No description available.

Existing theories which include the effects of shear deformation in elastic beans and plates are compared and their relationship with each other examined. Three approaches are applied to a range of problems in the bending of beams and circular and square plates. The first of these uses Reissner's theory, or, where this is not immediately applicable, a theory is developed based on his fundamental assertions. Secondly, the possibility of employing a partial deflection method for homogeneous isotropic cases is considered, in which the effects of bending and shear can be separated. the third approach is a theory of specified order of accuracy, developed as a modification to Reissner's theory. It leads to a sixth order system of equations, thus enabling three conditions to be satisfied at each boundary of a rectangular plate, and is in terms of transverse displacement as the single variable. The application of finite difference and localised Rayleigh-Ritz techniques to the solution of these three approaches is considered. Two series of experimental tests are reported which investigate the effects of shear deformation on the deflection of beams and square plates.

This thesis is mainly concerned with the prediction of one class of structural failure, namely that due to the extrapolation of existing design or construction procedures to fit new situations. Four failures were examined in depth in an attempt to establish a realistic procedure for avoiding such accidents. The. structures studied were large metal bridges because these have represented the forefront of technology for as long or longer than any comparable example. The examples chosen were the Dee Railway Bridge (collapsed 1847), the Tay Bridge (1879), the first Quebec cantilever bridge (1907) and the Tacoma Narrows suspension bridge (1940). Great care was taken to study the accidents and preceding events as contemporary' engineers would have seen them, and it is believed that this is the first time this type. of investigation has been made. The pattern that emerged from this was that the designers all used existing data which they were confident applied to their work. Not until after the accident did it become apparent that this was not the case, and that the data had originally been derived with very different conditions in mind, often for applications which seemed insignificant alongside the failed structure. In conclusion the author suggests how similar situations could be avoided in the future by the setting up of review procedures to assess new developments in the light of existing practices and the facts on which these are based. An outline of the costs of the accidents studied suggests very strongly that such work would be economically justifiable.

Recent legislation, LOLER, removed the compulsion of periodical proof testing of lifting equipment to ascertain its "fitness for purpose". It has become the responsibility of a competent person to assess equipment's fitness for purpose and ability for continued safe use. This thesis reviews the technologies available to the competent person to enable him/her to come to an informed decision regarding the condition of mechanical structures. It was identified that an optimal methodology would interrogate structural integrity whilst the equipment performed its intended function. Coupling a means of assessment with the equipment's operation allows the investigator to focus on only defective conditions that will limit the future operation. Such an approach of condition monitoring structural integrity as opposed to employing traditional methods of inspection that are essentially failure finding tasks permits the discrimination between benign and malignant defects. Restorative and replacement activities can therefore take place based upon the likelihood of equipment's functional failure. The supplementary monitoring of Acoustic Emission (AE), with the established industrial practice of proof testing, was considered to provide data to monitor structural integrity and provide the basis upon which a structure can be re-qualified for future service. The nature of failure of engineering materials was examined which identified failure modes such as corrosion, creep and fatigue resulted in a progressive degradation of a localised area. The AE is a proportion of energy released during such deterioration. Further it was determined that the rate at which the deterioration increased was non-linear. Within a laboratory environment wire ropes with seeded faults were subjected to a simulated life during which the qualitative and quantitative nature of the AE was investigated.It was found that the quantity of the emission generated during proof tests was indicative of the severity of the induced defect. This substantiated the claim that AE could be used to enhance the proof test and provide a means by which a condition assessment could be made at intervals throughout the life of a structure. A series of five case studies explored the use of AE on a variety of differing in-service mechanical structures, mostly lifting equipmept. The case studies were conducted on pad-eyes,link-plates, cranes, both Electrical Overhead Travelling (EOT) and pedestal cranes and finally, an underwater vehicle pressure hull. The approach of using the combination of AE with a proof test was verified in the cases of pad-eyes and EOT cranes. In the instance of link plates, simultaneous measurement of strain and AE during a load test demonstrated the ability of AE to detect localised yielding. During the destruction test of a pedestal crane boom section, various conventional methods of AE evaluation were utilised to investigate which would provide the most reliable condition indicator; it was found that Intensity Analysis generated the most effective trendable measurement. A study on a pressure hull with known fatigue cracks that were subjected to both static and dynamic testing whilst monitoring with AE was conducted. The fatigue cracks were sized pre and post the trial using Time of Flight Diffraction (ToFD). During the trial Alternating Current Potential Drop (ACPD) was used to detect any growth as it occurred. Such techniques were used to substantiate claims AE could detect a propagating defect. When the AE is viewed in conjunction with ACPD results and the measurements attained with the ToFD it was clear that all three techniques concluded that crack growth occurred at two sites. Finally the investigation returns to a laboratory to exarnine the robustness of the technique through the life of a mechanical structure. The objective being to identify if periodical measurement of AE taken during the course of the life of the structure would repetitively generate information pertaining to the identification of the flaw as well as the severity of the flaw as it initiates and propagates through to failure. A power law was fitted to the data acquired during the proof tests. The use of a power law was considered appropriate due to the previously identified non-linear nature of material failure. A Scanning Electron Microscope was used to visually examine the fracture surfaces. It was found that increasing increments between striations on the fracture surface illustrated the non-linear increase of crack extensions during fatigue and corroborated the appropriateness of fitting a power law to the proof test data. Such an investigation permitted the conclusion that the approach of fitting a power law to the discrete energies from sequential proof tests is an appropriate method of attaining a trendable condition indicator. The competent person could employ such a methodology for the purposes of attaining information upon which an informed decision can be made on the continued safe use of mechanical structures.

No description available.

The research project is concerned with the stress distribution in, and stability of, space frames. Particular emphasis is placed on the study of radial ribbed domes. The development and classification of the main types of space frame are discussed and a brief history of dome construction is included. Braced dome systems are detailed comprehensively. Methods for determining the stresses in space frames are given. These include analysis procedures for statically determinate and statically indeterminate pin-jointed structures. The solution of statically indeterminate space frames without pin-joints is also considered. Specific methods for analysing the stresses in braced domes are reviewed. Radial ribbed dome stress analysis methods are discussed. in detail. In particular, the analysis of three-pinned unstiffened semicircular radial ribbed domes, by the method of Makowski and Gogate, is reproduced. The method has been modified to simplify the analysis of low rise-to-span domes with three-pinned unstiffened circular arc radial ribs. A computer program, based on this method, has also been developed. Literature relating to loads on domes is reviewed. Special reference is made to snow loading and wind pressure distribution. To compare radial ribbed dome theoretical stress analysis values with results obtained experimentally, a model dome has been constructed. Calculations and design drawings for the prototype structure are included along with details of the model. Results of tests on the materials employed in the construction of the model dome are also presented. By using a displacement technique on the model, indluence line diagrams of force have been obtained with, and without, bracing. Rib strains and apex ring deflections are tabulated. An assessment of the analysis methods for space frames is given and comments on dome loading are included. ThP test results are discussed and conclusions are drawn. Suggestions are also made for further research.

Double-layer grids are a relatively new form of three-dimensional skeletal structure which have come into use during the last two decades or so. They are usually metallic structures used to provide a flat cover for large unobstructed areas. The exact analysis of double-layer grids, even with the aid of an electronic computer, is an onerous task and approximate methods are often used instead. The approximate methods developed have their drawbacks, their reliability has not always been checked and the knowledge about the structural behaviour of double-layer grids still remains limited. In this thesis, the structural behaviour of a type of double-layer grid is investigated by exact analysis and suitable approximate methods are developed. The results of exact analysis for a large number of different conditions are presented in Chapter Two, and lead to certain important conclusions about the structural behaviour as given in Chapter Six. In Chapter Three an original method is developed for approximate analysis of double-layer grids. The formulation is general, suitable for electronic computation and results in substantial savings. A computer programme was written to check its reliability, and the errors were small in all cases considered. The technique developed in Chapter Four consists in deriving a simple interpolation function, which can be used to approximate the displacements and forces in the grid for different values of a variable feature in the grid. It provides a means to study the structural behaviour of double-layer grids and other structures, and is suitable to be used in optimization processes. An experimental investigation carried out as a counter check on the experimental analysis is presented in Chapter Five. Details of the computer programme and a computational technique developed for the exact analysis of the grids are given in Appendices A and B. Appendix C contains a paper, the material of which is associated with the method developed in Chapter Three.

A general purpose finite element computer program has been written for the large-deflection, elasto-plastic analysis of plate assemblages upto and including collapse. The approximate Ilyushin's yield criterion has been adopted, where sudden plastic flow in the full section depth of the plate is assumed. The program has been compared with other theoretical and experimental treatments, and gives acceptable results. In the present work, the computer program has been used to study the interaction between the webs, flanges and diaphragm on the collapse behaviour of single cell rectangular box girders in the support region. A special beam element has been incorporated into the program to represent portions of the structure away from the support that may be assumed to behave in a linear elastic manner. The imperfection sensitivity of the box whose dimensions are shown to be in a critical range regarding interaction between two types of collapse has been established. Suggestions are made for a simplified two dimensional treatment to give safe values of collapse load involving the flange-diaphragm interaction.

The influence of re-entrant corners on the distribution of bending moments in a flat slab structure is the subject matter of this thesis. Two groups of problems have been investigated. Typical of the first group being a slab supported on columns placed at the intersections of two regular grids and incorporating in the central panel a rectangular hole which varied in size. The second group being that of slabs of rectangular configurations although not quite so regularly supported and each having a rectangular cut-out in one of the peripheral panels. The method of Finite Element has been employed to obtain the theoretical results. A method has been presented which enables one to modify the basis element stiffness matrix such that multi-valued stresses at a re-entrant corner can be faithfully represented. A series of tests on models has been carried out on the Moire Apparatus to determine the bending moments. Although various loading conditions have been tested, it has not been possible due to the volume of work to reduce the results but for the uniformly loaded cases. Good agreement between the experimental and the theoretical results indicates that the analysis yields realistic results. The results are not directly comparable with the Code of Practice C.P.114 values, however, on the basis of the code's recommendation for the values in a slab disturbed by the presence of a halo, a set of values has been calculated and compare with the experimental and the theoretical values. Conclusions have been drawn regarding the overall behaviour of the slabs and the importance of the position of the re-entrant corner on the distribution of the bending moments.

An investigation is made of the instability of thin-walled sections. A versatile computer program based on the finite element method of structural analysis is developed which is capable of determining the critical loads and buckling modes of arbitrarily shaped closed or open thin-walled sections under arbitrary loading. The effectiveness and validity of the program is checked against some classical problems and then applied rigorously to the study of the local buckling of box columns and the overall stability, of thin-walled box girders in cantilever. An experimental programme is performed on the buckling of thin-walled plastic box-columns for comparison with the analysis.