Preface To The Second Edition

In the present edition several corrections and many important changes and additions have been made, and some parts have been almost entirely re-written. The formulas and calculation of weights of girders, both deck and through, are new.

Preface To The First Edition

For railway as well as highway bridges, there is probably no other form of girders that are more extensively used and daily being constructed than plate girders. The reason for this lies mainly in the simplicity of their construction and their stiffness as compared with open-girders. That the construction of a plate-girder is simple, is, however, no reason to suppose that the stresses produced in it by external forces are, also, simple. On the contrary, to determine the actual stresses in every part of a plate-girder is one of the most complicated problems that can come in the way of bridge engineers.

The abundance of plate-girder drawings in almost every engineering office, no matter whether their designs are correct or not, has usually been the source from which many draughtsmen "design" a new girder. Indeed even in regular bridge works with the rush of work, usual in these places, there is hardly an opportunity for the draughtsmen to examine whether each part is rightly proportioned or not, unless they are thoroughly posted in the ground principles upon which every part of the design of a structure rests. This is not always the case, and as a consequence plate-girders are often designed and constructed in a most careless manner, no particular attention being paid to the proportion and arrangement of parts, the spacing of rivets, etc., each of which forms a most important factor in the strength of a girder. The mere fact that a structure is standing is not the indication of the correctness of its design.

It is the aim of the writer, in the little volume now given to the public, to present, in as simple a manner as possible, a somewhat rational mode of designing girders of this class with special reference to American practice. And in the absence of any particular treatise on the subject within the reach of everyone as yet, it is hoped that it may be of some help to beginners in bridge designing.

I. H.