Introduction to bridges

• A bridge is a structure that allows a road, path or railway line to cross a river/depression/gully/gap
• The simplest bridge can be made using a beam lying across the gap
• However such as bridge becomes impractical as its span(length between support beams) increases
• The longer such a bridge becomes the weaker it becomes
• As it’s length increases the bridge’s bending also increases
• Increasing the thickness of such a bridge also increases its weight(self-load)
• This results in the bridge bending more instead of reducing it
• When designing and building bridges in the real world the following techniques are employed:
• The span of the bridge is divided into smaller sections
• The amount of bending is minimized
• Ways are found to reduce the self-load/weight of the bridge
• Decreasing the thrust on the supports/abutments
• Minimizing the cost of construction and maintenance
• Reinforcing the materials e.g. concrete used to make them stronger
• Modern bridges are made of chiefly two materials:
• steel and concrete
• Steel is very expensive while on the other hand
• Concrete is cheaper but more of it is required to make a strong bridge structure
• A bridge has two main parts:
• The deck on which traffic (including humans) move/cross
• the abutments and piers which support the deck(s)
• in a steel-concrete structure steel beams support a concrete slab
• A reinforced concrete deck may span(have a length of) up to 30m
• While a steel deck may span up to 50m
• Ways have to be found to balance the strength and cost of the structure

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