PREFACE. THE following pages on the Elements of Practical Construction have been compiled for students in Engineering, on the same general plan as that adopted by the author in a work on Practical Hydraulics, which has been received with considerable favour by those for whose use it was intended. The present work treats only of the resistance of materials to direct compression and tension, leaving to another volume the subjects of elasticity, indirect compression, and tension, transverse resistance and torsion, &c. In treating of each material a Proposition is first given stating its average ultimate resistance; this is followed by experimental proofs; and then are given illustrations of the material so strained taken from completed and successful structures of eminent engineers. The experiments and some of the examples now published in a collected form have been taken from the Proceedings and Transactions of learned Societies, which are not easy of reference, and cannot readily be purchased, and from Reports of Commissions, with their Appendices, all which are too bulky for the library of beginners in a profession which demands frequent change of residence. To give the chief points of these in a more portable form, with practical examples added, may, it is hoped, be of some use. The Provost and Senior Fellows of Trinity College, Dublin, have paid a part of the expenses of this work, and the author takes the present opportunity to thank them for their liberality. ELEMENTS OF PRACTICAL CONSTRUCTION. RESISTANCE OF MATERIALS. I. AN attentive examination of any engineering structure, or of any machine in motion, must lead the observer to the conclusion that the several component parts are resisting, in very different modes, the diverse pressures and strains known to be in action. Four classes of these resistances are generally enumerated: - FIRST. The resistance to direct extension; a force being in action tending to tear asunder the fibres or particles of the body. Tie-rods, tie-beams, the links of the main chains of a suspension bridge, the pump rods of pumping engines, ropes and chains, chain cables, rivets, and screw bolts, and the external plates of steam-engine boilers, &c., are instances of this description of resistance being brought into action. SECOND. The resistance to direct compression, a force being present tending to crush the particles or fibres. Pillars, piers of bridges, posts and struts, the shafts of columns, the main ribs of iron arches, and voussoirs of bridges of masonry, afford examples of this particular class of resistance to the external forces in action. THIRD. The resistance of a beam supported at one or both extremities to a force acting in a direction transverse to its length, and in fibrous material, as wrought iron and timber, perpendicular to the line of fibres. The girders of bridges, all beams, bresummers, and joists, and the beams of steam B |