This study presents a method for predicting the undrained behavior of plate anchors, including out-of-plane loading of simple plates and performance of suction embedded plate anchors (SEPLA). Three dimensional finite element models are used to investigate the behavior of square and rectangular plate anchors under normal loading with eccentricity in any direction. Upper bound analyses are performed for parallel loading and torsion loading. A simple model is then fit to the FE and upper bound solutions to determine required fitting parameters for both square and rectangular plates. The simple models can, in turn, be used both to predict anchor capacity and as yield surfaces for conducting plastic limit analyses, a method capable of predicting post yield anchor trajectory. The model predictions are shown in reasonable good agreement with the experimental results. For SEPLA, a theoretical model of plastic limit analysis is developed to predict the trajectory during the “keying” process and the ultimate capacity after the “keying” is complete. The predicted results are consistent with relevant known solutions.

Due to most studies on vibration of pre-loaded rectangular plate being subject to uniform loading, this thesis will investigate vibration of plate under preloading with sine functional distributions. The approach behind this study is using first-order shear deformation plate theory and finite element method to analyze vibration frequency. Study results show that, when a plate¡¦s boundary condition is CCCC, SSSS, CFCF, or SFSF with sine functional pre-loading, its vibration frequency will increase to an extent with little difference when the number of modes increases. Vibration frequency will increase shortly then decrease when increasing the number of sine waves. Vibration frequency will also increase when increasing stress parameters. However, obvious frequency changes are observed only at lower modes with SFSF boundary condition.

The first instability of circular tubes compressed into the plastic range is axisymmetric wrinkling, which is stable. Compressed further the wrinkle amplitude grows, leading to a limit load instability followed by collapse. The two instabilities can be separated by strain levels of a few percent. This work investigates whether a tube that develops small amplitude wrinkles can be subsequently collapsed by persistent cycling. The problem was first investigated experimentally using SAF 2507 super-duplex steel tubes with D/t of 28.5. The tubes are first compressed to strain levels high enough for mild wrinkles to form and then cycled axially under stress control about a compressive mean stress. This type of cycling usually results in accumulation of compressive strain; here it is accompanied by growth of the amplitude of the initial wrinkles. The tube average strain initially grows nearly linearly with the number of cycles, but as a critical value of wrinkle amplitude is approached, wrinkling localizes, the rate of ratcheting grows exponentially and the tube collapses. Similar experiments were then performed for tubes involving axial cycling under internal pressure and the combined loads cause simultaneous ratcheting in the hoop and axial directions as well as a gradual growth of the wrinkles. The rate of ratcheting and the number of cycles to collapse depend on the initial compressive pre-strain, the internal pressure, and the stress cycle parameters all of which were varied sufficiently to generate vii a sufficient data base. Interestingly, in both the pressurized and unpressurized cases collapse was found to occur when the accumulated average strain reaches the value at which the tube localizes under monotonic compression. A custom shell model of the tube with initial axisymmetric imperfections, coupled to the Dafalias-Popov two-surface nonlinear kinematic hardening model, are presented and used to simulate the experiments performed. It is demonstrated that when suitably calibrated this modeling framework reproduces the prevalent ratcheting deformations and the evolution of wrinkling including the conditions at collapse accurately for all experiments. The calibrated model is then used to evaluate the ratcheting behavior of pipes under thermal-pressure cyclic loading histories experienced by axially restrained pipelines. / text

Failures of high mast illumination poles (HMIPs) in recent years have raised concerns on the long-term fatigue performance of the poles by various transportation officials around the US. The thesis documents a study sponsored by the Texas Department of Transportation focused on the fatigue behavior of in-service HMIP systems. This study is an extension of previous investigations on the fatigue behavior of the poles that have demonstrated that many poles have poor performance and fail in fatigue before the AASHTO category E' limit. Galvanized specimens were also tested and some of them showed evidence of initial cracking, impacting the fatigue performance such that the galvanized poles behaved worse than the uncoated specimens. Ultrasonic Testing (UT) has shown several poles around the state of Texas contain cracks in the welds between the shaft and base plate. To further investigate the performance of the poles in-service, a field study was initiated to measure the wind speed and direction, as well as the corresponding stresses in the pole shaft. This thesis presents results from the field investigation. A data acquisition system was developed to gather wind data and induced stresses. The system was powered by a solar panel and can be remotely accessed via a wireless modem. Data collected throughout the year details the intensity and number of stress cycles experienced by the poles, and could be correlated with the measured wind velocity. Using the field data, more accurate estimates of expected fatigue life for the poles were made. The study provides TxDOT with valuable data on the performance of in-service poles so that the most critical fatigue cases can be identified and proper decisions can be made on the appropriate inspection or repair schedule. / text

published_or_final_version / Mathematics / Master / Master of Philosophy

The loading problem in a Flexible Manufacturing System (FMS) lies in the allocation of operations and associated cutting tools to machines for a given set of parts subject to capacity constraints. This dissertation proposes a hierarchical approach to the machine loading problem when the workload and tool magazine capacity of each machine are restrained. This hierarchical approach reduces the maximum workload of the machines by partially grouping them. This research deals with situations where different groups of machines performing the same operation require different processing times and this problem is formulated as an integer linear problem. This work proposes a solution that is comprised of two phases. In the first phase (Phase I), demand is divided into batches and then operations are allocated to groups of machines by using a heuristic constrained by the workload and tool magazine capacity of each group. The processing time of the operation is different for each machine group, which is composed of the same identical machines; however, these machines can perform different sets of operations if tooled differently. Each machine and each group of machines has a limited time for completing an operation. Operations are allocated to groups based on their respective workload limits. In the second phase (Phase II), demand is divided into batches again and operations are assigned to machines based on their workload and tool magazine capacity defined by Longest Processing Time (LPT) and Multifit algorithms. In Phase II, like Phase I, partial grouping is more effective in balancing the workload than total grouping. In partial grouping, each machine is tooled differently, but they can assist one another in processing each individual operation. Phase I demonstrates the efficiency of allocating operations to each group. Phase II demonstrates the efficiency of allocating operations to each machine within each group. This two-phase solution enhances routing flexibility with the same or a smaller number of machines through partial grouping rather than through total grouping. This partial grouping provides a balanced solution for problems involving a large number of machines. Performance of the suggested loading heuristics is tested by means of randomly generated tests.

No description available.

Bone is a 3D dynamic and unique tissue that structurally adapts in response to mechanical stimuli. Comparative skeletal morphology is commonly utilized to infer ancient hominins' modes of locomotion; however, instances of remarkable gross similarity despite different modes of locomotion do occur. A common cited example is the similarity between the skeletal elements of bipedal human (Homo sapiens) hands/feet and quadrupedal black bear (Ursus americanus) front/hind paws. Through novel 3D Micro-CT and 2D histomorphology analysis, this thesis tests the hypothesis that a 3D microscopic analysis of biomechanically regulated cortical bone structures provides a more representative and accurate means to infer a species' mode of locomotion. Micro-CT data were collected at the mid-diaphysis of human (n=5) and bear (n=5) third metacarpal/metatarsal pairs and compared with independent and paired t-tests, Pearson correlation coefficients and Bland-Altman plots. Bone microarchitecture is quantifiable in 3D and accessible through non-destructive Micro-CT. Interspecies variation was present, however no significant cortical differences between elements of humans and bears was found. Histological inspection revealed further variation between and within species and element. A key limitation was sample size and further investigation of the relationship between mechanical loading and mode of locomotion is warranted.

The main aim of the research was to study the behaviour of a silty clay under two-way cyclic loading. Equipment was developed for the application of a sinusoidally varying deviator stress to a sample in the triaxial cell. The equipment was designed to apply deviator stresses in both compression and extension during each cycle. ii A programme of monotonic and two-way cyclic triaxial tests has been performed on samples of Keuper Marl, isotropically consolidated to a range of stress histories. The build-up of strain and pore pressure during repeated loading is discussed. A model is developed, within the framework of the critical state theory of soil mechanics, to predict the amount of pore pressure produced by a given number of loading cycles at a known stress level. An extension of the model is suggested whereby the varied loading, more appropriate to offshore foundation conditions, may be analysed. In addition, a programme of monotonic and cyclic simple shear tests has been performed. The equipment has been developed, during the course of the research, to enable the direct measurement of pore pressure during shear. At attempt has also been made to monitor the change in lateral stress during shear by means of an instrumented membrane. The results of the simple shear tests have been analysed and are presented in terms of horizontal shear stress and effective vertical stress. An attempt has been made. to deduce the principal stresses present in a sample subject to simple shear loading and a method of relating the results from monotonic tests using simple shear and triaxial devices is discussed.

Bone is a 3D dynamic and unique tissue that structurally adapts in response to mechanical stimuli. Comparative skeletal morphology is commonly utilized to infer ancient hominins' modes of locomotion; however, instances of remarkable gross similarity despite different modes of locomotion do occur. A common cited example is the similarity between the skeletal elements of bipedal human (Homo sapiens) hands/feet and quadrupedal black bear (Ursus americanus) front/hind paws. Through novel 3D Micro-CT and 2D histomorphology analysis, this thesis tests the hypothesis that a 3D microscopic analysis of biomechanically regulated cortical bone structures provides a more representative and accurate means to infer a species' mode of locomotion. Micro-CT data were collected at the mid-diaphysis of human (n=5) and bear (n=5) third metacarpal/metatarsal pairs and compared with independent and paired t-tests, Pearson correlation coefficients and Bland-Altman plots. Bone microarchitecture is quantifiable in 3D and accessible through non-destructive Micro-CT. Interspecies variation was present, however no significant cortical differences between elements of humans and bears was found. Histological inspection revealed further variation between and within species and element. A key limitation was sample size and further investigation of the relationship between mechanical loading and mode of locomotion is warranted.