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When a building is exposed to fire, it is required to remain structurally stable for a period of time. The regulations do however allow some types of localised failures within this time frame. The damage area of these failures must be contained and remain proportional to the initial triggering action and not continue into a widespread collapse, commonly referred to as a progressive collapse. In order to prevent progressive collapses, it is necessary to first identify which types of failures that could result in a progressive collapse. In a recent study (Iqbal N., Ph.D. thesis, Luleå University of Technology, 2016), single-storey steel frame buildings affected by localised fires were analysed. In the study it was identified that an initial failure in the truss’ top chord could potentially result in a progressive collapse. The reason for this is because when the top chord fails, the truss and its roof sheeting deflect and transitions into only handling catenary forces. The catenary forces present in the roof sheeting are then transferred to the adjacent trusses which therefore risks collapsing. The analysis could however not determine the possibility of progressive collapses and how factors such as truss span length affect the possibility of progressive collapses. The purpose of this thesis therefore became to analyse how span length affect the roof sheeting’s catenary forces and try to determine if a failure in the top chord could result in a progressive collapse. To answer this, finite element analyses where conducted on two different truss models with varying span lengths, i.e. 18- and 36-meter. Each model consisted of three trusses along with columns, bracings, and roof sheeting. Additionally, a hand calculation model was adopted to determine the strength of the catenary forces. From the finite element analysis, it could be seen that the adjacent trusses of the 36-meter truss model became grossly deformed. Hence indicating that a longer span length would increase the possibility of a progressive collapse. However, the hand calculation model used to calculate the strength of the catenary forces indicated that catenary forces present in the roof sheeting of the longer truss model, was relatively weak compared to the shorter truss model. The reason for this could not be determined, but some adjustments to the hand calculation model might be necessary to make it compatible with the analysed truss model. Consequently, it was impossible to determine the possibility of a progressive collapse. Additionally, during this work it was identified that other factors, such as truss model, bay length and roof sheeting thickness, could affect the possibility of progressive collapses. Hence, further work is necessary to determine the possibility of a progressive collapse. / När en byggnad utsätts för brandpåverkan ska den förbli strukturellt stabil under en viss tidsperiod. Regelverken tillåter dock att vissa typer av lokala skador inträffar redan under denna tidsperiod. Dessa skador måste begränsas till en viss area och förbli proportionerliga mot den initiala skadan och inte resultera i utbredda kollapser, det vill säga fortskridande ras. För att kunna förhindra fortskridande ras är det nödvändigt att först identifiera vilka typer av skador som skulle kunna resultera i fortskridande ras.  I en relativt ny analys (Iqbal N., Doktorsavhandling, Luleå tekniska universitet, 2016) analyserades den bärande konstruktionen i enplans stålhallar då konstruktionen utsattes för lokala bränder. Där det identifierades att ett brott i balkens överram eventuellt skulle kunna resultera i ett fortskridande ras. Brottet i överramen medförde nämligen att balken och dess takplåt sjönk ihop och övergick till att endast hantera linkrafter. Takplåtens linkrafter fördelades ut till de angränsade balkarna som därmed riskerade att kollapsa. Analysen kunde dock inte verifiera att ett fortskridande ras var möjligt eller avgöra hur faktorer såsom balkspännvidd påverkade sannolikheten för ett fortskridande ras. Syftet med detta arbete blev därför att analysera om balkspännvidd påverkade takplåtens linkrafter samt att försöka avgöra om ett brott i överramen kan resultera i ett fortskridande ras eller inte. För att besvara detta genomfördes finita elementanalyser på en 18- och en 36-meter lång balk. Varje modell bestod av tre balkar med tillhörande pelare och takplåt. För att sedan kunna uppskatta styrkan av linkrafterna i takplåten tillämpades en handberäkningsmodell.  Resultatet från finita elementanalyserna visade att den längre balkmodellen utsattes för högre påkänningar i jämförelse med den kortare balkmodellen. Detta indikerar att en längre spännvidd ökar sannolikheten för fortskridande ras. Handberäkningsmodellen som användes för att beräkna styrkan av linkrafterna gav dock generellt mindre linkrafter för den längre balkmodellen jämfört med den kortare balkmodellen. Anledningen till detta gick inte att fastställa men det skulle kunna vara så att handberäkningsmodellen behöver justeras för att kunna tillämpas på den undersökta balkmodellen. I och med detta var det omöjligt att avgöra sannolikheten för ett fortskridande ras. Under detta arbete identifierades det även att andra faktorer så som balkmodell, centrumavstånd mellan fackverk och plåttakstjocklek skulle kunna påverka linkrafternas styrka. På grund av detta är fortsatt arbete nödvändigt för att kunna avgöra möjligheten och sannolikheten för ett fortskridande ras.

The Accelerated bridge construction (ABC) techniques are gaining popularity among the departments of transportation (DOTs) due to their reductions of on-site construction time and traffic delays. One ABC technique that utilizes precast deck panels has demonstrated some advantages over normal cast-in-place construction, but has also demonstrated some serviceability issues such as cracks and water leakage to the transverse joints. Some of these problems are addressed by applying longitudinal prestressing. This thesis evaluates the service and ultimate capacities in both flexure and shear, of the finite element models of the post-tensioned system currently used by Utah Department of Transportation (UDOT) and a proposed curved-bolt system to confirm the experimental results. The panels were built and tested under negative moment in order to investigate a known problem, namely, tension in the deck concrete. Shear tests were performed on specimens with geometry designed to investigate the effects of high shear across the joint. The curved-bolt connection not only provides the necessary compressive stress across the transverse joint but also makes future replacement of a single deck panel possible without replacing the entire deck. Load-deflection, shear-deflection curves were obtained using the experimental tests and were used to compare with the values obtained from finite element analysis. In flexure, the ultimate load predicted by the finite element model was lower than the experimental ultimate load by 1% for the post-tensioned connection and 3% for the curved-bolt connection. The shear models predicted the ultimate shear reached, within 5% of the experimental values. The cracking pattern also matched closely. The yield and cracking moment of the curved-bolt connection predicted by the finite element model were lower by 13% and 2%, respectively, compared to the post-tensioned connection in flexure.

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.

Indiana University-Purdue University Indianapolis (IUPUI) / Finite element analysis (FEA) in implantology is performed in design applications concerning the complex topology of an implant, according to theoretical assumptions about and clinical data concerning the biomechanical nature of skeletal tissue. Implants are placed in topologically and physiologically complex sites, and major disagreement exists in literature about various aspects concerning their modeling and analysis. Current research seeks to improve the implementation of an implant by the use of short implants, which negate the necessity of additional surgical procedures in regions of limited bone height. However, short implants with large crown heights introduce biomechanical complications associated with increased stress and strain distributions in skeletal tissue, which may cause bone loss and implant failure. The short implant is characterized by the geometric ratio of the crown height to the implant length, called the crown-to-implant (C/I) ratio. In this work nonlinear FEA was performed to investigate the effects and significance of the C/I ratio on long-term implant stability. A finite element model was developed according to literature, and emulation of previous research and comparison of reported results were performed. Comparison of results demonstrated significant sources of error in previous research, which are argued to be caused by mesh-dependency from common model idealizations in literature. A convergence test was then performed, which verified the mesh-dependency of results and challenged the reliability of some common model assumptions and methods of analysis in literature. A 16-point design of experiments was then performed to evaluate the significance and influence of the C/I ratio, considering a proposed novel method for evaluating results and predicting long-term stability. Analysis of results demonstrated that the C/I ratio augments the inherent biomechanical effects of an implant design, particularly overloading strain concentrations at implant interface features. The use of short implants with high C/I ratios is determined to be inadvisable, considering the physiological response of tissue to strain distributions and biological context. A novel, multiscale material model is then proposed to describe the short-term accumulation of damage and biomechanical remodeling response in orthotropic skeletal tissue, as a potential solution to the mesh-dependency of results.

Indiana University-Purdue University Indianapolis (IUPUI) / Advances in peripheral nerve electrode technology have outpaced the advances in chronic implantation reliability of the electrodes. An observable trend is the increased deposition of fibrotic encapsulation tissue around the electrode to shift its position away from the implantation site and subsequently reducing performance. A finite element model (FEM) is developed in conjunction with tensile testing and digital image correlation of strain to understand the relationship between cuff electrode attachment and the strain environment of the nerve. A laminar and bulk nerve model are both developed with material properties found in literature and geometry found from performing histology. The introduction of a cuff electrode to an axially stretched nerve indicates a significant behavior deviation from the expected response of the axial strain environment. When implemented in ex-vivo tensile testing, results indicate that the reduction of strain is statistically significant but becomes much more apparent when paired with a digital image correlation system to compare predicted and measured effects. A robust FEM is developed and tested to emphasize the effect that the boundary conditions and attachment methodology significantly effects the strain environment. By coupling digital image correlation with FEM, predictive models can be made to the strain environment to better design around the long term chronic health of the implant.