Bascule bridge

Types of bascule bridges

Bascule bridges allow for the lifting of the entire bridge to allow vessels to pass under them. There are different types of bascule bridges:

• Trunnion bascule bridge

  In this type of bascule bridge, the bascules or levers are hinged at one end. A counterweight is attached to the bascule lever, and as the bridge rotates upwards, the counterweight moves in the plane of the bridge. The hinges and counterweights' location is what differentiates a trunnion bascule from other bascule bridge designs. Trunnion bascule bridges are usually built over high-traffic navigable waterways.

• Counterweight bascule bridges

  This type of bascule bridge has a heavy weight, located on the side of the pivot point, which balances out the bridge span. The counterweights are designed in such a way that they are hidden within the structure of the bridge. They work by balancing out the bridge span to enable it to rotate around the horizontal pivot point so that ships can pass under them.

• Electro-mechanical bascule bridges

  Electro-mechanical bascule bridges use motors and gears to control the lifting and lowering of the bridge. These motors and gears are located within the superstructure of the bridge and are used to operate bascule spans. The bridge spans are lifted vertically to create a clear passage for vessels to pass under.

• Hydro-mechanical bascule bridges

  These types of bascule bridges use hydraulic cylinders to lift and lower the bridge spans. The hydraulic cylinders are integrated into the bridge structure and are used to operate the spans of the bridges. The bridges lift vertically to create a clear passage for vessels, and then they lower to allow traffic to pass.

• Rolling bascule bridges

  This is a special type of bascule bridge in which the entire span of the bridge rotates around a horizontal axis. The bridge spans rotate around a horizontal axis to create a clear passage for vessels.

Function and Features of Bascule Bridges

A bascule bridge has a bridge deck that moves vertically. Bascule bridges come in various designs depending on the span configuration and roadway alignment. Each design features unique characteristics, as outlined below.

• London or Pan and Tilt-Style Bascule Bridges

  The typical London bascule bridge features a pair of bascule leaves framing the bridge's road. Each leaf is counterweight balanced. When raised, the bascule leaves rotate upwards and away from each other. The bridge leaves also rotate around horizontal axes, tilting or panning to align with passing vessels.

• Split/Semi-Closed Bascule Bridges

  Split bascule bridges have sections that can be raised to accommodate vessel passage. However, unlike traditional bascule bridges, where the bridge leaves are fully vertical, the leaves of split bascule bridges are only partially raised, hence the term 'semi-closed.' This allows for the bridging of traffic while still permitting vessel passage.

  Split bascule bridges are typically longer than traditional bascule bridges. Their bridge leaves can rotate from a partially raised position for vessel passage, similar to drawbridges.

• Vertical Bascule Bridges

  Vertical bascule bridges are typical bascule bridges but with extreme vertical clearance requirements. They are commonly found in port areas with significant vessel mast heights. Instead of raising the bascule leaves horizontally, these bascule bridges lift the leaves vertically, achieving ample clearance.

• Counterweights

  Every bascule bridge is equipped with counterweights to balance the heavy bridge decks. Counterweights enable smooth lifting and lowering of the bridge decks using minimal power. They are positioned on the bascule bridges' opposing ends' inner sides.

  The design of the counterweights often incorporates platforms for operation and maintenance. Additionally, depending on the space available, the counterweights can be placed either on the same side as the road or on the opposite side, away from the traffic lane.

• Clearance

  This refers to the vertical or horizontal space between a structure and an object, such as the ground or another structure. When bascule bridges are raised, clearance is provided between the road and water surface for vessels to pass. Clearance dimension requirements are determined based on national navigation clearance standards and regulations.

• Bridge Decks

  The roadbed or functional surfaces of bascule bridges are known as bridge decks. They primarily support the weight of vehicles and pedestrians and comprise steel and concrete. The materials used to construct bridge decks depend on the expected traffic load and volume.

ScenariosBascule bridge

Bascule bridges, which are skillful in structure and versatile in function, are widely used in many areas.

• Span railway and highways: Bascule bridges are mainly used to span highways and railways. They can be lifted to allow the passage of ships, and then the bridge spans are lowered for the trains and vehicles to pass.
• Restricted areas: When the areas to be crossed have low clear heights or limited widths, bascule bridges are suitable as they can replace traditional bridges and avoid removing or raising structures.
• Cross rivers and canals: Bascule bridges are usually built across rivers and canals to facilitate the passage of vessels.
• Harbors and channels: Bascule bridges can be seen in harbors and channels with regularly traffic, allowing vessels of certain sizes to be pass for constructing, repairing, or navigating through interior sections of the city.
• Over harvesting areas: It is necessary to build bascule bridges over areas that are frequently harvested, such as fishery zones or areas with under-ground pipelines, to avoid disturbing the harvests while allowing ship traffic.

How to choose bascule bridges

Civil engineers use many factors to decide the type of bridge to build. They consider the available space, how many cars and trains will cross it, and the ground under the bridge. They check local laws and regulations, as well as the cost and time to build the bridge. Bascule bridges work well for places with limited space because they can lift out of the way without needing a lot of land. Engineers like them because they take up less room and can be lifted easily. They also found that these bridges require less regular care over time.

Some critical factors to consider include the following:

When deciding which bascule bridge design to use, engineers must first think about how much weight the bridge will hold. They also need to consider the bridge's span, which is the distance between its supports. The height and width of boats and other vehicles passing under the bridge are also essential.

When choosing the location for a bascule bridge, engineers check things like local laws, the ground conditions, and where utility lines like water and electricity are buried. They also think about how heavy traffic will cross the bridge and choose a design that fits. Recent advancements in bridge design and machinery have made bascule bridges simpler to build and operate.

• Mechanical Systems and Controls: The designers used advanced drive systems and control mechanisms to operate bascule bridges. These systems provide precise and reliable bridge operation.
• Bridge Design: The needs of the site and the span length determine the bridge design, whether it is a single large span or multiple smaller spans.
• Operator Training and Maintenance: Proper operator training is essential for smooth bridge operation. Regular maintenance ensures the long-term reliability of the bridge mechanisms.

Bascule bridge Q & A

Q1: How long does it take to build a bascule bridge?

A1: It takes approximately 1-3 years to manufacture and build a bascule bridge. The building time usually depends on the bridge's size and the number of spans. However, it may take longer if the bridge is large and has many spans. Additionally, factors like weather conditions and location constraints can extend the construction period.

Q2: What type of foundation does a bascule bridge need?

A2: There are different types of foundations for bascule bridges. The type chosen depends on factors like soil conditions, load-bearing capacity, and foundation depth. The most common types of foundations include spread footings, pile foundations, and caissons or drilled shafts. A geotechnical investigation is usually done first to determine soil conditions before deciding on a suitable foundation type.

Q3: What is the difference between a bascule and a drawbridge?

A3: The main difference between a bascule and a drawbridge is how each bridge operates. A drawbridge relies on a series of pulleys and counterweights to hoist the bridge section (the drawspan) vertically. On the other hand, bascule bridges use counterweights to help raise the bridge deck (the bascule) in a vertical position that allows boats to pass underneath.

Q4: How often does bascule bridges need maintenance?

A4: Bascule bridges require regular maintenance to ensure they operate safely and efficiently. Routine inspections should be done at least once every few months to check critical components like the mechanical systems, electrical systems, safety devices, and structural integrity. These bridges only open occasionally, so routine inspections are vital.