Driven Pile Design George Goble. Basic LRFD Requirement η k Σ γ ij Q ij ≤ φ g R ng η k –...
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Transcript of Driven Pile Design George Goble. Basic LRFD Requirement η k Σ γ ij Q ij ≤ φ g R ng η k –...
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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