UBC Static and Dynamic analysis for earthquake(Open Discussion for very important points)

The 'Base' is defined as ground floor (level 1) because of the perimeter wall and the diaphragm that resist the lateral load causing reduction in bending moment below the ground lever and shear reversal and amplification below the ground level (in basement levels).

There are a lot of different definition of Base depending of the building configuration, see your local code.

Imagine a cantilever wall and restraint it near the root.

Thank you so much.

Your word are deep and I need more simple explanation to fit in my head please
also please consider all the questions i asked

1.why we use calibration between static and dynamic
2.the static case is dependent on fundamental period not all modes ,so from my point of view why we calibrate to static
3.last question why we calibrate from ground floor.

Please excuse me,but consider me as small child who want deeply understand this

Thank you again

drastixxx said:

why we calibrate to static

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Dynamic analysis methods often result in lower seismic design actions when compared to static procedures. The folks responsible for the development of the code have decided that the extent of such improvements should be limited to a particular ratio of the static procedure values. That's all that there is too it. It's just a judgement thing. The code provision is not a calibration but, rather, a statement of minimum strength expectation. Note that the base shear scaling does not apply to drift calculations.

drastixx said:

why we calibrate from ground floor.

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The "calibration" is performed at the seismic base because that that is where higher mode effects will usually have the least effect on seismic story shear. Thus, the base is a logical choice for an apples to apples comparison.

One way to think of the seismic base is as the vertical location where the acceleration of the building matches the acceleration of the ground. Obviously, in many structures with deep, expansive basements, that location is likely to be close to the ground floor level.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

Note that the base shear scaling does not apply to drift calculations

This mean I have to check drift purely form Spect x and spect y without calibration?? (+where is your reference) in UBC?

The "calibration" is performed at the seismic base because that that is where higher mode effects will usually have the least effect on seismic story shear. Thus, the base is a logical choice for an apples to apples comparison.

One way to think of the seismic base is as the vertical location where the acceleration of the building matches the acceleration of the ground. Obviously, in many structures with deep, expansive basements, that location is likely to be close to the ground floor level.

This portion I didn't get it, however my interpretation is if the retaining wall under ground is connected with diagram and shear walls,so the load will be transferred and concentrated in retaining walls ,leaving the core with insignificant load, in this case we can ignore the earthquake in basement floors as well as calibrate for ground floor(I am not quite sure, but this how my mind is thinking)

OP said:

This mean I have to check drift purely form Spect x and spect y without calibration?? (+where is your reference) in UBC?

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Yes. I do not know of a particular UBC reference for this.

OP said:

This portion I didn't get it,

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Welcome to the club. In my opinion, treatment of basement conditions is the most frustrating part of lateral design. There is great diversity of opinion on the subject and an even greater diversity of practice. You should, however, be careful about assuming that everything is honky dory in your shear walls below grade (PicoStruc's comment). Refer to the following:

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I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

@drasticxx

check the ASCE seismic provisions, that's where it mentions [as KootK said] that if you're going to make a reduction of the applied shear forces, you have to make the same reduction in drift (a bit to counterbalance damage to the structure due to ductility)

As for the shear in the base

You'd ignore it so there wouldn't be an applied shear at the basement floors but you'd still have to deal with the transferred shear from the upper stories. The treatment of applied shears is of course dependent on structure-soil interactions,on whether you can actually say that the building's basement is indeed confined, like PicoStruc said, it's an interesting topic.


@KootK

How many documents are there in your library ?

sponton said:

How many documents are there in your library?

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Clever. 999,999? Just kidding. About 3,500. I set my automated filing app up with considerable room to grow. I plan to read voraciously in retirement.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

@KootK

Can you expand upon your document filing system? I am trying to find a good solution for my personal and our office libraries.

@KootK, yeah I second BadgerPE notion, I would like to organize mine as well, it's already hell and I don't have a tenth of your amount of documents

I use a Microsoft Access database that allows for:

1) Semi-automated filing.
2) Customizable tagging.
3) Very powerful searching.
4) Push button display of PDF docs.
5) Retrieval independent of doc location.

It's funny that you should ask BadgerPE. Every few months, someone here asks me about my filing system. Yesterday while eating lunch I was contemplating posting a cleared out version of the database here for other people to use or improve. I'm not looking to show off or anything. I've just found my system to be incredibly useful to me and when I think about how I could best make a meaningful contribution around here, that's it.

The tough part of sharing my database is that there's no user's manual. And I'll never get around to writing one. If I had a few members here who were committed to giving it a go, I thought that I could just post the file here with some incomplete instructions and, together, we could fill in the blanks via question and answer and turn the thread into a living user's manual of sorts.

If I were to do this, would you be interested in participating BadgerPE? This would represent a fair bit of work for me so I'd like to get buy in from at least 3-5 members before I embark on the project. I harbour a special love for WI so it would be great to have you as an early adopter.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

I volunteer given the unorganized heap that is my paper and electronic documents.

I'd like to check it out too.

I would love to, but right now many in our office, including myself, do not have access to Access (pun intended). I will be working on that in the near future.

BadgerPE said:

I would love to, but right now many in our office, including myself, do not have access to Access (pun intended)

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?#@*&%!

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.