Structure to interconnect two branches of a suspension bridge fr

Details Structure to interconnect two branches of a suspension bridge fr Structure to interconnect two branches of a suspension bridge fr

1995-05-26

1996-10-29

Graysay, Tamara L.

Bridges

Suspension

Simple system

14 73, 14 745, 14 75, E01D 204, E01D 1902

Patent

active

055686672

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 are highly exposed to winds, the effects of which have to be taken into account--in many respects--when planning the bridge. The present invention particularly concerns the effects produced by crosswind pressure, which tends to cause a horizontal inflection of the bridge framework, thereby creating remarkable stresses especially in correspondence of the point of anchorage of said framework to the end piers supporting the bridge.
It is also known, in fact, that this area of the bridge framework is subject to stresses, which become higher--on the one hand--the wider the span of the bridge, and--on the other hand--the longer the distance of the bridge lateral edges from its central axis.
In a bridge--for instance like that described in EP-A-0,233,528, filed by the same Applicant--having a span wider than 3 Km and a transversal verse dimension of about 50 m, the stresses in correspondence of the point of anchorage of the framework to the end piers can become inadmissible.
Hereinafter, reference is made to a bridge framework formed of a fixed stiff branch--corresponding to the framework part extending from the pier axis towards the embankment--and of a flexible branch, corresponding to the framework part extending from the pier axis towards the central bay. Of course, this assumption is quite arbitrary since, in real fact, no part of the bridge framework can be considered totally fixed and stiff; nevertheless, it helps to better understand the invention and define its contents in a conventional way.


OBJECT OF THE INVENTION

The object of the present invention is to thus propose a structure to interconnect two branches--a substantially fixed stiff branch and a substantially flexible branch--of a suspension bridge framework, in correspondence of the end piers supporting the bridge, said structure allowing to substantially reduce the stresses determined by horizontal inflection.


SUMMARY OF THE INVENTION

This result is obtained--in a bridge framework, wherein each of said branches comprises three parallel longitudinal, mutually spaced, box-like bodies, a central body for railway traffic and two lateral bodies for roadway traffic, said bodies being interconnected by transverse ledgers positioned at regular intervals along the bridge--due to the fact that said structure comprises: a central body section forming a fixed joint between the central longitudinal bodies of the two bridge branches; two lateral body sections mounted slidable in respect of the lateral longitudinal bodies of the two bridge branches; and a hinge joint between said bridge branches, in correspondence of the pier axis.
The invention is based on the consideration that, when a bridge is overstressed by horizontal inflection, it is possible to annul the over-stressing effects by interrupting the solution of continuity in correspondence of the end piers supporting the bridge, and providing for a hinge system--instead of a fixed joint--to prevent the horizontal inflection of the bridge from being transmitted to the end piers.
On the other hand, to allow railway traffic to take place in safe conditions, it is necessary to preserve the continuity of the horizontal rotation of the bridge at least in correspondence of the railway traffic lane.
These contrasting requirements are now in fact brilliantly solved by the present invention, according to which the continuity is preserved for the central longitudinal body of the bridge--designed for railway traffic and, besides, also less subject to stresses--while a hinge system is provided for the lateral sections of the bridge, designed

REFERENCES:
patent: 4741063 (1988-05-01), Diana
patent: 5400454 (1995-03-01), Cunningham

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