Master of Science / Department of Civil Engineering / Hayder A. Rasheed / The Kansas Department of Transportation’s (KDOT) Bridge 059-045 is a reinforced concrete box girder bridge constructed in 1965 to connect the rural Shawnee Drive across Interstate 135 near McPhearson, Kansas, in between Salina and Wichita. The bridge was observed, during an annual inspection in 1998, to have experienced some settlement, which was further found to be due to its proximity to a sinkhole. This settlement progressed to noticeable levels in 2012 necessitating a semi-annual elevation profile survey that was consistently conducted by KDOT. In April 2016, KDOT determined that the bridge required a detailed finite element analysis to determine the safety and suitability of the bridge to stay open to traffic. Accordingly, a two-level Finite Element Analysis was performed using RISA 3D and Abaqus to assess the level of distress in the bridge due to the continuous differential settlement as a result of the active sinkhole deep in the soil under the bridge. The force-moment results were taken from the RISA 3D model for further analysis of various structural components that make up the bridge, including the box girder, piers, and piles. The stress distribution results from the Abaqus model were investigated for the same components of the bridge. A strengthening design scheme using near surface mounted fiber reinforced polymer rebar was developed to extend the service life of the bridge.

No description available.

Caribbean-style hybrid concrete-masonry structures consist of a reinforced concrete frame with partially grouted and reinforced infill masonry walls. The infill walls are typically connected to the RC frame with cast-in-place dowel reinforcement along one or more edges of the wall. There is limited guidance in masonry codes to design these types of structures, and their seismic performance has not been characterized with experimental tests. In this work, an experimental program characterized the seismic behavior of hybrid concrete-masonry frames and showed they do not exhibit the typical strut mechanism observed in unreinforced masonry infill structures. In addition, a detailed finite element modeling scheme and calibration methodology was developed for modeling partially grouted masonry. This model includes a novel calibration method to account for the difference in the shear and tensile behavior of bed joints with grouted and ungrouted cells, and a method to account for the contribution of vertical reinforcement to the shear capacity of the bed joints with grouted cells. Finally, simplified models were proposed for use in engineering design. A modification of the TMS 402 strut model for hybrid concrete-masonry was suggested to incorporate the effects of the masonry infill and connections in large models.

Heart failure (HF) is one of the leading causes of death and impacts millions of people throughout the world. Recently, injectable hydrogels have been developed as a potential new therapy to treat myocardium infarction (MI). This dissertation is focused on two main topics: 1) to gain a better understanding the transmural contractility in the healthy left ventricle (LV) wall and 2) investigate the efficacy of the hydrogel injection treatment on LV wall stress and function. The results indicate that a non-uniform distribution of myocardial contractility in the LV wall provide a better representation of normal LV function. The other important study explored the influence altering the stiffness of the biomaterial hydrogel injections. These results show that a larger volume and higher stiffness injection reduce myofiber stress the most and maintaining the wall thickness during loading. The computational approach developed in this dissertation could be used in the future to evaluate the optimal properties of the hydrogel. The last study used a combination of MRI, catheterization, finite element (FE) modeling to investigate the effects of hydrogel injection on borderzone (BZ) contractility after MI. The results indicate that the treatment with hydrogel injection significantly improved BZ function and reduce LV remodeling, via altered MI properties. Additionally, the wall thickness in the infarct and BZ regions were significantly higher in the treated case. Conclusion: hydrogel injection could be a valuable clinical therapy for treating MI.

Automotive structures contain hundreds of welds. Most of the time, failure occurs at the weld ends (weld toe or weld root). Thus, welds affect the structural integrity of an entire structure. Thus, the modeling of welded joints is very important from a design point of view. In this research, the primary aim is to develop a weld model to assess the structural integrity of welded joints based on stress analysis by using a finite element method (FEM) and through experimental validation. The stress distribution in welded joints mainly depends on the geometry, loading type and material properties. Therefore, it is greatly challenging to develop a weld model that can predict the behavior of stress distribution and weld stiffness in joints. There are several approaches for modeling welded structures by using FEM. However, the effective notch stress approach has been used for weld joint modeling in this research which is gaining in popularity in the automotive industry. The effective notch stress approach calculates the local stress at a notch (weld toe or root) assuming that there is linear-elastic material behavior. Parameter tuning of the weld model has been done to obtain the lowest validation error with the experimental results. The effective notch radius is chosen as the only tuning parameter in this weld model. Through this investigation, the weld model based on the effective notch stress has been experimentally validated for the first time through parameter tuning. Two different types of welded joints are investigated. Both types of joints are analyzed with a fine meshed 3D finite element model by using the effective notch stress approach. The FEM model of these two joints is validated with the experimental results. The calculated FEM results show a good agreement with the experimental results (obtained by using strain gages) for the ASTM model. This modeling technique is also validated with real world data of a bus window pillar. The model of the bus window pillar shows a close approximation with the experimental results. / October 2016

A análise da formação e crescimento de fissuras em peças de concreto armado permanece como uma das principais dificuldades no campo da engenharia estrutural. Considerando que as fissuras têm uma influência muito grande no comportamento estrutural global, estudos para prever e controlar a fissuração do concreto são de essencial importância. O objetivo deste trabalho é apresentar um modelo numérico do tipo incorporado para representar as fissuras em peças de concreto armado submetidas aos esforços de flexão e corte, ou seja, um modelo que seja capaz de simular, além das fissuras perpendiculares ao eixo da peça, fissuras inclinadas. Os modelos de fissura incorporada se baseiam no conceito de descontinuidades incorporadas dentro de elementos finitos padrões. No modelo empregado neste trabalho, a fissura é representada através de uma descontinuidade no campo interno de deslocamentos do elemento. O modelo incorporado implementado é uma continuação do trabalho desenvolvido por d’Avila, que baseou-se no modelo de Dvorkin Cuitiño e Gioia que, por sua vez, não inclui a contribuição da armadura no equilíbrio interno de forças do elemento. A interação entre as barras de aço e o concreto é simulada através um modelo de transferência de tensão por aderência entre os dois materiais, conforme Russo, Zingone e Romano e FIB - Bulletin 10. Para representar o comportamento do concreto intacto, utiliza-se o modelo constitutivo de Ottosen. Já para representar as barras de aço da armadura, emprega-se o modelo incorporado desenvolvido por Elwi e Hrudey, que permite uma disposição arbitrária das barras de aço no interior dos elementos de concreto. O modelo constitutivo adotado para a armadura é do tipo elasto-plástico com endurecimento. Foi possível simular a fissuração em flexão e corte em vigas de concreto armado com boa correlação com resultados experimentais. Tais situações não poderiam ser analisadas pelo modelo básico sem as modificações propostas nesta dissertação. / The analysis of the formation and growth of cracks in reinforced concrete members remains as one of the main difficulties in the field of structural engineering. Considering that the crack has a considerable influence in the global structural behavior, studies to predict and to control concrete cracking are of essential importance. The aim of this work is to present a numerical model of the embedded type to represent the cracks in reinforced concrete members under bending and shearing efforts, i. e. , a model that is capable to simulate not only cracks that are perpendicular to the axle of the members but also inclined cracks. The embedded crack models are based on the concept of incorporated discontinuities inside of standard finite elements. In the model used in this work, the crack is represented by a discontinuity in the internal field of the element displacements. The embedded model proposed is a continuation of the work developed by d’Avila, which is based on the model of Dvorkin, Cuitiño e Gioia, that does not consider the inclusion of the reinforced contribution in the internal force equilibrium of the element. A bond stress-transfer approach is used to include this reinforcement contribution. To represent the behavior of the uncracked concrete, the Ottosen constitutive model was used. The embedded model presented by Elwi and Hrudey was employed to represent the reinforcement bars, that allows an arbitrary disposal of the bars of steel inside of the concrete elements. The constitutive model adopted for reinforcement is elasto-plastic with hardening. It was possible to simulate the cracking in bending and shearing in reinforced concrete beams with good agreement with experimental results. These cases could not be analyzed by the basi model without the present proposed modifications.

Cervical myelopathy is the most common form of spinal cord injury in North America with roughly 19,000 new cases in the US every year. It results from chronic compression of the spinal cord by osteophytes, intervertebral disc herniation, and ossified ligaments. It commonly affects adults over the age of 50 years and causes upper extremity numbness, loss of hand dexterity, gait disturbances, and decreased proprioception. Recent studies imaging studies have shown this injury is highly dependent on the dynamic motion of the spine, often worsening in extreme flexion and extension. Surgical intervention is the accepted mode of treatment with the aim of decompressing the spinal canal and stabilizing the spine. However, 25% of patients have reoccurrence of symptoms indicating that surgical treatments may not be adequately addressing the injury. A main reason for this is little data has been reported on the spinal cord mechanics during cervical spinal motion in either healthy or cervical myelopathy subjects. To address this, we utilized MR imaging and finite element modeling to investigate spinal cord mechanics. As far as we know, we are the first group to obtain in vivo 3 dimensional spinal cord displacement and strain data from human subjects and the first to develop a C2 to T1 FE model of the healthy and cervical myelopathic spine and spinal cord. Utilizing high resolution 3T MR imaging in neutral, flexion, and extension positions we were able to obtain spinal cord displacement and strain fields from both healthy subjects and cervical myelopathy subjects before and after surgical intervention. In healthy subjects, flexion motion of the spine causes the spinal cord to move superiorly and in extension the spinal cord moves inferiorly. During extension, localizations of high principal strain can be seen in healthy subjects at areas of bony impingement and dural buckling. In both flexion and extension, cervical myelopathy subjects exhibited very little spinal cord displacement due to spinal cord compression. Principal strains during flexion and extension were greater in cervical myelopathy patients than healthy patients, specifically at the C4-6 vertebral levels. Surgical treatments for cervical myelopathy did restore spinal cord motion however, not in the same pattern or direction as healthy subjects. Additionally principal strains of the spinal cord were not reduced after surgical intervention. This indicates that surgical interventions are not adequately addressing the altered mechanics of the spinal cord during cervical myelopathy. To determine the how common surgical techniques for cervical myelopathy affect spinal cord mechanics, a FE model of the cervical spine and spinal cord was developed. The spinal cord motion was validated against MR imaging data obtained from normal subjects. Once validated, the model was used to develop a FE model of cervical myelopathy and surgical interventions. The native FE model predicted spinal cord motion well and replicated bony spinal cord impingement and dural buckling seen in healthy subjects. The FE model of cervical myelopathy also replicated spinal cord motion well as compared to MR imaging data of cervical myelopathy. Principal strains obtained from the healthy and cervical myelopathy FE models were similar in flexion however in extension, principal strains were higher at the C3, C6 and C7 levels. This is different than the patterns exhibited in the MR imaging and is most likely due to the percent of spinal cord compression induced in the FE model. Three, C4 to C7 surgical interventions were introduced to the model: anterior discectomy and fusion, anterior discectomy and fusion with laminectomy, and double door laminoplasty. In flexion, all surgical treatments doubled spinal cord principal strains at the C3 level and minimally reduced tensile strain at C4. The majority of strain reduction occurred at C5-7. In extension, all surgical techniques increased principal strains at the C3 and C4 levels. Little or no reduction in principal strains was seen at the C5 and C7 levels. All surgical techniques reduced principal strains at the C6 level. Of the surgical techniques, ACDF tended to reduce spinal cord principal strains the least in both flexion and extension and tended to induce the highest von Mises stresses. Combining the data obtained from MR imaging and FE modeling we can see that cervical myelopathy alters spinal cord mechanics by limiting spinal cord motion and increasing spinal cord strain. Additionally, current surgical techniques are not addressing the change in spinal cord mechanics effectively. Specifically after surgery, and especially with ACDF, spinal cord displacements and strains are being increased and transferred to different sections of the spinal cord. This indicates not only the need and importance of further research in spinal cord mechanics but also the need to improve treatments for cervical myelopathy which adequately restore the spinal cord mechanics.

The majority of the bridges in the United States are already reaching the years that the design process took into account when determining the time the structure would be functional. This means that many of the bridges in the nation are in need of increasing maintenance, and in some cases, major retrofitting. Researchers at Utah State University in conjunction with the Long-Term Bridge Performance (LTBP) Program, under the direction of the Federal Highway Administration’s (FHWA’s) Office of Infrastructure Research and Development, directed dynamic testing on the New Jersey Pilot Bridge, structure number 1618-150. The purpose of the LTBP Program is to monitor the nation’s highway bridges for a 20-year period to analyze and understand the behavior over time of the selected bridges and then promote the safety, mobility, longevity, and reliability on those bridges. In order to perform the monitoring of the bridge, ambient vibration analysis was selected for this structure, which was instrumented with an array of velocity transducers to record the response coming from the excitation. A finite element model was also created to compare the results from the ambient vibration testing. The results of this testing will be used with the LTBP Program to improve the knowledge of the bridge performance and foster the next generation of bridges and bridge management in the nation.

In order to incorporate fiber-reinforced composite materials in space structures, adhesive joining techniques are required. Because analytical models have a hard time capturing the complex stress state inherent to adhesively joining dissimilar materials, a different modeling technique was deemed necessary. A two-dimensional axisymmetric finite element model capable of capturing the three-dimensional stress state of cylindrical adhesive joints was developed. In order to rigorously validate the model, testing was undergone to ensure the model accurately predicted joint displacements. Displacement data was acquired via an Epsilon axial extensometer. Load data was taken simultaneously via the load cell incorporated in the Tinius Olsen tensile test machine used. The measured force vs. displacement data was found to agree with the model’s predicted displacement for a given load. Displacement data was also taken, again with the extensometer, as the joints were rapidly cooled to liquid nitrogen temperature. It was found that the joints behave much like laminated plates in that after the first several cycles they “settle down”. The term “settle down”, in this context, means that after the first several cycles the displacements of the joints when placed from a room temperature environment to a cryogenic environment become consistent and smooth. This result allows for the joints to be modeled. The finite element model was shown to accurately predict the settled down displacement given the prescribed temperature change. The joints were also shown to maintain structural integrity post thermal cycling. Transient temperature tensile tests were performed until sample failure. One result with major design implication coming from this test was that the material properties do not change significantly enough over the temperature range tested to affect the joint’s behavior. The same properties used in the room temperature model were used to model the measured data of the transient temperature data and were found to match satisfactorily. Having validated that the developed axisymmetric finite element model accurately predicts cylindrical joint displacement fields, the model becomes an invaluable tool in design. The model can now be used in confidence, in conjunction with design requirements for a specific joint, to reduce the maximum displacements below any specified operating requirements.

The problem of damage accumulation in laminated composite materials hasreceived much attention due to their widespread application in the aerospace, automotive,civil, and sports industries. In the aerospace industry, composites are usedto make light weight and efficient structural components. In the Boeing 787, forexample, more than 50% of the structure is made of composite materials. Althoughthere have been significant developments in analyzing cross-ply laminates, none ofthe present approaches provides reasonable predictions for multidirectional laminatesin which intralaminar cracks may form in multiple orientations. Nevertheless, theprediction of damage accumulation and its effect on structural performance is a verydifficult problem due to complexity of the cracking processes.This study presents a synergistic damage mechanics (SDM) methodology to analyzedamage behavior in multidirectional composite laminates with intralaminarcracks in plies of multiple orientations. SDM combines the strengths of micro-damagemechanics (MDM) and continuum damage mechanics (CDM) in predicting the stiffness degradation due to these cracks. The micromechanics is performed on a representativeunit cell using a three-dimensional finite element analysis to calculate thecrack opening displacement accounting for the influence of the surrounding plies, theso-called constraint effect. This information is then incorporated in the CDM formulationdealing with laminates containing cracks in different ply orientations through a `constraint parameter'. Following CDM, a separate damage mode is defined for eachtype of crack and the expressions for engineering moduli of the damaged laminateare then derived in terms of crack density and the constraint parameter. The SDMmethodology is implemented for [0m/±θn/0m/2]s laminates containing cracks in ±θplies. It is then extended to [0m/±θn/90r]s and [0m/90r/±θn]s laminates with cracksadditionally in the 90°-plies. The predictions agree well with published experimentaldata as well as independent FE computations. Limited parametric studies areperformed to show usability of SDM for more general laminates.To predict the initiation and growth of intralaminar cracks, an energy basedmodel is proposed in which these cracks initiate and multiply when the work requiredto form new set of cracks exceeds a laminate dependent critical energy release rate.The approach requires determination of average crack opening and sliding displacementsat varying crack spacing. This task is performed through a suitable 3-D FEanalysis. In case of off-axis ply cracking, a mixed mode fracture criterion is utilized,where the critical energy release rates in normal and shear modes are determinedby fitting the damage model with the experimental data for a reference laminate.The predictions from the model for [0/± θ4/01/2]s and [0/90/ ± 45]s laminates showremarkable agreement with the experimental results.The methodology and the results covered in this dissertation will be of interest tomechanics of materials researchers as well as to engineers in industry where compositematerials for structural applications are of interest.