Browsing by Author "Ohanehi, Donatus C."

Now showing 1 - 5 of 5
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    Characterization and Lifetime Performance Modeling of Acrylic Foam Tape for Structural Glazing Applications
    Townsend, Benjamin William (Virginia Tech, 2008-09-12)
    This thesis presents the results of testing and modeling conducted to characterize the performance of 3M™ VHB™ structural glazing tape in both shear and tension. Creep rupture testing results provided the failure time at a given static load and temperature, and ramp-to-fail testing results provided the ultimate load resistance at a given rate of strain and temperature. Parallel testing was conducted on three structural silicone sealants to compare performance. Using the time temperature superposition principle, master curves of VHB tape storage and loss moduli in shear and tension were developed with data from a dynamic mechanical analyzer (DMA). The thermal shift factors obtained from these constitutive tests were successfully applied to the creep rupture and ramp-to-fail data collected at 23°C, 40°C, and 60°C (73°F, 104°F, and 140°F), resulting in master curves of ramp-to-fail strength and creep rupture durability in shear and tension. A simple linear damage accumulation model was then proposed to examine the accumulation of wind damage if VHB tape is used to attach curtain wall glazing panels to building facades. The purpose of the model was to investigate the magnitude of damage resulting from the accumulation of sustained wind speeds that are less than the peak design wind speed. The model used the equation derived from tensile creep rupture testing, extrapolated into the range of stresses that would typically be generated by wind loading. This equation was applied to each individual entry in the data files of several real wind speed histories, and the fractions of life used at each entry were combined into a total percentage of life used. Although the model did not provide evidence that the established design procedure is unsafe, it suggested that the accumulation of damage from wind speeds below the peak wind speed could cause a VHB tape mode of failure that merits examination along with the more traditional peak wind speed design procedure currently recommended by the vendor.
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    Characterization of a Pressure Sensitive Adhesive (PSA) for Mechanical Design
    Hennage, John B. (Virginia Tech, 2004-10-12)
    This thesis outlines a methodology for formatting and applying stress models, collecting visco-elastic material properties, and presenting the material data for use in adhesive joint designs. There are a number of models/theories that can be applied to the design of Pressure Sensitive Adhesive (PSA) joints. Unfortunately, few design engineers are familiar with these models and the models are not formatted in a manner that can easily be applied to joint designs. By developing a format that is based on the existing knowledge of the designer and presenting them in a familiar manner the theories/models can easily be used in joint designs. This technique was demonstrated with Beam-on-Elastic Foundation, Shear Lag, and Shape Factors. Design examples successfully demonstrated the application of all of these models in the analysis and design of simple adhesive joints. The material properties of PSAs are a function of loading/displacement rate, temperature, relative humidity, and stress state. The Arcanm fixture was used to test VHB™ 4950 over a range loading and stress states including fixed load and displacement rates. Several bond widths were tested to determine the extent of the shape factor effect. A second fixture was used to determine the impact of gradient-tensile stresses on the failure strength. All of the collected data was used to generate design plots. The strength data was presented as allowable strength envelopes with respect to rate. The moduli were calculated from the load-displacement data and plotted with respect to the displacement rate. The failure strength from the fixed load and displacement data were used to transform from one loading case to the other and a plot was generated. These three plots were used in the design and analysis of several adhesive joints. The methods demonstrated in this thesis show a great deal of promises as a design tool, but there is still a large amount of work to be done. The design space for this material is much larger than what was covered by this work. Additional strength testing needs to be conducted to fully characterize the material for all key applications. The principle of time-temperature superposition, beam-on-elastic foundation, shear lag, and shape factors all need to be validated for this material.
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    Linear and Nonlinear Finite Element Analyses of Anchorage Zones in Post-Tensioned Concrete Structures
    Hengprathanee, Songwut (Virginia Tech, 2004-06-14)
    Linear and nonlinear finite element analyses are used for the investigation of rectangular anchorage zones with the presence of a support reaction. The investigation is conducted based on four load configurations consisting of concentric, inclined concentric, eccentric, and inclined eccentric loads. The method of model construction is illustrated thoroughly. The influence of several parameters, including anchorage ratio, inclination of prestressing load, eccentricity, magnitude of the reaction force, bearing plate ratio, and the location of the reaction force, is studied. Both graphical and numerical presentations of the results from each load configuration are given. Improved equations, which are modified from the equations presented in the AASHTO Standard Specifications (2002), are proposed. The results from the equations are compared to those from the finite element method. Nonlinear finite element analysis is used to verify the applicability of the equations and to study a new bursting steel arrangement. Linear and nonlinear finite element analyses are also used for the study of non-rectangular anchorage zones. Four basic load configurations, including concentric, eccentric, inclined concentric, and inclined eccentric loads, are investigated. The shell element is selected for the construction of the finite element models. Several parameters, consisting of anchorage ratio, inclination of prestressing load, eccentricity, web thickness, ratio of web thickness to flange thickness, and flange width, are chosen for parametric studies. The results from the studies are presented graphically and numerically. Equations to calculate the bursting force and location of the force are developed from the Strut-and-Tie Model approach. The verification of the formulations and the investigation of bursting steel arrangement are conducted using nonlinear finite element analysis.
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    Numerical Model for the Lateral Compression Response of a Plastic Cup
    Dapic, Ignacio (Virginia Tech, 2003-06-09)
    A numerical analysis based on the finite element method is developed to simulate the mechanical response of a typical sixteen-ounce plastic drink cup subjected to a lateral compressive load. The aim of the analysis is to simulate a test in which the cup is supported horizontally in a fixture on a testing machine platen, and a loading nose attached to the actuator is displaced downward into the cup. The numerical model is developed using the software packages MSC.Patran, ABAQUS/CAE, and ABAQUS/Standard. The high impact polystyrene material of the cup is modeled as linear elastic, considering isotropic and orthotropic material behavior. The structural model of the cup is a truncated conical shell including a ring at the open end of the cup and circumferential stiffening ribs. The analysis is based on small strain, large rotation shell kinematics, and the loading apparatus of the test is simulated with a rigid, circular cylinder contacting the cup. Coupons cut from the wall of a cup are subjected to tension to determine the ranges of the meridional and circumferential moduli of elasticity. Rings cut from the open end of the cup were tested in diametrical tension to aid in validating the finite element modeling. Reasonable correlation of the simulation to available cup compression test data is achieved. Parametric studies are conducted for several meridional thickness distributions of the cup wall, and for a range of orthotropic material properties.
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    Performance of Pressure Sensitive Adhesive Tapes In Wood Light-Frame Shear Walls
    Jacobs, William P. V. (Virginia Tech, 2003-04-28)
    The performance of connections and full-scale shear walls constructed with acrylic foam pressure sensitive adhesive (PSA) tape is the focus of this thesis. The objectives of this study were first to investigate the bonding characteristics of adhesive tape to wood substrates and then to expand this investigation to cover adhesive-based shear walls subjected to high wind and seismic loadings. A total of 287 monotonic connection tests and 23 reversed cyclic wall tests were performed to achieve these objectives. Connection tests were performed in accordance with ASTM D 1761-88 (2000), and walls were tested using the CUREE (Consortium of Universities for Earthquake Engineering) general displacement-based protocol. Variables investigated within the main study were the following: the use of OSB versus plywood sheathing, the effect of priming and surface sanding on adhesion, and the comparison of connections involving mechanical fasteners with those that utilized only adhesive tape or a combination of the two. It was found that an application pressure of 207 kPa (30 psi) or greater was needed to form a sound bond between the acrylic foam adhesive tape and a wood substrate. Properly bonded OSB and plywood connections provided fairly ductile failure modes. Full-scale walls constructed with adhesive tape performed similarly to traditional wall configurations, while walls constructed with a combination of adhesive tape and mechanical fasteners provided significant gains in strength and toughness. The results of this study serve to provide a foundation for expanding the engineering uses of acrylic foam adhesive tape for structural applications.