Graphical Analysis of Roof Trusses; For the Use of Engineers, Architects and Builders (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1876 edition. Excerpt: ...figure, by either the parallelogram or triangle of force, will give the amount and direction of each reaction from the combined load. Wind on the other side will exactly reverse the amounts and bring them on the opposite side of the vertical line. If the truss is simply placed upon the wall-plates, and either of the supporting forces makes a greater angle with the vertical than the angle of repose between the two surfaces, the truss should be bolted down to the wall; otherwise there will be a tendency to slide, diminishing the tension in the tie, perhaps causing compression in that member, and changing the action of the other parts of the truss. This matter will be treated of further. If the weight of snow is also to be provided for, it may readily be done by taking the proper fraction of the stresses from the steady load and adding them to the above table. We propose, in the example illustrated by Fig. 19, to consider the truss as supported on a rocker or rollers at the end T, where the small circle is drawn, to allow for the expansion or contraction of the iron frame from changes of temperature. It is therefore plain that the reaction at T must always be vertical. The truss is supposed to be 79 feet 8 inches in span, and 23 feet in height, which gives an angle of 300 with the horizon, and makes the length of rafter 46 feet. It would be proper usually to support the rafter at more numerous points; but our diagram would not then be so clear, with its small scale, from multiplicity of lines, and one can readily extend the method to a truss of more pieces. / This frame supports 8 ft. of roof, and the steady load per square foot of roof is taken, including everything, as 14 lbs. The total vertical load will then be 14 X 46 X 2 X 8 = 10304 lbs., or...