Civil Engineering Professional Engineer Practice Exam

How do arch bridges distribute the load they carry?

1. Evenly along the span

2. Directly down to the ground

3. To the abutments

4. Only to the middle of the arch

The correct answer is: To the abutments

Arch bridges are designed to efficiently distribute loads through their curved structure. When a load is applied to an arch bridge, the shape of the arch allows the forces to be transmitted along the curve of the arch to the supports at each end, known as the abutments. The primary function of the arch is to convert vertical loads into compressive forces that travel along the arch and down to these abutments, which effectively support the weight of the bridge and any traffic on it. This method of load distribution is beneficial since it utilizes the material strength of the arch in compression, rather than tension. The shape of the arch inherently directs these load forces outward and downward, which reduces stress concentrations and maximizes stability. This design allows arch bridges to span large distances while effectively supporting significant loads. Other choices don't accurately represent how arch bridges function. An even load distribution along the span does not account for the arch's unique geometry and load transfer mechanism. Stating that loads are distributed directly down to the ground overlooks the critical role of the abutments in this process. Moreover, asserting that loads are only transferred to the middle of the arch fails to recognize that the force follows the curvature of the entire arch along its length to reach the supports.