The water is pumped out of the cofferdam to provide a dry area for constructing the pier. Refinements of traditional designs include minimizing the construction of large, submerged pits to receive counter-weights when the bridge is open. Nuttall Gear designed and manufactured the new gearbox that drives the single bascule leaf. A large crane was parked behind the trunnion of one leaf, just above a counter-weight that had not been lightened to compensate for the paving removal. As they are being refurbished or replaced, two types of improvements can be made. Originally built in 1922, the Fort Street fixed-trunnion bascule bridge in Detroit, Michigan allows large cargo ships to travel the Rouge River while transporting material to the nearby Ford Motor plant. The heel-trunnion bridge, also known as the fixed-trunnion, has the counterweight and bridge on separate pivots.
The rebar cage is lowered into position inside the forms. As pieces are added to the leaf, an appropriate amount of weight must also be added to the counterweight to maintain stability. The original steel bridge, however, had dangerously deteriorated due to saltwater corrosion. The drive features through-hardened gearing, a fabricated steel housing, and bearing L10 life 40,000 at rated load. This was the with two symmetrical spans of 76m built in 1890 and replaced in 1959 by a double span vertical lift. The steel and aluminum structure is designed to carry pedestrian and bicycle traffic across the 410-ft 125-m wide River Tyne.
The Tower Bridge in London is a double leaf bascule bridge. It was built in 1959 and replaced a horizontal swing bridge with two 76m spans. Bridge 3A was built to replace the original Bridge 3, which was destroyed in an accident. In total, 2 miles of new roadway was put in to service. For example, on the Casco Bridge, large concrete cylinders were erected upstream and downstream from each pier to support the ends of a steel fender.
Sometimes it is impractical to build a bridge high enough; for example, it may rise too steeply or block the view of an important landmark. Strongwell recently replaced the deck on the 106-year-old Hawthorne Street bridge in Covington, Va. Rather than being gear-driven, the 82-ft 25-ni long single-leaf bascule is moved by a powerful hydraulic system. Under heavier impacts, the fender can deflect against rubber bumpers and, if necessary, against crushable hollow concrete boxes that would keep the impact from damaging the pier itself. Nuttall manufactured three enclosed drives featuring custom lubrication systems to ensure gearing immersion during the 75-degree rotation of the bascule leaf.
When the bridge is closed, one arch is horizontal and the other is vertical. In such cases, the bridge can be designed so it can be easily moved out of the way for vessels that are too large to sail under it. For a fixed span bridge to allow ocean going ships to pass beneath, a clearance of 70 metres is normally required. Retractable bridges are made so the movable span slides back underneath an adjacent section of the bridge. By the end of the fifteenth century, Leonardo da Vinci was not only designing and building bascule bridges but also drawing plans and constructing scale models for a swing bridge and a retractable bridge.
As an example, each pair of 500-ton 450-metric-ton leaves on the Casco Bay Bridge is balanced with an 800-ton 720-metric-ton counterweight. Second, some new bridges are operated hydraulically rather than being driven with gear mechanisms. Bridge 4 is a twin-leaf, Chicago-type bascule bridge, with its counterweights located under the road deck. The girder may be equipped with gears that will mesh with the lift mechanism, or it may be fitted with paddles that hydraulic rams can push against. Our focus is on seasonal food, local produce, innovative recipes, and the drinks that pair best with them. Video Demonstration You can watch the demonstration by clicking on the image below. In some of the modern day bridges the centre shaft lifts the bridge clear of the pier and then rotates it.
The raising and lowering times are different. This is achieved by ensuring that the bridge is balanced. Seventy-five hundred short tons 6,804 metric tons of structural steel and 150,000 short tons 13,6080 metric tons of concrete were used in the Casco Bay Bridge A typical draw bridge. When it closed and mated with the side that had remained down, the static half was jarred enough to release its unbalanced energy. In double-leaf or four-leaf a double-leaf bridge with separate leaves for each direction of vehicular traffic bascule bridges, each leaf can be raised and lowered independently. Some modern replacements must be opened only one-fourth to one-third as often their predecessors.
Steel braces are attached between the side girders and any other longitudinal girders. But they were not commonly used until the European Middle Ages. With a slight stretch of the imagination, it could reflect other engineering disciplines also, e. However, it wasn't until the 19th century that these bridges became popular for aiding the navigation of large ships. The counterweight is attached to the heel section.