Sensitivity Analysis performed using DYNA6 - Static Load on Pile

Static load on pile is an important design Input in DYNA6. Preliminary pile load calculation and verification of its impact of changes on final design. Sensitivity Analysis performed using DYNA6 for a recent project.  

A 1500 Horsepower pump foundation (shown in Fig 1), used for this sensitivity analysis and the summary of Information provided below:

1)   Weight of Pump               8500 Kg

2)   Weight of Motor               4150 Kg

3)   Weight of Gear Box          1560 Kg       

4)   Weight of Base Frame      5200 Kg

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5)   Total Weight                    19410 Kg

6)   Operating Speed=1800 RPM.

7)   Starting Speed = 0; Step increasing =120 RPM, Max. Speed =4320 RPM

8)   CG location of individual & combined machine are provided by vendor

9)   Concrete piles 500mm Dia. Initial length of 9.000m, increased to 12.0m

10) Concrete pedestals(m): 3.3x5.9x1.135, 2.946x5.715x0.305, 1.0x1.504x1.0

11)  Unbalance forces calculated as per ACI 351.3R-04 & Industry Standard. 

Fig 1: Pump Foundation Details

Following cases are investigated and impacts are investigated

a)   Average shear wave velocity (vs)

b)   Pile-soil interaction considered

c)    Pile-soil interaction neglected

d)   Pile bottom floating condition 

e)   Pile bottom end beading considered

f)     Pile length nominal 9.000m

g)   There can be more cases of sensitivity analysis and some of them are covered in my other published articles, shall be undertaken on the basis of project cost, quality and schedule requirement.

Other Notes:

● Response of displacement amplitudes are used for plotting the graphs at the combined CG location of machine + foundation, and same equipment parameters are used throughout the study.

●Two gray vertical lines on the graphs are +/- 20% of operating speed 1800 RPM resonance Area.

● Translations are plotted in mm and rotations are in radianx1000. 

● Depth of soil layers and shear wave velocities used are given below:

Table 1: Soil Layers

● Machine is placed along the Y axis with pump at near end, motor on further end on the pedestal, gearbox is in-between. X is transverse, Y is longitudinal and Z is vertical axis.

● The peak value of the response curve is associated with natural frequency.

Table 2: Sensitivity Variables

Fig 2: Axis of Displacement Amplitude

Note: Fig P140- S240 combined below for ease of comparison; enlarged diagrams are available later for clarity.

Translation Response (Displacement)

Insignificant variations are observed in Y direction (longitudinal displacement, red line in the graph) translation due change in various design parameters.

 X translation (transverse displacement, blue line) peaks are below the resonant frequency area. Magnitude of X displacement increases when pile-soil interactions are ignored, see Fig 3 & 4 below.

 Z Translation (vertical displacement, green line) is behaving opposite to X, peak is within the resonance zone, magnitude of displacement much higher if pile- soil interaction is consider. No impact of pile bottom end floating or end bearing.

Fig 3: Translation Amplitude at Combined CG

PILE-SOIL INTERACTION CONSIDERED

Pile Bottom Floating (P140-P240), Pile Bottom End-Bearing (R140-R240)

Fig 4: Translation Amplitude at Combined CG

PILE-SOIL INTERACTION IGNORED

Pile Bottom Floating (Q140-Q240), Pile Bottom End-Bearing (S140-S240)

Rotational displacement (Rocking)

Insignificant variations are observed in rotation due change in various design parameters. Rotation about Y longitudinal direction (red line in the graph, rocking) is most significant (shall be coupled with horizontal X displacement). See Fig 5 and Fig 6 below, the peak displacement is outside of resonance area (±20% of operating speed of 1800rpm). The resonance area is indicated by 2 gray vertical lines on the graphs.

Fig 5: Rotation Amplitude about Combined CG

PILE-SOIL INTERACTION CONSIDERED

Pile Bottom Floating (P140-P240), Pile Bottom End-Bearing (R140-R240)

Fig 6: Rotation Amplitude about Combined CG

PILE-SOIL INTERACTION IGNORED

Pile Bottom Floating (Q140-Q240), Pile Bottom End-Bearing (S140-S240)

Summary

Velocity and acceleration shall be obtained from the above displacement calculation (translations) and shall meet the requirements machine manufacturer. Fig 7, 8, and 9 shall be used to verify the performance of foundation design and machine together. Uncertainty in soil parameters, pile length change during construction, and various other assumptions may cost a lot when equipment is failed while in operation. Due diligence during the foundation design stage is very important for a successful plant operation and can save huge maintenance cost.

Fig 7: (Fig 3.9 ACI 351.3R-04) Vibration Criteria for rotating machinery (Blake 1964, as modified by Arya m O’Neill, and Pincus 1979)

Fig 8: (Fig 3.10 ACI 351.3R-04) General Machinery Vibration Severity Chart (Baxter and Bernhard 1967)

Fig 9: (Fig 3.13 ACI 351.3R-04) Reiher-Meister Chart ( Richart Hall, and woods 1970

Fig P140: Average shear wave velocity, Pile-soil interaction considered, Pile bottom Floating, Pile length 9.0m, Static Load on Pile 140kN

Fig P160: Average shear wave velocity, Pile-soil interaction considered, Pile  bottom Floating, Pile length 9.0m, Static Load on Pile 160kN

Fig P180: Average shear wave velocity, Pile-soil interaction considered, Pile  bottom Floating, Pile length 9.0m, Static Load on Pile 180kN

Fig P200: Average shear wave velocity, Pile-soil interaction considered, Pile bottom Floating, Pile length 9.0m, Static Load on Pile 200kN

Fig P220: Average shear wave velocity, Pile-soil interaction considered, Pile bottom Floating, Pile length 9.0m, Static Load on Pile 220kN

Fig P240: Average shear wave velocity, Pile-soil interaction considered, Pile bottom Floating, Pile length 9.0m, Static Load on Pile 240kN

Fig Q140: Average shear wave velocity, Pile-soil interaction neglected, Pile bottom Floating, Pile length 9.0m, Static Load on Pile 140kN

Fig Q160: Average shear wave velocity, Pile-soil interaction neglected, Pile bottom Floating, Pile length 9.0m, Static Load on Pile 160kN

Fig Q180: Average shear wave velocity, Pile-soil interaction neglected, Pile bottom Floating, Pile length 9.0m, Static Load on Pile 180kN

Fig Q200: Average shear wave velocity, Pile-soil interaction neglected, Pile bottom Floating, Pile length 9.0m, Static Load on Pile 200kN

Fig Q220: Average shear wave velocity, Pile-soil interaction neglected, Pile bottom Floating, Pile length 9.0m, Static Load on Pile 220kN

Fig Q240: Average shear wave velocity, Pile-soil interaction neglected, Pile bottom Floating, Pile length 9.0m, Static Load on Pile 240kN

Fig R140: Average shear wave velocity, Pile-soil interaction considered, Pile  bottom End-Bearing, Pile length 9.0m, Static Load on Pile 140kN

Fig R160: Average shear wave velocity, Pile-soil interaction considered, Pile  bottom End-Bearing, Pile length 9.0m, Static Load on Pile 160kN

Fig R180: Average shear wave velocity, Pile-soil interaction considered, Pile  bottom End-Bearing, Pile length 9.0m, Static Load on Pile 180kN

Fig R200: Average shear wave velocity, Pile-soil interaction considered, Pile  bottom End-Bearing, Pile length 9.0m, Static Load on Pile 200kN

Fig R220: Average shear wave velocity, Pile-soil interaction considered, Pile  bottom End-Bearing, Pile length 9.0m, Static Load on Pile 220kN

Fig R240: Average shear wave velocity, Pile-soil interaction considered, Pile  bottom End-Bearing, Pile length 9.0m, Static Load on Pile 240kN

Fig S140: Average shear wave velocity, Pile-soil interaction ignored, Pile  bottom End-Bearing, Pile length 9.0m, Static Load on Pile 140kN

Fig S160: Average shear wave velocity, Pile-soil interaction ignored, Pile bottom End-Bearing, Pile length 9.0m, Static Load on Pile 160kN

Fig S180: Average shear wave velocity, Pile-soil interaction ignored, Pile bottom End-Bearing, Pile length 9.0m, Static Load on Pile 180kN

Fig S200: Average shear wave velocity, Pile-soil interaction ignored, Pile bottom End-Bearing, Pile length 9.0m, Static Load on Pile 200kN

Fig S220: Average shear wave velocity, Pile-soil interaction ignored, Pile bottom End-Bearing, Pile length 9.0m, Static Load on Pile 220kN

Fig S240: Average shear wave velocity, Pile-soil interaction ignored, Pile bottom End-Bearing, Pile length 9.0m, Static Load on Pile 240kN