Dissapating corner moments in a rectangular underground tank

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SUMMARY

The discussion focuses on addressing excessive corner moments in a rectangular underground tank, measuring approximately 60x20x22 feet. Engineers are replacing the tank's roof, which necessitates bracing the walls due to their integral nature. The corner in question is unrestricted and experiences significant lateral loading, leading to concerns about potential cracking in the 100-year-old concrete walls. Proposed solutions include the use of corner struts and various types of buttresses, such as plain taper, flying, and groin buttresses, to effectively dissipate the excessive moments.

PREREQUISITES
  • Understanding of structural engineering principles
  • Knowledge of lateral loading effects on concrete structures
  • Familiarity with reinforcement techniques, including buttresses
  • Experience with construction bracing methods
NEXT STEPS
  • Research "buttress design for lateral loads" to explore effective reinforcement strategies
  • Study "corner moment dissipation techniques in concrete structures" for advanced solutions
  • Learn about "historical masonry reinforcement methods" used by cathedral builders
  • Investigate "structural bracing systems" applicable to underground tanks
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Civil engineers, structural designers, and construction project managers involved in the design and reinforcement of concrete structures, particularly those dealing with lateral loading and moment dissipation.

Infinitybyzero
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This is a conceptual question based on a project I and a few other engineers finished at work. We are replacing the roof of a concrete tank that is part of a larger pump station for a river. Unfortunately, the roof is very integral in this structure, which means that once it's removed, the walls need to be braced.

The tank is roughly 60x20x22' deep and the long direction will have continuous shoring across mid height. The tank is integral on 3 corners with the rest of the station, but there is a corner that's unrestricted. From a theoretical standpoint, the soil, surcharge, and hydrostatic conditions on the outside of the walls cause a very large moment around that corner. The walls are close to 100 years old with no indication of corner steel/dowels, which obviously means that a large corner moment will crack the concrete quickly. There's no cracks in any of the tank right now and we certainly don't want to create any during construction.

Our solution was to provide corner struts to redirect some of the stresses, but realistically it won't go down that much because the walls are infinitely stiff compared to some 3" pipe. I'm not looking for a design recommendation, but more rather what you would do to dissipate excessive moment at the free standing corner of a tank (or wall intersection in a building) that is subject to significant lateral loading.
 
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The great cathedral builders and the later millwrights knew all about this sort of problem .

Many problems were solved using buttresses and other masonary reinforcement .

For example :

Two buttresses one on each face near but not on corner . Plain taper or flying

Groin buttresses wrapped around corner .

Castellated corners .