Parabolic bearer
A parabolic girder is a lattice girder with a straight, horizontal belt for the roadway and a belt curved according to a parabola , the ends of which are connected to one another. When viewed from the side, the beams have the shape of an arch segment.
The parabolic truss was often used in England and especially in North America as a bowstring truss or, more precisely, bowstring arch truss . It is no longer used in more modern bridges.
description
In the most common form of the parabolic girder, the framework and the curved upper chord are arranged above the horizontal lower chord for the roadway. The connecting rods of the curved top chord are subjected to pressure.
But parabolic girders were also designed as fish-belly girders, in which the arch lies below the straight strap. The connecting rods of the arch are therefore subjected to tension there.
The nodes of the arch lie on a parabola, but the connecting rods of the belt between the nodes are straight. Instead of a belt running according to a parabola, circular belts that are easier to manufacture were also used.
With the parabolic girder, a weight saving of 10 to 15% can be achieved compared to a lattice girder with parallel, straight chords, but this is offset by the higher manufacturing costs of the curved girders. The acute-angled merging of the straps at their ends in large gusset plates with the associated problems is unfavorable .
The roadway is usually at the level of the lower chord. In order to ensure a sufficient headroom , the arches of the upper chord can only be supported against one another in the middle part of the parabolic girder by cross braces. Near both ends of the arch, the cross connections would be so low that they blocked the passage. These two problems were avoided by the further development of the semi-parabolic beam .
Forms related to the parabolic carrier are the lens carrier and the Pauli carrier , in which the second strap was also designed in a parabolic shape.
Individual evidence
- ↑ a b parabolic carrier. In: Röll, Freiherr von: Enzyklopädie des Eisenbahnwesens , Volume 4. Berlin, Vienna 1913, pp. 176–201. On Zeno.org
- ↑ Parabolic carrier . In: Otto Lueger (Ed.): Lexicon of the entire technology and its auxiliary sciences . Vol. 7, Stuttgart, Leipzig 1909, pp. 21-23. On Zeno.org