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Structural
- Apr 1, 2014
- 19
If a soil supported mat supports 4 piers with 2 of the piers subjected to compressive loads and the other 2 piers subjected to uplift loads for a certain load combination, what is the correct way to calculate stability ratio about an edge of the mat?
1. Would the uplift loads contribute to the overturning moment about an edge of the footing or is it just the applied shears and moments on the piers that contribute to overturning?
2. In continuation of 1 above, in calculating resisting moment, is it appropriate to algebraically add all the vertical loads on the piers (both compressive and uplift), add the weight of the piers, footing and the soil and use this resultant load as contributing towards resisting?
3. In general, SR is defined as Mr/Mo where Mr is the resisting moment and Mo is the overturning moment. Would SR = L/2e be correct under all circumstances and equate to SR calculated using Mr/Mo?
Sorry, this may seem like a repeat of one of the questions in the forum regarding stability ratio calculation for a spread footing but wanted to get a clarification for stability calculation for a mat foundation.
Thank you
1. Would the uplift loads contribute to the overturning moment about an edge of the footing or is it just the applied shears and moments on the piers that contribute to overturning?
2. In continuation of 1 above, in calculating resisting moment, is it appropriate to algebraically add all the vertical loads on the piers (both compressive and uplift), add the weight of the piers, footing and the soil and use this resultant load as contributing towards resisting?
3. In general, SR is defined as Mr/Mo where Mr is the resisting moment and Mo is the overturning moment. Would SR = L/2e be correct under all circumstances and equate to SR calculated using Mr/Mo?
Sorry, this may seem like a repeat of one of the questions in the forum regarding stability ratio calculation for a spread footing but wanted to get a clarification for stability calculation for a mat foundation.
Thank you