South Africa has recently experienced challenges regarding electricity consumption and availability. As part of the country's Integrated Resource Plan, these challenges are to be addressed. This involves a 20 year plan which aims to increase electricity supply capacity as well as reduce the reliance on coal power as part of the global trend to become more environmentally friendly. Wind power, specifically, is to account for a large portion of the renewable energy that is expected to become available by 2030. This results in the need for the understanding of wind turbine design by South African engineers. The dynamic analysis of wind turbine structures, is of particular interest to Civil Engineers. Wind turbine towers are recently of the monopole or tubular type tower, predominantly constructed of either concrete or steel or a combination of both. Steel tubular towers above a height of 80m are generally not recommended for wind turbines owing to cost concerns as well as difficulties in meeting dynamic behaviour requirements. Concrete towers and steel-concrete hybrid towers are recommended for this height regime. The aim of this study was to assess the prospective use of steel tubular towers of varying geometric shape for wind turbines with tower heights of 80m or greater. The study focussed on the analysis of natural frequency and assessing the applicability of steel tubular towers of geometric shapes that have not been previously explored or reported. The turbine of choice for this study was the Vestas V112 3MW type as this is one of the most commonly used and more efficient turbines for towers of this height regime. The results of this study showed that steel monopole towers of heights of 80m and more are still viable options for wind turbine towers. Various geometric tower cases of heights varying from 80m to 120m, produced acceptable fundamental natural frequencies within the allowable frequency range for a Vestas V112 3MW turbine.

This study explores the membrane stresses of hydrostatically loaded elliptical and circular toroidal tanks. Equations are derived, using the membrane theory of shells, to obtain equations which can accurately describe the meridional and hoop stress behaviour at locations sufficiently far away from any bending disturbance occurring within the shell. The derived expressions are validated using the finite element software ADINA, indicating excellent agreement between the analytical and numerical solutions. A parametric study is undertaken, whereby the membrane profiles for prolate, oblate and circular toroidal shells is investigated. Parameters which are varied are the opening and aspect ratio of toroidal shells. Stress resultant profiles are shown for numerous cases in order to aid designers on suitable ratios to minimise membrane stresses for use when designing hydrostatically loaded toroidal shells. Lastly, numerical examples are investigated, keeping the volume constant and comparing the surface area due to a variation of opening and aspect ratios. It was found that when investigating toroidal shells, considerations are required when choosing the aspect ratio and opening ratios. Based on the results obtained, compromises between prolate and circular cross-sections with relatively small opening ratios are recommended in order to minimise the cost and maximise the structural efficiency, based on the membrane stresses occurring within the shell.

No description available.

When continuously welded rails are placed over a bridge, the track and the bridge interact via the ballast in the case of ballasted track or track slab in the case of non-ballasted track. This interaction, commonly referred to as track-bridge interaction results in force transfer between the track and the bridge. With the demand to increase freight haulage on heavy haul railway lines intensifying to meet mineral export demands, there is a need to understand the manifestation of rail bridge interactions in heavy haul railway bridges. Understanding the manifestation of these forces is critical for the management of the infrastructure during operation. Whilst track-bridge interactions effects design limits in high-speed rail have been documented, to the author's knowledge there has been no documented report that addresses track bridge interactions in the design of new heavy haul railway bridges and the management old heavy haul railway bridges. Resultantly, this study explored the observed patterns of rail forces, longitudinal deck displacements, ambient temperature, concrete temperature and rail temperature on the Olifants River Railway Bridge. Thereafter, the observed patterns were used investigate the effect of rail temperature variation on rail forces and the longitudinal displacement of the deck. Examine the effect of variation in concrete temperature on the longitudinal deck displacement, rail forces and variation in rail temperature as well as the effect of longitudinal deck displacement on rail forces. The effects of the presence of a train on the longitudinal displacement of the deck, rail forces and concrete temperature will also be investigated. Finally, this study developed a predictive multiple linear regression model that will assist in the management and maintenance heavy haul railway bridges. This study demonstrated that rail temperature variation is inversely proportion to the rail forces in the rail, longitudinal deck displacement is directly proportional to concrete temperature variation and that longitudinal deck displacement of the bridge deck and rail forces in the rail are inversely proportional. However, the correlation between the longitudinal deck displacement and the rail temperature, rail temperature in the track and concrete temperature in the deck, concrete temperature in the deck and the rail forces in the track could not be established conclusively. The effect of the presence of the train on the longitudinal displacement of the deck, rail forces and concrete temperature could also not be established conclusively

Progressive collapse occurs when damage from a localized first failure spreads in a domino effect manner resulting in a total damage disproportionate to the initial failure. Recent building failures (e.g., World Trade Center twin towers) highlight the catastrophic outcome of progressive collapse. This research proposes a reliable and realistic retrofit technology which installs thin steel panels into steel building structural frames to enhance the system progressive collapse resistance. The steel frames with simple beam-to-column connections, under different boundary conditions (i.e., sidesway uninhibited and sidesway inhibited, respectively), and the loss of one bottom story column were retrofitted using the proposed technology (i.e. installing thin steel panels in the structural frames). Performance of these frames was investigated. Two Finite Element (FE) models which require different modeling efforts were developed to capture the system behavior. The first model explicitly models the infill plates to capture the plate buckling behavior. The second model known as strip model represents the infill panels as diagonal strips. In addition to the FE models, a plastic analysis model derived from the prior research on seismically designed Steel Plate Shear Walls (SPSWs) was considered. The system progressive collapse resistance obtained from the two FE models and the plastic analysis procedure were compared and good agreements were observed. It was observed that installing infill plates to steel structural frames can be an effective approach for enhancing the system progressive collapse resistance. Beyond the strength of the overall system, the Dynamic Increase Factor (DIF) which may be used to amplify the static force on the system to better capture the dynamic nature of progressive collapse demand was evaluated for the retrofitted system. Furthermore, the demands including axial force, shear force and bending moment on individual frame components (i.e., beams and columns) in the retrofitted system were quantified via the nonlinear FE models and a simplified procedure based on free body diagrams (FBDs). Finally, the impact of premature beam-to-column connection failures on the system performance was investigated and it was observed that the retrofitted system is able to provide stable resistance even when connection failures occur in all beams.

Recent research reports that steel Concentrically Braced Frames (CBFs) (even the code-compliant ones) may be susceptible to soft-story failures during strong earthquakes. Such a failure mode causes catastrophic outcomes and should be definitely avoided in practice. This thesis focuses on development and validation of a seismic retrofit strategy for low-rise and mid-rise steel CBFs vulnerable to soft-story failures. The considered retrofit strategy consists of a sufficiently stiff rocking core (RC) pinned to foundation and connected to the existing frame. For demonstration purpose, two representative benchmark steel CBF buildings, which are the three-and six-story CBFs designed forLos Angelesin the SAC Steel Project, are considered. Finite element (FE) models of the benchmark buildings are validated using the published results and explicitly take into account gusset plates, member yielding, brace buckling, brace rupture, and P-Delta effect. Eigenvalue analyses are first conducted to investigate the effect of RC on system modal properties. It is found that the added RC generally does not significantly change the fundamental period and therefore does not attract excessive earthquake force to the system. Additionally, nonlinear static pushover analyses are performed to address the beneficial contribution of RC to the system under the performance objectives including immediate occupancy, life safety, and collapse prevention. The Monte-Carlo simulation technique is used to take into account uncertainty in lateral force distribution and its effect in system seismic performance. It is found that sufficiently stiff RC creates more uniform inter-story distribution along the vertical direction in all considered scenarios. Furthermore, nonlinear dynamic analyses are conducted using three different ground motion suites. It is shown that the systems with properly selected RC can achieve the Best Safety Objective defined in FEMA 356 and ensure the collapse prevention performance under near-fault earthquakes.

This thesis investigated the application of seismic analysis methods and the response of idealized shear frames subjected to seismic loading. To complete this research, a Design Basis Earthquake (DBE) for a project site in San Luis Obispo, CA, and five past earthquake records were considered. The DBE was produced per the American Society of Civil Engineers’ Minimum Design Loads for Buildings and Other Structures (ASCE 7-10) and used for application of the Equivalent Lateral Force Procedure (ELFP) and Response Spectrum Analysis (RSA). When applying RSA, the modal peak responses were combined using the Absolute Sum (ABS), Square-Root-of-the-Sum-of-Squares (SRSS), and Complete Quadratic Combination (CQC) method. MATLAB scripts were developed to produce several displacement, velocity, and acceleration spectrums for each earthquake. Moreover, MATLAB scripts were written to yield both analytical and numerical solutions for each system through application of Linear Time History Analysis (THA). To obtain analytical solutions, two implicit forms of the Newmark-beta Method were employed: the Average Acceleration Method and the Linear Acceleration Method. To generate a comparison, the ELFP, RSA, and THA methods were applied to shear frames up to ten stories in height. The system parameters that impacted the accuracy of each method and the response of the systems were analyzed, including the effects of classical damping and nonclassical damping models. In addition to varying levels of Rayleigh damping, non-linear hysteric friction spring dampers (FSDs) were implemented into the systems. The design of the FSDs was based on target stiffness values, which were defined as portions of the system’s lateral stiffness. To perform the required Nonlinear Time History Analysis (NTHA), a SAP2000 model was developed. The efficiencies of the FSDs at each target stiffness, with and without the addition of low levels of viscous modal damping are analyzed. It was concluded that the ELFP should be supplemented by RSA when performing seismic response analysis. Regardless of system parameters, the ELFP yielded system responses 30% to 50% higher than RSA when combing responses with the SRSS or CQC method. When applying RSA, the ABS method produced inconsistent and inaccurate results, whereas the SRSS and CQC results were similar for regular, symmetric systems. Generally, the SRSS and CQC results were within 5% of the analytical solution yielded through THA. On the contrary, for irregular structures, the SRSS method significantly underestimated the response, and the CQC method was four to five times more accurate. Additionally, both the Average Acceleration Method and Linear Acceleration Method yielded numerical solutions with errors typically below 1% when compared with the analytical solution. When implemented into the systems, the FSDs proved to be most efficient when designed to have stiffnesses that were 50% of the lateral stiffness of each story. The addition of 1% modal damping to the FSDs resulted in quicker energy dissipation without significantly reducing the peak response of the system. At a stiffness of 50%, the FSDs reduced the displacement response by 40% to 60% when compared with 5% modal damping. Additionally, the FSDs at low stiffnesses exhibited the effects of negative lateral stiffness due to P-delta effects when the earthquake ground motions were too weak to induce sliding in the ring assemblies.

No description available.

A non-linear finite element model has been developed to analyse reinforced concrete structures taking into account : (1) non-linear concrete behaviour under biaxial stress, (2) progressive cracking of the concrete, and (3) interaction between the reinforcement and the concrete matrix commonly known as bond. Three dimensional reinforced concrete components are analysed by an approximate two dimensional plane stress model. Bond is considered to be a concentric layer surrounding the reinforcement modelled by a 6 noded rectangular 'shearing' element. The concrete is represented by 8 noded isoparametric membrane elements and the reinforcement by 3 noded isoparametric bar elements. The finite element model uses, an incremental iterative solution technique known as the 'Initial stress method' and a special solution technique to allow for cracking of the concrete. stiffnesses within elements are evaluated by numerical integration using Gaussian Quadrature, with elastic moduli stored at the sampling positions. The bond model is based upon an assumed non-linear relationship between bond stress and slip in which the localised ultimate bond stress' is a function of both the lateral pressures exerted by the concrete on the reinforcement and the radial contraction of the bar' due to Poisson's effect. Allowance is also made for the deterioration of bond when the slip exceeds a tolerance value. The concrete model is a non-linear elastic fracture model based upon the 'Equivalent uniaxial strain approach' as developed by Darwin and Pecknold (1974). Cracking of the concrete is assumed to be 'smeared' within the concrete element. Reinforced concrete components which have been analysed include; the ordinary pullout test, double ended pull out test, a transfer test, and a beam-column intersection. A small experimental programme was conducted to obtain reliable data as to the nature of the bond stress and reinforcement strain distributions in the double-ended pullout test, the transfer test and the beam-column intersection. To determine the reinforcement strain distributions, plain round bars or ribbed reinforcement bars in the case of the beam-column, were embedded in the concrete specimens with electrical strain gauges attached . The author's computer programs are explained and listed in the appendices.

No description available.