Vertical Tubular Pile - Nonlinear lateral soil supports (2D analysis)

sam_wegener — Wed, 04 Aug 2021 08:39:18 GMT

Good day

I am modelling a single vertical tubular pile in RSA Professional 2021 (V34.0.0.7777) - 2D Frame analysis. The pile is subject to lateral and axial (tensile) loads.

The pile is to be fully embedded in rock - with loading applied to the pile top. I am modelling lateral support to the pile as a series of nonlinear nodal supports at 250mm depth intervals. The nonlinear supports have been defined using the "function" parameter type by importing discrete points as a text file (see below image).

My queries are the following:

1. Nonlinear function units: Please clarify and confirm the unit system for the nonlinear function definitions. The units in my text files are N (Force) and m (displacement). It seems the RSA software automatically converts the values of the imported text file. Is this correct? In my case:

Displacement values are multiplied by 1000 (m to mm)

Force values are divided by 1000 (N to kN)

2. Nonlinear function diagram display: It seems the nonlinear function diagram in the "Non-linear Model Definition" window does not display the imported values correctly. The force values should be symmetric with the "Symmetry" box ticked. The vertical axis values indicate this is not the case. (Conversely, it is noted that the nonlinear functions shown in the Calculation Note are symmetric -and therefore do not agree with the function shown in the "Non-linear Model Definition" window")

3. Model Convergence: The model is not converging. Various attempts have been made to achieve convergence, including:

- fixing the support at the pile base,

- increasing tolerances for the nonlinear analysis,

- increasing the load increment number and max. iteration number for the nonlinear analysis,

- allowing matrix updates after each iteration, and

- simplifying the nonlinear function nodal supports to bilinear functions.

Please advise and assist: What are the reasons for the non-convergence? How may convergence be achieved? (The rtd. and txt. files are attached for reference.)

(cc @Anonymous )

Re: Vertical Tubular Pile - Nonlinear lateral soil supports (2D analysis)

sam_wegener — Thu, 12 Aug 2021 07:29:26 GMT

Good day @okapawal . This is a follow-up on the above query. Could you perhaps please assist?

Many thanks

Sam

(cc @Anonymous )

Re: Vertical Tubular Pile - Nonlinear lateral soil supports (2D analysis)

Krzysztof_Wasik — Fri, 13 Aug 2021 10:49:39 GMT

Hi @sam_wegener

Model converges when all nonlinear support functions were updated by point (0;0).

As far as I could check diagram description corresponds to units set in Job Preferences (Forces and displacement), Values are rescaled after units modification.

Issue with presenting shifted function diagram (which should be symmetrical) was corrected in RSA 2022.

Re: Vertical Tubular Pile - Nonlinear lateral soil supports (2D analysis)

sam_wegener — Fri, 13 Aug 2021 11:21:38 GMT

Thank you @Krzysztof_Wasik

topic Re: Vertical Tubular Pile - Nonlinear lateral soil supports (2D analysis) in Robot Structural Analysis Forum

Vertical Tubular Pile - Nonlinear lateral soil supports (2D analysis)

Re: Vertical Tubular Pile - Nonlinear lateral soil supports (2D analysis)

Re: Vertical Tubular Pile - Nonlinear lateral soil supports (2D analysis)

Re: Vertical Tubular Pile - Nonlinear lateral soil supports (2D analysis)