Browsing by Subject "Finite element modeling"
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Item Finite element analysis of wood shoring towers used in Urban Search and Rescue(2012-12) Blair, Robert Stevenson; Wheat, Dan L.; Engelhardt, Michael DThis thesis focuses on the finite element modeling and analysis of wood shoring towers used by Urban Search and Rescue (US&R) teams during emergency response situations. These shores are constructed on site to provide temporary stabilization to a damaged structure. A high demand exists for experimental testing of the performance of these shores under non-ideal loading conditions, and for possible design modifications that could improve their overall behavior. To respond to this need, a total of thirteen vertical shores of the type laced post (LP) and plywood laced post (PLP) were constructed and tested at the Ferguson Structural Engineering Laboratory (FSEL) in Austin, Texas. The tests conducted on these shores aimed to investigate their performance under purely vertical load as well as various combinations of vertical and lateral loads. Finite element models for eight of the shores tested at FSEL were built and analyzed in Abaqus to compare the computed results with the actual linear elastic response of the shores. Material properties for the posts in each shore were obtained through further material testing at the conclusion of each shore test. Shore members were assumed to be isotropic. Solid elements were used to model each member, and Cartesian connector elements with a predefined nonlinear stiffness were used to model each nail. In general, the vertical load-displacement response computed from Abaqus exhibited good agreement with the laboratory results for the linear elastic range. The same general modeling scheme was then used to make design changes to the original shores based on observations gained during testing as well as modeling. Each design change was modeled, analyzed, and then compared with the computed results from the original shore design as well as the other design changes. The basis for evaluating the effectiveness of a given shore design involved comparing the bending moment diagrams for each post and the maximum first story nail slips (connector displacements). Recommendations were made for improved shore designs to be verified by experimental testing.Item Finite element modeling of twin steel box-girder bridges for redundancy evaluation(2010-05) Kim, Janghwan; Frank, Karl H.; Williamson, Eric B., 1968-; Tassoulas, John L.; Wood, Sharon L.; Mear, Mark E.; Helwig, ToddBridge redundancy can be described as the capacity that a bridge has to continue carrying loads after suffering the failure of one or more main structural components without undergoing significant deformations. In the current AASHTO LRFD Bridge Design Specification, two-girder bridges are classified as fracture critical, which implies that these bridges are not inherently redundant. Therefore, two-girder bridges require more frequent and detailed inspections than other types of bridges, resulting in greater costs for their operation. Despite the fracture-critical classification of two-girder bridges, several historical events involving the failure of main load-carrying members in two-girder bridges constructed of steel plate girders have demonstrated their ability to have significant reserve load carrying capacity. Relative to the steel plate girder bridges, steel box-girder bridges have higher torsional stiffness and more structural elements that might contribute to load redistribution in the event of a fracture of one or more bridge main members. These observations initiated questions on the inherent redundancy that twin box-girder bridges might possess. Given the high costs associated with the maintenance and the inspection of these bridges, there is interest in accurately characterizing the redundancy of bridge systems. In this study, twin steel box-girder bridges, which have become popular in recent years due to their aesthetics and high torsional resistance, were investigated to characterize and to define redundancy sources that could exist in this type of bridge. For this purpose, detailed finite element bridge models were developed with various modeling techniques to capture critical aspects of response of bridges suffering severe levels of damage. The finite element models included inelastic material behavior and nonlinear geometry, and they also accounted for the complex interaction of the shear studs with the concrete deck under progressing levels of damage. In conjunction with the computational analysis approach, three full-scale bridge fracture tests were carried out during this research project, and data collected from these tests were utilized to validate the results obtained from the finite element models.Item Modeling flexural failure in composites using ANSYS ACP(2021-05-07) De Sousa Burgani, Thiago; Tehrani, MehranWith composite materials showing extensive growth in aerospace, automotive, medical, energy, and other sectors, it is paramount that engineers understand the key differences between “classical” materials, such as steel, aluminum, and titanium (isotropic), and composite materials (anisotropic) when designing. Carbon fiber reinforced polymers (CFRPs) are among the most used composites in industries. Benefits of CFRPs include higher strength- and stiffness-to-weight ratios, established material supply, chemical resistance, and being biologically inert. However, CFRPs, like many composites, can fail in catastrophic ways with no indication of failure. As such, understanding the material and using modern tools, such as finite element analysis (FEA), is critical in ensuring the high standard of safety required by the industries which most use composites. This report has two major sections, both focusing on the modeling of CFRPs using the FEA package ANSYS. The first major section focuses on the development of an add-on program to the engineering curriculum, which attempts to introduce ANSYS FEA, specifically for the Composites Design & Manufacturing class currently taught by Dr. Mehran Tehrani. Through a series of video tutorials and two assignments, I teach students how to apply the theoretical knowledge obtained through the class into modeling and understanding mechanisms of failure in composites. I additionally branch into common techniques that accompany FEA, such as verification, validation, and mesh convergence studies. The second major section focuses on my research work in the strength prediction of composite materials. Through using ANSYS ACP and ANSYS Mechanical, I develop finite element models that simulate ASTM D7264, a testing standard for 3-point bending tests of fiber reinforced polymer composites. I develop a model to predict the flexural strength and verify and validate the model using beam theory, as well as external experimental data. Finally, I evaluate several failure criteria in composites, and draw conclusions on their performance when predicting flexural strength of select CFRP systems.Item Pipeline health monitoring using helical guided ultrasonic waves(2022-02-14) Livadiotis, Stylianos; Salamone, Salvatore; Haberman, Michael R; Kinnas, Spyridon A; Sela, PolinaPipelines are a vital component in the gathering, transmission, and distribution networks of oil and gas products around the globe. Monitoring the structural integrity of pipes is extremely important because it enables normal operational conditions, minimizes fatal accidents, and eliminates environmental destruction. Many pipeline accidents are reported each year in the US with corrosion being one of the most common forms of failure causing significant wall-thickness and pressure loss. To this aim, this thesis investigates the use of active and passive acoustic methods to localize, monitor, and quantify corrosion in steel pipelines. This is achieved by exploiting the helical guided ultrasonic waves (HGUW) in combination with numerical modeling and advanced data processing techniques. The main advantage of using the HGUW over traditional guided waves is the ability to use a small number of permanently attached sensing units, shifting the paradigm towards an automated and autonomous pipe health monitoring scheme. As far as active monitoring is concerned, a two-step corrosion localization and quantification algorithm has been developed using the HGUW. This algorithm combines a well-establish medical imaging algorithm, the algebraic reconstruction technique (ART), along with 2-dimensional acoustic modeling to detect and reconstruct different defects. This method relies on the scattering of the incident guided waves on surface anomalies. To establish the sensitivity of the guided modes to different corrosion profiles, finite element simulations were carried out using ABAQUS commercial software. Several experiments have been conducted to evaluate the performance of the algorithm including an accelerated corrosion test with the findings suggesting that a 5-ft long, 12-in diameter pipe can be effectively screened for high contrast defects using only six sensors. Furthermore, the potential of using the acoustic emission (AE) technique to passively monitor corrosion was also investigated. This was achieved by collecting HGUW-type AE activity produced by corrosion mechanisms like pitting and surface peeling. The use of the b-value analysis was proposed for processing the AE activity which could reveal the corrosion intensity as well as indicate critical states of the corrosion evolution in the pipe. This method was validated using an accelerated corrosion experiment as well as finite element simulations. Overall, a good correlation was observed between theoretical, experimental, and numerical results suggesting that the HGUW can be utilized in both active and passive modes to assess the structural condition of pipelines.