IN FRAMED STRUCTURES, WITH NUMEROUS PRACTICAL APPLICATIONS ΤΟ CRANES-BRIDGE, ROOF AND SUSPENSION TRUSSES-BRACED ARCHES ALSO, DETERMINATION OF DIMENSIONS AND DESIGNING OF DETAILS-SPECIFICATIONS uguster BY A. JAY DU BOIS, C.E., Ph.D., HIGGIN PROFESSOR OF DYNAMIC ENGINEERING IN THE SHEFFIELD SCIENTIFIC SCHOOL OF YALE COLLEGE; AUTHOR OF "ELEMENTS OF GRAPHICAL STATICS," ETC.; MEMBER OF AMERICAN SOCIETY OF MECHANICAL ENGINEERS; AMERICAN OF MINING ENGINEERS, ETC. NEW YORK: JOHN WILEY & SONS. COPYRIGHT, 1883, BY JOHN WILEY & SONS. PRESS OF J. J. LITTLE & CO.. PREFACE. To those who make use of this work, whether teacher or student, a few words as to its plan may be of service. The work is divided into two PARTS. PART I. consists of two SECTIONS. SECTION I. gives, in four short chapters, the principles which lie at the bottom of all methods of calculation. In these chapters all unnecessary detail has been avoided, the object being to familiarize the student first with the fundamental principles. Each chapter contains the ground-work of a separate method of calculation, and the same illustrative example is used in each. The student who has thus familiarized himself with the four fundamental methods of calculation, can afterwards combine these methods in the solution of any particular case, as may seem best. It is believed that every method in use will be found on analysis to be a combination of two or more of the methods set forth in these first four chapters, and, so far as known to the writer, the present work is the only one in which such division has been made, and each method given clearly by itself independently of the others. In SECTION II. the application of these methods to the solution of various structures is given with all necessary detail. It has been the aim of the writer to make this section very complete in full solutions of every existing form of bridge. The student, already familiar with the four fundamental methods, is now in no danger of being confused by detail, and can easily devise for himself other methods of solution for individual cases, as good, or even better, than those given. In Chapter I. of this section will be found a more complete treatment of Roof Trusses than has been thus far given in any work known to the writer. In Chapters III. and IV. a simple bridge girder is taken, and calculated fully, first by each of our four fundamental methods, and lastly by that combination of methods which seems best adapted to the case in hand. The remainder of the section gives the complete calculation of every form of bridge known, each case illustrated by an example carefully worked out. In Chapters VI. to VIII. upon the continuous girder, pivot or swing bridge and braced arch, much new matter will be found, and it is thought that the methods given will commend themselves as practical and easy of application. Whatever may be thought of the comparative advantages or disadvantages of these forms of bridges, they cannot well be omitted from a work which aims at any degree of completeness. For the average student, perhaps, so full a course is not desirable, at least at first, and therefore the attempt has been made by means of finer print to mark out two courses of study. In any case the intelligent teacher will know what to omit, and it is no disadvantage to a student to be possessed of a Text Book which includes more than he has been able to read, and which may, therefore, be of future benefit instead of being laid on the shelf when finished. In Chapter IX. the suspension system is given at considerable length, perhaps more than its importance demands. The entire chapter is believed to be new, and so far as the writer knows, it is the only solution of this construction which is free from assumptions known to be false. It is, therefore, given here for what it is worth as a contribution to the science of Bridge Calculation. In the Supplement to Chapter IX. the ordinary theory is also given with all requisite fulness. Everywhere it has been the aim of the writer to keep mathematical demonstrations out of the body of the work, so far as possible to do so. In the APPENDIX to PART I. will be found, in connected form, all the mathematical deductions referred to and made use of in the Text. The chapter upon the Theory of Flexure is especially full, and in that upon the Continuous Girder new matter will be found. The mere calculation of strains alone is but one part of the general problem of design, and by no means the most important. It is quite as necessary to properly proportion a structure for the stresses it has to sustain, as to know beforehand what these stresses are. In PART II., therefore, will be found as full a treatment of the important topics of cross-sectioning and designing of details and connections as the writer has been able to give. That practical bridge builders will find here much to criticize, goes without saying. The writer will be glad of any and all such criticisms, and will avail himself of them in the improvement of this very important part of the work. He can only ask for the present attempt the indulgence which, perhaps, it can claim, as among the first in a work of this character to combine "practice" with "theory," and hopes that portions of it may not be without interest and value even to the practical engineer. The same may be said for the "complete design for an iron railway bridge," and the "specifications and contracts" which close the volume. The specifications given have been compiled from a careful comparison of those furnished by a large number of our best railroad and bridge engineers, whose kindness in furnishing them for this purpose can only be acknowledged in this general manner. All other acknowledgments will be found fully made in the Text, but my indebtedness to Prof. J. A. L. Waddell, and also to the Kellogg & Maurice Bridge Co., is so great, that it is but justice to acknowledge it here also. NEW HAVEN, June, 1883. |