Thesis (M.A.)--Ohio State University, 1978. / Includes bibliographical references (leaves 135-137). Available online via OhioLINK's ETD Center

The creep and shrinkage of concrete and the relaxation of cables cause long-term redistribution of internal forces and time-dependent deformations in concrete structures, steel-concrete composite structures and concrete cable-stayed bridges. They should be properly modelled for accurate prediction of their long-term behaviour and its effect on instantaneous structural responses at service. An equivalent stress relaxation model is proposed for prestressing tendons based on the intrinsic stress relaxation, from which the equivalent creep coefficients can be obtained through a recursive algorithm. Based on the equivalent stress relaxation model, an accurate finite element analysis of time-dependent behaviour by time integration has been devised considering concrete creep, concrete shrinkage and cable relaxation. Concrete members are modelled by beam-column elements while tendons are modelled by truss elements with nodes connected to the beam axis by perpendicular rigid arms. It is found that the proposed relaxation model with time integration can provide a reliable method as well as benchmark solutions for time-dependent analysis. The numerical results obtained indicate that the interactions among these factors should be properly considered in analysing the long-term performance of concrete bridges. Although time integration provides a reliable method for time-dependent analysis, both the computing time and memory requirement increase drastically with the number of time steps as the time-dependent strains of concrete and tendons within a time interval depend on the loading history up to that time. It is therefore necessary to develop a more efficient method to conduct time-dependent analysis. The relaxation-adjusted elasticity modulus is introduced on the basis of equivalent creep coefficients of tendons. Then, an efficient tendon sub-element is put forward to cope with cables with arbitrary profiles. Finally, a more general single-step method is devised using the classical age-adjusted elasticity modulus to account for external loading and creep effect, the shrinkage-adjusted elasticity modulus to consider shrinkage effect and its interaction with concrete creep, and the relaxation-adjusted elasticity modulus to consider the effect of cable relaxation based on the finite element method. The numerical results obtained indicate not only the accuracy of the single-step method but also the significance of interaction among various time-varying factors. Based on the time integration or single-step method, a systematic method is developed to monitor the long-term variations of dynamic properties of cable-stayed bridges taking into account various time-varying factors and geometric nonlinearities. Numerical studies show that, although geometric nonlinearities tend to reduce the natural frequencies, the time-dependent behaviour of concrete more than offsets it and tends to increase the natural frequencies in the long run. A generic method is further presented to investigate the long-term dynamic response of vehicle-bridge interaction systems taking account of time-dependent behaviour. The vehicles are represented by a combination of mass-spring-damper systems while the bridge is modelled by finite elements. The surface roughness of bridge deck is simulated by spectral representation method and introduced to the coupled system properly. Based on the method, the individual and combined effects of various time-varying factors are studied in detail using various numerical examples. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Vertical cable seismic methods are becoming more relevant as we require high quality and high resolution seismic data in both land and marine environments. Our goal in this thesis is to demonstrate the impacts of vertical cable surveying in these areas. Vertical cable methods have been applied to the marine environment with encouraging results. Data quality is similar to that of traditional towed-streamer data, without the long, cumbersome towed-streamers which are difficult to maneuver in congested areas. The current marine vertical cable processing schemes tend to use primaries and receiver ghosts of primaries for imaging. Therefore, we demonstrate the ability of the current multiple attenuation algorithms developed by Ikelle (2001) to preserve either primaries or the receiver ghosts of primaries. As we focus on land acquisition, we discover that vertical cable surveying can overcome many of the traditional problems of land seismics. In fact, our investigations lead us to believe that problems such as ground roll, guided waves and statics can be avoided almost entirely using vertical cable acquisition methods. Furthermore, land vertical surveying is naturally suited for multi-component acquisition and time-lapse surveying. To fully analyze the applicability of vertical cable surveys in marine and land environments, we also investigate the problem of cable spacing and sampling within each cable. We compare the resolution of vertical cable data and horizontal data by calculating the maximum angular coverage of each acquisition geometry and measuring the occurrence of each angle within this coverage, such that more occurrences means better resolution. From our investigations, we find that by using vertical cables of no more than 500 m in length at 500 m intervals, we can acquire higher resolution seismic data relative to horizontal surface methods for an image point, horizontal reflector or a dipping reflector. The key tool used in these investigations is fully elastic finite-difference modeling. We chose this technique based on its ability to properly and accurately model the full wavefield through complex models, all the while preserving amplitudes and the phase of reflected, diffracted and converted wavefields.

No description available.

Industrial robots and automation technology have advanced rapidly in the last several decades. New types of manipulators that uses parallel mechanisms are becoming more popular due to their high speed and high stiffness. This thesis focuses on a sub-class of parallel manipulators that uses cables to replace rigid links for further increase in speed. The design strategies in this study were expanded from research works by Khajepour. Behzadipour, and Edmon Chan. This thesis presents analysis and development of a new cable-based planar parallel manipulator that is based on a previous prototype built by Edmon Chan. The new manipulator design added a new rotational DOF to the end-effector, and the number of cables are doubled in order to increase the stiffness. New methods for kinematics and dynamics analysis are formulated to make the procedure more systematic. A new mathematical formulation for stiffness matrix of the end-effector is presented. The resultant stiffness matrix is equivalent to the stiffness matrix formulated by Behzadipour. Additional stiffness analysis is conducted on valid range of stiffness calculation and comparison of different cable configurations. A multi-objective optimization problem is formulated in order to search for the best set of design parameters for the manipulator, and it is solved with an exhaustive complete search method. A physical prototype of the manipulator is modelled and manufactured with the help of partners from Conestoga college. Experiments with the manipulator show that more powerful motors are needed to run the robot at full speed. Motor torque measurements show that the dynamics analysis of the manipulator is valid. Stiffness of the manipulator is measured by applying external force to the end-effector, and it is shown to be strong. The manipulator is able to demonstrate a sort and pick-and-place operation at 60 cycles per minute while running at 70% of the maximum speed, with an acceleration of 2.8 g and velocity of 4 m/s.

Thesis (M.S.)--Ohio University, November, 1998. / Title from PDF t.p.

Thesis (M.S.C.E.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science in Civil Engineering." "A thesis entitled"--at head of title. Bibliography: leaf 66.

Thesis (M.A.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 43-51).

Thesis (MInt (Prof)) -- University of Pretoria, 2008. / Abstract in English. Includes bibliographical references.

Thesis (M.A.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 43-51). Also available in print.