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ECGD 4122 – Foundation Engineering Lecture 6

Faculty of Applied Engineering and Urban Planning. Civil Engineering Department. 2 nd Semester 2008/2009. ECGD 4122 – Foundation Engineering Lecture 6. Content. Eccentrically Loaded Foundations Foundations with two-way eccentricity Field Load Test. Stress Concept.

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ECGD 4122 – Foundation Engineering Lecture 6

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  1. Faculty of Applied Engineering and Urban Planning Civil Engineering Department 2nd Semester 2008/2009 ECGD 4122 – Foundation Engineering Lecture 6

  2. Content • Eccentrically Loaded Foundations • Foundations with two-way eccentricity • Field Load Test

  3. Stress Concept

  4. Stress Distribution – Rigid Footings

  5. Effect of Eccentricity

  6. Effect of Eccentricity Q = total vertical load on the foundation M = moment on the foundation e = M/Q

  7. Effect of Eccentricity Meyerhof’s Principle Of Effective Area Method

  8. Ultimate Load with Eccentricity Step 1: Find Eccentricity, If e ≤ B/6 If e > B/6

  9. Ultimate Load with Eccentricity Step 2: Determine the Effective Dimensions If eccentricity is in the direction of B B΄= B – 2e L΄ = L If eccentricity is in the direction of L B΄= B L΄ = L – 2e

  10. Ultimate Load with Eccentricity

  11. Ultimate Load with Eccentricity Step 3:Use general equation to calculate the soil ultimate bearing capacity q'u= c΄ Nc Fcs Fcd Fci + q Nq Fqs Fqd Fqi + 0.5 γ B΄Fγs Fγd Fγi USE B΄ to calculate: Fcs , Fqs , Fγs DON’T use B΄ to calculate: Fcd , Fqd , Fγd

  12. Ultimate Load with Eccentricity Step 4:Determine the total ultimate load: Qult = qult A΄ = qult B΄ L΄ Step 5:Factor of safety against bearing failure:

  13. Example 1 For the footing shown below, determine the ultimate vertical loading with an 0.15 m eccentricity using the general formula. Take Nq = 18.4, N = 22.4.

  14. Example 1 - Solution

  15. Example 1 - Solution

  16. Example 1 - Solution

  17. Two Way Eccentricity

  18. Two Way Eccentricity

  19. Two Way Eccentricity USE B΄ and L΄ to calculate: Fcs , Fqs , Fγs DON’T use B΄ and L΄ to calculate: Fcd , Fqd , Fγd

  20. Two Way Eccentricity Case I: eL/L ≥ 1/6 and eB/B ≥ 1/6

  21. Two Way Eccentricity Case II: eL/L < 0.5 and 0 < eB/B < 1/6

  22. Two Way Eccentricity

  23. Two Way Eccentricity Case III: eL/L < 1/6 and 0 < eB/B < 0.5

  24. Two Way Eccentricity

  25. Two Way Eccentricity Case IV: eL/L < 1/6 and eB/B < 1/6

  26. Two Way Eccentricity

  27. Example 2 Refer to Example 1 and the figure shown below to determine the ultimate vertical loading using the general formula.

  28. Example 2 - Solution

  29. Example 2 - Solution

  30. Example 2 - Solution

  31. Example 2 - Solution

  32. Field Load Test

  33. Field Load Test

  34. Field Load Test Clayey Soil Sandy Soil qu(F) Ultimate capacity for proposed foundation qu(P) Ultimate bearing capacity for test plate B F Width of foundation B P Width of test plate

  35. Example 3 Refer to the accompanied figure for the results of a plate load test on a sandy soil. Define the dimensions of a square footing to carry a load of 2500 kN with a permissible settlement of 25 mm. The test plate is 1’ in diameter.

  36. Example 3

  37. Example 3 - Solution

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