Bridges – Suspension
Patent
1995-07-03
1997-06-24
Lisehora, James
Bridges
Suspension
14 19, 14 78, E01D 1100
Patent
active
056407327
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns suspension bridges comprising an essentially flat main structure, or framework, the top surface of which forms the roadway for the transport means crossing the bridge, and a suspension system formed of catenary cables anchored to end piers of the bridge and of a plurality of vertical stays or hangers to suspend the bridge framework to the catenary cables.
BACKGROUND OF THE INVENTION
As known, these suspension bridges have vibration frequencies of their own; normally, with no wind, the basic flexural vibration frequency differs from the basic torsional vibration frequency, both being generally very low. Nevertheless, the action of side winds varies said typical vibration frequencies, particularly because--especially in bridges with large transversal dimensions and/or a wide span, for instance motorway bridges--the flat suspended structure behaves, when actually exposed to side winds, similarly to a wing surface, hence with a "lifting" effect which greatly varies from one moment to the next.
As wind increases its strength, the two aforespecified vibration frequencies tend to approach, up to the point of coinciding: in these circumstances, the structure is thus subjected to so-called "flutter" conditions, i.e. to flexural-torsional stresses which may even result dangerous for the stability of the whole bridge.
These flutter conditions, and the problems connected therewith, are described in more detail in EP-A-0.233.528, filed by the same Applicant, to which reference is made for a better understanding of the present invention.
The main object of EP-A-0.233.528 is a wing structure, which is rigidly fixed to the lateral edges of the bridge and is meant to increase its flutter speed beyond the top speed of the wind expected in the bridge area.
The same EP-A-0.233.528 also discloses a windbreak barrier, whose main function is to reduce the crosswind pressure on the vehicles travelling along the bridge; such a barrier essentially consists of a grating, having a typically convex surface apt to cooperate with the wing structure, so as to control the action of the wind.
OBJECT OF THE INVENTION
The object of the present invention is to propose a windbreak barrier having a remarkable aerodynamic damping action on the bridge structure, such as to limit the use of additional wing structures, or even--at least in certain cases--give it up completely.
SUMMARY OF THE INVENTION
This result is essentially achieved due to the fact that said windbreak barrier comprises a grille wall, mounted onto a carrying framework formed of a plurality of uprights and of at least two ledgers, at least one of said ledgers consisting of an aerodynamic element formed as a wing surface with a substantially horizontal axis.
According to a preferred embodiment the invention, said wing surface has a wing chord of 100 to 150 cm and a thickness, in correspondence of its highest point, of 20 to 30 cm, while said grille wall has a transparency of about 70%.
BRIEF DESCRIPTION OF THE INVENTION
Further characteristics and advantages of the windbreak barrier according to the present invention will anyhow be more evident from the following description of a preferred embodiment thereof, illustrated by way of example on the accompanying drawing, in which:
FIG. 1 is a diagrammatic, partial, cross-section view of the lateral edge of a bridge carrying a windbreak barrier according to the invention;
FIG. 2 is a diagrammatic, enlarged scale, cross-section view of one of the wing surfaces forming part of the windbreak barrier of FIG. 1; and
FIG. 3 is a partial side view of the barrier, in the direction of arrow A in FIG. 1.
The bridge structure to which the present invention refers substantially corresponds to that described in EP-A-0.233.528, whereby a detailed description thereof need not be given herein. FIG. 1 thus illustrates only the lateral edge 1 of the bridge, with the roadway 2 and the conventional guardrails 3, fixed on uprights 4 the height h.sub.0 of which may vary between 1 and 1.5 m.
REFERENCES:
patent: 2333391 (1943-11-01), Robinson et al.
patent: 3673624 (1972-07-01), Finsterwalder et al.
patent: 4741063 (1988-05-01), Diana
patent: 5287578 (1994-02-01), Lovret
Diana Giorgio
Falco Marzio
Lisehora James
Stretto Di Messina S.p.A.
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