Truss-type girder for supporting a movable body

A girder for supporting a movable body, having a truss structure of a cross-sectional shape forming an isosceles triangle with a horizontal base, comprising:

• only three main tubes, each of said main tubes having a circular cross section and being located in a position corresponding to a respective one of three corners of the triangle and extending continuously over the length of the girder;
• a plurality of joint pieces, said joint pieces being arranged at equal intervals along each of said main tubes with each joint piece on one main tube being secured abreast a respective joint piece on the other two of said main tubes;
• a plurality of branch tubes of a circular cross section, each of said branch tubes being disposed between a respective two of said main tubes and being fixed at its ends by respective joint pieces, wherein the respective joint pieces arranged abreast one another on the three main tubes are connected by a respective three of said branch tubes that lie in a plane extending through the respective joint pieces perpendicular to the longitudinal axes of the main tubes so as to form said isosceles triangle;
• a pair of rail support means, each being secured to a respective lower one of the main tubes at a position disposed upwardly and outwardly of the center of the respective lower main tube;
• and
• a pair of rails along which said movable body is traversable, each rail being supported on one of said rail support means.