Basic Structural Material Research Articles

OPTIMUM LIMIT STATE DESIGN OF HIGHWAY BRIDGE SUPERSTRUCTURES USING GEOMETRIC PROGRAMMING

Abstract A number of studies, by the author and others, have shown that the Limit State Design method can, when applied to the design of bridge superstructures, produce more rational and economic designs than conventional methods. Most studies have been made on the assumption that the basic structural layout, proportioning, and material characteristics would be determined by the rules used for conventional design. The authors have pointed out that these rules are possibly no longer applicable and that greater economies could be obtained by some form of optimization procedure. This paper describes the application of Geometric Programming to the solution of such a problem. It is shown that excellent results can be obtained with a simplified version of the technique in which the “degree of difficulty” is reduced to zero. The superiority of Geometric Programming as an optimum design technique is demonstrated by comparing the results for the example chosen with those obtained by alternative methods.

Architectural Research in the Use of Foam Plastics

This program of research is being sponsored by the Agency for International Development of the U. S. Department of State in the interest of exploring the possibility of using foam plastics as a basic structural material for application in underdeveloped areas of the world. The preliminary investigation included a study of the mechanical properties of cellu lar plastics, methods for producing such ma terials (alone or in combination with other materials), as well as erection techniques which could result from the use of these ma terials. On the basis of this investigation certain conclusions were reached as to the kinds of structures which would make logical use of foam plastics, utilizing their unique properties and designing around their short comings.

Comparison of steel and aluminum subway cars

MILD STEEL has been the usual basic structural material for subway-car strength members with aluminum generally utilized for decorative or low-stressed sections.

The Twenty‐First S.B.A.C. Show

THE convincing demonstrations of smooth and completely controlled transition from vertical to horizontal flight by the Short S.C.1 must surely be regarded as the highlight of the Society of British Aircraft Constructors'Twenty‐First Flying Display and Exhibition held at Farnborough. The S.C.1 was built and designed as part of a Ministry of Aviation research programme and first achieved transition at the Royal Air‐craft Establishment at Bedford on April 6 of this year. The design of its control system followed on from the work done on the Rolls‐Royce Flying Bedstead and a rig constructed by the Royal Aircraft Establishment, and for hovering and low speed flight control is dependent on four nozzles, at the wing tips and nose and tail, which are supplied with high pressure air bled from the lift engines. These engines are specially designed lightweight units, the Rolls‐Royce R.B.108, of which four are used for lifting purposes and the fifth for forward motion. The fuselage is of monocoque construction composed of channel section frames about 7 inches apart and a minimum number of channel section longerons which are riveted to the skin sheeting. The delta wing of 10 per cent thickness cord ratio is a two‐spar structure with an auxiliary spar at the 76 per cent chord position and closely spaced chordwise ribs. This structure allows the four closely grouped lift engines to be accommodated between the main spars at the air‐craft centre of gravity. Medium strength aluminium alloys form the basic structural material of the S.C.1, with a certain number of titanium sheet components for fire‐walls. The wing centre‐section spars form an integral part of the bulk‐heads at the front and rear ends of the lift engines bay.