Driven Pile Design

George Goble

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

Definition of Loads

N – Axial load DC – Structural Dead LoadFT – Load transverse to the LL – Vehicular Live Load bridge centerlineFL – Load parallel to the IM – Vehicular Dynamic Load bridge centerline MT – Moment about the ML – Moment about the transverse axis longitudinal axisWL – 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

Force Effects

Load Set 1, Maximum axial effect with overturning effect All 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

Force Effects Load Set 2, Maximum overturning effect with axial effect

All 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

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

Table 2Factored Loads

LOAD N FTFL 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

SoilBoring

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

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

WaveEquationBearing Graph

Concrete Stress-Strain Curve

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

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

FinalDesign

Results

Bi-Axial Interaction Diagram Pile 4, Load Case 2

Critical Conditions

Load Case Max. Pile

Load, Pile No.Kips

Max. Uplift

Load, Pile No.Kips

Demand/Capacity

Ratio, Pile No.

Str I Max 847, 9 0.700

Str I Min 791 68, 4 0.654

Str III 561 1.000, 4

Str IV 691 0.570

Str V Max 783 0.673

Str V Min 712 0.649

Required Axial Capacity

Rn = Un-Factored Capacity/φ

Rn = 847/0.80

Rn = 1060 kips

Wave Equation Analysis

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,

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