The development of an experimental method of obtaining an influence diagram for stress in structural frames

The function of an engineering structure is to receive external and gravitational forces which must be transmitted and distributed to some external medium, and the structural efficiency is a measure of the utilization of the force resisting capacity of' the structure. Structural efficiency is, however, no overall criterion of structural suitability, for aesthetic, economic and constructional qualifications must also be considered. Originally the structural efficiency was limited severely by these latter three considerations. With the development of high grade materials and manufacturing processes with closely controlled quality and precisely predictable strength, and strength deformation characteristics, it has become economically and constructionally desirable to use them efficiently. The advent or arc welding and reinforced concrete has enabled these basically more efficient structures to be economically constructed. This increased structural efficiency introduces greater degrees of indeterminancy in the structure and requires more precision in the design which in their turn have resulted in a necessary examination of load prediction, factors of safety and design method. The external forces to be transmitted by a structure will generally be continuously variable and not precisely predictable, although in some instances the load may be quite specifically defined for the whole of the life of the structure. The life of a structure is rarely known for those exposed to natural forces such as flood, earthquake or wind loads, the design loads specified in the governing code of practice are based upon the phenomenon of certain severities being definitely cyclic, the longer the cycle the greater the severity. If these loadings are then accepted a probable life period is also accepted. Similarly, the live loading values for various type structures laid down in these codes are values which have been found by experience to be satisfactory or safe for the normal life period of buildings in the area concerned, and which may or may not be proved by involuntary full scale tests