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Driven Pile Design

Driven Pile Design. George Goble. Basic LRFD Requirement. η k Σ γ ij Q ij ≤ φ g R ng η k – factor for effect of redundancy, ductility and importance γ ij – Load factor for the i th load type in the j th load combination Q ij – The i th load type in the j th load combination

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Driven Pile Design

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  1. Driven Pile Design George Goble

  2. Basic LRFD Requirement ηk Σ γij Qij ≤ φg Rng ηk – factor for effect of redundancy, ductility and importance γij – Load factor for the ith load type in the jth load combination Qij – The ith load type in the jth load combination φg – The resistance factor for the ath failure mode Rng - The nominal strength for the ath failure mode

  3. Definition of Loads N – Axial load DC – Structural Dead Load FT – Load transverse to the LL – Vehicular Live Load bridge centerline FL – Load parallel to the IM – Vehicular Dynamic Load bridge centerline MT – Moment about the ML – Moment about the transverse axis longitudinal axis WL – Wind on Live Load BR – Vehicular Braking WS – Wind Load on Structure Force Note: Two different wind loads are specified – winds greater than 55 miles per hour and winds less than 55 miles per hour. At greater than 55 miles per hour no traffic loads are included

  4. Force EffectsLoad Set 1, Maximum axial effect with overturning effectAll units are kips and feet • LOAD N FT FL MT ML • DC 5564 0 0 0 0 • LL 894 0 0 0 3742 • WS (>55) -254 182 145 4334 5454 • WS (<55) -142 107 66 1961 3226 • WL 0 20 -4.2 -125 600 • BR 0 24.2 -54.5 -1636 727

  5. Force EffectsLoad Set 2, Maximum overturning effect with axial effectAll units are kips and feet LOA N FT FL MT ML DC 5564 0 0 0 0 LL 662 0 0 0 12552 WS (>55) -254 182 145 4334 5454 WS (<55) -142 107 66 1961 3226 WL 0 20 -4.2 -125 600 BR 0 17.9 -40.0 -1208 537

  6. AASHTO Load Combinations • STR I MAX = 1.25 DC + 1.75 (LL + IM + BR) • STR I MIN = 0.9 DC + 1.75 (LL + IM + BR) • STR III = 0.9 DC + 1.4 WS • STR IV = 1.5 DC • STR V MAX = 1.25 DC + 1.35 (LL + IM + BR) + 0.4 WS + 1.0 WL • STR V MIN = 0.9 DC + 1.35 (LL + IM + BR) + 0.4 WS + 1.0 WL

  7. Table 2Factored Loads LOAD N FT FL MT ML z x y Mx My STR I MAX 8520 42 -95 -2863 7821 STR I MIN 6166 31 -71 -2114 22906 STR III 4652 255 203 6068 7635 STR IV 8346 0 0 0 0 STR V MAX 8105 95 -51 -1549 7924 STR V MIN 5845 87 -32 -971 19561

  8. Soil Boring

  9. TRY • 18 inch Square Prestressed Concrete pile • Use 7000 psi Concrete • Structural Axial Strength • Pn = 0.80 [ 0.85f’c Ag–(fpe- 85.5) Ag ] • Pn = 1360 kips

  10. Wave Equation Results • D-36-32 Hammer • 3 inches plywood !! • Capacity 1100 kips • Blow Count 10 Blows per inch • Maximum Compression Stress 3.6 ksi • Allowable Driving Stress • φ(0.85f’c - fpe), - φ = 1.0 • For 7.0 ksi Concrete, Allowable Stress = 5.1 ksi

  11. Wave Equation Bearing Graph

  12. ConcreteStress-Strain Curve

  13. Trial No. 1 • 1100 kips Pile Capacity • 16, 18 inch Square Piles 4 x 4 Group • FB-Pier Input • Structural Elements and Material Properties • Soil Properties • Structural Geometry • Loads • Lateral – O’Neil Sand Model • DRIVEN Axial Model • Increase Axial Capacity by a Factor of 2.0 • Effective Prestress – 800 psi • Linear Analysis – No P-Δ – But Non-Linear Soil

  14. Results • Several Tries - 4 x 4 Group Doesn’t Work – Pile Top Structural Failure • Change to 20 Inch Square Pile – 4 x 4 Group • Very Safe • Try 3 x 4, 20 Inch Pile Group • Successful After Several Trials

  15. Final Design

  16. Results

  17. Bi-Axial Interaction Diagram Pile 4, Load Case 2

  18. Critical Conditions

  19. Required Axial Capacity Rn = Un-Factored Capacity/φ Rn = 847/0.80 Rn = 1060 kips

  20. Wave Equation Analysis

  21. Final Requirements • 12, 20 Inch Square Piles • Estimated Length – 85 Feet – (Bottom of Cap, -10 Feet) • Required Blow Count – 80 Blows per Foot • Maximum Compression Stress – 3.3 ksi • Maximum Tension – 1.5 ksi – Excessive, Throttle Back

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