Composite materials are increasingly being used in a wide range of structural applications. These applications range from bicycle frames and building facades to hulls of marine ships. Their popularity is due to the high specific strength and stiffness properties, corrosion resistance, and the ability to tailor their properties to a required application. With the increasing use of composites, there is a need to better understand the material and damage behaviour of these structures. In recent years, the increased frequency of wars and terror attacks have prompted investigations into composite failure processes resulting from air-blast. Most of the research has been focused on flat panels, whereas there is relatively little on curved structures. This dissertation reports on the effect of air-blast loading on concave, singly curved fibre reinforced sandwich and composite panels. Sandwich panels and equivalent mass glass fibre laminates were manufactured and tested. Three types of curvature namely a flat panel (with infinite curvature), a curvature of 1000 mm radius and a curvature of 500 mm radius were produced, to determine the influence of curvature on panel response. The laminates were made from 16 layers of 400 g/m² plain weave glass fibre infused with Prime 20 LV epoxy resin. The sandwich panels consisted of a 15 mm thick Airex C70:75 core sandwiched between the 12 layers of 400 g/m² plain weave glass fibre and infused with Prime 20 LV epoxy resin. This arrangement produced a balanced sandwich panel with 6 layers of glass fibre on the front and back respectively. For all panels, vacuum infusion was used to manufacture in a single shot process. Mechanical properties of samples were tested for consistency in manufacturing. It was found that mechanical properties of the samples tested were consistent with low standard deviations on tensile and flexural strength. The panels were tested in the blast chamber flat the University of Cape Town. Blast specimens were clamped onto a pendulum to facilitate impulse measurement. Discs of plastic explosive, with charge masses ranging from 10 g to 25 g, were detonated. After blast testing, a post-mortem analysis of the damaged panels was conducted. Post-mortem analysis revealed that the failure progression was the same irrespective of curvature for both the sandwich panels and the laminates. Sandwich panels exhibited the following failure progression: delamination, matrix failure, core crushing, core shear, core fragmentation, core penetration and fibre fracture. The laminates displayed the following progression: delamination, matrix failure and fibre fracture. Curved panels exhibited failure initiation at lower charge masses than the flat panels. As the curvature increased, the failure modes initiated at lower charge masses. For example, as the charge mass was increased to 12.5 g the front face sheets of the flat and the 1000 mm radius sandwich panels exhibited fibre fracture, but the 500 mm radius sandwich panel exhibited fibre fracture and rupture through the thickness of the front face sheet. The 500 mm radius laminate exhibited front face failure earlier (15 g) than the 1000 mm radius (22.5 g) and flat panel (20 g). Curved laminates exhibited a favoured delamination pattern along the curved edges of the panel for both 1000 mm and 500 mm radii laminates. As the curvature increased, more delamination was evident on the curved edges. The curved panels displayed more severe damage than flat panels at identical charge masses. Curved sandwich panels experienced through thickness rupture at 20 g charge mass whereas the curved laminates did not exhibit rupture at 25 g charge mass. The flat laminates were the most blast resistant, showing no through-thickness penetration at 25 g (the highest charge mass tested) and initiated failure modes at higher charge masses when compared to the other configurations.

Explosive threats have become more prevalent in both military and terrorist theatres of conflict, showing up largely in the form of Improvised Explosive Devices (IED) which are often buried in soil to conceal them and increase their effectiveness. The response of a structure subjected to a blast load is influenced by many factors, namely stand off distance, mass of explosive, degrees of confinement and medium surrounding the charge. This study focuses on characterizing the transient deformation of test plates which have been exposed to different explosive loading conditions including free air blasts (AIR), backed charge (VBP) and buried charge (SBP) configurations. In the three loading configurations, four charge masses are considered, utilizing 10g, 15g, 20g and 25g masses of PE4 plastic explosive which were moulded into cylindrical charges of a constant 38mm diameter. The transient deformation of the test plates was captured using high speed Digital Image Correlation (DIC), which utilized two high speed cameras to record the experiments. Extensive modifications to the blast pendulum to incorporate the cameras was necessary to adapt this technique in a different method to that used in previous literature. The mounting method proposed allowed the cameras to record the experiment while capturing the impulse imparted on a test plate using a blast pendulum. The experimental plates exhibited only Mode I failure, which is plastic deformation, enabling the effect of different loading configurations on the transient and final plate deformation profiles to be identified. Numerical simulations of the experiments were developed to further the understanding of the load arising from the three configurations and the deformation mechanisms involved. The experimental results are used to validate the numerical models, which allow for a better understanding of the evolution of the deformation and strains across the plate. The transient data for the numerical simulation and the experiments were found to match closely. This work clearly shows the effect that the different loading conditions have on the tests plates, specifically the impulse distributions and transient strain in the plates. It was observed in this study that the impulse imparted on a test plate increases with the addition of sand while keeping other test conditions constant. The impulse recorded was observed to increase by 490-540% and 19-100% when compared to AIR and VBP 50mm SOD tests respectively. The loading profile acting on the test plate as a result of the specific impulse changes significantly with the inclusion of sand. The midpoint deflection increases with a decrease in stand off distance, increase in charge mass, increase in level of confinement or the inclusion of an overburden of sand. The observed increase in midpoint deflection of between 90-160% and 30-40% when compared to AIR and VBP 50mm SOD tests respectively was reported. The transient plate profile does not match the final deformation profile.

Structures deform at high strain rates and temperatures when exposed to impulsive loads. To accommodate the macro change there are microstructural changes that occur, i.e., grain morphology and shear banding. Most studies report on macroscopic response, i.e., large inelastic deformation and tearing of the structure, while limited studies have reported on microscopic changes that develop in the structure. The microstructure is directly related to the mechanical properties and performance of the material. Therefore, understanding the effect of high strain rate loadings on the microstructural evolution and subsequent mechanical properties of metals and alloys is necessary for mechanical design. The main objective of this research was to investigate microstructural changes to characterise the strain distribution and plastic deformation, owing to impulsive loading. Features within the microstructure that could be used to characterise deformation included grain size morphology changes, the presence of shear bands and sub-grain networks. The electron backscatter diffraction (EBSD) technique, which used Kikuchi patterns to characterise the strain distribution in the crystal of the deformed material, was also used as a characterisation tool. The first step in the experimental procedure was to select the appropriate material to investigate these microstructural changes. There was also the systematic investigation into the use of single and double heat treatments. These were used to achieve a large equiaxed grain structure, which was desirable from a microstructural point of view but was not desirable for blast-resistant material selection. The two-step heat treatment was concluded to be the most suitable heat treatment for the annealing and homogenisation of the AISI 430 stainless steel plates. The AISI 430 stainless steel plates used were 244 mm by 244 mm in size and had a circular exposed area of 106 mm. These plates were subjected to repeated explosive blasts, using a plastic explosive (PE4). The charge mass was varied for each test and the stand-off distance was kept constant at 150 mm for uniform loads and 13 mm for localised loads. Two plates were selected to investigate the uniform loading scenario. The first plate, a torn plate, used a charge mass of 30 g and one blast and the second plate, an inelastically-deformed plate, used a charge mass of 10 g and was exposed to three blasts. These two plates offered the same overall charge load with a different strain path. A further two plates were chosen for the investigation into the localised loading scenario. One plate, a petalled plate, used a 6 g charge mass and was exposed to two blasts and the second plate, an inelastically-deformed plate, used a 5 g charge mass and was also exposed to two blasts. The latter two plates offered an investigation into the effect of an increased charge load, where charge load affected the strain rate of the deformation resulting from the blast load. All four plates were sectioned across the midline of the dome and then ground and polished to a mirror finish, using OP-S. The polished samples were analysed, using optical microscopy and EBSD. In addition, Vickers hardness tests were carried out along the midline of the sectional plate profiles, in order to evaluate the extent of strain hardening. All the plates showed either a response of inelastically deforming or of complete or partial tearing failures when subjected to blast loads. For inelastic deformation failures, a global dome was characteristic of the uniform loading condition and an inner dome superimposed by the global dome was characteristic of the localised loading condition. Variation of charge mass and the number of blasts showed an increasing linear relationship between the impulse and midpoint deflection. The macrostructure showed a large variation of failures in the localised condition. The microstructural characterisation results produced micrographs showing regions of long, flat grains with multiple sub-grain networks, indicating deformed microstructures of the blast loaded plates. Parts of the microstructures displayed equiaxed/recrystallised grains characteristic of restoration processes, owing to high temperatures. Vickers hardness tests indicated an increase in material hardness as the number of blasts was increased, with a maximum hardness in the central region of the plates. In the first investigation, into uniform loading, the material characterisation results, combined with the fractography results, indicated brittle failure modes typical of high strain rate failures in strain rate sensitive materials, such as the chosen AISI 430 stainless steel plates. In the second investigation, into localised loading, the material characterisation results, combined with the fractography results, indicated a more ductile failure, owing to a 1 g incremental increase of charge mass, which confirmed the strain rate sensitivity of this material.

Detonation of an explosive charge, such as a mine or an improvised explosive device (IED) at the ground surface or buried at shallow depth in soil, can produce high airblast pressures and significant dynamic soil debris loads on an overlying or nearby structure, such as a vehicle passing over the explosive. The blast loading environment is a function of many factors including the explosive type, configuration, mass, and depth of burial, soil characteristics, and the distance between the ground surface and the structure or object. During the past several years, the US Army has focused considerable attention on developing improved methods for predicting this environment, particularly for use by vehicle/armor analysts, thereby, improving the survivability of these platforms. Research is needed to better understand the aboveground environment created by the detonation of a shallow-buried explosive in order to design adequate protective measures for an aboveground structure. Unfortunately, there is no accurate methodology for predicting these airblast and soil debris loads to support the designs. Development of the required prediction tools is hampered by lack of well controlled and documented experimental results for these complex loads. Without detailed experimental data, the numerical simulations of these loads cannot be adequately validated for the large deformation, stress, and motion gradients and the resulting interactions with structures. The focus of this research is to quantify the influence of soil properties on the aboveground environment from the detonation of a bare explosive charge resting on the soil surface or shallow-buried. In order to fully quantify the influence of soil parameters, well-controlled experiments were designed to directly measure soil debris and airblast loadings on an aboveground reaction structure due to the detonation of explosives at the surface of and shallow buried in three very different soils. The experiments were performed using specifications and strict quality controls that limited the influence of outside variables and ensured the experiments were repeatable. The experiments provided blast pressure, soil stress, and impulse data for each soil type. These data were analyzed to investigate the influence of the properties of the different soil types on the aboveground environment.

Ultra-high performance fiber-reinforced concrete (UHPFRC) is an advanced cement-based composite with enhanced compressive strength, tensile resistance and toughness when compared to conventional concrete. Interest in the application of UHPFRC as a retrofit material has been rapidly increasing, and a few existing studies have examined the ability of UHPFRC to retrofit and strengthen existing reinforced concrete (RC) structures under static loading; however, very limited studies have examined the effectiveness of UHPFRC to improve the response of RC members under blast loading. This thesis aims at filing this research gap and investigates the behavior of UHPFRC retrofitted RC flexural members under both static and blast loads. A total of twenty-one (21) specimens, in two different series are tested. Series 1 includes nine (9) singly-reinforced beams built with high-strength concrete (HSC) and strengthened by UHPFRC to improve shear and flexural behaviour. Series 2 includes a further twelve (12) doubly-reinforced beams/columns built with normal-strength concrete (NSC), and strengthened by UHPFRC to improve response under blast, or combined blast-axial loading. Various test parameters are examined including the effects of varying retrofit types (full jacket, U-jacket or T-sided), surface roughening methods, longitudinal steel reinforcement ratio, single vs. repeated blasts, and the effects of axial loading. The results from this thesis are presented in six journal articles. Papers 1 and 2 study the effects of UHPFRC jacketing on the static and blast behaviour of the singly-reinforced HSC beams in Series 1, while Paper 3 discusses the effects of additional parameters such as: the effect of retrofit type, roughening method and steel detailing on blast behaviour. Under static loading (Paper 1), the UHPFRC jacketing was found to be effective in increasing shear resistance (by preventing shear failure), and improving flexural behaviour (by increasing strength, stiffness, ductility and overall toughness) when compared to control beams built without UHPFRC. Similarly, under blast loads (Paper 2) the use of UHPFRC jacketing prevented shear failure, and improved flexural behaviour by reducing displacements at equivalent blasts, increasing overall blast capacity, and improving damage tolerance. On the other hand, the results show that UHPFRC-retrofitted beams with low longitudinal steel ratios may be vulnerable to brittle bar fracture failures. As part of the numerical research, finite element (FE) modelling is used to predict the static and blast behaviour of the test beams using software LS-DYNA (Papers 1 and 2). The results from Paper 3, provide further insights into the effects of retrofit type (FJ, UJ and T) and roughening method on blast performance; both the UJ and FJ retrofits were found to be effective in increasing shear resistance, reducing blast-displacements and increasing blast capacity, while the benefit of the T-sided retrofit was limited by the crushing capacity of HSC concrete. The effect of roughening method was found to be negligible, except at the very late stages of blast loading. Papers 4, 5 and 6 present the experimental results from the doubly-reinforced NSC beams tested in Series 2, with a focus on the effect of UHPFRC jacketing, UHPFRC retrofitting type and Axial loading, respectively. Paper 4 shows that the UHPFRC jacketing increased the stiffness and strength of the beams under both static and blast loading, however the high bond capacity of the UHPFRC and relatively low tension steel ratio increased the vulnerability of bar rupture failure. The numerical parametric study investigates the effects of steel ratio and blast load scenario, jacket thickness and interface location on blast performance and failure model. Paper 5 confirms that the blast performance of the beams is influenced by the retrofit type, with optimal performance obtained when using full- or U-jacketing. The efficient use of localized "hinge" retrofits was also found to be effective, and reduced the vulnerability to bar rupture. The numerical parametric study investigates the effects of steel ratio and blast load scenario (single vs. repeated) on the blast performance of the beams. Paper 6, studies the effect of UHPFRC jacketing in columns tested under combined axial and blast loading. The retrofit is shown to increase blast capacity and reduce blast-induced displacements and damage, though the final failure of the columns was governed by bar rupture. As part of the numerical parametric study the effects of axial load ratio, boundary conditions, steel ratio, jacket thickness and jacket design are studied numerically and found to have significant effects on blast behaviour and failure mode.

No description available.

Heavy timber construction is emerging as a viable alternative to conventional building materials, such as steel and concrete, for mid- and high rise structures. With the increasing presence of timber structures at or near potential targets comes an increased risk for damage to the structure and more importantly human casualties. The current provisions related to wood in the blast code (CSA, 2012) are limited and based on general understanding of the material behaviour rather than thorough research studies. Also, the standard does not clearly distinguish between the various types of engineered wood products. A study was undertaken to assess the behaviour of cross-laminated timber panels subjected to simulated blast loading using a shock tube apparatus. More specifically, the aim of this study was to investigate the behaviour of CLT panels subjected to static and dynamic loads to determine a dynamic increase factor in order to quantify high strain rate effects on this material. Testing was completed on a total of 18 CLT panels, with panel thicknesses of 105 and 175 mm corresponding to a 3-ply and 5-ply panel, respectively. An average dynamic increase factor of 1.28 on the resistance and no apparent increase in stiffness from static to dynamic loading were observed. Two resistance material predictive models that account for high strain-rate effects and the experimentally observed post-peak residual behavior were developed. A single degree-of-freedom model was validated using full-scale simulated blast load tests, and the predictions were found to match well with the experimental displacement-time histories.

High-strength steel (HSS) conforming to ASTM A1035 is becoming increasingly used in various structural applications, including in high-rise buildings and bridges. Due to their chemistry and manufacturing process, ASTM A1035 steel bars result in a combination of high tensile strength to yield ratio and varying levels of corrosion resistance. One potential application of ASTM A1035 bars is in the blast-resistant design of concrete structures, where their use can allow for reduced steel congestion, and increased blast resistance. Despite their high initial cost, stainless steel (SS) reinforcing bars are also seeing increased use in concrete construction. Solid stainless steel bars are referenced in ASTM A955, which is applicable to various stainless steel alloys. In addition to their inherent corrosion resistance, most stainless steel bars possess greater tensile strength, and importantly, exceptional ductility, when compared to ordinary steel reinforcement. This unique combination of strength and ductility makes SS bars well-suited for blast design applications. The overarching aim of this thesis is to gain better understanding of the blast behavior of RC flexural members designed with high-strength (HSS) and stainless steel (SS) reinforcement. This objective is achieved through a combined experimental and numerical research program. As part of the experimental research, a large set of beams, subdivided into three series, are tested under either quasi-static bending or simulated blast loads using the University of Ottawa shock-tube. Series 1 (HSC-HSS) and Series 2 (HSC-SS) aim at examining the effects of blast detailing (as recommended in modern blast codes,) on the quasi-static, blast and post-blast behaviour of high-strength concrete (HSC) beams reinforced with either ASTM A1035 high-strength bars (8 beams) or ASTM A955 stainless steel bars (16 beams). In addition to the influence of detailing, the effects of steel grade/type, steel ratio and steel fibers are also studied. Series 3 further studies the benefits of combining higher grade or higher ductility reinforcement, with more advanced ultra-high performance concrete (UHPC). This series includes 20 UHPC beams built with either ordinary, HSS or SS reinforcing bars (UHPC-NSS, UHPC-HSS and UHPC-SS). In addition to the effect of steel grade/type, concrete type, steel ratio and steel detailing are also studied. The results from Series 1 and 2 demonstrate the benefits of implementing high-strength and stainless steel reinforcement in HSC beams subjected to blast loads, where their use leads to increased blast capacity, reduced support rotations, and higher damage tolerance. The results further demonstrate the benefits of “blast detailing” on the ductility and resilience of such beams, under both static and blast loads. The results also show that the use of steel fibers can be used to relax blast detailing in the beams with high-strength or stainless steel by increasing the required tie spacing from d/4 to d/2. The results from Series 3 confirm that the use of UHPC in beams enhances flexural response (in terms of strength and stiffness), which in turn results in superior blast resistance. Conversely, the high bond capacity of UHPC makes such beams more vulnerable to bar fracture. Increasing the steel ratio is found to effectively increase the failure displacement and ductility of the UHPC beams. The use of high-strength steel is found to increase load capacity and blast resistance, while the use of stainless steel results in remarkable ductility, which further enhances beam response under blast loading. As part of the numerical research program, the static and blast responses of the test beams are simulated using either 2D or 3D finite element (FE) modelling, using software VecTor2 and LS-DYNA. The numerical results show that the 2D FE modelling using software VecTor2 can provide reliable predictions of the static and blast responses of the HSS or SS reinforced HSC beams built with varying detailing, in terms of load-deflection response, cracking patterns, failure mode, displacement time histories and dynamic reactions. Likewise, the 3D FE modelling using software LS-DYNA with appropriate modelling of UHPC (using the Winfrith Concrete or CSCM models) can well predict the blast responses of UHPC beams with ordinary, high-strength and stainless steel, in terms of displacement/load-time histories, damage and failure modes.

<p> This study deals with a method of analysis and the associated computer program that can capture the full nonlinear response of twodimensional reinforced concrete and steel plane frames subjected to dynamic loads, including blast and impact. Most of the relevant parameters that are normally neglected by similar available analysis tools have been considered in the present study. These include tension stiffening and concrete cracking, confinement effect and strain rate effect. Interaction between axial and bending deformations has also been accounted for. Four different constitutive models for concrete have been used and compared to each other together with multiple formulae accounting for the strain rate effect. The proposed analysis procedure was verified against other sophisticated software and experimental results and has proven to be a reliable means of analysis. </p> <p> The strain rate effect is shown to be a key parameter that plays an important role in the overall behaviour of structures under blast loads. Neglecting this effect does not necessarily lead to a more conservative design because it increases the overall stiffness of the structure which causes it to attract higher forces. This increase is proportional to the strain rate, which makes it particularly important in the case of blast loading where the strain rate can reach up to 1000 sec⁻¹. </p> / Thesis / Master of Applied Science (MASc)

The behavior of cryogenic double-walled pressure vessels, such as thoseused in space launch vehicle infrastructure, under blast loading is a somewhatunderstudied topic. This is of interest due its implications on, among otherthings, launch site design and safety in the event of a launch vehicle failure.The detonation of a 100 kg charge of TNT at a distance of 1 m from a simplifiedmodel of a horizontal cryogenic (double-walled) pressure vessel was simulatedusing Ansys Mechanical and AUTODYN. As a result, the inner and outershells of the pressure vessel underwent significant deformation which, in thecase of the outer shell, reached one third of its radius. No rupture occurred.Various other structural parameters, such as von Mises equivalent stress, strain,and element velocity were also studied. The results presented in this reportimply that cylindrical cryogenic pressure vessels are highly resistant to blastoverpressure, but does not take surrounding piping, valves, supports, and other infrastructure into account.