BSI Newsletter - Issue #4, Fall 2005

Welcome to the Fall issue of the BSI Newsletter!

In this issue, Dr. Frank C. Townsend shows how to convert dilatometer test results into P-Y curves for use with FB-MultiPier or FB-Deep in this issue's Discussions article. In the Technical Corner we explain how you can transfer the custom cross-sections you designed in FB-PierV3 to FB-MultiPier.

The articles "Technical Corner" and "Discussions" are open for input from all readers. If you have a topic that you think should be discussed, let us know. Did you create a great model with features that you want to share? Everyone is welcome to submit articles for possible inclusion in subsequent issues. Please contact BSI at BSI@ce.ufl.edu with your ideas.

Several users who have moved from FB-Pier v3 to FB-MultiPier have asked how they can transfer the custom cross-section designs they have created from one program to the other. This would make the switch to the new program easier and would save time that would be spent recreating the sections.

The cross sections are saved as individual files with .PLD or .SMD as the file extension. They are plain text files that use an incremented file name. You can open them with Notepad and read the first line of the file which is the section name. The format of these files has not changed from FB-PierV3 to FB-MultiPier so you can safely use the same files with both programs.

In FB-PierV3, the cross section files were located in the FB-Pier install directory along with all of the program source files. With FB-MultiPier, we did some reorganizing and created a number of new subdirectories, including 'CrossSections', where all cross section files are stored.

You will need to save any custom files that you have created in FB-MultiPier, because they may be overwritten when importing the FB-PierV3 files. You will need to find these files by opening the files and checking the name and backing up the files you want to keep by placing them in a different location.

Navigate to the FB-PierV3 install directory, which is 'Program Files/BSI/FB-PierV3' by default. Select and copy all the .PLD and .SMD files. This will be much easier if you sort them by type. Now place a copy of these files in 'CrossSections' subdirectory. The default location is 'Program Files/BSI/FB-MultiPier/CrossSections'. The computer will ask if you want to overwrite the existing files with the same name. Say 'Yes to All' and when you are finished move the files that you backed up earlier back into this directory. You will most likely need to rename these files so that the numeric component does not match an existing file. For example if you have files pile1.PLD through pile13.PLD in the directory already and you want to place a file named file11.PLD there, just rename this file to the next unused number, in this case pile14.PLD.

FB-MultiPier will read the new files automatically the next time you load a file. The names of your custom files will be displayed and will be available just like they were in FB-Pier.

Robertson, Davies and Campanella [1] suggested a method that adapts the early methods for estimating p-y curves using empirical strength parameter correlations. The dilatometer test only produces one millimeter of lateral deformation. This means that there are no increments of pressure with which to develop a load-deformation curve. Therefore, the properties determined from the dilatometer indices are used in conjunction with a parabolic function to develop p-y curves.

For cohesive soils a cubic parabolic p-y curve was suggested:

where

where y_c in cm, D = Pile diameter in cm, F_c ≈ 10, E_D is the dilatomet modulus, and S_u is the undrained shear strength.

The evaluation of the ultimate lateral resistance P_u is given as

At considerable depths N_p ≈ 9, but near the surface, it reduces to a range of 2-4 accordingly,

where x = depth, σ _vo = effective stress at depth x, and J = 0.5 (soft clay) to 0.25 (stiff clay).

For Cohesionless soils, the same cubic parabola was suggested:

where P_u is from Reese et al. [2] and Murchison and O'Neill [3] and is the lesser of

where β = 45° + Φ '/2, K_p = coefficient of passive earth pressure, K_a = coefficient of active earth pressure, Φ ' = effective friction angle, χ = depth, and y_c is

where F_Φ is an empirical factor equal to 1 for cohesionless soil.

Example: Bypass Bridge, Wilmington, NC DMT-1

Given for DMT data reduction:
χ = 1.83 m, Pile Diameter = 30cm, Φ _Marchetti = 39°, σ _v' = 0.153 bars, E_D = 72.5 bars, I_D = 3.68, K_a = tan²(45-39/2) = 0.22, K_p = tan²(45+39/2) = 4.39, and bar/cm = .0057 kips/in.

Solution:

1) Since I_D > 1.2 Cohesionless
2)
3)
4)
5) Assume 10 values of P from 0 to 1.8 kips
6)
7) Let P = 0.2,

Test at -3.29 m

P
(kips/in) Y
(in)

0.0 0.000

0.2 0.005

0.4 0.042

0.6 0.142

0.8 0.337

1.0 0.658

1.2 1.138

1.4 1.807

1.6 2.697

1.8 3.840

References:
[1] Robertson, P.K., Davies, M.P. & Campanella, R.G. (1987). "Design of Laterally Loaded Driven Piles Using the Flat Dilatometer". Geot. Testing Jnl, Vol. 12, No. 1, Mar., 30-38.

Test at -3.29 m
P (kips/in)	Y (in)
0.0	0.000
0.2	0.005
0.4	0.042
0.6	0.142
0.8	0.337
1.0	0.658
1.2	1.138
1.4	1.807
1.6	2.697
1.8	3.840

[2] Reese, L. C., Cox, W. R. and Koop, F. D. (1974). "Analysis of Laterally Loaded Piles in Sand," Paper No. OTC 2080, Proceedings, Fifth Annual Offshore Technology Conference, Houston, Texas, GESA Report No. D-75-9.

[3] Murchison, J. M. and O’Neill, M. W. (1984). "Evaluation of P-Y Relationships in Cohesionless Soils," from Analysis and Design of Pile Foundations, proceedings of a symposium sponsored by the ASCE Geotechnical Engineering Division, ASCE National Convention, San Francisco, CA, pp. 174-191.

Released: October 10, 2005 - Continuing Development - Technical Support Available

FB-MultiPier is the successor to FB-Pier. In addition to all the capabilities of FB-Pier the FB-MultiPier program allows for the modeling of a whole bridge that consists of multiple piers that are connected with bridge spans. In addition to the multiple load cases and the AASHTO coefficients that are available in FB-Pier, the new program is capable of performing dynamic analysis for the whole bridge. For more information about FB-MultiPier, click here.

Released: November 1, 2004 - Continuing Development - Technical Support Available

The FB-Deep computer program is a Windows based program used to estimate the static axial capacity of drilled shafts and driven piles. The methodology is based upon Federal Highway Administration (FHWA) reports. FB-Deep guides the user through pile and shaft materials data, shape and dimensional inputs, soil properties, and boring log info. FB-Deep presents the data analysis in both clear graphical and text form. For more information about FB-Deep, click here.

Released: October 15, 2004 - Final Release - Technical Support Available

This program has been replaced by FB-MultiPier and all sales or renewals will be directed to the FB-MultiPier program. FB-Pier is still available for download by valid licensed holders.

FB-Pier was designed for the analysis of bridge pier structures composed of nonlinear pier columns and cap supported on a linear pile cap and nonlinear piles/shafts with nonlinear soil. FB-Pier couples nonlinear structural finite element analysis with nonlinear static soil models for axial, lateral and torsional soil behavior to provide a robust system of analysis for coupled bridge pier structures and foundation systems. The program performs the generation of the finite element model internally given the geometric definition of the structure and foundation system as input graphically by the designer. For more information about FB-Pier, click here.