Bridges with low clearance are vulnerable to collision with overheight vehicles. Collisions of overheight vehicles can cause fatalities and injuries to the drivers and passengers of the overheight vehicles, and damage to bridge girders. The repair of the damaged bridges can be costly and time consuming. This research investigates the feasibility of developing a bridge bumper that minimizes the physical injuries and the likelihood of fatalities and protects the structural elements of bridges by absorbing the impact energy. The thesis describes a small-scale impact experiment using the proposed bridge bumper with several options of energy absorbing materials to protect a reinforced concrete beam. A finite element analysis is done to simulate the small-scale impact experiments. Optimization of the finite element model is carried out for the response quantities of interest with respect to the geometrical parameters and the material properties of the proposed bridge bumper. Such analysis can guide the design of an optimal bridge bumper that maximizes the energy dissipation and minimizes the damage to the bridge girder and the likelihood of fatalities and injuries.

Bridges with low clearance are vulnerable to collision with overheight vehicles. Collisions of overheight vehicles can cause fatalities and injuries to the drivers and passengers of the overheight vehicles, and damage to bridge girders. The repair of the damaged bridges can be costly and time consuming. This research investigates the feasibility of developing a bridge bumper that minimizes the physical injuries and the likelihood of fatalities and protects the structural elements of bridges by absorbing the impact energy. The thesis describes a small-scale impact experiment using the proposed bridge bumper with several options of energy absorbing materials to protect a reinforced concrete beam. A finite element analysis is done to simulate the small-scale impact experiments. Optimization of the finite element model is carried out for the response quantities of interest with respect to the geometrical parameters and the material properties of the proposed bridge bumper. Such analysis can guide the design of an optimal bridge bumper that maximizes the energy dissipation and minimizes the damage to the bridge girder and the likelihood of fatalities and injuries.

Wood structural elements are more vulnerable to blast loading due to the inherent brittle nature and low density of the material, as demonstrated by recent significant research efforts on the behaviour of timber elements subjected to the effect of blast loading. These studies showed that wood performs poorly under blast loading. A way of improving this performance is to provide additional ductility or energy absorption capabilities to wooden elements. Recently, there was interest in investigating and developing energy-absorbing connections (EAC) to improve timber assemblies’ ductility and energy absorption capabilities. Although some research effort has been made to investigate the use of EACs to enhance the ductility of reinforced concrete or structural steel members, only limited work is available on this topic about timber elements. The current study aims to systematically investigate the use of various shapes of EACs to be used to enhance the post-peak performance of timber assemblies. Preliminary finite element analysis led to selecting nine steel EACs with varying geometries for further experimental investigation. A total of eighteen specimens were tested statically. In comparison, a total of eighteen specimens were tested dynamically in the shock tube facility of the University of Ottawa to simulate the effects of far-field blast explosions. The experimental results showed that decreasing the leg length or increasing the thickness of EACs manufactured with steel angles and reducing the diameter of EACs manufactured with circular HSS caused an increase in yield load and elastic stiffness while reducing the densification displacement. Connections with angles and a centre weld, and connections with 90-degree arcs from circular HSS, were identified as unsuitable for the application of EACs. The experimental program also showed that EACs manufactured from angles offer a well-defined plateau able to absorb a large quantity of energy, making them particularly suitable for blast mitigation. EACs manufactured from multiple circular HSS were shown to achieve multiple load-displacement plateaus and present an interesting option for systems with multiple failure modes occurring at different levels. SDOF analysis and FEA were conducted to predict the experimental behaviour with some success. The importance of the weld type was also highlighted from both the analytical and experimental results. A methodology for developing idealized load-displacement curves from experimental results of EACs was also proposed and evaluated.

The majority of research on high strain-rate effects in timber structures has been limited to the study of the load-bearing members in isolation. Limited work has been conducted on timber connections and full-scale timber assemblies under blast loading, and these have generally been constrained to qualitative observations. In North America, the increasing prevalence of mid- and high-rise timber structures makes them susceptible to blast effects. In addition, questions remain on how to design and optimize these timber assemblies, including the connections, against blast loads, due in part to the limitations on comprehensive design provisions. The effects of far-field blast explosions were simulated using the University of Ottawa shock tube. A total of fifty-eight dynamic tests were conducted on connection-level and full-scale specimens. The research program aimed to investigate the behaviour of heavy-timber connections when subjected to simulated blast loads. The experimental results showed that connections with a main failure mechanism consisting of wood crushing experienced significant increases in dynamic peak load when compared to the static peak load. In contrast, connections where steel yielding and rupturing occurred experienced no statistically significant increase in dynamic peak load. Full-scale glulam specimens with bolted connections designed to yield via wood crushing and bolt bending performed better than those with overdesigned connections. Bolted connections which failed in splitting led to premature failure of the glulam assembly. Reinforcement with self-tapping screws allowed these bolted joints to fail in a combination of bolt yielding and wood crushing, and provided more ductility when compared to unreinforced specimens. Specially designed energy-absorbing connections significantly increased the energy dissipation capabilities of the timber assemblies. The basis of these connections was to allow for connection yielding while delaying failure of the wood member. This was achieved via elastoplastic connection behaviour, which effectively limited the load imparted onto the wood member. Based on the experimental results, limitations in the current Canadian blast provisions were highlighted and discussed. A two-degree-of-freedom blast analysis software was developed and validated using full-scale and connection-level experimental results and was found to adequately capture the system response with reasonable accuracy. Sensitivity analyses regarding the applicability of using single-degree-of-freedom analysis were presented and discussed.

Indiana University-Purdue University Indianapolis (IUPUI) / Traumatic Brain Injuries (TBI) are one of the most apprehensive issues today. In recent years a lot of research has been done for reducing the risk of TBI, but no concrete solution exists yet. Helmets are one of the protective devices that are used to prevent human beings from mild TBI. For many years some kind of foam has been used in helmets for energy absorption. But, in recent years non-traditional solutions other than foam are being explored by different groups. Focus of this thesis is to develop a completely new concept of energy absorption for helmet liner by diverting the impact forces in radial directions normal to the direction of impact. This work presents a new design of an advanced layered composite (ALC) for energy dissipation through action of a 3D array of compliant mechanisms. The ALC works by diverting incoming forces in multiple radial directions and also has design provisions for reducing rotational forces. Design of compliant mechanism is optimized using multi-material topology optimization algorithm considering rigid and flexible material phases together with void. The design proposed here needs to be manufactured using the advanced polyjet printing additive manufacturing process. A general and parametric design procedure is explained which can be used to produce variants of the designs for different impact conditions and different applications. Performance of the designed ALC is examined through a benchmark example in which a comparison is made between the ALC and the traditional liner foam. An impact test is carried out in this benchmark example using dynamic Finite Element Analysis in LS DYNA. The comparison parameters under consideration are gradualness of energy absorption and peak linear force transmitted from the ALC to the body in contact with it. The design in this article is done particularly for the use in sports helmets. However, the ALC may find applications in other energy absorbing structures such as vehicle crashworthy components and protective gears. The ultimate goal of this research is to provide a novel design of energy absorbing structure which reduces the risk of head injury when the helmet is worn.

Whiplash is a neck injury caused by the sudden differential movement between the head and torso. Whiplash injuries are most commonly reported as a consequence of rear impacts in car accidents. They are regarded as minor injuries, but can still lead to long-term disablement and discomfort in the neck. Whiplash injuries can be mitigated by better car seat designs. For this purpose, head restraint geometry must be improved first, and then the dynamic performance of the whole seat must be assessed at all crash seventies. A biofidelic human-body model is a key requirement in designing whiplash mitigating car seats. This thesis presents the development of a 50th percentile male multi-body human model and several energy absorbing car seat designs. The human-body model is specifically designed for rear impact and validated using the responses of seven volunteers from Japanese Automobile Research Institute (JARI) sled tests, which were performed at an impact speed of 8 kph with a rigid seat and without head restraint and seat belt. A generic multi-body car seat model is also developed to implement various seatback and recliner properties, anti-whiplash devices (A WDs) and head restraints. Using the same driving posture and the rigid seat in the JARI sled tests as the basic configuration, several anti-whiplash seats are designed to allow different types of motion for the seatback and seat-pan. The major findings of this research are: -The human-body model simulates the effects of muscle contraction and its overall response is superior in comparison to the currently used models and dummies. -A criterion called the S-shape index (SSI) is developed based on the intervertebral angles of the upper and lower cervical spine. -The car seat design concepts are able to control and use crash energy effectively with the aid of anti-whiplash devices for a wide range of crash seventies. -In order to reduce whiplash injury risk, this study advocates energy absorbing car seats which can also provide head restraint contact as early as possible.

As many of the world’s nuclear power plants are near the end of their supposed life span a need arise to assess the components crucial to the safety of these plants. One of these crucial components is the concrete reactor confinement; to assess its condition, non-destructive testing (NDT) is an attractive method. Traditional testing of concrete structures has comprised of drilling out a sample and performing stress tests on it, but because of the radioactive environment inside the containment this method is far from ideal. NDT is of course possible to use at any structure but at reactor containments the benefits from not creating holes in the structure are prominent; NDT is also an attractive option from an esthetical point of view because it leaves the structure intact. The NDT method pertaining to this study is the impact echo method which comprise of applying a force on the structure, usually a hammer blow, and measuring the response with a receiver. The impact will excite waves propagating in the structure which gives rise to Lamb modes. Lamb modes are structural oscillations of the wall and it is the frequency of these modes that are used to determine the thickness of the wall. The elastic properties of the structure can in turn be obtained by measuring the velocities of the waves propagation. It is also possible to use the impact echo method to detect irregularities in the structure such as cracks or delamination. To simulate the dynamics of a system using NDT numerical methods such as finite element modeling (FEM) is often used. The purpose of this study is to assess the possibility to utilize absorbing layers using increasing damping (ALID) in models to reduce the computational time of FEM analyses. ALIDs are used at the edges to simulate an infinite system and are thus supposed to cancel out incoming waves to prevent unwanted reflection from the edges. The models in this study have all pertained to two dimensional plates utilizing infinitesimal strain theory; the decrease in computational time is significant when using ALIDs and for three dimensional models it would be even more so. The ALIDs are specified by length and maximum mass proportional Rayleigh damping (CMmax), in this study three different lengths are tested, 0.5, 1.5 and 4.5 m for CMmax ranging from 103 to 2*105 Ns/m. The damping is increased with increasing distance into the ALID with specified maximum value at the back edge. However, it should be noted that the increase in damping causes difference in impedance between elements and if this difference is too large it will cause reflections of waves at the boundary between the elements. The ALID must thus be defined so that it sufficiently cancels out the wave without causing unwanted reflections due to impedance differences. The conclusion is that the 0.5 m long ALID does not provide good results for any choice of maximum mass proportional Rayleigh damping. Both the 1.5 and 4.5 m long ALIDs are, however, concluded to be applicable; the 1.5 m ALID having 2*104 < CMmax <5*104 Ns/m and the 4.5 m ALID having 5*103 < CMmax < 104 Ns/m are choices that have shown promise in the performed simulations. The hope is that the results obtained in this study will aid in the development of numerical analysis techniques for NDT methods that can be used in the construction of new reactor confinements and/or maintenance of existing reactor confinements and other thick concrete structures. / Många av världens kärnkraftverk närmar sig slutet på sin beräknade livslängd och ett behov uppstår då att kunna utvärdera de komponenter som är väsentliga för säkerheten på dessa verk. Reaktoromslutningen i betong är en av dessa komponenter och oförstörande provning (NDT) är en attraktiv metod för att bedöma dess tillstånd. Traditionellt har utvärdering av betongkonstruktioner bestått av stresstester på borrprover men p.g.a. den radioaktiva miljön på insidan av omslutningen är denna metod ej att föredra. NDT är självklart möjligt att använda på allsköns betongkonstruktioner då det ger både konstruktionsmässiga och estetiska fördelar. NDT metoden som rör denna studie kallas impact echo och går ut på att man med en hammare slår till en punkt på väggen och mäter responsen en bit därifrån. Lasten ger upphov till vågor i form av deformation som propagerar i väggen och dessa ger i sin tur upphov till Lamb moder. Lamb moderna är strukturella oscillationer av väggen och genom att studera dess frekvenser kan väggens tjocklek bestämmas. Elastiska egenskaper i väggen erhålls utifrån de olika vågornas propageringshastigheter. Impact echo metoden kan även användas för att finna strukturella oegentligheter inuti väggen så som sprickor och delaminering. För att utföra numeriska simuleringar av dynamiska system med NDT-metoder är finita elementmetoden (FEM) användbar. Syftet med denna studie är att bedöma vilka möjligheter som finns för att implementera absorberande ränder med ökande dämpning (ALID) i datamodeller för att minska beräkningstiden av FEM-analyser. ALID används vid kanterna för att simulera ett oändligt system, dess uppgift är att dämpa bort inkommande vågor så att dessa ej reflekteras tillbaka och stör mätningarna. Samtliga modeller i denna studie är två-dimensionella med antagen oändligt liten spänning i normalriktningen. Vinsten i beräkningstid av att använda ALID är stor och ökar ytterligare om modellen utökas till tre dimensioner. Ett ALID definieras genom dess längd och maximala massproportionerlig Rayleigh-dämpning (CMmax). I denna rapport har längderna 0.5, 1.5 and 4.5 m använts med CMmax i intervallet från 103 till 2*105 Ns/m. Dämpningen ökar med ökat avstånd in i ALID med det specificerade maxvärdet vid den bakre kanten. Det bör noteras att skillnad i dämpning mellan element leder till skillnad i impedans; reflektioner av vågorna uppstår vid övergång från ett element med lägre impedans till ett med högre impedans. Ett ALID måste således vara definierat så att det dämpar bort tillräckligt av de inkommande vågorna utan att oönskade reflektioner i ALID uppstår. Studien pekar på att ett 0.5 m långt ALID inte åstadkommer önskvärda resultat för något av valen för CMmax som använts i denna rapport. Både det 1.5 och 4.5 m långa ALID har däremot get bra resultat; ett 1.5 m långt ALID bör ha 2*104 < CMmax <5*104 Ns/m och ett 4.5 m långt ALID 5*103 < CMmax < 104 Ns/m. Förhoppningen med studien är att resultaten skall underlätta utvecklingen av NDT-metoder som kan användas vid konstruktion och underhåll av reaktoromslutningar och andra tjocka betongkonstruktioner.

No description available.