What is the maximum allowable eccentricity to prevent tensile stress at the base of a gravity dam__________________?
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Answer: D. B/6
Explanation
Keeping the resultant force within the middle third of the base prevents any tensile stress from developing. When eccentricity exceeds one-sixth of the base width, tension occurs on the upstream heel. Gravity dams cannot sustain significant tensile stresses because mass concrete is weak in tension. Gravity dams rely on their own massive weight to resist water pressure forces pushing against them. Base stress analysis uses combined axial and bending stress formulas assuming linear stress distribution. The middle third rule is a fundamental criterion in structural design for masonry and concrete dams.
Dam safety engineers check base eccentricity under various reservoir loading and uplift pressure conditions. Preventing tension avoids structural cracking and subsequent destabilizing seepage through the dam base. Strict adherence to this limit ensures long term stability against sliding and overturning failures. Option a allows an excessive eccentricity of half the base width, which would cause massive tension and failure. Option b represents the middle third zone boundary itself, not the maximum allowable eccentricity value. Option c proposes a quarter base width limit, which is overly conservative compared to the proven middle third rule.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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