Eurocode partial safety factors and probability distribution

[SuG89]

Hello,

What is the purpose of using the word 'partial' with safety factors? Is it because different factors are applied to different types of load and materials.

Refer to the attached figure. Can someone please explain this graph to me? What is resistance-load and how was the probability of failure determined?

Best regards,
Su

 

[HTURKAK]

I have copied and pasted the attached figure ;

This is the graph of Resistance - Load (Resistance minus load ) function which is by definition , the performance function (g)...The use of the same graph is misleading..There should be a seperate graph for ( Resistance - Load ) curve with; X axis is probability ,vs Y axis Recurrence..


The Eurocodes use different partial safety factors when different load cases are combined. The actions are combinations of
( Permanent Actions + Prestress Actions + Leading variable Actions + Accompanying variable Actions )

R is the resistance and design resistance Rd = Rk/γm and Ed is design value of effect of actions Ed ≤ Rd

In short , R is the resistance and E the effect of actions

g = R – E and probability of failure Pf = Prob(g ≤ 0)

I will suggest you to look BS EN 1990:2002 +A1:2005 . If you do not have one , you may buy from,

https://shop.bsigroup.com/ProductDetail/?pid=000000000030227154

 

[IDS]

I think the wording used is confusing, in that the term "safety factor" is rarely used in describing the limit state design approach. Factors are applied to increase the design load (load factors) and reduce the design capacity (capacity reduction factors).

The term "partial factors" is usually applied to the capacity reduction factors, because there are two different approaches to applying the factors:

In USA codes the member capacity is calculated using the full specified material strength, then the calculated capacity is factored down with a single reduction factor, which varies depending on the type of action (bending, shear, axial load etc).

In the Eurocode codes the materials have different "partial factors", and the member capacity is calculated using the reduced material strengths.

So the term "partial factors" is usually applied to the Eurocode approach to calculating the member capacity.

Different load types also have different factors, in both Euro and USA codes, so these could be called partial factors, but the term is rarely used in this context, as far as I know.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[klaus.]

Yes..there are different factors to use on loadings...maybe thats why we use the word 'partial'