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 φ g – The resistance factor for the a th failure mode R ng - The nominal strength for the a th failure mode

Definition of Loads N – Axial loadDC – 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 LoadBR – 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 LL WS (>55) WS (<55) WL BR

Force Effects Load Set 2, Maximum overturning effect with axial effect All units are kips and feet LOA N FT FL MT ML DC LL WS (>55) WS (<55) WL BR

AASHTO Load Combinations STR I MAX = 1.25 DC (LL + IM + BR) STR I MIN = 0.9 DC (LL + IM + BR) STR III = 0.9 DC WS STR IV = 1.5 DC STR V MAX = 1.25 DC (LL + IM + BR) WS WL STR V MIN = 0.9 DC (LL + IM + BR) WS WL

Table 2 Factored Loads LOADN FTFL MT ML z x y Mx My STR I MAX STR I MIN STR III STR IV STR V MAX STR V MIN

Soil Boring

TRY 18 inch Square Prestressed Concrete pile Use 7000 psi Concrete Structural Axial Strength –P n = 0.80 [ 0.85f’ c A g –(f pe ) A g ] –P n = 1360 kips

Wave Equation Results D 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 - f pe ), - φ = 1.0 –For 7.0 ksi Concrete, Allowable Stress = 5.1 ksi

Wave Equation Bearing Graph

Concrete Stress-Strain Curve

Trial No 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

Final Design

Results

Bi-Axial Interaction Diagram Pile 4, Load Case 2

Critical Conditions Load CaseMax. Pile Load, Pile No. Kips Max. Uplift Load, Pile No. Kips Demand/Capacity Ratio, Pile No. Str I Max847, Str I Min79168, Str III , 4 Str IV Str V Max Str V Min

Required Axial Capacity R n = Un-Factored Capacity/φ R n = 847/0.80 R n = 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, Throttle Back