Supposing a warehouse floor is to be supported by flitch beams, 10 ft. centre to centre, the span of the beam being 20 ft. and the load to be supported being 3 cwt. per superficial foot, the size of the beams and the thickness of the flitch may be arrived at as follows. Formula for flitched beam W = d2/L (Cb + 30t). Where W = breaking weight in cwt. in centre; b = total breadth of timber in inches; d = depth of timber in inches; t = thickness of flitch plate in inches; L = length of span in feet; C = 3 for Baltic fir. From the question, 20 x 10 x 3 = 600 cwt. to be carried by each beam. Factor of safety, say, 6. Assume b = 12 and t = .75, then 600 x 6 = d2/20 (3 x 12 + 30 x -75); 3000 = d2/20 (36 + 22.5); d2 =(3600x20)/58.5 = 1230.

This is evidently very wide of the mark, and an ordinary flitch beam will not meet the case. Assume oak timber (C = 3.7) in three flitches, each 6 in. thick, and two flitch plates, each 1 in. thick, then 3600 =d2/20 (3.7 x 18 + 30 x 1 x 2); 3600=d2 126.6/20; d2 = (3600 x20)/126.6 =568; whence d = √616 = 23.83; so that 24 in. deep would do, and the whole section would be as in the accompanying figure. If the question was correctly copied from the examination paper, it is clear that the examiner was wanting in a practical grasp of the conditions, as flitched beams are never used of such a size.

Strength of Flitched Beam.