Sean Johnson's Communities Activities

Plaxis: Site response facility

원호 정 — Wed, 08 Sep 2021 09:06:34 GMT

I have a query about Plaxis 2D (v.21 Ultimate) Site Response function that can be used for 1D Site Response Analysis (SRA). When we select “Site Response” from the “Modify soil layers” menu, Plaxis automatically converts the main geometry of the model into 1D geometry and the meshing is also done with 6-noded elements.

I would like to know, whether such meshing is OK for the Site Response Analysis, OR I have to modify the mesh size as suggested in Plaxis 2D (2015) Ground Response Analysis report, i.e., the suggestion of Kuhlmeyer & Lysmer (1973).

Secondly, I would like to know whether the following conditions are OK while selecting dynamic loading.
The Static Line displacement (U_x,start,ref) in the Dynamic module should be,
1) U_x,start,ref = 0.5 m ; In case of Rock outcrop motion ?
2) U_x,start,ref = 1.0 m ; In case of Bedrock (underlying of soil layer) motion ?

Criteria for Dynamic Slope Failure

Mustafa Erten — Wed, 06 Apr 2022 16:43:06 GMT

Hi,

I am using PLAXIS 2D to perform earthquake time-history analysis for a slope using different accelerograms. As a result of this analysis, I will need to estimate the potential volume of soil that may fail and mobilize as a result of the earthquake event. Could you please help me on what criteria to use to identify to potential soil failure surface? I was thinking of using a horizontal displacement criteria but I am not sure what displacement to use to identify fail/unfail situation. I can also look at the cartesian strains but I am not sure about what limiting value to use.

Could you please provide some guidance or may be direct me to some references which dealt with the same type of problem?

Adding damping values in a dynamic analysis

Jack Rice — Fri, 08 Apr 2022 14:03:11 GMT

I have a pile in a block of sand, with a horizontal load being applied at the top of the pile for 7 seconds, then being released allowing free vibration for 13 seconds. I added 1% damping to the pile and 0.6% damping to the soil materials. After this, the output computes no displacements in either stage of the analysis - loading or vibration. Without the damping values applied I get increased displacement until the load is deactivated, and then slowly decaying oscillations due to geometric dissipation. I expect to see the same output when I add the rayleigh damping values, except the oscillations should decay more. Why am I getting flat lines and how can I apply damping correctly?

The Geosynthetic-Reinforced Pile-Supported (GRPS) embankments under dynamic loads

rashad alsirawan — Wed, 02 Mar 2022 23:45:42 GMT

Hi all

A validation process of GRPS embankment (over soft soil layers) under static loads was conducted, HS and SSC models are utilized to simulate the behavior of the embankment with a good agreement.

can we apply the traffic load (dynamic analysis) if the model was validated under static loads? If yes, Do HS or SSC models work in the Dynamic analysis?

thanks in advance

Dynamic loading in PLAXIS

Aamir Gulzar — Tue, 08 Mar 2022 06:12:21 GMT

How can I place the earthquake load within the model?

Is it possible with the surface prescribed displacements?

Should I be using free field and complaint base boundaries while using line prescribed displacements for earthquake simulation?

Global acceleration - Pseudo static input

AHMED ABD ELSHAKOUR — Sun, 09 Jan 2022 21:49:50 GMT

Hello,

First of all, I want to thank you very much, every single one who works in the technical support of the Bentley communities, the quick respond, the efficiency, the Bentley Communities is perfect

My problem is that I am running a dynamic phase, earthquake by a time history applied by means of prescribed displacement to the bottom boundary. Followed by a plastic phase, which I need to take into account the deformations that took place in the dynamic phase. So. I will use the pseudo static option in the model conditions at the plastic phase.

So I was asking how to calculate the global acceleration in every direction (x, y &z), Should I calculate it from the dynamic phase !? but at which node in the whole model !?

Sincerely,

Ahmed Abd Elshakour

Pseudo static input

AHMED ABD ELSHAKOUR — Wed, 19 Jan 2022 17:30:11 GMT

Hello,

I am running a dynamic phase, earthquake by a time history applied by means of prescribed displacement to the bottom boundary. The dynamic phase is followed by a plastic phase, I need the dynamic phase deformations to have an effect on the plastic phase . So. I will use the pseudo static option in the model conditions at the plastic phase.

So I was asking how to calculate the global acceleration in every direction (x, y &z)

Sincerely,

Ahmed Abd Elshakour

Pseudo static

AHMED ABD ELSHAKOUR — Fri, 21 Jan 2022 15:40:02 GMT

Hello,

So I was asking how to calculate the global acceleration in every direction (x, y &z)

Sincerely,

Ahmed Abd Elshakour

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Earthquake input value

AHMED ABD ELSHAKOUR — Fri, 07 Jan 2022 14:26:15 GMT

Hello,

The dynamic loading is specified by means of an input value and a multiplier. The actual dynamic value at each time step equals to the input value times the multiplier.

As an example, the earthquake analysis problem in the tutorial manual, the earthquake is simulated by a dynamic prescribed displacement of a value 0.5m as in the figure below

the multiplier is a time-history (strong motion CD-ROM) which its peak acceleration is 2.399m/s2 and the time interval input is 20s. the categorizing of this earthquake is empirically "between 6 to 6.9 Richter" and the perceived shaking is "very strong", and if we use scaling factor 2 and 3,the categorizing will be like that

this table is considered empirical not an accurate.

However, as it is mentioned in the reference manual "The actual dynamic value at each time step equals to the input value times the multiplier". So, the input value 0.5m has an influence on the categorizing of the earthquake!

So, my question is the input value of the dynamic prescribed displacement , what it actually means!? is it a component of the earthquake!?
and if I want to categorize the earthquake by the its peak acceleration, how can I calculate its actual value?

sincerely,
Ahmed Abd elsakour

prescribed displacement force value separetely from any other prescribed displacement in the same phase

AHMED ABD ELSHAKOUR — Sun, 24 Oct 2021 10:56:29 GMT

If there are two prescribed displacements at the same phase, one of them is static (shallow foundation) and the other is dynamic (time-history analysis), can I get the force of the static prescribed displacement by any way other than ( curves manager - project - Fz ) ..because it is in this case combined of the static and the dynamic prescribed displacement not only the static.

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Fri, 29 Oct 2021 12:29:01 GMT

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