noted therefrom that for light loads the simple spans have less concrete, and that for heavy girders there is but little difference in the concrete quantities, excepting that for exceedingly-heavy, long-span girders the continuous type is the lighter. There is always more steel required for the continuous type than for the non-continuous one.

From the foregoing remarks it is evident that simple-span girders are generally cheaper than the continuous ones. It will be found, however, that the bents or other supports are cheaper for continuous girders than for simple ones, and that floor joints in simple spans are expensive, also that the continuous girders give a solid, monolithic structure. The continuous-girder construction is very generally used in highway bridges; but the railway companies have adopted as standard the simple-girder type. However, nearly all railway concrete-bridges up to the present have been of solid-slab construction, rather than of that of the slab-girder.

The foregoing comparisons are based upon girders in which the reinforcement was liberally proportioned for positive moments, negative moments, and shears, making full provision for impact and a small allowance for uncertainties of stress distribution in continuous girders. It is possible to skimp the reinforcing of concrete girders considerably, and this practice in highway bridgework is altogether too common. It is an evil that should be stamped out, if not by the engineering profession, then by the laws of the land; for while it is most reprehensible to skin a steel bridge in which the skinning cannot be hidden from the expert eye, it is criminal to trim down to dangerous limits of strength a reinforced-concrete structure in which the flaws and weaknesses are buried out of sight.

The character of the foundations should be duly considered in deciding between simple and continuous girders; for, if there is danger of settlement, the simple-girder type is far preferable—in fact, it is obligatory.

The balanced-cantilever type of girder is beginning to be used, each monolithic unit consisting of a pier and two half-spans. In this the foundation pressure is centric for dead load and for live load over the two arms; but with the latter loading on one arm only, the pressure on the base is decidedly eccentric, subjecting the pier shaft to bending. This type of layout permits of a very shallow depth at the center of the span, and is thus specially applicable to long spans, where the weight of the concrete in the central portion of either simple or continuous girders is an important factor. The balanced-cantilever girder usually shows for the superstructure a small economy over either the simple or the continuous girder for short spans and a larger saving for long ones. The substructure, though, is always more expensive, as it has to be designed for the unbalanced load on one arm. If the live load is small in comparison with the dead load, this increase in sub-structure cost is not great; but otherwise it is so large as to outweigh the economy in the girders themselves. This type of layout should not be used on soft foundations