No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

The work presented is a theoretical and experimental investigation into the effect of coupling between torsional and flexural modes of vibration in cantilever beams. Two theoretical approaches are made: firstly, a finite element idealisation in which the beam is divided into a number of elements which possess cubic variations of deflection and rotation along their lengths; and, secondly, a more analytical method in which the simultaneous differential equations of motion are solved directly by application of Laplace Transforms. The investigation is restricted to the simplest cross section which possesses a single axis of symmetry, the isosceles triangle. The exact solutions for the torsion and flexure of such sections of general shape do not as yet exist, but use is made of several approximate techniques which have been developed for this section for the calculation of the torsional stiffness and position of the centre of flexure. It is shown experimentally and theoretically that torsional oscillations do not talce place about the centre of flexure ( or centre of torsion ), but about a point which may be considered to be coincident with the centrold. It is shown theoretically and confirmed experimentally that the effect of coupling on either mode is extremely small unless the original frequencies of torsional and flexural motion are almost coincident, in which case the two frequencies are separated into coupled modes which possess both torsion al and flexural characteristics. The effect is not, however, as significant as the coupling of flexural modes due to pretwist in sections which approximate to those of turbine blades.

The work carried out during this research project has been concerned with the performance of large structures and in the introduction to this thesis a justification for full-scale testing is presented. Full-scale testing techniques relating to both dynamic and quasi-static movements occurring in large civil engineering structures such as multi-storey buildings and bridges have been studied. Dynamic characteristics of buildings were obtained during full-scale testing with the use of seismometers and servo-drive accelerometers. Oscillations produced from both by wind and by forced vibration have been studied and the methods and results obtained are compared. The slow movement of structures, occurring at a frequency less than approximately 1 Hz, has been studied with the use of a specially developed laser based system. The system consists of a laser located at a stationary reference position while an X-Y plotter is positioned on the moving structure. Linked with four photo-cells and associated electronics, the system proved capable of monitoring the most significant movements occurring in civil engineering structures. A Theoretical control system analysis and frequency response of the device was performed. Extensive trials with the equipment and monitoring of the atmospheric temperature effects on the laser beam were undertaken and are described. Deflection data obtained on a multi-storey building and the Tamar suspension bridge and discussions on the problems encountered are presented. A small scale dynamic survey on the Tamar suspension bridge and results from an analytical model are described in Chapter Seven. Simple structural analysis models of multi-storey buildings have been used to yield values of natural frequencies. A finite element package has also been used to develop an accurate analytical model of a building to which different wind loading profiles were applied and deflections obtained.

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