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IT is first desirable to explain how designers in the past have estimated the forces to be resisted. The few reliable determinations available have forced the designer into two courses, one based upon a horizontal force bearing some arbitrary proportion to g, while the other rests upon a wind pressure acting upon any face of the building under consideration. Following the San Francisco earthquake of 1906, much support was given to the latter method; but it is now held to be untenable on the grounds that the lateral force on a building weighing 1,000 tons would be the same as on one weighing 10,000 tons were the exposed dimensions the same in both cases. This is obviously absurd, as the force of any moving body is proportional to its mass.
Sir,-I shall be glad if you will kindly find space for a reply to Mr. R. A. Skelton’s remarks in the June issue of the Journal, regarding my letter in the April number.
THE design of a bridge or any other engineering project implies the adjustment of certain means to certain ends, and both means and ends are considered in terms of money. Co-existing with the financial problems involved is economic design. Further, a
bridge project implies not only the expenditure of money for the attainment of certain ends, but the meeting of all costs as they arise. The expenditure of a capital sum of money in first cost, and the meeting of capital charges and revenue costs out of income, is undoubtedly a financial problem, and the methods by which financial equilibrium is to be obtained must be established before the design is completed. Economic design implies financial equilibrium. In analysing a bridge project a wide interpretation must be given to the term "Finance" met in Economic Science.
W. Nelson Elgood