PREFACE The primary object which the author had in view in writing this book was to prepare a text-book for students attending the first portion of his lectures on Materials and Structures; but he considers that the work may be found useful not only to engineering students in Technical Colleges and Universities, but also to those engaged in the design of constructional iron and steel work. The modern methods of determining the safe intensity of working stresses in structures have been considered in the first chapter, and have been employed more or less throughout the work. The subjects treated in the various chapters have been considered as briefly as possible, and the numerous examples given are relied upon for more complete explanation. The special feature of the work lies in the various examples which illustrate the design of the most important classes of structures in iron, steel, and timber; these have all been selected from existing works. The author's experience in teaching has convinced him of the necessity of thoroughly illustrating the various principles underlying the theory and practice of construction, as a student is never certain whether he understands these principles or not until he has attempted to apply them. The author has freely availed himself of the works of others, which he has endeavoured to acknowledge as far as possible throughout the work : but he is especially indebted to the Proceedings of the Institution of Civil Engineers, the American Society of Civil Engineers, the Specifications of Mr. Theodore Cooper, M.Amer.Soc.C.E. ; the works of Professors Dubois, Burr, and Waddell; also to Mr. Hickson, M.Inst.C.E., Commissioner and Engineer-in-chief for Roads and Bridges, New South Wales, for drawings of the continuous-girder road bridge, the swing bridge, and the hinged-arch bridge. Although the subject of foundations is at least as important as that of superstructures, it has only been treated briefly for pile trestle viaducts and cylinder piers. The author considers that the subject of foundations could be more conveniently dealt with in connection with a book on Engineering Construction in Brickwork, Masonry, and Concrete, which he hopes to write as soon as time will permit. In spite of the care which has been exercised in preparing this work, it is possible that in a first edition errors may have escaped detection; the author will therefore be thankful for any information as to errors in diagrams or calculations. UNIVERSITY OF SYDNEY, New South Walzs. CONTENTS The methods of testing the strength and elasticity of materials Ductility as measured by the percentage of elongation and contraction of area The commercial and the true limit of elasticity Artificially raised yield-point. The determination of the true limit and modulus of elasticity Tutographic stress-strain diagrams Local and general extension of a test-piece The strength and specific gravity of various kinds of cast iron . Table of strength and elasticity of wrought iron and steel in tension, Tables of strength and ductility of various qualities of wrought iron Working stress and factor of safety Wöhler and Bauschinger's endurance tests Launhardt's and Weyrauch's formulæ Various formulæ for the determination of the safe intensity of stress in CHAPTER II. STRENGTH AND ELASTICITY OF TIMBER. General remarks on the testing of timber The tensile and compressive strengths and elasticity of timber Tables of strengths of Anierican, European, and Australian timber columns Shearing strength of timber. Tables of shearing strengths of American, European, and Australian timber . Transverse strength and elasticity of timber Tables of strength and elasticity of American, European, and Australian timbers Safe values of the modulus of rupture Increase in deflection of beams due to long-continued application of load Factor of safety in timber structures General remarks on the growth, felling, and preservation of timber 23 24 25 26 27 27 28 30 30 31 31 Beam fixed at one end and loaded in various ways Beam supported at both ends and loaded in various ways Beam supported at two points with overhanging portions and loaded in MOMENTS OF RESISTANCE-INTENSITY OF HORIZONTAL AND VERTICAL SHEARING STRESSES. General expression for the moment of resistance of the section of a beam Relation between the modulus of rupture and the tensile strength Examples of the moment of inertia of symmetrical and unsymmetrical sections Moment of resistance of built girders and cast-iron girders Graphical method of determining the moment of resistance of various sections Tables of dimensions, weight, and moduli of section of rolled girders of iron Distribution of shearing stress in rectangular beams Ratio of depth to span in timber beams in regard to transverse strength and 81 S3 SPAN IN TIMBER AND IRON. Example of a timber beam bridge for road traffic Table of beams and corbels for beam bridges Example of a timber viaduct of 10 feet spans of ironbark timber with open deck Method of determining the sizes of timbers in the open deck 87 90 90 91 |