The bottom portion of a concrete or a masonry gravity dam is usually stepped in order to _______a)increase the overturning resistance of the damb)increase the shear strengthc)decrease the shear strengthd)increase the frictional resistanceCorrect answer is option 'B'. Can you explain this answer?

Question

Answer

The foundation is stepped at the base to increase the shear strength at the base and at other joints and measures is taken to ensure a better bond between the dam and the rock foundation. By ensuring a better bond between the surfaces the shear strength of these joints should be made as good as possible.

Answer

Explanation:

Stepping is a common design feature used in the bottom portion of concrete or masonry gravity dams. It involves creating a series of horizontal steps or offsets along the dam's base. The primary purpose of these steps is to increase the shear strength of the dam.

Reason for stepping:

The stepping of the bottom portion of a dam is done for the following reasons:

1. Shear strength: The steps in a gravity dam help to increase the shear strength of the structure. Shear strength is the ability of a material to resist sliding along a plane parallel to the applied force. By providing steps, the dam is effectively divided into smaller sections, reducing the length of potential sliding surfaces. This increases the overall shear strength of the dam.

2. Overturning resistance: Stepping also helps to increase the overturning resistance of the dam. Overturning occurs when the horizontal forces acting on a dam exceed the resistance offered by the foundation. By introducing steps, the dam's weight is distributed more evenly over the foundation, reducing the potential for overturning.

3. Frictional resistance: Stepping can also increase the frictional resistance between the dam and its foundation. The steps create additional surface area for contact between the dam and the foundation, enhancing the frictional resistance to sliding. This helps to prevent the dam from shifting or sliding due to external forces.

Conclusion:

In summary, the bottom portion of a concrete or masonry gravity dam is stepped in order to increase the shear strength of the structure. This stepping design feature helps to enhance the dam's resistance to sliding and overturning, ensuring its stability and integrity.

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