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Blog | Eurocode 7: Geotechnical Design - How to apply Eurocode7 to FEM software?

2020.12.01

Partial factor for FEM Software

If you haven't read the Eurocode series >> 

1- What is Eurocode?
2- Design Approach and Partial Factor

 

03- Verification



The partial factors in EC7 (1997-1) can be applied to analysis with hand calculation or automatically considered in the analysis program. From the load (surcharge), it needs to multiply the partial factor from the original load (surcharge). From the soil parameters (strength), they need to be divided by partial factor from original parameters.

For example, if design approach 1 combination 1 (DA1C1) is applying to the FEM analysis as below,

DA1C1

If design approach 1 combination 2 (DA1C2) is applying to the FEM analysis as below,

DA1C2

They should have the same results, such as displacement and forces from the analysis when the partial factor has been applied with hand calculation and function from the FEM analysis program.

 

 

Eurocode Webinar

 

 

04- Apply to FEM Program

 

Now a day, FEM programs are supporting the partial factor function, and it will be automatically considered factored values in the FEM analysis. But, there is something that we need to make engineering judgment. For example, FEM analysis for excavation works.
“where do we need to apply partial factor during the excavation stage?”

 

There are different concepts from different engineers as below,

If the original analysis stage is,

Original-analysis-stage

 

Concept 1) Perfectly consider design approaches to analysis stage

 

[Normal Case]   [DA1C1 Case]   [DA1C2 Case]

Initial Stage

Initial Stage

Initial Stage

Cast RW and Surcharge

Cast RW and Surcharge

Cast RW and Surcharge

1st Excavation

1st Excavation

1st Excavation

Install 1st Reinforcement

Install 1st Reinforcement

Install 1st Reinforcement

2nd Excavation

2nd Excavation

2nd Excavation

Install 2nd Reinforcement

Install 2nd Reinforcement

Install 2nd Reinforcement

Final Excavation

 

Final Excavation

 

Final Excavation

 

 

Concept 2) DA1C1 is assumed by SLS (Serviceability Limit State) case and partially consider design approaches to analysis stage

 

[DA1C1 Case]   [DA1C2 Case]

Initial Stage

 

 

Cast RW and Surcharge

 

 

1st Excavation

→ 

1st Excavation

Install 1st Reinforcement

 

 

2nd Excavation

→ 

2nd Excavation

Install 2nd Reinforcement

 

 

Final Excavation

Final Excavation

 

From the above concepts, we cannot say whether it is correct or not. Those are done by engineering judgment from the geotechnical engineer who is carrying out the FEM analysis with partial factor.

And from concept 2), Applying surcharge and excavation stages are extracted as substages. Those stages are critical stages from the FEM analysis so that ULS (ultimate limit state) will apply to those stages. It is just for your reference, and no need to apply forcibly.

 

 

Topics #Partial Factor Eurocode7 Finite Element Method Ultimate Limit State Singapore National Annex to Eurocode 7 Limit State Design

MIDAS GEO TEAM

Written by MIDAS GEO TEAM

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