Earthquake design - code says...... 1

[mar2805]

Hi folks!
Does your CODE egsactly says, when, you have to design something for earthquake action?
Im eurocode based but I cant find any info when I should take earthquake actions into account.....

 

[Agent666]

Maybe mention what country you are designing in so someone can point you in the right direction regarding particular use of EC8. I'm guessing but would it be in a particular countries national annex?

But to answer your question, yes most nations codes or building codes should outline when you need to design for earthquakes. Here in New Zealand it's easy because everything is designed for seismic loads.

 

[mar2805]

ok thanx

 

[IRstuff]

Not making sense of your question; you either design for seismic, or not. Once that decision is made, the "when" is when you start the design, isn't it?

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[Agent666]

IRstuff I believe the question is as simple as when or perhaps more correctly whether you need to design for seismic loads in the first place.

Some countries only have certain areas of the country that are seismically active for example and you'd like to think this would be outlined in standards or other national building codes. Some codes may not require seismic design of lower importance structures (i.e. your garden fence or shed for example). There are also exceptions sometimes regarding the design of individual parts of buildings, for example anything less than a certain weight may not require specific design of fixings for seismic loading.

 

[EireChch]

mar2805 - sorry to be blunt but you're wasting peoples time. Agent666 was polite enough to answer your question and also recommended providing some more information so he/she could help more.

Then you reply with "ok thanx"

C'mon Mar, work with us a bit better...give the country, structure type etc. and you will get better answers. Agent666 is willing to try help. Take it when you can get it!

More info = better answers

 

[WinelandV]

I'll bite.

In the ASCE 7 (Minimum Design Loads for Buildings and Other Structures), you are required to determine your S1 and Ss factors (% of gravity, laterally) for your site. From there you manipulate them to their "design" values, plug them into a table and determine what seismic design category you are in. If by some miracle you are in category A, then you have a minimum lateral force of 0.01*W to design for. However, it's likely that wind on the structure will control.

Long story, short: In the US, you need to determine you seismic forces, even if they don't end up controlling the design.

Caveat: each local municipality (village, city, township, county, etc.) can adopt the IBC (and thus the ASCE 7) and amend it as they see fit. So, you could run into a local jurisdiction that says "don't worry about seismic here".

All that being said, I have zero knowledge of Eurocodes. So take this with a grain of salt (if you're even still looking at this thread).

 

[ThomasH]

This may seem strange to some members but Eurocode does not tell you when to do it, only how to perform the design. The "when" should be specified in the national annex (NA).

If there is no seismic parameters defined in the NA when my interpretation would be that seismic design is not required.

I am Eurocode based and have worked with seismic design according to several codes, one of them being Eurocode.

Thomas

 

[kingnero]

@ ThomasH, I consider the NA's to be part of the eurocodes, so they actually do tell you when to take seismic into consideration...
A part of the eurocode is not valid without its national annex!

 

[ThomasH]

@kingnero
Perhaps I was unclear. I agree, the national annex is the part of the Eurocode that specifies how to use the Eurocode in a specific country. But if the national annex hasn't specified a seismic load or if there is no NA for Eurocode 8, I would say it is reasonable to assume that seismic action does not need to be considered.

It may be that there is no NA for Eurocode 8 or that there is no chapter for Eurocode 8 in the NA package. I know that the approach has been used so I am not guessing .

I would say we have the same conclusion from two different points of view.

Thomas

 

[estructe]

You have to always consider quake effects on the structures that you design. Common engineering judgement may be required if seismic loads are considered as not critical, for example when design a floor grillage.

Structural Analysis of 2D Structures software
Static, Dynamic,Linear and Non-Linear Analysis
of frames, trusses, beams etc.

 

[msquared48]

I always design for both seismic and wind to establish in writing which force governs, both in the shear wall design and the connections.

Doesn't matter to me what is required via the codes - it's just good engineering practice.

Mike McCann, PE, SE (WA)

 

[ThomasH]

@msquared48
If the code doesn't give you any information regarding the seismic forces, what seismic forces do you use for the design?

Thomas

 

[klaus.]

The answer is easy
You need to consider if it is necessary for design.....
Code tells you how to consider...but not when to consider
this is up to us as engineers

 

[AaronMcD]

Always consider seismic. That doesn't mean seismic always controls, or even running seismic calcs. Here in SF we still have to consider wind. But it almost never controls the main lateral system. I've gotten permits without showing a single calc for total wind loads (but I always seem to have something designed for wind - parapet, double story window, screen walls, etc).

http://www.hellodwell.design

 

[msquared48]

@ ThomasH:

What code are you using in that there is no guidance for seismic forces?

Mike McCann, PE, SE (WA)

 

[ThomasH]

What code are you using in that there is no guidance for seismic forces?

As mentioned before, the Eurocode tells you how to design but not when. That information can be found in the national annex, and that information includes the seismic properties like accelerations etc.
So if there is no information in the NA, or, if there is no NA regarding seismic, how do you do the design?

Thomas

 

[msquared48]

In similar situations in the States, I have gone to the local jurisdiction for the information I need. If there is no information there then I assume there is little seismic activity in the region and design to a minimum of 7%g. Wind will usually control.

Mike McCann, PE, SE (WA, HI)

 

[ThomasH]

@msquared48
I assume that this is a method to create general robustness in a structure? In the Eurocode that requirement is specified i a specific part.

I would say that "local jurisdiction" in a Eurocode context is the national annex. If you shall design for seismic loads it is specified in the NA.
In the Eurocode there are "known" and "unknown" accidental loads. The design for unknown accidental loads is a general robustness requirement. Rules to avoid an unreasonable consequence for a local damage, that applies for most structures. That you have the known accidental loads, like seismic loads, explosions or vehicle collisions. The known loads shall be treated with applicable methods. Thee is a specific part of Eurocode for seismic loads.

It is actually not very difficult.

Thomas