l. From the standpoint of purely theoretical design all the members in a framed structure should be made of such dimensions that their material will be stressed to the
allowable limit under the external load system considered, since a structure proportioned in this way will ensure maximum economy in the use of material. In many
cases such an ideal structure may be impracticable, and will have to be modified to
meet a variety of conditions imposed byconsiderations other than those of theoretical
design. Whatever modifications are necessary, however, to meet such conditions the ideal design will have considerable value as a basis for the development of the final
scheme embodying the requirements of practical engineering. In some cases, e.g., in the design of all aircraft structures, the reduction of weight is such an important
consideration that very little is permitted to stand in the way of its attainment, and in such cases this ideal structure would be very closely followed.
Professor A.J. Sutton Pippard