Earthquake resistance to Eurocode 8 1

[Agent Coconut]

Hi Enginners,

I have a project where the clients has specific several engineering parameter for us beforehand.
The parameter is listed as below:-
- Design Code - Eurocode 8 (Fine)
- PGA = 0.05g (Lesser than National Annex)
- Return period = 2,475 years (Why?)

My question is, Eurocode is based on 475 years for no collapse requirement and 95 years for damage control.
How do I change the equation/coefficient of parameter when come to design when client specific 2,475years?

 

[HTURKAK]

My points ,
- EN 1998 has 6 parts and 1998 Part 1: General rules, seismic actions and rules for buildings ..
- There is a near collapse (NC) limit state concept . It is used as a conservative approximation of structural collapse and in Eurocode 8, Part 3, the NC limit state is defined as follows:
LS of Near Collapse (NC). The structure is heavily damaged, with low residual lateral
strength and stiffness, although vertical elements are still capable of sustaining vertical
loads. Most non-structural components have collapsed. Large permanent drifts are
present. The structure is near collapse and would probably not survive another
earthquake, even of moderate intensity.
- NC limit state is typically based on a mean return period of 2475 years (2% probability of being exceeded in 50 years).

The standards are minimum requirements IMO , provide legal shield for the designer. Moreover , the client / owner has the right to ask more to design with more stringent requirements. Sometimes the owner may ask for designing with higher importance factor .

Suggest you to look to the following doc. (Performance Based Design , performance requirements )

 

[Agent Coconut]

My points ,
- EN 1998 has 6 parts and 1998 Part 1: General rules, seismic actions and rules for buildings ..
- There is a near collapse (NC) limit state concept . It is used as a conservative approximation of structural collapse and in Eurocode 8, Part 3, the NC limit state is defined as follows:
LS of Near Collapse (NC). The structure is heavily damaged, with low residual lateral
strength and stiffness, although vertical elements are still capable of sustaining vertical
loads. Most non-structural components have collapsed. Large permanent drifts are
present. The structure is near collapse and would probably not survive another
earthquake, even of moderate intensity.
- NC limit state is typically based on a mean return period of 2475 years (2% probability of being exceeded in 50 years).

The standards are minimum requirements IMO , provide legal shield for the designer. Moreover , the client / owner has the right to ask more to design with more stringent requirements. Sometimes the owner may ask for designing with higher importance factor .

Suggest you to look to the following doc. (Performance Based Design , performance requirements )

Hi,

Thanks for your insight.
Part 3 is for existing building. Does it applicable in my case where we are designing a completely new structure? or it is a good practices to take into account of the provision of Part 3?
Also, I get confused as following:-
No collapse is 475year while near collapse is 2475years seem confusing as no collapse should require a more critical case but 475 years of return period sound required lesser support than return period of 2,475years?

 

[HTURKAK]

Part 3 is for existing building. Does it applicable in my case where we are designing a completely new structure? or it is a good practices to take into account of the provision of Part 3?
Also, I get confused as following:-
No collapse is 475year while near collapse is 2475years seem confusing as no collapse should require a more critical case but 475 years of return period sound required lesser support than return period of 2,475years?

-It is true that Part 3 is for existing buildings but you can use the same rules to see the performance level of an existing design.
- No collapse requirement should cover operational levels . If the performance is at life safety level , my interpretation is , could be assumed reasonable for very rare event only ( 475 yrs).
- Near collapse level is severe damage . Repair generally not possible. But still collapse is not allowed. ( 2475 yrs)

EC 8 considers setting the 475 year event as the “minimum” for new designs . However If the region has low seismic activity ( your case ) , specifying engineer / owner respresentative may decide that the hazard could be under-predicted by the 475 year event and revise the minimum considered ground motion definition to a 2 % probability of exceedance in 50 years, or a recurrence interval of about 2500 years.

I hope my respond answers to your question and make sense.

 

[Agent Coconut]

-It is true that Part 3 is for existing buildings but you can use the same rules to see the performance level of an existing design.
- No collapse requirement should cover operational levels . If the performance is at life safety level , my interpretation is , could be assumed reasonable for very rare event only ( 475 yrs).
- Near collapse level is severe damage . Repair generally not possible. But still collapse is not allowed. ( 2475 yrs)

EC 8 considers setting the 475 year event as the “minimum” for new designs . However If the region has low seismic activity ( your case ) , specifying engineer / owner respresentative may decide that the hazard could be under-predicted by the 475 year event and revise the minimum considered ground motion definition to a 2 % probability of exceedance in 50 years, or a recurrence interval of about 2500 years.

I hope my respond answers to your question and make sense.

Hi

Yes and I would like to apologise, I just reread and found that I have misinterpreted the wording near collapse which should be more critical.

And yes your answer is definitely the exact answer to my question.

While I am waiting for my client to confirm if the return period of 2,475years requirement is referring to no collapse or near collapse, I would like to ask if he is referring to no collapse, any references on how we modify the ground motion acceleration? is it referring to 3.2.1(3) will do?
I have not yet going thru the reference you share in the previous post but I will read it in this weekend.

Edit as bold above