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ECGD 4122 – Foundation Engineering Lecture 7 Faculty of Applied Engineering and Urban Planning Civil Engineering Department 2 nd Semester 2008/2009 1.

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Presentation on theme: "ECGD 4122 – Foundation Engineering Lecture 7 Faculty of Applied Engineering and Urban Planning Civil Engineering Department 2 nd Semester 2008/2009 1."— Presentation transcript:

1 ECGD 4122 – Foundation Engineering Lecture 7 Faculty of Applied Engineering and Urban Planning Civil Engineering Department 2 nd Semester 2008/2009 1

2 Content 2 Design of Strap Footings

3 A strap footing is usually used to connect an eccentrically loaded column footing to an interior column footing. 3 Design of Strap Footings

4 4

5 5

6 Basic considerations for strap footing design: Strap must be rigid to control rotation of the exterior footingStrap must be rigid to control rotation of the exterior footing Footing dimensions should be proportioned for approximately equal soil pressures and avoid large differences in B to reduce differential settlementsFooting dimensions should be proportioned for approximately equal soil pressures and avoid large differences in B to reduce differential settlements Strap should be out of contact with soil so that there are no soil reactions to modify the design assumptionsStrap should be out of contact with soil so that there are no soil reactions to modify the design assumptions 6 Design of Strap Footings

7 Design Procedure: 1.Assume (e), i.e. assume L 1 2.Compute S 1, R 1, R 2 4. Calculate L 1, B 1, L 2, B 2 7 Design of Strap Footings

8 8 Example 1

9 Assume: e = 1.0 m S 1 = S – e = 6.2 – 1.0 = 5.2 m ΣM R2 = R (580) = 0R 1 = kN ΣM R1 = (580) + 5.2(900) – R 2 (5.2)= 0R 2 = kN L 1 = 2(e + x) = 2( ) = 2.4 m B 1 = R 1 /(L 1 q ult ) = 691.5/[(2.4)(183)] = 1.57 (Use 1.60 m) B 2 = L 2 = (R 2 /q ult ) 1/2 = (788.5/183) 1/2 = 2.08 (Use 2.10 m) 9 Example 1 - Solution

10 10 Types of Mat Foundations

11 11 Types of Mat Foundations

12 For Saturated Clays with ϕ = 0 Applied Stress 12 Stress Analyses of Mat Foundations

13 13 Determine the net ultimate bearing capacity of a mat foundation sized 13.0 × 9.0 m 2 on a saturated clay deposit with c u = 94 kPa,  = 0, and D f = 2.0 m. Example 2

14 14 Example 2 - Solution

15 Compensated Mat Foundations For no increase in the net soil pressure 15

16 16 A mat foundation sized 30.0 × 40.0 m 2 is to withstand a total dead and live load of 200 MN and located on a soft clay deposit with c u = 12.5 kPa and  = 18.8 kN/m 3. Determine the depth of foundation for: 1) A fully compensated case 2) A factor of safety = 3.0 Example 3

17 17 Example 3 - Solution

18 18 Example 3 - Solution

19 Pressure Under Mat Foundations 19

20 Pressure Under Mat Foundations 20

21 21 Pressure Under Mat Foundations


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