Bascule
Many draw bridges in the world are classified as Bascule. A Bascule
type draw bridge is balanced so that when one end is lowered the other end is
raised. For example, the leaf of a draw bridge is usually made of steel and concrete
with considerable weight. To counteract the bridge weight a counterweight is
installed usually at the end of the leaf to give it balance. It would take a
tremendous amount of power to raise a bascule bridge without the counterweight. A 75
hp is all that's required to raise the Park Street Bridge using full power. The
emergency drive motor is only 5hp and will also raise the bridge with no problems just
slowly.Bridge Height Restriction
Park and High Street Bridge have an overhead steel superstructure that limits
vehicles with certain heights. Many vehicles, mostly large trucks have hit the
bridges causing damage to the bridge and their own vehicles. It's advised to check
with the bridge tender to make sure you can clear the bridge superstructure or see the
height restriction data located on these pages. Miller- Sweeney Bridge has no height
restriction when in doubt.
Bureau of Electricity
The City of Alameda operates it's own power supply company.
It buys power from various sources and then distributes power to the businesses and
residents of the city.
MHHW
Mean Higher High Water: A tidal datum
MLLW
Mean Lower Low Water: A tidal datum
Oakland Tidal Canal
The City of Alameda before 1903 was a peninsula extending out from East Oakland and into
the San Francisco Bay. The Oakland Estuary use to end around somewhere around
the current Park Street Bridge location. During these times the estuary was
fouled with sewage and debris. There was also a silting problem which limited the
usefulness of the harbor. In 1903 the United States Army Corp Of Engineers completed
the construction of the Oakland Tidal Canal. With the canal completed it not only made
Alameda a island City the tidal action flushed the Oakland Estuary of its sewage, debris
and stopped the silting-up of the estuary. This also created a need for bridges
there are currently 6 draw bridges of various designs that cross the water way.
The Oakland Estuary has been dredged many time over the years. There is a current
dredge project underway that will allow large container vessel's to utilize the Port of
Oakland more effectively. The Port of Oakland is one of the largest Containerized
Ports in the Untied States and this project is vital to the economic vitality of the Bay
Area.
PG&E
Pacific Gas and Electric is a large power utility company that supplies gas and
electric power to most of Northern California.
Trunions
It may imply other things but in drawbridge speak it's usually the
main bearing that bridge pivots on. The ones used on our drawbridges
are made of brass and are very large. See the virtual tours for
pictures of the various trunions.
Vertical Lift Bridge
Another common type of draw bridge is the Vertical Lift Bridge. While a
Bascule Bridge is usually a counterbalanced leaf. A Vertical Lift Bridge is usually
a center draw span supported by two towers. Each Tower has a massive counterweight
to help lift the bridge. While there are many different designs all Vertical Lift
Bridges are based on the same engineering principle.
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