This book was written because it was believed that a practical treatise on the design of movable bridges and their machinery would be of interest and value to practicing engineers and advanced students in engineering schools. Many authors have treated the design of the superstructure of movable bridges in connection with that of fixed spans, but few have discussed the special problems peculiar to the arrangement and design of the machinery. The data formerly available in this important branch of the subject were scattered through treatises on machine design, handbooks, the technical periodicals, and the publications of engineering societies; or had been developed by the engineers of manufacturing bridge companies and closely held for their own use. One of the objects of this book is to collect and arrange the best of this material in convenient form for study and use, and to put the results of original investigations and the lessons learned from long experience before fellow-engineers, in the hope of rendering a real service to the profession.<br><br>After a brief history of the development of early designs, the various types of bridges are discussed, and enough statistical information is given to assist in determining the most desirable type of bridge for particular conditions; and also to serve as a basis for preliminary calculations. The various methods of stress analysis are so well known that only a brief statement of some of the simplest and most practical is given. The chapter on the elastic deflections of structures has been made more complete. The chapter on details of design includes discussions of camber, end-lifting mechanism, disc and roller-bearing centers, and other details which apply to swing bridges. The analysis of end-lifting mechanism, and the illustrative example are typical of convenient and practical methods which may be applied to the design of similar mechanism for other purposes. End-rail joints, operators' houses, and counterweights are treated briefly in the remaining chapters.<br><br>Appendix A gives an analysis of the stresses in lenticular discs, and Appendix B proposes a new method for the design of the tread plates on the supporting and segmental girders of rolling-lift bridges.