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JUST for the sake of experiment it may be desirable to imagine a building or group of buildings, putting the greatest possible strain upon its constructional members. Obviously it would be difficult to find a better instance of a building so disposed than some habitable structure suspended aloft in the air. It is not sufficient, however, to imagine an occasion for the exercise of the engineers’ greatest capacities, for one must also find a social excuse for the structure, however unusual this latter may be. It is so easy to picture fantastic buildings of unheard-of sizes and shapes, but the design of such is not architecture, for architecture has not only a form but a subject, and this subject must be an intelligible one. Figure XI. illustrates a group of buildings raised about four thousand feet above the ground. The constructional problem is a fascinating one, and, of course, could be solved in a great variety of ways. Also the aesthetic problem is of interest for the organic union of the super-structure with its supports is especially difficult of accomplishment. It would be absurd, however, to engage one’s energies upon the solution of either the constructional or aesthetic problem unless one could first visualise a social occasion which would justify re-erection of such an extraordinary structure. Imagine a great plain extending over many miles and in this plain a city in an advanced degree of social development. At the period in which one may conceive this city to exist, let us assume that the standard of hygiene is a high one, and that abundant money is available for social services. What could be more natural in such a community that means should be found for erecting health resorts, hospitals, sanatoria, rest and amusement centres, which would enjoy the advantage of a pure and rarefied atmosphere, such as usually can only be obtained on mountain tops, not readily accessible to even the richest inhabitants of great cities, and totally inaccessible to those of small means. Here, then, is the social occasion for this little township so raised on stilts. It will be observed that although I have described them as stilts, the supporting members are nevertheless quite thick enough to contain large lifts, for passenger and other services. The reader is almost sure to remark that in such an advanced state of civilisation as the diagram illustrates, there would surely be aeroplane services brought by that time to a high state of efficiency, and yet he might complain I have apparently made little provision in the way of landing stages for aircraft. But even this design shows a certain number of horizontal platforms or flat roofs which could be utilized for aircraft. It must be borne in mind, however, that with the coming of the helicopter large landing stages for aircraft will be quite unnecessary, for the aeroplanes could hover like birds in front of the entrances to the building and come to rest on the ground with perfect safety. In a structure o
When the paint is too thin the heavy particles of lead gravitate downwards, and so it happens that a thicker deposit is formed on certain parts of the surface by partial denudation of other parts, and if a suitable portion of paint skin cut from a vertical
painted surface were examined under the microscope this would be readily observed. The obvious remedy for this would be to fill the paint up with dryers so that the lead would not be given time to settle, which remedy is as bad, if not, worse, than the evil. If such paints are used it is at all times necessary to rub well into the surface inequalities of the metal and to use sparingly, since the adhesion of the first coat is of prime importance.
In the design of steel roof truss members but little consideration is usually given to the bending actions which often occur. The most important of these may be conveniently
grouped under the following heads:-
(1) Lateral loading on rafters.
(2) Eccentricity of riveting.
(3) Non-intersection of axes of members at joints.
(4) Rigidity of joints and deformation of truss under load.