The best works on the subject of construction, that have fallen into the hands of the writer, contain but little that will furnish the means of calculating the strains upon the timbers of a bridge truss, or of determining their relative sizes; and they do not furnish information as to what constitute the elements Of a framed truss, or the most advantageous disposition of these elements to attain the maximum strength and stiffness with a given quantity of material. In the following pages, the object has been, not so much to detail particular plans, as to establish general principles. An attempt has been made to explain the mode of action Of the parts Of structures, and their mutual influence when combined; to point out the ways by which the strains can be estimated, and the relative sizes of the timbers accurately determined; new combinations of the elements in the construction of bridge trusses have been suggested, the defects of many plans in general use pointed out, and several simple means proposed for remedying these defects and adding to the strength Of structures.
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