Movable bridges are constructed and designed to change its position and shape as and when it is required. They are basically made to make a passage for vessels and boats in the waterway. When the bridge over the waterway is open to vessels and ships, traffic is stopped and opened when the bridge is in a horizontal position.
Types of Movable Bridges:
There are various types of movable bridges and three of them are pretty much in use and desired. They are:
- Bascule Bridge
- Vertical Lifting Bridge
- Swing Bridge
Advantages of Bascule Bridge
- It opens a waterway for ships and vessels with considerable speed and also permits small size boats to pass through even if the passage is not completely open.
- It is reported that the passage of small boat through partially opened bascule bridge is safer compared with partial opening other types of movable bridges.
- Most of bascule Super-structure Bridge is out of vessel reach during the collision, whether fully or partially opened, hence suffers minimal damage.
- Vessels pass through Bascule Bridge faster than other. This is because vessels may come closer to the partially opened bascule.
- The depth of the span that extended from the pier to the centre of the bridge can be decreased.
Advantages of Vertical Lifting Bridge
- Vertical lifting angle can be built approximately with any length that is required according to the project location and it is only restricted by ultimate simple span.
- Compared with swing and bascule bridges the design and construction of vertical lifting bridge is much easier.
- It is suitable to support heavy load structures like Railroad Bridge since vertical lifting bridge spans are approximately fixed.
- There is no restriction on the width and the number of trusses or main girders of vertical lifting bridge.
Advantages of Swing Bridge
- Compared to other types of movable bridges, wind load on Swing Bridge is minimum.
- Since swing span moves horizontally during the opening of the bridge, the moment generated by wind force is smaller compared with other movable bridge types.
- Two movable spans in one moving structure can be achieved in symmetrical swing bridge. This would be greatly advantageous to manage busy waterway properly.
- It is a desirable option for locations where aesthetic play significant role in the construction of movable bridge because Swing Bridge does not move up to open so aesthetic of the bridge would not be affected as the bridge is opened for ships to pass through.