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The Whipple Cast and Wrought Iron Bowstring Truss Bridge. locally known as the Normanskill Farm Bridge, is located near the entrance to Stevens Farm in southwestern Albany, New York, United States. It was built in 1867, but not moved to its present location until 1899. It is one of the oldest surviving iron bridges in the county, one of the few that use both cast and wrought iron and one of only two surviving examples of the Whipple bowstring truss type. In 1971 it was listed on the National Register of Historic Places, the only bridge in the city of Albany so far to be listed individually.〔 A Syracuse-based builder copied Squire Whipple's original bowstring truss design, the patent for which had expired by the time of its construction. Where it was originally located is not known;〔 ''See also:'' 〕 it is believed to have been somewhere west of the city, possibly in Schoharie County. When the old Albany and Delaware Turnpike, today Delaware Avenue, was rerouted in 1899 to what is now Normanskill Drive, it was moved to its present location to make the farm more accessible from the main road. When Delaware was straightened out into what is today New York State Route 443 (NY 443), traffic on the bridge went down, allowing the bridge to remain in use, although only for cars. Today it is limited only to pedestrian use, and is closed in winter. The city recently approved a small-scale restoration project. ==Site and structure== The bridge carries Mill Road across a deep ravine about 100 feet (30 m) west of Normanskill Drive. The surrounding area is wooded; to the west of the ravine the woods give way almost immediately to the Stevens Farm complex. The ravine is dry most of the time, but after heavy rains it carries water from a small basin extending northeast a quarter-mile (400 m) as far as the New York State Thruway (Interstate 87) to the Normans Kill to the south, which at this point is the boundary between the city of Albany and the town of Bethlehem to the south. To the east the land rises steeply. The wooded, park-like area gives way to a more developed residential neighborhood along the north side of today's Delaware Avenue (NY 443), opposite a large cemetery. The approach road is a narrow gravel strip. The bridge itself is a long and wide, supported by abutments on either side of concrete on the upper level and stone laid in a random ashlar pattern below. Its main components are the two top and two bottom chords.〔 On top, the chords form an arch of nine tangential castings of an inverted-U cast-iron bars which compress in response to a load. They are matched by bottom chords of two lines of nine wrought-iron open links, made from one-and-a-half-inch () square bars, which restrain the compression. They are connected by eight vertical rods on each side, with tie rods additionally bracing the two in the middle that rise the highest.〔 The four central vertical members on each side are inverted V's of two ⅝-inch () bars welded together at the top and inserted into the floor beams via threaded bottom ends. At the ends the verticals are four rods. Rods ⅞ of an inch wide () form the diagonals, double in each panel,〔 bracing the bridge against wind.〔 Latitudinal and longitudinal I-beams supported by the bottom chords provide a deck frame. They are trussed with two ⅞-inch wrought iron rods and braced by tie rods. Wooden planks laid horizontally across the frame serve as the deck.〔 Modern box girder guardrails run along both sides. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Whipple Cast and Wrought Iron Bowstring Truss Bridge」の詳細全文を読む スポンサード リンク
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