the peak reactions are unlikely to be sensitive to temperature. However, they indicate that a margin of safety of 2.4 will need to be incorporated in the design anchorage strength to resist in-plane tension in the PVB membrane at reduced temperature. The thesis develops an improved design method under blast loading for laminated glass and double glazing incorporating laminated glass, although some of the values used in the method should be considered tentative. The thesis also indicates a level of anchorage strength sensitivity to temperature reductions that needs to be taken into account in practical glazing designs.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The automated analysis and design of underground concrete nuclear shelters

Two topics are covered in this thesis; the implementation of the SemiLoof shell element into ANSYS and a .finite element analysis of an underground nuclear shelter subjected to a blast load, using SemiLoof shells. The SemiLoof Shell is an eight noded, isoparametric, thin shell element. Its main advantage over its competitors is its faster matrix calculation and solution time due mainly to the fact that it has only 32 degrees of freedom (3 translationals at each node, plus 2 rotationals at each midside node), rather than the usual 48 degrees of freedom (6 at each node). The User Element Utility was used to link the original SemiLoof Fortran subroutines into ANSYS as a linear element. As these subroutines were already available, the main task was to design and write interfacing subroutines which were required to translate parametric and array names, serve subroutine callingmarguments and overcome inconsistencies in the arrangement of the ANSYS/SemiLoof degree of freedom sets. The original SemiLoof calculations are limited to displacements, element forces and bending moments, hence further stress calculation subroutines had to be written in order to make the element of practical use to the engineer. SemiLoof is referenced by ANSYS as Stif100 can be used in the same way as any other ANSYS element. All the linear analysis types, pre- and postprocessing features and wave front solution are available for use by SemiLoof, which can also be mixed with other ANSYS elements having a suitable degree of freedom set. Benchmark tests on SemiLoof in ANSYS have shown it to be a quick and accurate performer and a useful alternative to ANSYS's eight node thin shell - Stif93. SemiLoof in ANSYS was then used to analyse an underground, reinforced concrete nuclear shelter, subjected to an impulsive blast load. The aim of this analysis was to determine if the design data-bending moments were of a realistic magnitude. The SemiLoof analyses showed that they were less than adequate and that the shelter is probably slightly underdesigned. It suggested in this thesis that the design criteria of moderate damage was unsuitable for the purposes of the shelter and that it would be advantageous to design the shelter so that it would remain in good condition after the blast load, and thereby service the basic needs of comfort and hygiene for the occupants

Analytical and Experimental Evaluation of Precast Sandwich Wall Panels Subjected to Blast, Breach, and Ballistic Demands

Due to heightened security concerns federal as well as many public facilities require some level of blast design, whether it be intentional or accidental. In addition, with the increasing cost in utilities and continuous rise in global warming, a movement has begun to streamline the construction process and limit the environmental footprint of every building. In response, the federal government now requires that all government buildings not only be designed for blast loads, but also sustainability.Insulated wall panels are capable of meeting both the blast and sustainable requirements due to the inherit strength of a reinforced concrete slab and the thermal resistance provided from the insulating layer; however, limited experimental testing is available to prove that insulated wall panels are an ideal system for both blast and sustainability. The objective of this research is to develop the tools to design a blast and ballistic resistant insulated wall panel system. As part of this research, experimental tests were conducted on insulated panels to validate models developed to predict panel behavior observed. Using the results of the research an approach was developed to create a 1) Thermally efficient, 2) Blast Resistant, 3) Spall/Breach Resistant and 4) Ballistic Resistant panel.Insulated wall panels are inherently thermally resistive due to the insulating foam located between the two layers of concrete. Parametric studies were performed via analytical calculations to determine the efficiency of the wall system. The calculations indicated that the insulating layer is fundamental to the resistance of the panel; an 8in. solid concrete panel had a thermal resistance of less than 10% of a panel 2in. of insulation sandwiched between two 3in. concrete wythes. Additionally, the parametric study indicated that the shear connectors located between the interior and exterior wythes can have a significant effect on the overall panel thermal resistance due to the thermal bridging phenomenon. Three panels were modeled with identical layout and wythe connectors with identical dimensions but different material: concrete, steel, and low-conductive material. The panel with concrete and steel wythe connectors saw a reduction in thermal resistance compared to the low-conductive material of nearly 78% and 62%respectively. Thus, to decrease the panel resistance while maintaining strength, a strong thermally resistive material must be used as a shear connector.To improve the response to far-field detonations, experimental tests were performed on small solid panels as well as larger insulated panels. Locally unbonding the small solid panels allowed the panel to reach support rotations past the 10° specified by the United States Army Corps of Engineers as the highest threat level while the bonded panels reached less than 5° before softening. Additionally, testing of insulated wall panels revealed that the panel behavior is highly dependent on the shear tie constitutive property and location along the span. A numerical model was created to predict the behavior of an insulated and as a result, a new shear tie was developed to improve the flexural response of the panel while at the same time, decreasing the production cost.To assess the response of insulated wall panels to close-in detonations, experimental tests and numerical models were conducted. The tests revealed that the insulation results in a detriment to panel performance as a panel with 2in. of insulation sandwiched between two 3in. thick concrete wythes breaches the exterior wythe while a 6in. thick solid concrete panel does not breach under the same demand. As the insulating layer thickness is increased, the panel does not breach due to the increased standoff created by the additional thickness. Additionally, the empirical formulas developed by the Unified Facilities Criteria for solid panels were shown to be inaccurate when used for insulated wall panels, while numerical simulations were able to bound the response of an insulated wall panel.To investigate the performance of insulated wall panels to ballistic and fragment demands, a probabilistic method was developed. The method results in the creation of fragility curves allowing a designer to assess the probability of perforation and residual velocity for a given threat at any wall thickness. Additionally, the likelihood of injury occurring to personnel behind the wall panel was assessed by using organ threshold tolerances provided in literature. Using the method developed, engineers can design the thickness of an insulated wall panel to achieve an acceptable probability of occurrence for injury.Finally, all of the material learned through the first four stages were combined to create a comprehensivedesign example. An 8in. thick panel with 2in. of insulation was designed using the newly designed shear tie as well as a ductile shear tie with the same strength, and then subjected to the demands reviewed throughout the research project. The tie system allowed the wall to reach a support rotation of 10° while behaving in a moderate to heavy damage level when subjected to the far-field detonation demand. From the conclusions of the close-in detonation study, the panel is known to breach under the load prescribed. Ballistic fragility curves were developed showing that the panel stops a low threat ballistic with 100% certainty, but under a high ballistic threat the projectile has an 86.5% chance of perforating the wall system. For the fragmenting munition considered in the study, the wall system has a 15.4% chance of causing injury to personnel behind the wall. Finally, by using the new shear tie system developed, the wall system results in a reduction of less than 3% in the total R-value when compared to an insulated panel without thermal bridges due to the low thermal conductivity of the shear tie material

A review of experimental and analytical studies on the out-of-plane behaviour of masonry infilled frames

This paper presents a literature review of research undertaken on the out-of-plane behaviour of masonry infilled frames. This paper also discusses the effects of bidirectional loads, openings, slenderness, boundary conditions etc. As numerous researchers have reported, these effects play a crucial role in achieving arching action cause, as they can bypass or limit its effectiveness. Namely, arching action leads to additional compressive forces which resist traversal ones. This is confirmed by inertial force methods of testing, while the same cannot be claimed for inter-storey drift or dynamical methods. It is to be acknowledged that most experimental tests were carried out using inertial force methods, mostly with the use of airbags. In contrast, only a few were undertaken with dynamical methods and just two with inter-storey drift methods. It was found that inertial force and inter-storey drift methods differ widely. In particular, inertial force methods damage the infill, leaving the frame more or less intact. Conversely, drift heavily damages the frame, while infill only slightly. Openings were investigated, albeit with contrasting results. Namely, in all cases, it was found that openings do lower the deformational but not all load-bearing capacities. Furthermore, analytical models have shown contrasting results between themselves and with experimental data. Models’ stabilities were checked with single- and multi-variable parametric analysis from which governing factors, influences of frame and other parameters were identified

Direct Strength Method and Response of Cold-Formed Steel Storage Rack Uprights in Global Biaxial Bending

This study seeks to investigate the global (lateral-torsional) buckling capacity of cold-formed steel (CFS) storage rack uprights under biaxial bending. A previously validated biaxial bending numerical model for local and distortional buckling of CFS rack uprights is used for global buckling. Biaxial bending response of nine unperforated upright cross-sections, each with nine different biaxial bending configurations, were considered. The findings demonstrate that the biaxial bending of the investigated uprights is governed by a nonlinear interaction behavior. DSM predictions including the classical method and the use of inelastic reserve capacity are compared to numerical capacities. The use of the DSM with inelastic reserve capacity as in the AISI-S100 and AS/NZS 4600, results in an overall 3% improvement of the predictions when compared with the classical DSM. A new extended range of the inelastic reserve capacity for global buckling is proposed. When compared with the classical DSM approach, the new extended range results in 14% improvement of the DSM predictions

Active thermography for the investigation of corrosion in steel surfaces

The present work aims at developing an experimental methodology for the analysis of corrosion phenomena of steel surfaces by means of Active Thermography (AT), in reflexion configuration (RC). The peculiarity of this AT approach consists in exciting by means of a laser source the sound surface of the specimens and acquiring the thermal signal on the same surface, instead of the corroded one: the thermal signal is then composed by the reflection of the thermal wave reflected by the corroded surface. This procedure aims at investigating internal corroded surfaces like in vessels, piping, carters etc. Thermal tests were performed in Step Heating and Lock-In conditions, by varying excitation parameters (power, time, number of pulse, ….) to improve the experimental set up. Surface thermal profiles were acquired by an IR thermocamera and means of salt spray testing; at set time intervals the specimens were investigated by means of AT. Each duration corresponded to a surface damage entity and to a variation in the thermal response. Thermal responses of corroded specimens were related to the corresponding corrosion level, referring to a reference specimen without corrosion. The entity of corrosion was also verified by a metallographic optical microscope to measure the thickness variation of the specimens