What is "bowstring girder"

Girder \Gird"er\, n. [From Gird to encircle.]

1. One who, or that which, girds.

2. (Arch. & Engin.) A main beam; a stright, horizontal beam to span an opening or carry weight, such as ends of floor beams, etc.; hence, a framed or built-up member discharging the same office, technically called a compound girder. See Illusts. of Frame, and Doubleframed floor, under Double.

   Bowstring girder, Box girder, etc. See under Bowstring, Box, etc.

   Girder bridge. See under Bridge.

   Lattice girder, a girder consisting of longitudinal bars united by diagonal crossing bars.

   Half-lattice girder, a girder consisting of horizontal upper and lower bars connected by a series of diagonal bars sloping alternately in opposite directions so as to divide the space between the bars into a series of triangles.
   --Knight.

   Sandwich girder, a girder consisting of two parallel wooden beams, between which is an iron plate, the whole clamped together by iron bolts.

Bowstring \Bow"string`\, n.

1. The string of a bow.

2. A string used by the Turks for strangling offenders.

   Bowstring bridge, a bridge formed of an arch of timber or iron, often braced, the thrust of which is resisted by a tie forming a chord of the arch.

   Bowstring girder, an arched beam strengthened by a tie connecting its two ends.

   Bowstring hemp (Bot.), the tenacious fiber of the Sanseviera Zeylanica, growing in India and Africa, from which bowstrings are made.
   --Balfour.