Listing of types of structure considered. — Rolled-I-beam spans. — Deck plate-

girder spans compared with articulated-truss spans. — Limiting lengths for plate-girder spans. — Shipment limitations. — Half-through, plate-girder spans. — Economic limit of length therefor. — Deck, open-webbed, riveted spans. — Plate-lattice girders. — Comparative economics of deck and through riveted spans. — Economics of various kinds of trusses ......................... 67

Duration of controversy. — Gradual solution. — Claims of contestants. — Lattice-

girder type. — Type of riveted structure finally evolved. — Unavoidable secondary stresses in riveted trusses. — Economic effect of using eye-bars. — Tabulated percentages of increase in weights of metal for riveted over pin-connected trusses. — Preference for riveted construction because of rigidity. — Replacement of worn pins. — Inferior limit of span-length for pin-connected railroad-bridges and highway-bridges. — Effect on economics from using a high-alloy of steel for eye-bars .................. 72

Differing opinions existing concerning the economics of these types. — When it is

permissible to use continuous trusses and when not. — Sciotoville Bridge. — Layouts used for investigation. — Conditions governing the computations for comparison. — Use of theorem of three moments. — Non-use of method of least work. — Determination of stresses. — Result of first set of computations. — Necessity for second set of computations and results thereof. — Necessity for third set of computations and results thereof. — Computations for highway bridges and results thereof. — Computations for short, spans and results thereof. — Summary of weight ratios. — Effect on economics due to semi-cantilevering and to necessity for keeping channel unobstructed. — Summary of conclusions ........ 75

Erroneous claim of some special virtue in cantilevers. — Crossing of deep and

swift currents. — Rigidity in cantilever bridges. — Economic limit of length of simple-truss spans as compared with cantilevers. — Minimum widths for