Recent terrorist attacks on critical infrastructures using car bombs have heightened awareness on the needs for blast resistance of structures. Blast design of civilian buildings has not been a common practice in structural design. For this reason, there is now an urgent need to mitigate the potentially devastating effects of blast shock waves on existing structures. The current research project, the results of which are reported in this dissertation, aims to expand knowledge on blast resistance of reinforced concrete building columns, while developing a technology and design procedure for protecting critical buildings columns against the damaging effects of impulsive blast loads through the use of externally applied fibre-reinforced polymer (FRP) jackets of different material architecture. The research project has a significant experimental component, with analytical verifications. A total of thirty two reinforced concrete columns were experimentally investigated under the effects of simulated blast loads using the University of Ottawa Shock Tube. Column dimensions were 150 mm x 150 mm in cross section and 2438 mm in length. Each concrete column was reinforced longitudinally with four 10M rebars which were tied laterally with 6.3 mm closed steel hoops, spaced at 37.5 mm and 100 mm c/c, representing seismic and non-seismic column details, respectively. The experimental research had two phases. Phase-I (sub-study) included blast tests of eight as-built, seismically detailed columns. The behaviour of these columns was explored under single and multiple blast shots, with and without the application of pre-blast axial loads. Phase-II (main-study) included column tests of different carbon FRP (CFRP) designs to investigate the significance of the use of different CFRP column jacket designs on dynamic response of twenty four seismic and non-seismic RC columns. Analytical investigation was conducted to assess and verify the significance of experimentally investigated parameters on column response. These included the use of Single-Degree-of-Freedom (SDOF) dynamic inelastic analysis, generation of dynamic resistance functions, the effects of variable axial loads, different plastic hinge lengths and the influence of secondary moments (P- moments) on column behaviour. The results indicate that the loading history has effects on column response, with multiple shots reducing column stiffness, and affecting dynamic response of columns relative to single blast shots of equivalent magnitude. The effect of concrete strength within the normal-strength concrete range is to increase strength and decrease deformations. Columns with CFRP jackets have considerable improvements in column deformability, with additional increases in column strength. The CFRP laminate design influences performance, with jackets having fibres in ±45o orientation especially improving column ductility and increasing plastic hinge lengths, thereby permitting redistribution of stresses and dissipating blast energy. Axial gravity loads vary during blast loads and can affect column strength. It was shown that SDOF dynamic inelastic analysis does capture key structural performance parameters in blast analysis. The consideration of experimentally observed parameters in column analysis; including the influence of CFRP design and associated change in plastic hinge length, variable axial load during response, and secondary moment (P- moments) result in significant improvements in the accuracy of blast analysis. The experimental results and the suggested improvements to the SDOF analysis technique can be used to implement a performance-based design approach recommended as part of the current research project for design of CFRP protection systems for concrete columns.This research project was conducted jointly by the National Research Council Canada (NRC) and the University of Ottawa.

This thesis describes the simulation of ERDC’s Blast Load Simulator (BLS) using MSU’s Loci/BLAST. The BLS was created to replicate waveforms found in blast scenarios. Loci/BLAST is an explicit, unstructured CFD code that specializes in moving waveforms. ERDC conducted various tests, and a grid for each scenario was created using the SolidMesh tool. Each grid was simulated, and the results were displayed as time history plots and spatial plots. Simulations were also performed that compared 2D and 3D grids and determined the effect of the grate and striker components. There was a strong correlation between the experimental and simulation results for each case, demonstrating that Loci/BLAST is fully capable of modeling the BLS waveforms. A 2D grid produced results comparable to those on a full 3D grid. The grate and striker were critical in the simulation because they significantly affected the waveform.

A three-dimensional finite element code to analyze coupled thermomechanical deformations of composites has been developed. It incorporates geometric nonlinearities, delamination between adjoining layers, and damage due to fiber breakage, fiber/matrix debonding, and matrix cracking. The three damage modes are modeled using the theory of internal variables and the delamination by postulating a failure envelope in terms of the transverse stresses; the damage degrades elastic moduli. The delamination of adjoining layers is simulated by the nodal release technique. Coupled nonlinear partial differential equations governing deformations of a composite, and the pertinent initial and boundary conditions are first reduced to coupled ordinary differential equations (ODEs) by the Galerkin method. These are integrated with respect to time with the Livermore solver for ODEs. After each time step, the damage in an element is computed, and material properties modified. The code has been used to analyze several static and transient problems; computed results have been found to compare well with the corresponding test results. The effect of various factors such as the fiber orientation, ply stacking sequence, and laminate thickness on composite's resistance to shock loads induced by underwater explosions has been delineated. / Ph. D.

The MSU Loci/BLAST CFD code was used to study blast wave interactions with structures for different urban environments. A series of analyses which included single building structures inside of ERDC's Blast Load Simulator (BLS) with different obliquity orientations to the flow direction, two building structures inside the BLS with varying gap distances between the structures, and open air blast simulations with four structure scenarios at different building spacings and different blast orientations were performed. Unstructured and overset grid techniques were used during the modeling process and were compared for consistency with shock physics and computational performance. Results show Loci/BLAST's capability to accurately model blast wave interactions in urban environments for both unstructured and overset grids.

The present work describes the finite element (FE) modeling and dynamic response of lightweight, deployable shelters (tent) to large external blast loads. Flexible shelters have been used as temporary storage places for housing equipments, vehicles etc. TEMPER Tents, Small Shelter System have been widely used by Air Force and Army, for various field applications. These shelters have pressurized Collective Protection System (CPS), liner, fitted to the frame structure, which can provide protection against explosives and other harmful agents. Presently, these shelter systems are being tested for the force protection standards against the explosions like air-blast. In the field tests carried out by Air Force Research Laboratory, it was revealed that the liner fitted inside the tent was damaged due to the air blast explosion at some distant from the structure, with major damage being on the back side of the tent. The damage comprised of tearing of liner and separation of zip seals. To investigate the failure, a computational approach, due to its simplicity and ability to solve the complex problems, is used. The response of any structural form to dynamic loading condition is very difficult to predict due to its dependence on multiple factors like the duration of the loading, peak load, shape of the pulse, the impulse energy, boundary conditions and material properties etc. And dynamic analysis of shell structures pose even much greater challenge. Obtaining solution analytically presents a very difficult preposition when nonlinearity is considered. Therefore, the numerical approach is sought which provide simplicity and comparable accuracy. A 3D finite element model has been developed, consisting of fabric skin supported over the frames based on two approaches. ANSYS has been used for obtaining the dynamic response of shelter against the blast loads. In the first approach, the shell is considered as a membrane away from its boundaries, in which the stress couple is neglected in its interior region. In the second approach, stress coupling is neglected over the whole region. Three models were developed using Shell 63, Shell 181 and Shell 41. Shell 63 element supports both the membrane only and membrane-bending combined options and include stress stiffening and large deflection capabilities. Shell 181 include all these options as Shell 63 does and also, accounts for the follower loads. Shell 41 is a membrane element and does not include any bending stiffness. This element also include stress stiffening and large deflection capabilities. A nonlinear static analysis is performed for a simple plate model using the elements, Shell 41 and Shell 63. The membrane dominated behavior is observed for the shell model as the pressure load is increased. It is also observed that the higher value of Young's modulus (E) increases the stresses significantly. Transient analysis is a method of determining the structural response due to time dependent loading conditions. The full method has been used for performing the nonlinear transient analysis. Its more expensive in terms of computation involved but it takes into account all types of nonlinearities such as plasticity, large deflection and large strain etc. Implicit approach has been used where Newmark method along with the Newton-Raphson method has been used for the nonlinear analysis. Dynamic response comprising of displacement-time history and dynamic stresses has been obtained. From the displacement response, it is observed that the first movement of the back wall is out of the tent in contrast to the other sides whose first movement is into the tent. Dynamic stresses showed fluctuations in the region when the blast is acting on the structure and in the initial free vibration zone. A parametric study is performed to provide insight into the design criteria. It is observed that the mass could be an effective means of reducing the peak responses. As the value of the Young's Modulus (E) is increased, the peak displacements are reduced resulting from the increase in stiffness. The increased stiffness lead to reduced transmitted peak pressure and reduced value of maximum strain. But a disproportionate increase lead to higher stresses which could result in failure. Therefore, a high modulus value should be avoided. / Master of Science

[Truncated abstract] As a consequence of the increase in terrorist incidents, many comprehensive researches, both experimental and numerical modelling of structure and blast interaction, have been conducted to examine the behaviour of civilian structures under dynamic explosion and its impact. Nevertheless most of the works in literature are limited to response of simple structures such as masonry walls, reinforced concrete beams, columns and slabs. Although these studies can provide researchers and structural engineers a good fundamental knowledge regarding blast load effect, it is more likely for blast load to act upon entire structures in actual explosion events. The interaction between blast load and structures, as well as the interaction among structural members may well affect the structural response and damage. Therefore it is necessary to analyse more realistic reinforced concrete structures in order to gain an extensive knowledge on the possible structural response under blast load effect. Among all the civilian structures, bridges are considered to be the most vulnerable to terrorist threat and hence detailed investigation in the dynamic response of these structures is essential. This thesis focuses on the study of the response of a modern cable-stayed bridge under blast loadings. ... Firstly, analysis is conducted to examine the failure of four main components namely pier, tower, concrete back span and steel composite main span under close proximity dynamic impact of a 1000 kg TNT equivalent blast load. Secondly, based on such results, the remainder of the bridge structure is then tested by utilizing the loading condition specified in the US Department of Defence (DoD) guideline with the aim to investigate the possibility of bridge collapse after the damage of these components. It is found that failure of the vertical load bearing elements (i.e. pier and tower) will lead to catastrophic collapse of the bridge. Assuming that terrorist threat cannot be avoided, hence protective measures must be implemented into the bridge structure to reduce the damage induced by explosive blast impact and to prevent bridge from collapse. As such, a safe standoff distance is determined for both the pier and tower under the blast impact of 10000 kg TNT equivalent. This information would allow the bridge designer to identify the critical location for placing blast barriers for protection purpose. For the case of bridge deck explosion, carbon fibre reinforced polymer (CFRP) is employed to examine in respect of its effectiveness in strengthening the concrete structure against blast load. In this research, appropriate contact is employed for the numerical model to account for the epoxy resin layer between the CFRP and concrete. In addition, to ensure that the CFRP can perform to its full capacity, anchors are also considered in the numerical study to minimize the chance of debonding due to the weakening of the epoxy. The results reveal that although severe damage can still be seen for locations in close proximity to the explosive charge, the use of CFRP did reduce the dynamic response of the bridge deck as compared to the unprotected case scenario. Further investigation is also carried out to examine the change in damaged zone and global response through variation in CFRP thickness.

In this thesis, the dynamic structural response of six scaled flexural masonry walls to scaled blast loading is experimentally investigated. These walls have been tested in at an open range with charge masses ranging from 5 kg to 25 kg of Pentex-D explosive material with a TNT equivalency of 1.2, and with a constant stand-off distance of 5 m throughout testing. The field properties of the blast wave, which includes the reflected and free field pressures, were recorded. Additionally, the displacement response histories of the wall over the blast test were recorded and the post-blast damage was documented. This study puts forth several potential models for the analysis of the experimental data. The experimentally obtained blast characteristics were compared to predictions of the Kingery and Bulmash (K-B) model. The strain rates used during the study are equivalent to those developed by a number of studies for the materials used in the construction of the specimens. The results obtained through the experimental program are compared to those from a variety of single degree of freedom models, ranging from simplified linear relationships to complex stress-strain relations accounting for the effects that arise because of the increased strain rate due to blast testing. The simplified model assumes a constant stiffness, mass, and triangular pressure profile to determine the peak deflection of the specimen during an experimental test. The bilinear and nonlinear models are based on the discretization of the wall sections into a number of layers, and using strain-rate dependent, stress-strain relations of the constituent materials to generate stresses within the layers. These stresses then iv form the basis of the resistance function to determine the structural response of the test specimens. In this study, the effect of higher modes of vibration on the test specimens is not included. The bilinear and nonlinear models are then implemented to develop Pressure-Impulse (P-I) diagrams, and the effect of the strain rate on P-I diagrams is investigated. The P-I are then available to be implemented into the recent blast code for reinforced masonry flexural walls. The fitted results of the recorded experimental blast pressure parameters are shown to be adequately approximated by the software ConWep in terms of the peak pressure and specific impulse. Comparing the K-B model, which forms the theoretical basis of ConWep, to the raw pressure profile data obtained from the experimental testing, a significant variations is found in the pressure data while significant scatter is found in the impulse. The analytical results show that increasing the nonlinearity of the material accounts for; the response predicted by the single degree of freedom model more closely relates to the response of the specimens. In addition, strain rate effects have a significant impact on the potential level of protection (LOP) provided by masonry flexural walls, as it has a noticeable effect on the curves of the P-I diagram. / Thesis / Master of Applied Science (MASc)

Historical accidents and experimental investigations have made apparent that blast loaded concrete members are prone to fail in brittle shear rather than a ductile flexure mode. Air blasts from accidental detonations or explosives may cause severe damage to buildings and infrastructure and it is of great importance that load carrying members can withstand the impulse that arise to avoid progressive collapses. The aims of this thesis are, through explanation of blast loads as dynamic loads acting on structures and measuring of the effects of blast loads on reinforced concrete beams with shear reinforcement, to understand the mechanisms governing shear failure. Two hypotheses are therefore tested: That for a reinforced concrete beam with shear reinforcement, the mechanism governing dynamic shear failure is similar to that of static shear failure and that blast induced shear failure in reinforced concrete beams can be prevented through a sufficient amount of shear reinforcement. To meet the stated aims and test the hypotheses, a literature study was conducted together with numerical simulations using explicit non-linear finite element analysis software LS-Dyna.Previous experimental investigations on blast loaded reinforced concrete beams have displayed a possible shift in failure mode from a ductile flexural failure at static loading to a brittle shear failure at dynamic loading. The shifting may be a property of higher exciting frequencies of blast loads, inducing modes of vibration with larger portions of shear energy. The results obtained from the numerical analyses indicated that an increased ratio of shear reinforcement reduces the risks of a brittle shear failure as well as decrease beam deflections and concrete strains, while increasing strains in the tensile reinforcement.Analysis of the shear capacity and shear reinforcement design through methods given in Eurocode 2 and FKR 2011 were considered as supplementary to the FE analysis. FKR 2011 provided accurate estimations of the maximum dynamic support reactions. Eurocode 2 uses a more conservative approach resulting in lower values of the design shear strength.The conclusions are that for the given beam and blast load, brittle shear failures may be prevented through reduction of the spacing and increase of the bar diameter of the shear reinforcement. The increased plastic strain of the tensile reinforcement as well as measurements of shear crack widths, support reactions and strains in the concrete suggests that the beams with large ratio of shear reinforcement exhibit more ductile behaviour without reaching failure. / Historiska händelser och experimentella undersökningar har gjort gällande att betongelement utsatta för luftstötvåg är benägna att gå till spröda skjuvbrott snarare än sega böjbrott. Luftstötvågor från oavsiktliga detonationer eller explosivt gods kan orsaka svåra skador på byggnader och anläggningar och det är därför viktigt att bärande strukturer kan motstå impulsen som uppstår för att fortskridande ras ska undvikas. Målen med detta examensarbete är att, genom att förklara det dynamiska beteendet hos luftstötvågor som belastar konstruktioner och mätning av de effekter som uppstår av luftstötvågor på armerad betong med tvärkraftsarmering, förstå de mekanismer som ligger till grund för skjuvbrott. Som påföljd testas två hypoteser: Att mekanismerna som ligger till grund för dynamiska skjuvbrott hos armerade betongbalkar med tvärkraftsarmering är liknande som för de som styr statiska skjuvbrott, och att skjuvbrott till följd av luftstötvågor kan förhindras genom att förse balken med tillräcklig tvärkraftsarmeringsinnehåll. För att nå målen och testa hypoteserna så genomfördes en litteraturstudie tillsammans med numeriska simuleringar med explicit icke-linjär finita elementanalys i kommersiella programvaran LS-Dyna. Tidigare experimentella undersökningar av armerade betongbalkar utsatta för luftstötvåg har visar på en förflyttning i brottmod, från sega böjbrott vid statisk belastning till spröda skjuvbrott vid dynamisk belastning. Förflyttningen kan härstamma från luftstötvågens frekvensinnehåll som framkallar högre vibrationsmoder med större andel skjuvenergi.De erhållna resultaten från de numeriska analyserna indikerar att ett ökat tvärkraftsarmeringsinnehåll minskar risken för spröda skjuvbrott, minskar utböjning och töjningar I balken samtidigt som töjningar i dragarmeringen ökar.Analyser av tvärkraftskapaciteten och dimensionering av tvärkraftsarmering genom metoder givna i Eurocode 2 och FKR 2011 användes som komplement till finita elementanalysen. FKR 2011 gav träffsäkra uppskattningar av de dynamiska störreaktionerna grundade i dynamisk jämvikt. Emellertid var Eurocode 2 det mer konservativa tillvägagångssättet, vilket resulterade i lägre dimensionerande tvärkraftskapacitet. Slutsatserna som drogs var att, för den givna balken och luftstötvågen så kunde spröda skjuvbrott motverkas genom minskning av avstånden mellan tvärkraftsarmeringen och ökning av stångdiametern. De ökade plastiska töjningarna i dragarmeringen tillsammans med mätningar av skjuvsprickornas bredd, stödreaktionerna och töjningarna i betongen föreslår att balkarna med högt tvärkraftsarmeringsinnehåll visar på ett segare beteende utan att gå till brott.

<p>In this thesis the dynamic response of wide-flange steel beams and columns to blast loading was experimentally evaluated. A total of twenty six steel members were field tested using live explosives, where the charge size ranged from 50 to 250 kg of ANFO and the ground stand-off distance from 7.0 to 10.3 m. Blast wave characteristics, including incident and reflected pressures were recorded. In addition, time-dependant displacements, accelerations, and strains at different locations along the steel members were measured, and the post-blast damage and mode of failure of the test specimens were observed. This study also presented detailed analysis of the experimental data. The blast load characteristics were compared with those obtained using the Technical Manual UFC 3-340-02 model (UFCM). The spatial and temporal variations of strain rate were computed from the recorded strain time histories and analyzed. In addition, time-dependant deformations were analyzed to study the contributing modes of vibration in the dynamic response using Power Spectral Density (PSD) function. Moreover, the effect of the axial load on the maximum deformations, vibration periods, strain rates, and contributing modes in the dynamic response were study by comparing the beam results with the column results tested in the same blast shots.</p> <p>The experimental results were compared with those obtained from an equivalent Single-Degree-of-Freedom (SDOF) model, which included material nonlinearity, strain rate effect, and <em>P-δ</em> effect. To account for strain rate effect on member stiffness and strength, its full moment-curvature response is determined by dividing its cross-section into a number of layers and a strain rate-dependent stress-strain relationship, based on the Cowper-Symonds strain rate model, was used to capture the nonlinear stress distribution over the section. The <em>P-δ</em> effect was modelled using the equivalent lateral load (ELL) method to simulate the secondary moment due to axial load. To determine the effects of higher modes of vibration and the variation of steel member mechanical properties along its length on its dynamic response, the test steel members were also analyzed using Multi-Degree-of-Freedom (MDOF) models, based on Finite Element Modelling (FEM). These dynamic models were also used to investigate the effect of axial-bending interaction and dynamic stability of columns. In addition, the results of the dynamic models were used to evaluate the results of the Moment Magnification Factor (MMF) commonly used in the interaction formulas to design steel beam columns under blast. Moreover, the effect of strain rate caused by the blast loading on the local stability of steel columns was also evaluated insofar as it might lead to a shift in the governing mode of failure.</p> <p>Results showed the UFCM pressure predictions compared reasonably well with the measured pressure in the positive phase in terms of both the peak pressure and overall time variations. Results also showed that when proper accounting for secondary-moment due to axial load and strain rate effect on the member resistance function, the SDOF model adequately captured both the overall response, such as the time-dependant deformations and internal forces, and instability behaviour of steel columns under blast loading. It is also shown that using MMF method overestimates the column capacity for ductility ratios <em>µ</em> greater than one, irrespective of the axial load to Euler elastic buckling load ratio (<em>P</em>/<em>P</em>_e). Also for <em>P</em>/<em>Pe</em> > 0.5, even if <em>µ</em> >1.0, the UFC method still overestimates the actual column capacity. The results of the dynamic models were used to generate stability diagrams for the assessment of the critical load and Pressure-Impulse (PI) diagrams for checking the column performance against the allowable deflection limits, which can be implemented in design standard of steel structures under blast loading.</p> / Doctor of Philosophy (PhD)

With the rise in hazards that structures are potentially subjected to these days, ranging from pre-contemplated terror attacks to accidental and natural disasters, safeguarding structures against such hazards has increasingly become a common design requirement. The extreme loading conditions associated with these hazards renders the concept of imposing generalized codes and standards guidelines for structural design unfeasible. Therefore, a general shift towards performance-based design is starting to dominate the structural design field. This study introduces a powerful structural analysis tool for reinforced concrete structures, possessing a high level of reliability in handling a wide range of typical and extreme loading conditions in a sophisticated structural framework. VecTor3, a finite element computer program previously developed at the University of Toronto for nonlinear analysis of three-dimensional reinforced concrete structures employing the well-established Modified Compression Field Theory (MCFT), has been further developed to serve as the desired tool. VecTor3 is extended to include analysis capabilities for extreme loading conditions, advanced reinforced concrete mechanisms, and new material types. For extreme loading conditions, an advanced coupled heat and moisture transfer algorithm is implemented in VecTor3 for the analysis of reinforced concrete structures subjected to fire. This algorithm not only calculates the transient temperature through the depth of concrete members, but also calculates the elevated pore pressure in concrete, which enables the prediction of the occurrence of localized thermally-induced spalling. Dynamic loading conditions are also extended to include seismic loading, in addition to blast and impact loading. Advancing the mechanisms considered, VecTor3 is developed to include the Disturbed Stress Field Model (DSFM), dowel action and buckling of steel reinforcement bars, geometric nonlinearity effects, strain rate effects for dynamic loading conditions, and the deterioration of mechanical properties at elevated temperatures for fire loading conditions. Finally, the newly-developed Simplified Diverse Embedment Model (SDEM) is implemented in VecTor3 to add analysis capability for steel fibre-reinforced concrete (SFRC). Various analyses covering a wide range of different structural members and loading conditions are carried out using VecTor3, showing good agreement with experimental results available in the literature. These analyses verify the reliability of the models, mechanisms, and algorithms incorporated in VecTor3.