Improved Design Method Research Articles

The Use of Viscoelastic Material to Damp Vibration in Buildings and Large Structures

Controlling the vibration response of structures is a problem which has received the attention of many engineers for many years. This paper discusses some recent developments of a special aspect of this general problem; namely the use of viscoelastic material to damp the low frequency vibration often associated with large scale structures and buildings. The growing concern of structural engineers with the airborne and structure borne vibration environment of their buildings is a reflection of the growing concern of the engineering profession, as well as the general public, with the problem of noise and vibration. Economic considerations and improved design methods have resulted in a trend to lighter weight structures and higher speed machinery, both of which tend to increase vibration levels. The engineer must either develop new methods of controlling vibration or adapt or improve existing methods if the public good is to be served. As an example of adaptation, this paper describes three cases in which constrained viscoelastic layers, first employed in the aerospace industry, have been used to control the vibration of large structures.

End Plate Connections in Plastically Designed Structures

A revolutionary improvement in design methods is resulting from the development of practical applications of the plastic strength theory of structural steel design. This could not be accomplished without the new design specifications reflecting the capabilities of these new theories, high tensile bolts and improved welding machines and techniques. Much has been said recently of the savings in tonnage per project in applying the plastic theory to the design of structures. However, theoretical economy, i.e., use of lighter sections, is not enough; the structural engineer must assure that the increased cost of intricate connections to develop the lighter members to their full potential does not offset any savings accrued solely by tonnage reduction. The new AISC Specification is the outcome of years of research and testing; its issuance has modified and liberalized structural design in steel. This new realistic approach to the true capacities of steel, properly designed, reflects appreciable savings in the cost of steel construction without lowering the safety requirements with which we are so familiar.

Paper 13: Tests beyond Yield on a Spherical Pressure Vessel Containing a Series of Oblique Nozzles

The paper describes the first of a series of three tests designed to obtain information about the nozzle assemblies on reactor pressure vessels under a variety of loading conditions, with a view to predicting their behaviour in service. This first test is concerned with the effect of loadings which cause yielding in the nozzle region, and while overloads as severe as those described cannot occur in practice, the results enable a quantitative assessment to be made of the margins between operating pressure and failure pressure as far as shortterm yielding is concerned. They also provide data which will be of interest when improved design methods, involving higher working stresses, are considered. The test was carried out on a spherical vessel containing a small group of oblique nozzles, manufactured to represent a nozzle layout typical of reactor vessels, at scale size. The vessel was hydraulically pressurized up to 1670 1b/in2 gauge when failure occurred through the heat-affected zones of the nozzle to shell welds. The basic shell stress at failure was approximately equal to the ultimate tensile strength of the material. Strain readings recorded during the tests, and the results of the metrological surveys, carried out on the vessel before and after testing, are discussed in the report.

ANALYSIS AND SYNTHESIS OF RADIATION PATTERNS FROM CIRCULAR APERTURES

Part I considers the problem of determining the source distribution over a circular aperture required to produce a prescribed radiation pattern. In particular, the problem of optimizing the narrow broadside pattern from a circular aperture is discussed in detail and an improved design method over Taylor's for line source is devised. Numerical examples are given.Part II deals with the analysis of the radiation pattern from a circular aperture from γ1 to γ2 with the traveling wave type source functions. Expressions suitable to the analysis and the synthesis are obtained and the narrow-beam and shaped-beam synthesis are discussed.