division of span-lengths. — Economic truss depths. — Legitimate economies in cantilever designing. — Wind stresses during erection. — Splaying the trusses. — Reducing weight during erection. — Solitary piers or pedestals are economic. — Adoption of intermediate trusses. — Division of stress on members meeting over main pier. — Choice between riveted and pin-connected construction. — Box-section chords. — Merriman and Jacoby's treatment of cantilevers. — Truss-depth constant for cantilevers: the practice is absurd. — Simple trusses and cantilevers compared. ............ 257

Much still to be learned about designing suspension bridges. — Suitable mostly

for highway structures. — Paper on "Comparative Economics of Wire Cables and High-Alloy-Steel Eye-bar-Cables for Long-Span Suspension Bridges." — Best floor to adopt. — Advantages and disadvantages of adopting many lines of cables. — Economics of stiffening trusses. — Best panel length. — Single-intersection versus double-intersection. — Ends free versus ends anchored. — Versed sine of cable. — Best type of approaches. — Suspending floor from backstays. — Design for anchorages. — Economics of cables. — Unsuitability of suspension bridges for steam railways. — Effect of anchoring ends of trusses upon the economics. — Comparative advantages and disadvantages of two types of cables. — Layout for proposed suspension bridge between Philadelphia and Camden and description of structure. — Outline of first economic investigation. — Live loads and intensities therefor. — Stress theory adopted for stiffening trusses. — Second set of computations. — Ratios of quantities of materials in eye-bar-cable bridges to those in wire-cable bridges. — Formulae for quantities of materials in suspension bridges. — Diagrams of quantities of materials. — Unit prices of materials. — Examples for illustration. — Mayarí steel comparison. — Heat-treated, carbon-steel-eye-bar comparison. — High-grade-nickel-steel comparison. — Heat-treated, chrome-molybdenum-steel comparison. — Résumé of findings. .............. 263

Types considered. — Swing-span versus either bascule or vertical lift. — One open-

ing versus two openings. — Shifting channel. — Vertical-lift versus bascule. — Future raising or lowering of grade-line. — Skew-crossings. — Carrying pipes and wires over movable spans. — Simplicity of vertical lift. — Economics of swing spans. — Rim-bearing versus center-bearing spans. — Bob-tailed swing versus ordinary swing. — Economics of bascule spans. — Single-leaf bascule versus double-leaf bascule. — Double-leaf bascule unfit for railway bridges. — Heel trunnion bascule. — Thomas Ellis Brown, Jr., type of bascule. — Rolling-lift bascule. — Trunnion type of bascule. — Waddell and Harrington axle details. — Roller-bearing type of bascule. — Brown-balance-beam type versus Strauss type of bascule. — Economics of vertical-lift spans. — Conditions favorable to the vertical lift. — Flanking spans for vertical lifts. — Skew layouts. — Wind-pressure on movable spans. — Widening of decks of movable spans.— Quickness of operation.— Economics in detailing of vertical lifts.—Best material for counterweights. —Balancing-chains. —Buffers.