Bridges – Suspension – Towers and anchors
Patent
1990-12-10
1992-06-16
Britts, Ramon S.
Bridges
Suspension
Towers and anchors
14 22, 14 18, E01D 1100, E01D 1700
Patent
active
051215187
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to guyed bridges with a concrete deck, which are intended especially for spanning distances of the order of 80 to 250 m, and to the construction of such bridges.
According to the present state of the art, the deck of such guyed bridges consists of a concrete caisson suspended at regular intervals by guys which themselves transmit the load to masts located on either side of the gap to be bridged.
The guys can be arranged in the mid-plane of the structure between the traffic lanes. The stability of the deck under the influence of the asymmetric loads when a single traffic land is loaded is thus ensured by the torsional resistance of the caisson.
In another known form, the guys are placed on either side of the deck in two vertical or oblique planes also inclined on either side of the axis of the structure, to allow the guys to converge at a single point on the head of the mast.
As regards this double lateral suspension, recent embodiments for simplifying the construction of the deck and reducing its cost have appeared. When the main span is sufficiently small (of the order of a maximum of 100 to 150 m), the deck then consists of a simple solid concrete slab suspended along its two lateral edges. Limits are placed on the use of this solution by the excessive flexibility of the deck in terms of the risk of general buckling or for the practical operation of the structure. Furthermore, the low transverse rigidity of the slab does not always satisfactorily ensure the stability of the structure relative to the wind.
For longer spans (for example, from 100 to 300 m), the deck has consisted of a slab ribbed in the transverse direction and equipped with longitudinal edge girders in which the guys are anchored.
In principle, such decks are easier to produce than caisson decks. However, they do not have the same longitudinal bending rigidity, and above all their torsional inertia is negligible. The effects of accidental phenomena, such as exceptional gusts of wind or the impact of a vehicle against a guy, therefore have much more serious consequences on these structures.
On the other hand, the decks, whether in the form of caissons or formed from a ribbed slab, can be made of successive prefabricated elements assembled to one another in the longitudinal direction. This less costly method of construction does not have an appreciable effect on the rigidity, and the comments made above remain applicable here.
The object of the present invention is to overcome the limitations or inadequacies mentioned above, making it possible to produce structures of a rigidity comparable to that of caisson decks, whilst at the same time preserving the simplicity of form and construction of the decks in the form of a solid or ribbed slab.
To achieve this result, the invention provides a guyed bridge comprising:
at least one deck formed from a series of at least partially prefabricated elements, each element extending over the width of the deck and over some of its length,
a mast which is carried by a pier and the top of which supports a series of guys supporting the deck and the particular feature of which is that each element has transversely elongate inner recesses and a vertical cross-section approximately symmetrical relative to a horizontal plane.
Thus, the main difference from the structures of conventional decks is that the bridge consists of a series of connected transverse caissons and no longer of longitudinal caissons or simple or ribbed plane slabs. The result of this a very high torsional rigidity of the deck for an equal weight.
The elements are fixed together to form the deck by all conventional means, especially by means of longitudinal prestressing cables extending over several successive elements and/or over the entire length of the deck.
According to a first embodiment of the elements, each of these is an element prefabricated in one piece and formed from a lower apron and an upper apron carrying the roadway, which are separated by inner voids extending over a large part of the transverse di
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Beton-und Stahlbetonbau, vol 75, No. 2, pp. 29-36 FIG. 4-6 Feb. 1980 (Berlin, DE), F. Leonhardt et al: "Die Spannbeton-Schragkabelbrucke . . . ".
Civil Engineering, vol. 56, No. 11 Nov. 1986 "Sunshine Skyway nears completion" pp. 32-35.
Beton-und Stahlbetonbau, vol. 75 No. 4 Apr. 1980 "Die Spahnbeton-Schragkabebrucke uber den Columbia river . . . " pp. 90-94.
Britts Ramon S.
Connolly Nancy P.
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