CIVIL ENGINEERING
UNIVERSE Knowledge educational article.
A bridge is a load-carrying system. Its structure must transfer forces from the deck through structural members and supports into the ground while remaining strong, stable, serviceable and economical.
Engineers ask where each important load goes. Vehicle weight, pedestrians, self-weight, wind and other actions create forces that must travel through beams, trusses, cables, arches, piers and foundations.
Structural members may carry tension, compression, bending, shear or combinations of these. Trusses are efficient because many members primarily carry axial forces. Arches make strong use of compression, while suspension systems use tension in cables.
A beam carrying a transverse load bends. Engineers check both strength and serviceability: a structure can be strong enough against failure but still deflect or vibrate too much for comfortable or reliable use.
Design values account for uncertainty in loads, materials, construction and modelling. Engineers use appropriate standards and safety factors rather than designing only for an ideal expected load.
Concrete, steel, timber and composite materials behave differently. Corrosion, fatigue, temperature, water and maintenance requirements can strongly influence the final design.