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Bridge Materials Different shapes resist forces in different ways, so as every material withstands forces differently. To design a good and safe bridge, an engineer must know the forces in every member of the bridge. In turn, he must choose the appropriate material for that member, or for all members. He must know the characteristic of every material under various forces which may occur on the bridge. For example, should he choose concrete or stone for the pier and abutment? Is it steel instead of concrete which is the best material for a particular bridge? In the ancient times, stone, wood, earth, and brick were used. In the mid 19'th century iron, both cast iron and wrought iron were used. The advent of steel replace those material. Nowadays, steel and concrete (reinforced concrete and prestressed concrete)are the most popular material. Why choose one over another? Basically, there are four reasons behind that: Characteristics Cost Technological Level Availability (1) Characteristics Every material reacts differently to different forces. For example, concrete is strong to withstand compression, but it breaks easily when tension force is applied. Another example is brick. It is a good material to support compression force. You can pile couple feet of bricks without affecting the lowest layer bricks. However, when you try to break it even with your bare hand, it will snap into two. Hence, it is said that brick has weakness in shear.
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