FB Multipier v.4. Single Pile Example

Transcription

1 FB Multipier v.4 Single Pile Example Professor s Driven Pile Institute Utah State University June 26, 2013 J. Brian Anderson (jbanders@auburn.edu) Department of Civil Engineering Auburn University

2 2 Deep Foundations FB-MultiPier Example 1a: Single Pile Axial Load Soil: N = 15 = 32 o k = 100 pci = 120 pcf G = 7.5 ksi = 0.33 f = 570 psf (from SPT97) Q tip = 384 kips (from SPT 97 Pile: Standard FDOT 24 Prestressed Square Section Default properties 40 ft

3 3 Start FB-MultiPier by selecting the shortcut on your desktop, or find BSI > FB MultiPier> FB MultiPier under the Start Menu. Select File>New from the menu at the top to create a new file. Fill in the appropriate project information. Select, for this case, choose Structure Type Single Pile Finally set Units to English (mixed units). Click OK to continue.

4 The editor windows will now appear. The top left window is the Model Data window where most info is entered. The top right window is the Pile Edit window shows the pile group in plan. The bottom left window is the Soil Edit window where the soil stratigraphy is shown. A 3-D view of the pile group is shown in the bottom right pane. A default problem is automatically loaded which you will need to change 4 Select Pile on the menu along the left side of the Model Data pane. Choose Edit under Cross Section Type

5 5 Under Database Section Selection, click on Retrieve Section and selection Rectangular > 24 Square FDOT Standard prestressed Change the length of the pile to 40 ft. Click OK to continue. Select Soil from the Model Data pane. Note that the Soil Layer drop down box contains the layers shown in the Soil Edit pane below.

6 6 Since we will be using a single soil layer for this example, select layer 2 then hit the delete button to remove the layer. Set the Soil Type, for Layer 1, to cohesionless. Enter Total Unit Weight equal to 110 pcf. Enter a friction angle of 32 o. Set the top of the layer at 0ft and the bottom at 60ft (for proper embedment). Since there is no water table in this problem, use water table depth of 100ft. Under Soil Layer Models, use the drop down box by Lateral to choose the lateral soil type, in this case, Sand (O Neill).

7 7 Click Edit. The unit weight and friction angle will be copied from before. Enter the value for subgrade modulus, 100 pci. Click OK to continue. Under Soil Layer Models, use the drop down box by Axial to choose the axial soil type, in this case, Driven Pile. Click Edit. The unit weight and friction angle will be copied from before. Enter the value for shear modulus, 7.5ksi, Poisson s Ratio, 0.3, Vertical Failure Shear, 570psf. Click OK to continue.

8 8 Under Soil Layer Models, use the drop down box by Tip to choose the end bearing type, in this case, Driven Pile. Click Edit. Enter the value for shear modulus, 7.5ksi, Poisson s Ratio, 0.3, Axial Bearing Failure, 384kips. Click OK to continue. Soil properties can also be input in table form. Click on the table button to bring up the soil properties table.

9 Soil Properties Input Table 9

10 k ( lb / inch 3 ) 10 Lateral Properties for Sand: Subgrade Modulus, rk Friction Angle, * N * e (Peck, Hanson, Thornburn, 1974) V ER Y LOOS E LOOS E M ED IU M D EN S E V ER Y D EN S E D EN S E S A N D A B OV E THE WA TER TA B LE S A N D B ELOW THE WA TER TA B LE D r (%) (Meyer and Reese, 1979) (Gibbs and Holtz, 1967) Relative Density of Sand Parameters Loose Medium Dense Blows/ft, N 4 to to to 50, degrees Dry or moist sand k lb/in Submerged sand k lb/in (Terzaghi, 1955) Relative Density of Sand Loose Medium Dense Dry or moist sand k lb/in Submerged sand k lb/in (Reese and Wang, 1993) Lateral Properties for Clay: (Robertson and Campanella 1983) Undrained Shear Strength, Su qc NKSU VO where: q c is cone tip resistance, Nk is a factor ~17, S u is undrained shear strength, and vo is the total overburden stress. q c, S u and vo are all in identical units.

11 SPT N Valu 11 Lateral Properties for Clay: Undrained Shear Strength, Su 25 Axial Properties for Sand and Clay Unit Skin Friction, f 110 N Plastic Clay: f ( tsf ) 2.0* N * Clay-Silt-Sand: Clean Sand: 110 N f ( tsf ) 2.0* N * f ( tsf ) 0.019* N Su / Pa Sowers (low PI) Terzaghi & Peck, Sanglerat (sandy clay) Sowers (medium PI) U.S.B.R (Houston clay-trend line) Schmertmann (Chicago clay) Sanglerat (silty clay) Sowers (high PI) (EPRI Manual, 1990) Subgrade Modulus, k Limestone: f ( tsf ) 0.01* N (SPT97 Users Guide) Shear Modulus, G Sand/Sand with Fines G(psi)= 500N [N<40] G(psi) = [N>40] Silt G(psi) = 500N [N<10] G(psi) = (N-10) [N>10] Clay G(psi) = 500N [N<10] G(psi) = (N-10) [N>10] (Reese and Wang, 1993) Strain at 50 % of the Failure Stress in an Unconfined Compression Test, 50 (PLAID) Ultimate Tip Resistance, Q TIP Plastic Clay: q ( tsf ) 0.73* N Clay-Silt-Sand: q ( tsf ) 1.6* N (Reese and Wang, 1993) Clean Sand: Limestone: q ( tsf ) 3.2* N q ( tsf ) 3.6* N (SPT97 Users Guide) (Reese and Wang, 1993)

12 12 Next, we need to specify the loads on the pile. Now, choose Load menu in the model data window. Two default load cases will be displayed. Highlight Load Case 2, then click in Del to delete it. For this case, we will edit load case 1. Click on Node 1 under Node Applied. Node 1 in this case is the top of the pile. Make sure that the only load listed is 310k in the Z direction.

13 Alternately, you can edit load cases using the load table 13 You should see an arrow representing this load in the 3dView box. This concludes the data input.

14 14 Use the save as.. command to save your problem before the analysis. The next step will be to perform the analysis. Click on the lightning bolt icon to run the analysis. You will get a warning that you will force a file save, accept and continue. The iterative process of FB-MultiPier will be shown while the analysis progresses.

15 15 Once the analysis is complete, click on the 3D Results icon to see a graphical depiction if the analysis. In the tool bar area, you can select the load case to view, in this problem there is only load case 1. In the 3D Display Control pane, you can select which node to display displacements or rotations, as well as the nodal coordinates. A 3 Dimensional representation of the results is shown in the 3D View pane. The deflection of node 1 (top of the pile should be approximately 0.5 inches)

16 16 Example 1b: Single Pile Lateral Load Use same input as for axial loading presented above: Lat = 30 k In the Model Data window, select Analysis from the menu, click user defined Phi ( ) factor and set = 1.0. This removes AASHTO phi factors from moment interaction diagram. Only use this for hand calculation verifications. In the Load Tab: click node # 1 and set Z = 0.0, and X = 30kips.

17 17 Click on the lightning bolt icon to run the analysis. You will get a warning that you will force a file save, accept and continue. Click Pile Results (icon next to lightning bolt) and see results below: a. X deflection = 0.176, soil lateral load = 13.7 kips b. Max moment = 136 ft-kips and Ratio = 0.172

18 18 Moment details: Click Pile Interaction and Biaxial moment and component selection a. Maximum moment for 24 x 24 PSC pile is to ft-kips 3 bh 3 3 I( moment of inertia 3 b. ( ) 12 b S ft ft C ( dist from neutral axis ) b 6 2 Moment 3 c. S ; Moment max ft 6ksi concrete 144 1, 152 ft kips yield stress d. However, more correctly is moment interaction shown by FB-Pier, where due to prestressing M max 654 ft-kips e. Moving up and down the segment selection finds element #4 giving highest moment (see on moment interaction diagram) Demand Ratio = (4b above) = 136 ft-kips / 654 ft-kips

19 19 Example 1c: Single Pile - Lateral Pushover Analysis Return to Edit icon and then select Load from the Menu. Add Load Case # 2 and set X = 5 kips. Click Pushover tab. Pushover will increment lateral load in 5kip increments until failure, either soil or maximum moment. Results of Pushover show: Lateral load producing failure = 120 kips (18 x 5 kips = 90 kips + original 30 kips load case #1 = 135 kips) Deflection = 2.17, Max moment = 648 ft-kips, Ratio = 648 / 654 = 0.99

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