Which type of deck is commonly found on older bridges and movable bridges?

The type of deck commonly found on older bridges and movable bridges is steel. Steel has been a popular material for bridge construction due to its high strength-to-weight ratio and durability. Older bridges often utilized steel for their decks because the material was widely available and provided the necessary structural support required for span lengths prevalent during the time of their construction.

Movable bridges, in particular, also commonly use steel decks, as these bridges must support dynamic forces and undergo movement while maintaining structural integrity. The rigidity, combined with the flexibility of steel, allows movable bridges to function effectively under the stress of opening and closing mechanisms. This is contrasted with other materials like concrete or timber, which may not offer the same performance characteristics under the specific conditions required for movable bridge applications.

Concrete, while also a common deck material, is more frequently associated with later bridge designs rather than older structures. Timber, on the other hand, is less commonly used in modern bridge design due to maintenance concerns, although it may still be found in some older structures. Composite materials, while gaining popularity in contemporary bridge engineering for their lightweight and high strength, are not typically associated with older bridge designs.