Bridge Engineering Practice Test

Long-span bridges need a deck that combines high bending stiffness with relatively light weight. An orthotropic steel deck achieves this by using a flat steel plate that is stiffened with weld-on ribs and cross-stiffeners, creating an anisotropic deck whose stiffness is much greater in the longitudinal direction than in the transverse. This stiffened plate system gives a very high stiffness-to-weight ratio, allowing a thinner deck and enabling longer spans while keeping deflections and vibrations under control. When a concrete wearing surface is added, the deck often works in composite action with the girders, further enhancing overall stiffness and performance. Other deck types don’t match this combination: timber decks lack durability for long spans; precast concrete decks add substantial dead load and aren’t optimized for the stiffness-to-weight benefits of a stiffened steel plate; corrugated steel decks are lighter but provide less stiffness than an orthotropic plate, making them less suitable for very long spans.