Bridges – Transportable
Patent
1988-11-28
1991-02-19
Britts, Ramon S.
Bridges
Transportable
14 73, 14 18, 14 6, E01D 1100, E01D 906, E01D 702, E01D 2104
Patent
active
049930940
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a new bridge structure composed of a deck and of means for supporting this deck, and particularly to a new wide-span guyed bridge structure and to a process for constructing such a bridge.
PRIOR ART
In the present state of the art, either suspension bridges or guyed bridges are used for crossing wide spans. Suspension bridges are justified in economic terms for exceptional spans, but their flexibility presents problems for traffic, especially railroad traffic, and for aeroelastic stability. Where guyed bridges are concerned, these do not have the sensitivity to wind of suspension bridges, particularly if the deck is constructed from concrete which is a material giving the structure a sufficient weight and a high rigidity. However, the weight limits the spans, so that, beyond the scope of use of concrete guyed bridges, decks of a composite steel/concrete structure or decks made completely of metal have been employed.
In the present state of the art, guyed decks of composite steel/concrete structure have always been composed of an upper chord made of concrete and forming a roadway slab, carried by transverse and longitudinal stiffening girders intended for transferring the loads to the guys, whilst ensuring that the deck has sufficient rigidity. Embodiments of this type are recent and highlight the current limitations of the known means as regards the following points: effects of shrinkage and the slow deformations of the concrete, to the sun of metal surfaces having low thermal inertia, instability of the lower chord of the longitudinal stiffening girders when the stresses attributable to the loads, added to the effects mentioned above, approach the compression yield limit of the metal, forces, such as the impact of a motor truck against a guy.
Several of these disadvantages can be overcome by increasing the height and size of the longitudinal stiffening girders, but this is at the expense of the wind and economy.
Lattice structures can also be used because they make it possible to obtain a high rigidity in terms of bending and torsion, whilst at the same time ensuring maximum wind transparency. In the present state of the art, such lattice structures usually combine steel and concrete, but despite considerable research in this sector, no truly satisfactory solution has been found for transferring the forces between the chords and the diagonal struts to the various nodes of the lattice. The long-term behavior of such solutions is not known and the cost prices remain high.
SUMMARY OF THE INVENTION
The object of the invention is to overcome all the disadvantages mentioned above by providing a new structure which is both light, rigid and easy to produce and therefore economical.
To achieve this result, the invention provides a bridge composed of a deck and of means for supporting this deck, the deck comprising: chords and directed obliquely both relative to the vertical and relative to the length of the bridge and forming with the chords a three-dimensional lattice, the particular feature of this bridge being that the axes of the diagonals converge on the longitudinal axis of the lower chord or the mid-plane of the upper chord.
By "three-dimensional lattice" is meant a structure composed of elements which are similar to plane parts or rectilinear segments and which are connected to one another, this structure not being contained in one plane. The junction points of plane parts and/or of rectilinear segments will be called "nodes" hereafter.
Preferably, the parts of the chords which are subjected to high tensile forces and the diagonals which are subjected to high tensile forces are prestressed by means which are particular to each of the said chords and to each diagonal or to two concurrent diagonals.
According to preferred procedures: reinforcements anchored at their two ends to the junction points of these diagonals with the upper chord and forming a V, the center of which is at the junction point of the said diagonals with the lower chord, equip
REFERENCES:
patent: 3712010 (1973-01-01), Porter et al.
patent: 3975476 (1976-08-01), Finsterwalder
patent: 4161088 (1979-07-01), Gugliotta et al.
patent: 4282619 (1981-08-01), Rooney
patent: 4489659 (1984-12-01), Kamohara et al.
patent: 4513465 (1985-04-01), Schambeck
patent: 4543008 (1985-09-01), Salama et al.
patent: 4746056 (1988-05-01), Thomsen
Britts Ramon S.
Scetauroute
Smith Matthew
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