Browsing by Author "Criswell, Marvin E., committee member"
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Item Open Access Application of model reduction tools in analysis of wind-induced pressures on low-rise buildings(Colorado State University. Libraries, 2012) Wu, Chieh-hsun, author; Bienkiewicz, Bogusz, advisor; Criswell, Marvin E., committee member; Sakurai, Hiroshi, committee memberRecent advances in laboratory and field measurement techniques and numerical simulations of wind-induced loading on buildings and structures made possible generation of large data sets, suitable for database-assisted wind-resistant design. In parallel, data reduction tools have been developed to aid storage, management and accessibility issues associated with large datasets/databases. In the presented research, application of such tools in analysis of stationary and non-stationary wind-induced pressures on a generic low-rise building is discussed. Both stationary and non-stationary cases are addressed. In stationary analyses, Proper Orthogonal Decomposition (POD) and Method of Snapshot (SPOD) were used to identify the most energetic spatio-temporal structures of the pressures. Linear Stochastic Estimation (LSE) and Gappy POD (GPOD) were employed to generate the pressures at specified target locations via extrapolation of the pressures provided at chosen reference locations. Optimized reference positions were determined using algorithm-based and empirical approaches. In non-stationary analyses, Wavelet De-noising and Two-Stage-Moving-Averaging were applied to decompose the non-stationary pressure into time-varying mean, standard deviation and normalized fluctuation. The techniques developed for stationary pressures were adapted for non-stationary cases. In analysis of the stationary data, the extrapolation techniques (GPOD and LSE) were found to reduce the data more efficiently than the modal reduction tools (POD and SPOD). In pressure extrapolation, LSE provided more accurate pressure predictions than GPOD. A hybrid approach combining the use of GPOD, with algorithm-based reference positions selection, and LSE extrapolation enabled the most efficient capturing of the primary and secondary spatio-temporal features of the pressure. This technique is recommended for analyses focused on development of reduced models of wind pressures induced on low-rise buildings. In the non-stationary investigations, the hybrid GPOD-LSE technique, developed in analysis of the stationary pressures and modified for the non-stationary cases, led to accurate pressure predictions and model reductions. This methodology appears to be a suitable tool for similar analyses of non-stationary wind-induced pressures on low-rise buildings. Follow-up investigations of stationary and non-stationary cases are recommended to assess potential for further optimization of the developed techniques and their application in analyses of wind-induced loading on other buildings and structures.Item Open Access Application of symbolic computing in analysis of modal properties of structurally coupled twin tall buildings(Colorado State University. Libraries, 2011) Richards, Eric Lee, author; Bienkiewicz, Bogusz, advisor; Criswell, Marvin E., committee member; Shuler, Scott, committee memberThis thesis develops non-dimensionalized symbolic expressions for the normalized natural frequencies of two identical tall buildings structurally connected by a skybridge. Symbolic expressions for the modal shapes are also developed to express the coupled movements of the two buildings. The mass and stiffness of the two tall buildings are generalized and reduced to the skybridge level, and the equations of motion are evaluated with Maple 13 math and engineering software. A parametric study of the effects of coupling stiffness on the modal properties is carried out using formulas resulting from symbolic computing. The obtained symbolic expressions are compared with the results of numerical analysis performed using Risa-3D structural engineering analysis software. Findings of this thesis show a good agreement between the symbolic expressions and Risa-3D results. The developed symbolic equations are proposed as a tool for use in the preliminary analysis of tall buildings connected by a skybridge.Item Open Access Energy use and emissions reduction strategies for structural steel fabricators: a case study(Colorado State University. Libraries, 2010) Bergstrom, Erik Anderson, author; Guggemos, Angela Acree, advisor; Criswell, Marvin E., committee member; Hamzeh, Farook, committee memberEnergy price escalation, natural resource depletion, and wide-spread environmental degradation are driving demand for more sustainable construction methods and materials. Steel fabricators working to operate more sustainably require detailed energy and environmental analysis of operational practices in order to make informed improvements. Yet only limited research exists on the energy use and emissions associated with fabrication and material sourcing for structural steel used in building construction. This research involves a life-cycle inventory assessment of structural members used in a case-study building to address this gap in research and identify high-impact areas for future process improvement at one fabrication facility. With a life-cycle inventory model developed, feasible process improvements are measured against standard practices, and the associated energy savings and environmental improvements are identified. The main discovery of this research is that while the fabricator has the ability to make significant energy and emissions reductions by modifying operational process within their own facility, the most impactful opportunities are in material selection alternatives, such as sourcing reused materials. Structural steel fabricators can use these findings to reduce environmental impacts and operating costs, while delivering a more environmentally preferable product.Item Open Access In vivo efficacy of antibiotic-eluting phospholipid coated implants(Colorado State University. Libraries, 2011) Triffo, Thomas, author; James, Susan P., advisor; Criswell, Marvin E., committee member; Ehrhart, Nicole P., committee memberImplant-associated infection can be a serious problem for patients that receive orthopedic implants, such as hip and knee replacements. This is a common cause for early implant loosening, which requires revision surgeries and results in an even greater risk of infection. To address this issue, our lab has developed a novel electrospraying technique for applying phospholipid coatings to orthopedic implants. These coatings consist of two layers of 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS), with antibiotic loaded in between layers. In vitro tests were performed to evaluate how modifications to these coatings affect coating retention, based on a clinically relevant test, and antibiotic elution from these coatings. Coating retention tests were performed by inserting implants through segments of mouse bone and then examining the implants under SEM. Antibiotic elution was performed using a total sink elution combined with OPA assay for detection of antibiotic. These results showed that the coatings that were retained the most and eluted antibiotic slowest were samples that were pre-treated with calcium and were electrosprayed with a mixture of 6:1 DOPS-to-cholesterol. This coating was selected to be used in an in vivo study to determine the efficacy of the coatings in treating osteomyelitis. Osteomyelitis was induced in a murine model using genetically modified bacteria, which allowed tracking of the infection prior to sacrificing the animals via bioluminescent imaging, a technique that makes use of genetically modified bacteria producing luciferin and luciferase which causes emission of photons. It was observed that antibiotic-eluting implants cleared the infection faster than implants without antibiotic during a 4 week study. Also, no kidney damage was observed based on creatinine, blood urea nitrogen, and urine protein tests. Histology confirmed observations from the bioluminescent imaging. These results show that our antibiotic-eluting implant coatings were able to reduce infection in vivo without resulting in adverse effects. Bioluminescent imaging showed significant reduction of emission of photons, p < 0.05, in the antibiotic loaded group compared to the control samples. The results also suggest that the implants exhausted their supply of antibiotic at the end of the study, and in future studies a greater amount of antibiotic will be loaded onto the implants.Item Open Access Performance-base seismic design of woodframe buildings using non-linear time history analysis(Colorado State University. Libraries, 2010) Liu, Hongyan, author; van de Lindt, John W., advisor; Criswell, Marvin E., committee member; Heyliger, Paul R., committee member; Senior, Bolivar, committee memberPerformance-based seismic design (PBSD) is a developing design methodology in the modern seismic design and research community and has already been applied to concrete and steel structures. However, the application to woodframe buildings, which represents the vast majority of the residential building stock in North America, is still under early stage of development. The total economic loss directly connected with woodframe structures was more than $20 billion after the 1994 Northridge earthquake in California. This lesson provided the impetus for both engineers and researchers to realize that seismic design should focus on system behavior during an earthquake event instead of just at the component behavior, in other words, explicitly considering system behavior and performance of a structure. The current focus in force-based design philosophy for wood looks at the component level and then makes the assumption that system performance is ensured by the component design. Because of the limitations in current design methodology and concerns of system level performance, the concept of PBSD is being adapted and applied to woodframe buildings. The ultimate goal of this study is to develop a generalized PBSD procedure that can provide a specific level of performance for woodframe buildings under prescribed earthquake loading levels. In order to achieve this goal, this study focuses on four objectives. The first objective is to develop a conceptual PBSD procedure suitable for woodframe buildings. This includes defining the performance expectations at system level with explicit probability measures, choosing an appropriate format for the design requirements, deciding on the numerical tools and steps to determine the design that satisfies these design requirements. The second objective is to improve the existing numerical model and include base isolation device as an option to woodframe buildings for the PBSD. This task involves numerical modeling and experimental testing of friction pendulum sliding bearing base isolation devices on the shake table at CSU. The third objective is to apply the proposed design procedure to realistic building designs. This includes several design examples in this study having different floor plans from low-rise to mid-rise buildings. The examples included in this study cover several typical floor plans in the U.S. for residential buildings. The design example also includes the use of FP base isolation on a mid-rise woodframe structure. Finally, the last objective of this study is to develop a simplified design procedure that can be used by average engineers without using advanced structural models and non-linear time history analysis. This was accomplished by developing the design tables that are generated through simplified models using non-linear time history analysis. The results are checked with full simulation thereby validating the approach. The most significant anticipated contribution of this study to the woodframe design and research communities will be the development of a generalized PBSD and is only applied to a limited number of examples in this dissertation, the format of this procedure was based on and improved from the current state-of-the-research and can be extended to many different situations including base isolation as demonstrated herein. The simplified design procedure and the format of the design table is a good candidate for incorporation of PBSD into design practice because of the prescriptive approach.Item Open Access Three-dimensional finite element model to predict pole strength(Colorado State University. Libraries, 1992) Franco, Nilson, author; Pellicane, Patrick A., advisor; Bodig, Jozsef, committee member; Criswell, Marvin E., committee member; Shuler, Craig E., committee memberA three-dimensional finite element model was used to predict the strength and location of failure of nine wood transmission poles. The poles were made from three commonly used species (western red cedar, Douglas-fir and southern pine) in North America. All poles were tested to failure as a cantilever beam with a concentrated load applied to the tip. The methodology involved was to select several eighteen inches long segments, located along the poles, which contained the most severe defects such as cluster of knots, spiral grain, including material inhomogeneity in the highly stressed region. Each segment was analyzed using the finite element technique with appropriate boundary conditions. Material properties for each segment were determined by measuring clear-wood elastic and strength parameters in boles taken from broken poles. The information about knots and spiral grain, obtained by visual inspection of the pole surface, was used to identify the worst knot clusters and grain deviation in any segment. Knots were modeled in the finite element mesh and the localized grain deviation around the knots were determined through the use of the flow-grain analogy model. Finite element computer analysis were performed through the use of the program GTSTRUDL. The model resulted in a total of 288 three-dimensional, isoparametric, linear strain, 20-node parallelopiped and 15-node wedge shaped elements. For the nine poles studied, the results showed good agreement between predicted and experimental strength. The predicted values for strength differed from the actual ones with an average deviation of 7% (below the actual). Concerning failure location, in six of the poles, failure was verified in the same places as those predicted by the model. In the three other cases the failure with the maximum error of three feet, except for one pole where the deviation was twelve feet. The study revealed that the three-dimensional finite element approach to model growth characteristics applied to the more critical segments along the pole length proved to be very useful tool for strength and failure location prediction of poles.Item Open Access Wind induced stresses on treehouse structures(Colorado State University. Libraries, 2011) Bradley, William Edward, author; Heyliger, Paul Roy, 1958-, advisor; Criswell, Marvin E., committee member; Glick, Scott A., committee memberTreehouses have recently become a profitable public attraction in the United States. With this increase in popularity, it becomes important to standardize treehouse engineering practices as an important step towards regulation of these structures. This thesis outlines common practices among treehouse engineers and makes suggestions for calculation of the self-weight of a tree and stresses due to gravity and wind loads. In particular, this thesis uses a finite element model to analyze a foliage-free cottonwood tree with a rectangular treehouse under typical maximum wind loadings. Six scenarios are investigated, with a treehouse at different heights. Elastic analysis is used to determine the stresses due to wind near the base of the tree.Item Open Access Wind tunnel modeling and analysis of wind effects on low-rise buildings(Colorado State University. Libraries, 2011) Endo, Munehito, author; Bienkiewicz, Bogusz, advisor; Criswell, Marvin E., committee member; Neff, David E., committee member; Young, Peter, committee memberWind tunnel modeling is a robust technique which allows determination of wind effects on buildings and other structures. Due to complexity of flows and induced wind loads, other techniques can not be reliably used in practical analyses of such effects. Information deduced from wind tunnel testing has been successfully employed in development of design guidelines and in direct applications in wind-resistant design of variety of structures, including low-rise buildings. Although wind tunnel modeling of wind loading has been generally accepted as a viable tool, over the years a number of questions regarding accuracy and limitations of this technique have been raised. Some of the questions related to modeling of wind loading on low-rise buildings were addressed in the research described in this dissertation. Investigation of reported discrepancies in the laboratory-field and inter-laboratory comparisons was one of main focuses of this study. To identify the origins of the discrepancies, careful studies of reported wind tunnel set-ups, modeling of field/target approach wind conditions, measurement techniques and quality of obtained data and data analyses were carried out. Series of experiments were performed in boundary-layer wind tunnels at the Wind Engineering and Fluids Laboratory, at Colorado State University, to aid these analyses. It was found that precise matching of characteristics of approach field wind and flows modeled in wind tunnels was essential to ensure compatibility of the simulated building wind loads. The issue of the accuracy of predictions of the extreme wind-induced loading based on the results of wind tunnel modeling was addressed. In this investigation, the peak wind-induced pressures on low-rise buildings were analyzed using two advanced techniques: the extreme value distribution theory (GEV) and the peak-over-threshold approach. The extreme roof suction pressures predicted from these two approaches were compared with field observations. The degree of convergence of the EVD fits was discussed for Type I and Type III EVDs. The advanced experimental tool, electronically-scanned 1024-channel pressure measurement system, was developed and employed in wind tunnel modeling of wind loads on low-rise building. The wind-induced pressures were simultaneously acquired at 990 locations uniformly distributed over the surfaces of a model of a generic low-rise building. The Proper Orthogonal Decomposition (POD) analysis was performed to capture the spatio-temporal characteristics of the acquired pressure field. It was found from POD analysis that the pressure data sets can be substantially reduced, while preserving the main spatio-temporal features of the building wind loading.