Step-by-step explanation:
The four primary materials used for bridges have been wood, stone, iron, and concrete. Of these, iron has had the greatest effect on modern bridges. Steel is used to make reinforced and prestressed concrete. Modern bridges are almost exclusively built with steel, reinforced concrete, and prestressed concrete.
Wood and Stone: Wood is relatively weak in both compression and tension, but it has almost always been widely available and inexpensive. Civil Engineers now incorporate laminated wooden beams and arches into some modern bridges.
Stone is strong in compression but weak in tension. Its primary application has been in arches, piers, and abutments.
Iron and Steel: Cast iron is strong in compression but weak in tension. Wrought iron has much greater tensile strength. Steel is superior to any iron in both tension and compression. Steel can be made to varying strengths, some alloys being five times stronger than others. The civil engineer refers to these as high-strength steels.
Concrete: Concrete is an artificial stone made from a mixture of water, sand, gravel and cement. It is strong in compression and weak in tension. Concrete with steel bars embedded in it is called reinforced concrete. Reinforcement allows for less concrete to be used because the steel carries all the tension; also, the concrete protects the steel from corrosion and fire.