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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Experimental and Analytical Investigation of Double Chord HSS Trusses

Chiu, Tin-Chung Ernest 02 1900 (has links)
<p>A research program into the investigation of the behaviour of double chord HSS Warren trusses is presented. The experimental results of eleven tests on five different types are reported; these include two Back-to-Back trusses, two Standard trusses and a Bolted type. One of the Back-to-Back trusses employed stiffening plates to reinforce gapped connections while the other had web members fully overlapped. The two Standard trusses had different eccentricities depending on whether the ends of the web members were square cut or angle cut. Gusset plates and tie plates were used to stiffen the connections for the Bolted truss. Retreats after reparations were undertaken in the event of a localized joint or member failure so that maximum information could be obtained from the program.</p> <p>An analytical model has been developed and incorporated into an existing plane frame program for analysis of the double chord HSS trusses. Three types of yield mechanisms that are accounted for are plastic hinge formation at the end of a member, member failure due to plastic limit load and yielding of the spring for modelling a connection.</p> <p>The experimental and analytical results are then compared thus confirming the validity of the analytical model. Finally, conclusions and recommendations are outlined for the analysis, design and feasibility of double chord Warren trusses with hollow structural sections.</p> / Master of Engineering (ME)
2

The Effect of Damping on the Seismic Response of Equipment in Buildings

Schriver, Allison S. January 1986 (has links)
<p>This thesis studies the effects that nonproportional damping has on the vibrational characteristics of two and three level systems. In additions, error levels in response prediction are estimated for two simplified time history procedures and a response spectrum technique. It is shown that nonproportional damping creates significant changes in the damped frequency, damping ratio and mode shape of each mode of vibration of the system relative to those found for a similar system exhibiting proportional damping. The study of the prediction of the maximum system response to seismic basic motions demonstrates that there exist three regions where different dynamic analysis procedures should be used. A physically uncoupled analysis should be used for large mass ratios. A complex modal analysis should be used if the mass ratio is of an intermediate value. Diagrams are supplied which allow one to readily determine which of the three methods is the most appropriate for a design.</p> / Doctor of Philosophy (PhD)
3

Evaluation of the seismic level of protection of steel moment resisting frame building structures

Biddah, Mahmoud Samy Aiman 07 1900 (has links)
<p>A large number of low and medium-rise buildings have steel moment resisting frames as the primary lateral load resisting system. During the past few decades, much confidence has been placed on this type of structural system for resisting seismic loads. However, after recent earthquakes (e.g. Northridge, California, in 1994, and Kobe, Japan, in 1995) the confidence in this system was reduced as a result of various types of damage that moment resisting steel frames suffered. This resulted in a recognition of the need to evaluate the performance criteria on which current provisions are based. While there have not been any major casualties dueu to earthquakes in Canada during the past few decades, in fact there is an actual seismic hazard which affects significant regions of the country, for example, the cities of Victoria, Vancouver, Quebec City, Montreal, and Ottawa. The design peak ground motions in such regions are moderate in comparison with those in California or Japan, however the uncertainties associated with estimating the expected ground motions are such that twice or three times the seismic design level motions are likely to occur. The main objectives of this research study are: (i) to evaluate the seismic level of protection afforded to steel moment resisting frame building structures designed in accordance with the current Canadian provisions (i.e. NBCC (1995) and CAN/CSA-S16. 1-94), and (ii) to investigate the effect of the different design philosophies and seismic hazard design levels on the inelastic dynamic response of multi-storey steel frame structures. Six storey office buildings located in regions of high, intermediate, and low seismic hazard, and a ten storey office building located in a region of intermediate seismic hazard are designed in accordance with the current Canadian provisions using three design philosophies, namely strong-column weak-beam (SCWB), weak-column strong-beam (WCSB), and strong-column weak-panel zone (SCWP). The scope of the research program includes: (a) modelling of the structural elements; (b) nonlinear push over static analyses/inelastic dynamic analyses, and (c) evaluation of the damage potential associated with each design. In the study analytical models are modified and incorporated into the PC-ANSR computer program in order to perform the inelastic dynamic analyses of the frames. The inelastic models take into account the spreading of inelastic deformations in beam-column elements, connection flexibility and panel zone deformations. A cyclic model for the panel zone element is developed and introduced into PC-ANSR. The performance of the frames is evaluated both statically using monotonically increasing lateral load (nonlinear push over static analyses), and dynamically by subjecting the inelastic model to an ensemble of actual strong ground motion records (time-history analyses). The main ensemble of time-histories used in the study consists of twelve earthquake ground motion records selected on the basis of Newmark-Hall design spectra amplification factors. An additional ensemble of time-histories (twelve records) is selected based on the uniform hazard spectrum for Vancouver which describes the new seismic hazard information given by the Geological Survey of Canada. The additional ensemble is used to investigate the implication of the new seismic hazard information on the performance of the six storey frames in the intermediate seismic hazard region. The results of the inelastic dynamic analyses are presented in terms of statistical measures of the maximum response parameters determined during the time-history analyses. Also, the results of the nonlinear push over analyses are presented and compared with those of the dynamic analyses. The performance expectations of the frames are evaluated in order to assess both the overall level of protection provided to the frames and the preferred design philosophy. It is concluded from the analyses that in high and intermediate seismic hazard regions, a well-designed and detailed ductile moment resisting frame (i.e. SCWB or SCWP) can withstand ground motions of twice the design level with a very little likelihood of collapse, while an ill-conditioned designed frame (i.e. WCSB) may develop a collapse mechanism even at the design level excitation. In regions of low seismic hazard activity, the three frame design types perform satisfactorily, and can withstand twice the design level excitations with only a moderate amount of damage.</p> / Doctor of Philosophy (PhD)
4

Centralised Time Series Management for Continuous Hydrology on Personal Microcomputer Networks

Unal, Ali 02 1900 (has links)
<p>Continuous hydrology packages such as Hydrologic Simulation Program--Fortran (HSPF) and Version 3 of the Storm Water Management Model (SWMM3) require extensive computing time even for certain cases of event modelling. In their original sequential, time-sharing, computing schemes, continuous modelling applications required a prohibitively expensive overall turn-around time and an overwhelming amount of manual Input/Output (I/O) time series (TS) data management effort. By decentralizing the processing, avoiding a time-sharing computing environment, and finding ways to keep track of I/O TS data as part of the processing, these problems can be overcome.</p> <p>Computational Hydraulics Group Time Series Manager (CHGTSM), a Database Management System (DBMS), was developed by the present author to provide easy access to TS data, independent of details of storage. CHGTSM is based on an unconventional data access technique, also developed by the author, that handles variable resolution continuous TS records. The CHG Time Series Store (CHGTSS) is prepared by the CHGTSM. CHGTSM is applied succesfully. In a case study, CHGTSM saved 88% in hard disk storage compared to the raw database. CHGTSM serves event as well as continuous modelling applications. A manual for CHGTSM is also written by the present author.</p> <p>CHGTSM can be used to distribute the database to the nodes of a linked configuration of microcomputers. Distributed processing (DISP) of centralized data is made possible by CHG Distributed Data Processing Software (CHGDPS). CHGDPS, developed by the present author, is a shell around CHGTSM which includes security provisions and node synchronization assistance. The simulation of a DISP application for continuous hydrologic modelling in a Local Area Network (LAN) improved the computing efficiency by 54% compared to sequential processing. CHGDPS will allow true concurrency only through a batch application.</p> <p>CHGDPS synchronization assistance relies on timing relations of the computational modules that are accessing the system. A program measurement (PM) technique was adopted, enhanced and applied by the present author to obtain the timing relations. Such DISP control helps the user to optimize overall system processing. For example, CHGDPS may decide (or help decide) a shift from one computational approach to another for considerations of time, space, numerical stability, and accuracy.</p> <p>The DISP scheme is flexible and can be implemented on any linked configuration of computers e.g. LAN' s, distributed data gathering and real time control (RTC) devices. The whole system, called the Computational Hydrology Work Group System (CHWGS) is assessed as an environment for continuous (or event) hydrologic modelling, distributed data gathering and distributed RTC.</p> / Doctor of Philosophy (PhD)
5

Pavement Deflection Analysis Using Stochastic Finite Element Method

Parvini, Mehdi 10 1900 (has links)
<p>In order to assess the structural charateristics of a pavement-subgrade system, non-destructive, in-situ tests together with backcalculation procedures are widely used. Traditionally, the analytical models adopted for this proccess are deterministic, however, in reality, the quantities involved in the problem may be random variables. Neglecting the variable nature of the system parameters, e.g., highway material properties, may affect the reliability of the pavement response prediction. On the other hand, inverse solutions to pavement problems are often ill-conditioned and sensitive to the input parameters. Past experience has shown that the estimated values of a blackcalculated parameter by different agencies may vary by several orders of magnitude, representing a high level of uncertainty in the estimated paramter. Unless the uncertainty is quantified, practitioners are forced to resort to higher safety factors, which is neither economical nor always conservative. The present study investigates, rigorously, the behavior of a pavement-subgrade system from a stochastic point of view, and addresses the sensitivity of response variation to variations in layer properties. The results of a forward analysis are utilized to establish a relation between input and output statistical moments in order to interpret the pavement deflection data stochastically. The proposed framework in this research allows one to quantify the uncertainty level in backcalculated system parameters. It also provides a tool to infer the accuracy of the pavement performance prediction based on mechanistic models. For the purpose of introducing the stochastic approach, the perturbation technique is applied to an idealized, two-layered, pavement-subgrade system for the case of: (a) a static solution based on Odemark definition of equivalent layer thickness; and (b) a frequency domain solution to a single degree of freedom (SDOF) system using an impedance function. The methodology is then extended to a stochastic finite element framework in order to analyze boundary-valued problems of more complex geometry and distribution of material properties. The perturbation method is a mean-based, second-moment analysis for the second-order accurate expected value, and first-order accurate cross-covariance function. For the dynamic analysis, viscoelastic response of the pavement is obtained by using the periodic-load analysis approach and Fourier synthesis. Based on the results of the simulations, it is demonstrated that, the sensitivity of surface deflections is significantly higher to the subgrade properties than those of the surface and base layers, both in a static and a dynamic analysis. Consequently, it is concluded that, the low dominant frequency of the falling weight deflectometer (FWD) load limits the capability of this test in characterizing surface layer properties. Using the concept of coefficient matrix, it is illustrated that, the low sensitivity of deflections to surface layer properties can be interpreted as a high level of uncertainty in the estimated pavement moduli in a backcalculation exercise. It is indicated that uncertainties in backcalculated parameters often result in an unacceptable pavement performance prediction. Moreover, the physical behavior of the layers are identified by finding the contribution of each layer to the total deflection of the system using the notation of contribution ratio.</p> / Doctor of Philosophy (PhD)
6

Contaminant Leaching From Cement-based Waste Forms under Acidic Conditions

Côté, Pierre 02 1900 (has links)
<p>A waste form can be prepared by mixing a hydraulic cement and, if needed, a bulking agent with an aqueous waste to cause it to solidify. A mechanistic leaching model was developed based on describing the chemistry of the waste form-Ieachant system and the flow regime of the leachant and assuming that transport takes place via diffusive exchanges through the waste form-Ieachant Interface. This model was successful in predicting Ieaching from simpIe waste matrices and in identifying important containment mechanisms effective in the more complex matrices.</p> <p>The cement-based waste forms studied had porosities ranging from 40 to 60%. Portland cement provided acid neutralization capacity to maintain the high pH environment where the waste form is stable; a typical waste form contains enough cement to neutralize between 2000 to 3000 times its volume of a pH 3 leachant.</p> <p>In a mild environment, leaching was controlled by the diffusion of the soluble fraction of a contaminant present in the connected pores of the matrices. Immobile species instantaneously solubilized to maintain chemical equilibrium between the soluble and insoluble fractions. In tests conducted over a period of almost 2 years, less than 1% of the initial amount of cadmium, chromium and lead contained in a specimen leached out.</p> <p>In an acidic environment, the leaching rates were limited by the availability of acid to dissolve the matrix. The leaching process was similar to a surface corrosion process. However, since waste matrices are not completely soluble in a mild acid, a leached layer develops, eventually protecting the core of the waste form from direct contact with aggressive groundwaters. Contaminants solubilized at the leaching front are subjected to concentration gradients that force them to diffuse both inward and outward. Only a fraction of the total concentration therefore leaches out.</p> <p>The mechanistic knowledge developed through the experimental programme and the modelling effort was used to develop eight long term leaching scenarios covering a wide range of waste form and groundwater conditions. In addition to allowing the prediction of leaching rates for periods of up to 100 years, these scenarios were useful in developing recommendations to prepare more efficient waste forms and design better landfills.</p> / Doctor of Philosophy (PhD)
7

Advection, Diffusion and Settling in the Coastal Boundary Layer of Lake Erie

Elzawahry, Eldin Alaa 04 1900 (has links)
<p>Pollution in the coastal zones of the Great Lakes has become more serious in recent years. This is due to increased use of coastal water as a result of population and industrial growth. A substantial portion of the contaminants that enters a lake do so from the shoreline via discharges from sewer overflows, industrial outfaIIs and runoff. Such discharges contain particulates and other materials of density greater than that of lake water. Many heavy metals with toxic components are present in these fractions. The dynamic behavior of these particIes in the coastal and offshore waters is thus of great importance. The principal removal processes for these materials are transport and particle settling. An understanding of the characteristics of nearshore currents, diffusion and temperature patterns is essentiaI to determine their effect on removal processes, and in turn, on coastal biological and chemical processes. This study is limited to the physical fluid mechanics of coastal zones.</p> <p>The structure of the nearshore flow in the vicinity of Cleveland, Ohio is analyzed in detaiI in this study. The impact of Cleveland, one of the largest urban and industrial agglomerations on the shoreline of Lake Erie, in terms of additional loading is thought to be considerable. A computer program (ADVDIFF) was developed to calculate the mean flow, horizontal turbulent length and time scales, horizontal diffusivities and kinetic energy. ADVDIFF uses filtering techniques, spectral analyses and statistical analyses. Five episodes representing three different flow regimes which may exist in the coastal zone were chosen for special analyses.</p> <p>To generate the coastal currents, a rigid-lid, channel-type model with fine grid size in the coastal zone was used. A model originally developed by Simons (1983) was modified to incIude nonlinear acceIeration terms and two different forms of the vertical eddy viscosity. Also, a two dimensional x-y model developed by Simons and Lam (1982) was modified and used to expIain some of the observations. Both new modeIs (ERCH, ONELAY) were verified, calibrated and applied to Lake Erie.</p> <p>A computer program (SEDTRAN) was developed to predict the inflow sediment concentration distribution within the coastaI zone. SEDTRAN soIves numericaIIy the three dimensionaI time-dependent mass transport equation including the settIing term. The modeI uses the currents and diffusivities computed by ERCH and ONELAY and the statistical analyses, respectively. SEDTRAN was verified using several test examples, and partiaIIy vaIidated using the avaiIable data set. The modeI was applied to many cases of settIing activity that may take place in the coastaI zone. The results were used to define a representative influence zone for a pollutant source at CIeveIand.</p> / Doctor of Philosophy (PhD)
8

Optimal Design of Water and Wastewater Networks

El-Bahrawy, Aly N. January 1985 (has links)
<p>The objective is the development of two reIated mathematical models to provide minimum cost designs of water distribution and waste-water collection networks.</p> <p>This wealth of literature is classified in terms of problems formation and method of solution. This places individual contributions in perspective and serves to identify the major shortcomings of existing techniques. These are:-</p> <p>1- Inability to handle large network systems efficiently. 2- lnadequate treatment of the hydraulics of the system. 3- Absence of a satisfactory discrete solution.</p> <p>The results presented are considered to be more comprehensive than any other technique reported in the literature to the author's knowledge. The major contributions presented are:-</p> <p>(i) Both problems are formulated in the form of a nonlinear programming problem and in terms of practical engineering variables and solved by application of the MINOS package.</p> <p>(ii) A standard data format is suggested which allows user input to be defined in a very compact and logical form.</p> <p>(iii) Pre-and Post-processors are developed which free the user from the complicated and extremely error-prone tasks of creating the necessary input data and interpreting the resultant output files of the MINOS package.</p> <p>(iv) For distribution networks, a comparison is presented between the explicit use of a network analyser (coupled with an efficient optimization package) and the implicit incorporation of the analysis stage within the linear and nonlinear constraints of a comprehensive nonlinear model. The latter method is shown to have significant advantages.</p> <p>(v) For collection networks, a model formulation is presented which properly represents the hydraulics of part full flow in circular sewers. The problem size is reduced by the introduction of an equality constraint which correlates velocity and discharge under these conditions. The accuracy of the method is checked by comparison with a more rigorous but significantly more expensive problem formulation.</p> <p>(vi) Methods are suggested whereby pumps, reservoirs, pressure reducing valves and minor loss devices can be easily and correctly incorporated in a distribution network design.</p> <p>(vii) Techniques involving variable transformation and the partitioning of basic, nonbasic and superbasic variables are developed which greatly increase the efficiency of solution.</p> <p>(viii) For both types of network, the models are augmented to allow a very good discrete solution to be obtained in terms of pipe diameter. A heuristic argument is presented which suggests that the solution for distribution networks must be very close to optimal although optimality cannot be rigorously proven. For collection networks it is shown that discretization may frequently be infeasible unless at least one of the constraints is relaxed in the form of a 'soft' constraint.</p> <p>(ix) Both types of network design are demonstrated using problems of substantial size. For distribution networks a method is demonstrated whereby the analysis or design problem can be solved as special cases of the more general optimization problem.</p> / Doctor of Philosophy (PhD)
9

LONG-TERM OPTIMAL OPERATION OF HYDRO-THERMAL POWER SYSTEMS

ADREKAANIAAN, REZAA 11 1900 (has links)
<p>When new construction projects are postponed or cancelled because of socio-economic concerns, greater emphasis is placed on enhanced operational planning -- to get the most at the least cost, from the existing projects. Of the approaches that made significant improvement in the operation of energy production systems is the co-ordination between hydro and thermal power plants. In this research, the problem of "Long-term Optimal Operation of Hydro-Thermal Power Systems" is addressed. Considering the uncertainty in reservoir in flows, the problem is defined as a "two-stage stochastic linear network programming with recourse". To avoid dimensionality problem generally associated with the employment of dynamic programming in large scale applications, Bender's decomposition approach is employed as the solution algorithm basis for the defined problem. Using the "General Algebraic Modelling System", a modelling code, the "Hydro-Thermal Co-ordinating Model (HTCOM)" is developed. In HTCOM, each sequence of hydrologic inflows generates a subproblem which is solved deterministically. The solutions of all subproblems are next co-ordinated by a master problem to determine a single feasible optimal policy for the original problem. This policy includes optimal reservoirs releases as well as allocation of energy generation at different power plants in the subsequent time period. The objective minimizes the expected total cost of meeting the energy demands while satisfying the system constraints over the long-term horizon of one to three years. To demonstrate the applicability of HTCOM, a real world case study named the "Khozestan Water and Power Authority (KWPA)" in Iran is employed as a system of two multipurpose reservoirs with five hydro-thermal power plants and transactions of energy. The KWPA system components are operating policies are stimulated as the network flow model and an integrated solution procedure is planned to determine the optimal operation policies. This procedure included the development of three specialized models: - HTCOM-I: to investigate the potential improvements of the current system; -HTCOM-II: to provide the required confidence in using the model in future simulations by evaluating the actual savings; and -HTCOM-III: to simulate the system operation under uncertainty, and determining the optimal operation policies for the next month. The results of employing all three cods in the KWPA system conclude that the selected approach for formulating the problem, the adopted algorithm based on Benders' decomposition technique, and the models (developed in the GAMS environment) are suitable, capable to handle stochasticity of inflows, and considerably cost-efficient.</p> / Doctor of Philosophy (PhD)
10

Behaviour of Thermal Density Currents in Cold Receiving Water Bodies

Marmoush, Yehla M.R. 04 1900 (has links)
<p>In cold climates, temperatures higher than the ambient have been observed near the bottom of water lakes in the vicinity of thermal discharges. Concern has been expressed about the adverse effects of such abnormally warm water on the winter ecology of lake bottoms. It is expected that the existence of a density extremum in water at 4° C and the resulting nonlinear relation between density and temperature gives rise to densimetric flows which are markedly different from those in the linear range.</p> <p>This thesis presents experimental and numerical investigations that give some insight into the phenomenon of the thermal bar and the manner in which it may infIuence nearshore transport processes in the vicinity of a thermal outfalI in a cold climate. The investigations are restricted to an idealized model where the lock exchange mechanism is selected due to the fact that its behaviour is close to that expected in the prototype situation.</p> <p>The experimental investigation provides dramatic proof that the existence of an extremum in the density-temperature relation has a profound influence on the behaviour of densimetric flows in general and lock exchange behaviour in particular. Three zones in the vicinity of a thermal bar are clearly demonstrated viz. (i) the thermal overflow region. (ii) the thermal bar, and (iii) the thermal underflow region. The experiments provide data on the horizontal scale at which sinking takes place.</p> <p>A numerical model has been constructed to develop a means of modelling the behaviour of a thermal bar at the outfall of a steam electric generating station cooling water system. The numerical model employs a finite-difference scheme where the resulting algebraic finite difference equations are soIved using an alternating direction implicit method and a sparse-matrix package. The numericaI modeI has been verified by comparing it to numerical solutions of four different cases of the idealized problem of steady laminar flow in an enclosed rectangular cavity with differentially heated end walIs. Moreover, additional acceleration techniques are introduced to improve the numerical solution procedure. The numerical model is employed to solve the actual problem of simulating lock exchange flows created between two water bodies having different temperatures around the temperature of maximum density (i .e. having temperatures above and below 4° C). The general behaviour which has been observed experimentally is also confirmed numerically. The sensitivity of the associated parameters is examined. The relative extension of the thermal bar is correlated with relevant system parameters. Difficulty was experienced in obtaining numerical results for the same (high) Rayleigh numbers as were used for the physical experiments. Despite this, an encouraging degree of consistency was observed between simulated and observed behaviour.</p> <p>The important aspect of the study is to draw attention to the adverse effects of the sinking phenomenon (thermal bar), which may occur in the vicinity of man-made warm effluents as well as in natural bodies of water during the spring warming period. The study is significant in terms of the horizontaI scaIe at which sinking takes place, for the design of power station once-through-cooling water systems that must operate in cold climate winter conditions.</p> / Doctor of Philosophy (PhD)

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