Browsing by Subject "Structural analysis (Engineering)"
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Item A study of matrix structural analysis(Texas Tech University, 1964-08) Scales, Morris RayNot availableItem An explicit iterative method for solving finite element equations(Texas Tech University, 1981-08) Chou, Gee DavidNot availableItem Analysis of a shell of elliptical cross-section under internal pressure and body force(Texas Tech University, 1997-12) Zheng, Qiu ShiCargo tank vehicles are responsible for the delivery of 79% of the hazardous materials transported by highway in the United States. The majority of these tanks have non-circular cross section (elliptical, oval). There are currently no analytical methods available to determine the stresses in the shells and heads of non-circular cross-section tanks. Basic methods must be developed to determine the distribution of stresses in such structures. A more accurate determination of thickness will impact safety, environmental and economic issues. In this dissertation, the explicit governing equations of linear elasticity for shells of elliptical cross section are obtained by defining the principal radii of curvatures in terms of local coordinates. Also, from those general equations, the system of equations for cylindrical shells of elliptical cross-section under intemal pressure is obtained. These equations are then solved for normal force, shear force, and bending moment. The solutions are compared with existing theoretical and FEA results, and the comparison shows good agreement. Additionally, the system of equations for cylindrical shells of elliptical cross-section under both body force and intemal pressure is obtained from those general equations. The expressions for normal force, shear force and bending moment are developed analytically and evaluated numerically. A comparison of these results with those for the case that considers only intemal pressure shows that in a range ofthe ratio of body force to intemal pressure, the maximum normal force and bending moment are reduced.Item Dynamic analysis of guyed towers subjected to wind loads incorporating nonlinearity of the guys(Texas Tech University, 1999-08) Kaul, RohitGuyed masts are unique civil engineering structures, structurally efficient, selfsupporting lattice towers. High structural efficiency of guyed towers is achieved by the use of pre-tensioned cables and a skeletal design. The height of guyed masts can exceed 600m (Sparling, 1995), therefore they are extensively used by telecommunication industry. Guyed towers also have the highest failure rate. Since 1959, there have been 100 confirmed collapses of guyed towers in United States (Madugula, 1998). Failure of guyed tower results in significant economic loss and human inconvenience. This report emphasizes on the study of guyed towers subjected to dynamic wind loads. A schematic of guyed tower is shown in Figure 1.1. Typically the guyed mast is constructed as a triangular space truss with warren or cross-praced configuration. The mast is pinned or fixed at the base while the top usually supports an antenna. Pretensioned cables, radiating symmetrically from the mast at several elevations, provide lateral support to the mast. Traditional techniques for the analysis of guyed towers rely on pseudo-static analysis and are insufficient because of significant secondary effects and nonlinear behavior of cables. Due to overall flexibility, slendemess and lightweight, guyed masts are susceptible to large deflections and also exhibit high dynamic sensitivity to turbulent winds. As a result, dynamic analysis is considered imperative for calculating the peak axial forces in the mast. Other environmental factors like icing and snow accumulation on cables can significantly enhance the mast response, sometimes resulting in structure failure.Item Evaluation of the effectiveness of API-modified Goodman diagram in sucker rod fatigue analysis(Texas Tech University, 2001-08) Nampoothiri, M. P ParameswaranIn petroleum engineering applications an understanding of the fatigue behavior of metals is of great importance primarily in the selection of sucker rods. Of all the components of the oil-well pumping mechanism, sucker rods have the greatest effect on the action and performance of the whole pumping system. The behavior of the sucker rods in the transfer of forces and loads determines the action of the pump. Their inherent characteristics affect the loads imposed on the surface equipment. For years, the Goodman diagram is the basis of analyzing the endurance (fatigue) life of ferrous material. Goodman published the diagram during the year 1908. An American Petroleum Institute (API) Committee suggested several design factors for Goodman Diagram in order to adapt it specifically to specifically sucker-rod pumping installations. The diagram is known as the API Modified Goodman diagram. The committee had suggested the following revisions to original Goodman Diagram. They are: (1) The apex of the diagram should be set at the tensile strength of the material. (2) The >^-intercept should have a factor of safety of two. (3) The safety factor on the material tensile strength apex should be 1.75. The result was the creation of API Modified Goodman Diagram. The design formula for the allowable stress line is given as: S,={T/4+MSmin)SF…………………………………………………………………………………(1) where Sa = Allowable maximum stress, psi, T= Minimum tensile strength, psi, M= Slope of the allowable stress line = 0.5625, Smin = Minimum stress, measured or calculated, psi, SF = Design Safety Factor. Since this diagram is used for the design of permissible stresses for sucker rod installations, it is imperative that the design engineer understands the loads imposed on the sucker rods; however, conventional polish rod dynamometer analysis does not provide sufficient information regarding down-hole load conditions. Since the rods available today is superior due to the improved manufacturing processes and testing facilities, this thesis is an experimental study the effectiveness and accuracy of the "API Modified Goodman Diagram." Tests conducted at 160% of the stress range as specified in the API Modified Goodman Diagram on 5/8 inch. Grade 'D' sucker rod specimens resulted in the following findings: 1. The Y-intercept of the diagram can be changed to r/2.5 as compared to T/4 given by the API Modified diagram. 2. The slope of the allowable stress line is found to be 0.3 as compared to the 0.5625 given by the Modified Goodman diagram. In effect, the test results indicate that the present API Modified Goodman diagram is conservative and the formula for the allowable stress line could be revised to Sa =(T/2.5+ MSmin)SF………………………………………………………………………(2) where, Sa = Allowable stress, psi, T = Minimum Tensile Strength, psi, M= Slope of the allowable stress line = 0.3, Smin= Minimum Stress, psi, SF= Safety Factor.Item Implementation of automated multilevel substructuring for frequency response analysis of structures(2001-12) Kaplan, Matthew Frederick; Bennighof, Jeffrey Kent, 1960-In the design of vehicles, such as automobiles, aircraft, spacecraft, or submarines, it is important to be able to accurately predict dynamic behavior of the structure. With the extremely high cost of building physical prototypes of these vehicles, there is a growing emphasis on analysis of computer models. In this dissertation, a method known as Automated Multilevel Substructuring (AMLS) is presented for accurately solving frequency response problems involving large, complex models with millions of degrees of freedom. Conventional methods for addressing these problems, such as mode superposition using a Lanczos eigensolver or model reduction using component mode synthesis, are reviewed. The Automated Multilevel Substructuring (AMLS) method partitions finite element models into substructures, similar to component mode synthesis methods, but uses an automated partitioning procedure that reduces the burden on the analyst. The finite element matrices are projected onto a reduced subspace, on which the frequency response is computed. Two frequency response algorithms are presented. Both methods require the solution of a global eigenvalue problem on the reduced subspace. The first method uses straightforward mode superposition. The second method employs a new iterative approach in which the modal frequency response leads to a residual problem that is solved using an iterative splitting method. The global eigensolution and frequency response algorithms are specifically designed to take advantage of the properties of the reduced subspace. Numerical examples are presented for models with millions of degrees of freedom. The performance and accuracy of the AMLS method are compared to the standard commercial software package for large-scale linear dynamic analysis. These examples establish that AMLS can be used to accurately obtain the response of very large models with significantly less computational resources than competing methods. In comparison to the modal frequency response obtained with the standard commercial software package using a shifted block Lanczos algorithm, AMLS ran up to 6.4 times faster, used less memory, and required an order of magnitude less data transfer. Thus, the AMLS method makes it possible to do frequency response analysis of large, complex structures at higher frequencies than was previously practical.Item Natural frequencies of two elementary rigid frames(Texas Tech University, 1964-05) Shadden, James ArthurThe natural frequencies of two elementary rigid frames, the rectangular bent and the two member frame, were determined for various ratios of length, moment of inertia, and mass per unit length of the vertical and horizontal members. The natural frequencies were found by solving the frequency equation which was obtained from the partial differential equation of motion of a distributed mass and elasticity beam. Both motion in the plane of the frame and motion perpendicular to the plane were considered. To verify the analysis, the natural frequencies were determined by an experimental method, and the two results compared.Item Parametric design methodology and visualization for single curvature tensegrity structures(2004) Kim, Jinman; Liapi, Katherine A.Tensegrity structures are a special type of tensile structures consisting of cables (in tension) and bars (in compression) that can offer an alternative to conventional space covering structures. Geometric complexity inherent to these structures has posed a significant challenge in their geometric and structural design and limited their applications in buildings. This research is intended to develop a parametric design methodology for single-curvature tensegrity networks to address problems in their configuration and analysis. An important feature of the methodology is the development of an integrative visualization environment to assist in their form exploration and performance. The methodology involves a) the development of algorithms to address the geometry of vaulted configurations that generate models of initial geometry b) integrating design algorithms to structural analysis and development of models of pre-stressed geometry, and c) importing the pre-stressed geometry model into a CAD environment. Specifically, 3D coordinates of a preliminary tensegrity structure are generated by the design algorithms, automatically processed by an existing analysis code, and visualized in CAD environment by the graphical interface. Resulting 3D solid models of the structure can then be used by architects and engineers to validate the design performance of preliminary configurations under consideration. The morphological variation considered in this study is that of vaulted configuration composed of tensegrity units of square-base with bar to cable connection.Item Roof pressures in the corner region measured on a full-scale low-rise building(Texas Tech University, 2003-05) Jokhu-Sowell, Urmilla NCorner vortices along the roof have proven to be one of the most destructive forces created when wind interacts with a building. Conical vortices are generated close to the corner along both edges of the roof when the wind angle of attack acts Into the roof corner. To better understand the characteristics of the pressures generated by the vortices on the roof corner, researchers at Texas Tech University densely instrumented a roof corner area of the test building at the Wind Engineering Field Research Laboratory (WERFL) with pressure transducers. The data collected results In a high-resolution spatial and temporal data set, which Is used to examine the correlation structure of point pressure coefficients, time-averaged, and area-averaged pressures beneath the corner vortex on a full-scale building with a flat roof. Area and time average pressures are compared with the wind load provisions of ASCE 7-02.Item Shielding effects on housing in neighborhoods(Texas Tech University, 2003-12) Stuckley, Ameri BIn this study, shielding is referred to as the effect upwind and/or downwind structures have on the wind loads of an instrumented model. Because of shielding, a home in a neighborhood of like sized homes or a home surrounded by a fence would feel the effects of the wind less than a home in an open field. Numerous tests were conducted in a wind tunnel study undertaken at Texas Tech University on a single model, with 98 total pressure taps, of a low rise building surrounded by like sized homes at differing arrangements. Tests were also conducted with a representative, 35% porosity fence at varying distances upwind of the instrumented model. Point pressures were integrated to give uplift and drag forces on the models. The aim was to obtain a better understanding of shielding and the parameters of significant influence in a domestic scale neighborhood. The results of this study have produced these conclusions: 1. The wind tunnel results for the isolated home agreed with codified values of ASCE7-02 and AS 1170.2 and with values found by the studies of Holmes and Best. 2. The addition of an adjacent row changes the overall drag (-5%) and uplift (+10%) forces very little. 3. Shielding is provided by a single row of like sized homes upwind up to 16 times the eaves height (Sx/h = 16) of the instrumented model. 4. When spaced at a distance of 4 times the eaves height, shielding remains when multiple rows are added upwind. When considering the mean values, shielding appears unaffected after two rows. When looking at the pseudo-steady values, however, there appears to be a decrease in shielding due to the reattachment of the separation bubble after 3 rows. 5. Maximum shielding is provided when the wind attacks normal to a wall. When rows are added upwind and downwind of the instrumented model, funneling occurs and larger forces were recorded on the instrumented model for wind directions other than normal to a wall for a regular array of elements. 6. At close spacing, 4 times the eaves height, the homes and fence provide the same shielding. As the spacing is increased, the fence provides greater shielding. This effect is more evident in the configuration with the additional row downwind. 7. When comparing the results from the wind tunnel to those of the Australian and American wind load codes, the current standards are conservative.Item Size limits for timber storm shelters(Texas Tech University, 2004-12) Davidson, Justin RayNot availableItem Structural analysis of aboveground storm shelters(Texas Tech University, 2002-12) Shamsan, Sanad Abdullah SallamNot availableItem Vibration absorbers for flexible structures under random excitation: theory and experiments(Texas Tech University, 1999-08) Çiçek, IsmailA large number of flexible mechanical stmctures such as aerospace and ocean stmctures which are subjected to random excitation may be modeled as a flexible beam with a tip mass. Under certain conditions (high excitation amplitude, etc.), large deformation may sometimes be produced in the stmcture, which may cause the system to fail. In this research, a flexible beam with a tip appendage, which consists of a masspendulum attached to its tip, is investigated under random excitation. The pendulum is used as an autoparametric vibration absorber. The energy transfer between the beam and the pendulum and the vibration absorption characteristics of the pendulum are observed both theoretically and experimentally. The equations of motion, in the form of integro-differential equations goveming the system dynamics, are obtained using D'Alembert's Principle. The Galerkin method is used to obtain the system ordinary differential equations. The equations are nondimensionalized, and the acceleration coupling terms are eliminated to write the equations in Markov space. The moment closure schemes, in conjunction with stochastic averaging, are used to solve for the mean-square response of the beam and the pendulum. The dependence of mean square responses on the frequency ratio is studied. For the experimental investigation, time histories, mean square responses, autocorrelation, power spectral density, and probability density functions of the system parameters are observed and presented to reveal the energy exchange between the beam and the pendulum. To observe the autoparametric interaction and vibration absorption characteristics of a continuous pendulum, a one-story building with a continuous pendulum system was also studied experimentally. The outcome of this research reveals the scope and limitations of the beampendulum oscillator as a vibration-absorbing device in applications where random disturbance occurs.