Which one of the following is the correct assumption made in two dimensional design of gravity dams?
- AThe loads are transferred to the abutments by beam action
- BThe foundation and dam behave as separate units
- CThe materials in the foundation and body of the dam are isotropic and homogeneousCorrect
- DThe stresses developed in the foundation and body of the dam are not within elastic limit
Solution
Concept
In 2D gravity dam design, a unit-width slice is analysed as a cantilever, assuming homogeneous, isotropic, elastic material that acts together with the foundation.
Step-by-step solution
1. In 2D design, take a 1 m wide slice of the dam between transverse joints. 2. Each slice is a vertical cantilever fixed at the base, so no load goes to the abutments by beam action. Option A is false. 3. The dam and foundation are assumed to act as one unit. Option B is false. 4. Materials of dam and foundation are taken as isotropic and homogeneous. Option C is true. 5. Stresses are assumed within the elastic limit. Option D is false. 6. Answer is C.
Explanation
In 2D design, each slice of the gravity dam is treated as an independent cantilever. The dam and foundation act as one unit, and the material is isotropic, homogeneous and elastic. So option C is correct.
Why the other options are wrong
A: There is no beam action to the abutments; each slice works as a cantilever. B: The dam and foundation are assumed to act as a single unit, not separately. D: Stresses are assumed to be within the elastic limit.
Shortcut
Remember the 2D gravity dam assumptions: single unit, homogeneous-isotropic, elastic, no beam action.
Common mistake
Confusing a gravity dam with an arch dam, where load is transferred to the abutments.
Correct answer: C) The materials in the foundation and body of the dam are isotropic and homogeneous