Bridges – Pier
Patent
1995-11-21
1997-10-07
Lisehora, James
Bridges
Pier
405 80, 405 81, E02B 302
Patent
active
056734492
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a flow compensation device for support pillars. More particularly, there is provided a flow compensation device used in conjunction with a support pillar, such as a bridge pillar, and which is normally erected in a flowing body of water such as a sound river or the like. Such water may at least periodically flow in different layers or strata in one as well as the other of two opposed stream directions.
BACKGROUND OF THE INVENTION
As a specific example of a flowing body of a water current in a river or ocean of the above-mentioned type, the Sound of Oresund may be mentioned. Oresund is a water body/sound between Sweden and Denmark which joins the Baltic Sea with a part of the Atlantic Ocean (the North Sea). The Baltic Sea, of itself, is an inland or brackish water sea in which the salt content in the North Sea is substantially higher (in the central parts thereof it lies in the range of 2,5-3,5%). The water motion through the sound mainly occurs by a stratified current or tide in which the brackish water from the Baltic Sea moves in a surface layer towards the North Sea at the same time as salt water from the North Sea moves in a bottom layer towards the Baltic Sea. The depths of these two layers vary during different times depending on a number of different factors, such as wind conditions atmospheric pressure conditions, time of the year, etc.
If great quantities of brackish water flow out of the Baltic Sea at the same time as only small volumes of salt water flow into it, the surface water layer will, of course, be deep and the bottom water layer will be shallow, and vice versa. The total water depth is on average within the range of 5-8 meters over a large portion of the Oresund sound, with the interface between the surface and bottom water layers then normally lying about 1.5-4 meters from the bottom.
For the plant life and animal life of e.g. the Baltic Sea area, it is of vital importance that the relatively small salt content, which typically occurs in a brackish sea water, be maintained at a certain minimum level or otherwise biological imbalances could result with fatal effects. For example, a fish such as cod is highly dependent on a certain minimum salinity for its reproduction. The inflow of fresh water into the Baltic Sea, occurring via rivers and creeks in adjoining countries, is greater than the evaporation volume of surface water from the surface, but has on the whole, always been compensated for by the fact that salt water from the North Sea at high water-levels and/or precipitous wind conditions from time to time pass through the Oresund sound and mix with the water in the Baltic Sea. Thus a minimum salinity occurs, which on average, is acceptable.
It is a general concern that pillars used in construction projects in flowing water conditions, and which are required for e.g. supporting arched portions of a bridge, may have an effect on the influx of salt water through the Sound, which is vital for the Baltic Sea. Provisional estimations indicate that bridge pillars could reduce the salt water inflow no less than 2 to 5%, at least during periods when the salt water inflow is great, i.e. the interface between the surface and bottom water layers lies near the surface or is completely disappeared in case just a throughout salt water flow occurs.
In order to cope with this problem, it has been proposed to dredge the sea floor in the area of any pillars for projected bridges so as to increase the water depth and thereby compensate for the flow restriction exerted by the pillars. Such a solution has, however, a number of disadvantages. Thus the bottom fauna of the body of water would be subjected to damage and could even be completely eliminated in certain areas. At the same time, dredging is an expensive operation which does not provide any permanent solution since the sea floor will subsequently be filled with sediments.
One system involving ice related conditions in flowing water is set forth in U.S. Pat. No. 2,845,104. This
REFERENCES:
patent: 2545104 (1951-03-01), Musial
patent: 3667234 (1972-06-01), De Lizasoain
patent: 5478167 (1995-12-01), Oppenheimer et al.
Henriksson Mats
Johansson Nils
Lisehora James
Vattenfall Utveckling AB
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