An arch is used in long span bridges because there isa)considerable reduction in horizontal thrustb)considerable reduction in bending momentc)reduction in shear and bending momentd)no change in shear and bending momentCorrect answer is option 'B'. Can you explain this answer?

Question

Answer

-An arch is used in long span bridges because there is considerable reduction in bending moment.

-A span is the distance between two bridge supports, whether they are columns, towers or the wall of a canyon. A modern beam bridge, for instance, is likely to span a distance of up to 200 feet (60 meters), while a modern arch can safely span up to 800 or 1,000 feet (240 to 300 m).

-An arch bridge is stronger than a beam bridge, simply because the beam has a weak point in the center where there is no vertical support while arches press the weight outward toward the support.

-Arch bridges, meanwhile, have been used to cover very long distances, with up to 800 feet for a single arch.

Answer

Explanation:
An arch is used in long span bridges because of the following reasons:

Reduction in bending moment:
When an arch is used in a bridge, the arch takes up the load of the bridge and transfers it to the supports. This results in a considerable reduction in the bending moment acting on the bridge.

Reduction in horizontal thrust:
An arch is a curved structure, and hence, it exerts a horizontal thrust on the supports. However, this horizontal thrust can be significantly reduced by using a series of arches or by using tie-rods.

Reduction in shear force:
The use of an arch in a bridge results in a reduction in the shear forces acting on the bridge. This is because the arch transfers the load of the bridge to the supports in a more efficient manner than other types of bridges.

Conclusion:
Hence, it can be concluded that the use of an arch in a long span bridge results in a considerable reduction in the bending moment acting on the bridge, and this is why an arch is preferred for long span bridges.

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