Inquiry about "Fundamental Principles" of EC8 (No-collapse & Damage limitation) 1

[M.Honda]

Greetings, all!
Pardon if this seemed a bit basic question as I do not own such profound knowledge neither in seismic analysis nor the Eurocode.

In the Eurocode 8, part 1, Clause 2.1 (1P) for the Fundamental Requirements states that structures in seismic regions shall be designed to fulfill the requirements of (No-collapse) and (Damage limitation) and quoted as follows:
"-No-collapse requirement:
The structure shall be designed and constructed to withstand the design seismic action defined in Section 3 without local or global collapse, thus retaining its structural integrity and a residual load bearing capacity after the seismic events. The design seismic action is expressed in terms of:
a) the reference seismic action associated with a reference probability of exceedance, Pncr, in 50 years or a reference return period, Tncr, and;
b) the importance factor (gamma)to take into account reliability differentiation.

-Damage limitation requirement:
The structure shall be designed and constructed to withstand a seismic action having a larger probability of occurrence than the design seismic action, without the occurrence of damage and the associated limitations of use, the costs of which would be disproportionately high in comparison with the costs of the structure itself. The seismic action to be taken into account for the "damage limitation requirement" has a probability of exceedance, Pdlr, in 10 years and a return period, Tdlr. In the absence of more precise information, the reduction factor (v) applied on the design seismic action in accordance with 4.4.3.2(2) may be used to obtain the seismic action for the verification of the damage limitation requirement."

My question is, does the context mean the structure is FIRSTLY designed with accordance to No-collapse requirement and THEN checked for serviceability according to Damage limitation requirement? Is it a similar process to design for strength (ULS) and check for serviceability (SLS)?
In other way, let's say I'm required to conduct a response spectrum analysis, do we build the response spectrum function according to (No-collapse condition) and run the analysis then later interstory drifts are checked from the results of the same model? Or do we build another model with a different response spectrum function following (Damage limitation requirement) and then serviceability is accordingly checked?

Second question is, if my structure return periods different from those recommended by the code, how can I include such differences in the analysis? Is it in terms of different Importance factors?

Pardon me again for the kinda basic question, I'm just shifting to another new codes than I get used to and I am eager to know the philosophy behind each.

Thanks for your time reading the post!

If you do not see it, you cannot design it!

 

[BridgeSmith]

I'm not familiar with the Eurocode, so I can't help you with the second question.

As to the first part of the first question, it appears you have to meet both criteria - no collapse due to the design seismic event and limited damage due to the prescribed smaller seismic event. Which criterion will govern the design could depend on many factors, with a significant possibility that each will control the design of different components of the structure. Which would be the most efficient to start with is likely not worth spending much time contemplating - either you have a fairly good idea about which aspect will govern, or you don't. If you don't, probably the most efficient thing to do is just pick a place to start and dive in.

I'm also not familiar with the design of buildings, so it may be different than what we do for bridges. Anyway, the response spectrums for bridges don't really change shape due to the magnitude of the seismic event; it's just a matter of scale. The period (stiffness) of the structure also doesn't change significantly for different magnitudes of loading, so the same model works over a broad range of earthquake magnitudes.



Rod Smith, P.E., The artist formerly known as HotRod10