Thesis (Ph.D.)--Brown University, 2005. / Vita. Thesis advisor: Eric Chason. Includes bibliographical references (leaves 21-22, 35, 55-56, 86-87, 119-120, 149). Also available online.

The two well-known methods for the plastic design of steel columns subjected to combined bending and normal force were reviewed and compared. The validity of some of the basic design assumptions was examined, and the influence of unknown variables affecting practical applications was investigated. It was assumed that the existing column criteria provide a true prediction of failure within the possible range of yield stress values of mild structural steel. It was found that bending moments in columns vary greatly depending on the assumed conditions of load application, the method of analysis, and the actual values of the yield stresses in the different structural members. Some of the recommended methods of analysis seem inadequate and in many cases unsafe. Elastic analysis appears to represent a necessary part of plastic design of rigid frames. A procedure based on an elastic analysis with subsequent redistribution of bending moments after the formation of plastic hinges was used to illustrate the possible variations in column end moments. This procedure takes into account the effect of the individual structural members having different yield stresses. It is shown that only through careful analysis and critical evaluation of unknowns can the main object of plastic design be achieved: The design of structures with consistent factors of safety. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

This thesis presents tables of coefficients for the prediction of moment amplification factors Ø across the span of symmetrical, parabolic arches. The prediction is accurate up to rise/span ratio f = 1.0 and may be applied to 0, 2 and 3-hinge arches with uniform or specified ei variations, for vertical and horizontal loads or couples (in the plane of the arch rib), and for specified support movements. A method of superposition is discussed and demonstrated for this non-linear analysis. Interpolation of the tables of coefficients for other ei variations is discussed. Using the tables to predict Ø for arches of other shapes is discussed and demonstrated. The tables of coefficients were developed from a curve-fitting process applied to elastic and deflection theory analysis of parabolic arches with specified loadings. An Alwac IIIE electronic digital computer was used for the developement and production work in this research. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

This thesis is concerned with developing a finite element model of infinite size to facilitate the stress analysis of three dimensional, semi-infinite bodies governed by time independent linear equations. An element of triangular plan form extending to infinity in one direction is devised. There are three nodes per element, each node having three displacement degrees of freedom. The infinite element is used in conjunction with regular finite elements to represent the stiffness of the semi-infinite solid which has previously been assumed to be zero or infinite in regular finite element models. The infinite element relieves the computational problem caused by large numbers of elements which has limited the use of the finite element method in three dimensional halfspace problems. A large reduction in the number of degrees of freedom is possible with the use of the infinite element because the artificial boundary of previous models is eliminated. The accuracy of the element is tested on two examples whose exact solutions are known. Both involve a semi-infinite solid, one loaded with a surface perpendicular point load, and the other with a surface parallel point load. The results compare favourably with the theory of elasticity solutions. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

No description available.

Digitized by Kansas Correctional Industries

The main purpose of Structural Health Monitoring (SHM) is the assessment of structural conditions in aerospace, mechanical and civil systems. In structural engineering, damage is defined as any permanent change in the structural and geometric properties of a system caused by an external action. Vibration-based damage assessment methods rely on the use of sensors that record the structural dynamic response of a system that is determined by its structural and geometric properties. External disturbances and environmental conditions in which the system operates cause fluctuations of these properties and might hide the change in signature induced by damage. To handle the uncertainties in the determination of the structure’s characteristics, a statistical pattern recognition approach is presented in this thesis. Any statistical approach relies on the statistics of some features that provide a compact representation of the structural properties and that are sensitive to damage. Such features are called damage sensitive features and are extracted from the dynamic response of the structure: their statistical distribution is then analyzed to assess the occurrence of damage. This dissertation focuses on the analysis of the statistical distribution of damage sensitive features which are extracted through parametric and nonparametric algorithms. Cepstral coefficients are features defined in the field of acoustics and, in this thesis, they have been adapted to SHM analyses in order to develop compact damage sensitive features whose extraction requires a low computational effort. In this thesis, cepstral coefficients have been mathematically transformed through a Principal Component Analysis in order to generate damage sensitive features that are barely sensitive to measurement noise, environmental conditions and different excitation sources. In an attempt to develop an automated strategy for structural damage assessment, the search for damage sensitive features has been extended to the estimation of structural mode characteristics obtained through an output-only version of the Inner Product Vector methodology, e.g. considering only the structural response time histories. This new damage assessment procedure requires low computational effort and is capable to identify both the presence of damage and its location. However, one of the critical points of the proposed procedure consists in the manual evaluation of the spectral content of the dynamic responses that requires the user’s intervention. To automatize this procedure, a Bayesian clustering algorithm and a classifier have been successfully implemented and tested. Finally, the robustness of Bayesian regression algorithms to overfitting led us to consider their applicability to the field of system identification in order to provide a reliable estimate of the structural modal parameters that can be used as damage sensitive fea- tures. In fact, one of the main problems of system identification algorithms is that they rely on a regression algorithm that tends to overfit data producing unreliable results. Results provided by the Bayesian regression based system identification algorithm are obtained and compared with the ones coming from standard system identification algorithms.

A simplified procedure that results in a significant reduction of the computation time and effort in the design of single plate framing connections is presented herein. This simplified method is based upon the current design procedure which is applicable to partially restrained shear connections. A total of 140 steel beams with 700 analyses and 500 composite beams were used to develop the simplified method. Tables are provided for the design of most commonly used connections. The simplified single plate design is applicable for fully tightened 3/4, 7/8, and 1. inch A325 or A490 bolts used in either standard round or slotted holes, or snug tight A325 or A490 bolts in standard holes. These studies have led to a single table of the restraint design moments which greatly simplifies the design procedure.

Finite element formulation based on compatible, assumed displacement fields and the principle of stationary potential energy is applied to analyze edge-stiffened plates. Shear deformation is considered in the formulation of the plate bending and beam bending elements by allowing independent interpolation for displacements and rotations. In addition to bending deformation, plane stress action is superposed on the plate element, while torsion and axial deformation are incorporated in the beam element, so that structural interaction between plate and edge beam elements can be facilitated. By enforcing compatible displacements and rotations across the interface between plate and beam elements, the degrees-of-freedom in one element can be related to the degrees-of-freedom of the adjoining element of a different type. Accordingly, the stiffness matrix and equivalent load vector are transformed to correspond to the common degrees-of-freedom as a result of invariance of the potential energy. By means of the direct stiffness method, the global equilibrium equation is thus established and solved by a frontal solution subroutine. Special features are introduced into the solution subroutine in order to handle varying degrees-of-freedom per node in an element and multiple loading cases. In addition, the speed of input-output transfer between in-core and peripheral storage is optimized. Convergence studies on displacements and stresses show that the current formulation with the program is capable of analyzing shear-flexible structures. The formulation allows convergence of shear-rigid solutions as a limiting case by making use of the selective reduced integration scheme when formulating individual elements. Graphs are presented to aid the design of edge-stiffened plates with two adjacent edges clamped and others cast with intersecting edge beams.

University of Macau / Faculty of Science and Technology / Department of Civil and Environmental Engineering