No description available.

This research work deals with the development of the shearbox apparatus by introducing a micro-computer to automatically collect all the results, and to apply normal and shear stresses. A continuous statement of time, channel number, and transducer input and output is produced for each test, the sequences of applied rates of displacement and normal stresses for which were programmed.

The effect of a minor disturbing force on the stability of a structure which already is subjected to a major load near the critical state has been studied and is reported here. The approach taken is to develop physical insight to the problem by analysing representative models. The analysis is further developed on a continuum basis and tests are carried out on a small scale structural model. Two types of disturbing force are considered, that is a step pulse or a rectangular pulse. The dynamic response of a structure subjected to such a disturbing force is obtained by numerical integration using the Runge-Kutta method. The analysis neglects the possibilities of changing mode shape during the transient response. The theory developed was compared with a complementary experimental approach. The transient response of a thin wall column was experimentally studied. Special equipment was developed to permit the monitoring of the dynamic effect during the experimental programme. The results of critical disturbance force predictions are in good agreement with the experimental results.

This thesis is concerned with multiple equilibrium path generation and imperfection sensitivity of elastic conservative systems, the behaviour of which may be described using a finite number of discrete displacement coordinates and which, in the ideal case, exhibit compound or m-fold branching points. A review of previous work has been made, including that on specific systems, distinct critical points, compound critical points, optimisation and stochastic approaches. An appreciation of the role of Catastrophe Theory in problems of elastic stability has been included. The literature relevant to two particular mechanical systems, examined in detail later in the Thesis, is discussed. Simple criteria, which govern the existence of post-buckling equilibrium paths passing through a symmetric type of m-fold branching point, have been developed. Explicit expressions for the initial curvatures and initial post-buckling stiffnesses of these paths, where they exist, have been found. Quantitative means for assessing the statical stability of paths have been devised. The equilibria and critical equilibria of ideal and imperfect two-fold doubly-symmetric branching points have been examined in great detail. A classification of this type of system has been suggested, which includes a distinction between non-hysteresis and hysteresis behavior. General algebraic forms for the critical load-displacement and imperfection sensitivity surfaces have been derived and their qualitative appearances suggested. A non-approximate numerical technique for calculating the equilibria, deriving the complete critical load-displacement and imperfection sensitivity surfaces of two-fold doubly-symmetric branching systems has been applied to two particular mechanical systems, namely: an axially loaded pin-ended strut on a linear Winkler-type elastic foundation; and a thin simply-supported rectangular plate subjected to proportional bi-axial in-plane compression. The strut problem was modelled by means of a two-mode Rayleigh-Ritz procedure applied to a suitable higher-order total potential energy expression. The plate problem was modelled using a two-mode Galerkin integral technique applied to the von Karman large deflection equations. The role played by the two major imperfections and the imperfection sensitivity surface in dynamic mode-jumping and buckling load degradation respectively was elucidated. The general conclusions reached in this Thesis are broadly supported by other analytical, numerical and experimental work from the literature.

This thesis is concerned with the linear and non-linear bending analysis of sandwich beams and plates with flexible cores and thick or profiled metal faces. the project commences with a review of previous work in structural aspects of sandwich construction. It reveals that analytical solutions have been obtained for a small number of simply supported and continuous sandwich beams with equal spans subjected to simple cases of loading. Due to the increasing popularity of such panels in the building industry, there have been demands for more general solutions. Therefore, the purpose of the first part of the present investigation is to find explicit solutions for both single and multispan sandwich beams subject to various cases of loading. The analysis of sandwich beams subject to combined uniform transverse load and compressive or tensile axial load is also presented. Furthermore, simple expressions are presented for the analysis of sandwich beams continuous over supports subject to settlement. This is followed by the derivation of more general solutions for sandwich beams with arbitrary loading and boundary conditions using the finite element technique. The method is exact because the solutions of the governing differential equations are used to derive the element stiffness matrices for sandwich beams subject to combined bending and axial loads. Attention is first confined to the general case of panels with profiled faces, followed by the analysis of panels with plane faces as a special case. Some tests for sandwich panels subject to axial compressive load are presented and the results compared with the theoretical values. In the second part of the investigation, the analysis of sandwich plates is considered. The general equations presented by Alien were first redeveloped in a different way. Then, the buckling and bending analysis of orthotropic rectangular sandwich panels with all edges simply supported and subject to uniform lateral and edge loads is presented. This analysis was based on a series solution of the governing differential equations. Expressions for determining the deflection, stress resultants and critical buckling load of such panels are also presented. This is followed by the linear and geometrically non-linear finite element analysis of multi-layer plates. The formulations were incorporated in existing, modified and new elements for the analysis of three and five layer plates. Finally, the thermal and flexural analysis of sandwich panels is carried out using a three dimensional composite element. Several illustrative examples are also presented to demonstrate the accuracy and versatility of the various formulations.

In torsion-box design of twin girder overhead cranes, the bridge rail on which the lifting unit runs is positioned eccentrically on the girder, directly above one of the web plates. This web is subjected to in-plane patch loading produced by the spread of a wheel load through the overlying rail and flange. This study concerns the load carrying capacity of plate box-girder web panels subjected to a wheel load at the midspan of the panel. Distribution of a wheel load through a rail and flange is investigated from recordings made of in-plane vertical stress distribution profiles along the upper edge of a web panel of a short-span model box-girder. The girder was loaded through various interfaces above the web by a wheel load. A simple method is proposed for relating a distributed wheel load to an equivalent uniform patch load. Methods for estimating distributed wheel loading lengths are investigated. It is shown that crane web panels are generally subjected to patch loads of short length, occupying less than one-quarter of the panel length. A computer analysis is presented to determine elastic buckling coeffic-ients for flat rectangular plates subjected to a uniform in-plane patch load centrally disposed on one edge and supported by shear stresses on the adjacent edges. Patch loads of various lengths are considered over a range of plate aspect ratios for plates with various combinations of simply supported and clamped edges. Also considered are some non-uniformly distributed patch loads modelling approximately a distributed wheel load. For the large majority of geometries considered, it is the support condition along the loaded edge which has greatest influence on the buckling load. Correlation with buckling loads estimated from experimental measurements on a model crane girder web panel indicated that an assumption of simply supported panel edges is over-conservative and that it is probably more representative to consider the edges attached to the flanges as clamped. Ultimate load carrying capacity is considered. A plastic mechanism analysis originally presented by Roberts and Rockey is studied and a modified form derived which reveals the transition region from collapse initiated by direct web yielding for girders with stocky webs to failure by a mechanism of out-of-plane web deformation for girders with slender webs. Certain approximations in the original analysis are shown to involve the omission of terms which can contribute significantly to the plastic work expression. Inclusion of these terms, however, whilst offering potential refinement, increases considerably the complexity of the analysis. Results are presented of a series of collapse tests conducted on short-span model box-girders subjected to a wheel load above one of the webs. The effect on the failure load of rail size, web thickness, panel aspect ratio, and longitudinal web stiffening is investigated. Snap buckling was exhibited by several of the test web panels. From the results, a simple expression is developed for predicting collapse loads of plate girders subjected to narrow patch loads. The main findings of the work are used as a basis for a series of recommendations to aid the structural designer in taking account of patch loading on slender web panels.

No description available.

In this thesis a finite element programme for material and geometric nonlinear analysis, has been modified with pre- and post-data processing and eigenvalue solution. More efficient methods to solve elastic and inelastic eigenvalue and eigenvectors have been developed to deal with stability problems in structures with arbitrary shape, irregular stiffness, loads and boundary conditions. The Generalized Beam Theory (GBT) with the facilities of elastic spring restraints, buckling under coupled loads, different load locations has been developed and programmed by the author. It has been applied to reveal the basic behaviour and the interaction between the modes of light gauge steel members. It has been found that the AISI design approach with elastic bucking stresses obtained using GBT can be used to correctly predict the strength of compression thin-walled columns. Three different types of widely used light gauge steel members, namely rack columns, purlins and decks, have been analyzed using both FEM and GBT. The comparison of results from the numerical analyses and comprehensive tests agrees well. The author has risen to the challenge of complicated buckling problems and a pseudo-plastic design procedure for a continuous purlins and roof decks has been established in order to make the best us of the materials. Through the highly complex analyses, some important conclusions for composite deck profiles in the wet concrete stage have been obtained. The ECCS and AISI design approaches for bending have been found to be conservative when the deck is subject to plastic buckling or strength failure. The calculation of the ultimate web crippling load without consideration of bending moment is awkward and further light is shed on this topical problem. The influence of dimples in reducing the deck bending resistance mainly depends on the flange slenderness.

This research examines the effect of lateral pressures on the bond characteristics of both plain and deformed reinforcing bars in lightweight aggregate (Lytag) concrete. Two common bond tests, the cube pull-out and the semi-beam test, were modified in order that lateral pressures could be applied to the bond specimens. The major variables studied were the magnitude of the lateral pressure, the bar diameter, the length of embedment and the concrete strength. The results of over 200 bond tests show that for round bars the application of a lateral pressure close to the cube-strength of the concrete can result in an increase in pull-out load of as much as 260% and that for similar sized deformed bars the corresponding increase is about 75%. The different bond mechanisms for round and deformed bars were highlighted by the failure modes of the bond specimens and this difference in behaviour is reflected in the theoretical work by a frictional bond strength criterion for round bars and a splitting or shearing criterion for deformed bars. As part of the experimental work a reinforcing bar was fully strain-gauged, enabling the strain distribution along the bar to be monitored for various combinations of lateral pressure and pull-out loads. The bond stress was found to be uniformly distributed along the bar for pull-out loads greater than about half the ultimate and the strain distribution relatively unaffected by increasing lateral pressure. Finally, to test the conclusions from the bond pull-out tests in a practical situation, a total of sixty-four lightweight concrete deep beams, with varying anchorage lengths, bearing block sizes and web reinforcement were tested. The results of these tests confirm that the high bearing stresses that occur at the supports of deep beams do have significant positive effects on the anchorage bond that can be developed. A method is proposed to take into account the enhanced bond strengths that occur over the supports of deep beams with span/depth ratios of less than 2.

No description available.