UBC seismic structure can withstand what.Richter earthquake? 1

[leeStruct]

Hello, everyone,

Our client in Europe brought a very tough question for us to answer, we designed a structure for them based on UBC seismic zone 3. They want to know, what magnitude of Richter scale earthquake it can resist, Richter 6, 6.5, 6.8 or what so ever. In other words, they want to know a certain relationship between UBC seismic zone designed structure and the Richter scale earthquake it can withstand.

I understand these two conceptions are two totally different conceptions and there is no correlation between these two. Say seismic 3 means the peak ground acceleration z= 0.3g, while, say Richter 6 earthquake means the energy released by the earthquake equals 6 calculated from the formula: ML=lgA-lgA0(delta). But is there possibly an empirical formula to relate this peak ground acceleration to the energy the earthquake relieved?

Thanks a lot for your help.

 

[msquared48]

You might be conservative with a 6, depending...

Normally, in this area, which was a UBC seismic zone 3, PML (Probable Maximum Loss) reports for insurance companies were based on the likely occurrence of a 7.

As to the year of construction of the structure, you would have to gage it's compliance to the current code, highlighting any weaknesses to make such a judgement.

Perslnally, the client may be asking for something he is not willing to pay for to adequately determine...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[asixth]

This thread might have some information

thread507-263864

 

[JoshPlumSE]

I feel confident that all the structures I have designed would be perfectly capable of sustaining a magnitute 8.6 earthquake without any significant damage.

The only caveat is that the epecitenter of the earthquake cannot be located in North America.

Sorry for making light of your question. But, Richter magnitude does not mean much.... You'd be better off deflecting the question and insisting that you reply back with what Modified Mercali Index level the building would be estimated to resist with damage or without damage.

 

[paddingtongreen]

As Josh implies, it is a meaningless question unless it includes the location of the epicenter.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[leeStruct]

Thanks very much for all of your responses. Special thanks to asixth, the document "Nuclear Reactor and Earthquake" in your linked thread does contains a lot of very useful informations. It actually gives a roughly relationship between earthquake magnitude and epicenter ground acceleration with Chart and Equation. The only thing I am still in confusion is that either based on Chart in Fig. 1.7A or (Equation 1.5), a Richter 6 earthquake will roughly produce 0.132g ground acceleration at epicenter, is this acceleration the same thing as the peak ground acceleration given in UBC Code as seismic zone factor z value? if it is the same thing then even a seismic zone 2A will have z=0.15g, which means structures (at epicenter) designed base on UBC seismic 2A can withstand a Richter 6 earthquake, can this be true?

 

[leeStruct]

JoshPlum,

As a structural engineer, I 100% agree with your view point. But in today's real world, "client is the god". give answer like yours to a client will make yourself kicked out of the game.


Now suppose a client reaches you request you to design a building in his hometown, the only information available is that in history this town as epicenter happened a Richter 6 earthquake. My question is base on which UBC seismic zone you will design this building ?

Thanks.

 

[racookpe1978]

It's a "probability" anyway: The building may "withstand" the quake (everybody inside safe during the quake, and able to leave safely after through doors and down the stairs to an exit) but the building is still likely to be damaged. (Interior and sheetrock, pipes, water and sewer connections, ground subheavals and drops, ceilings and non-structural, maybe even structural beams and walls deformation in places or joints that don't themselves get destroyed.) Two equal earthquakes two days apart with both at 5 km distance may not affect the building the same way. A strong quake on Monday may be followed by a weaker quake closer by two days later that causes more damage than the first.

So you have to define a region and limit your damage "prediction": pick a distance from the epicenter, define the magnitude of the quake, and define your probability and extent of damage: safe without collapse, safe for continued use after inspection and evaluation, safe for continued use immediately with no visible damage.

Further, earthquakes almost always have "resonance zones" around the epicenter where the acceleration is much greater locally than in nearby areas. These small rings or zones are also affected by the two kinds of waves (up and down or back and forth motion) and how they add of subtract from each other, and by the type of ground you are on, and the type of ground between you and the quake.

So an epicenter 4 km to the east at 3 km underground will almost certainly not give your building the same accelrations (loadings) as one 4 km to the west that is only 1 km underground.

So, you could say for example: "For an acceleration of abc.def g for z.z seconds (which corresponds to a Magnitude x.x earthquake at yyyy meters from the epicenter on firm ground at your site), this building is designed to be safe for continued occupation and use, but will require inspection by a certified inspector before you can re-enter for work. We expect no damage from a 0.2g acceleration for 5 seconds - which corresponds roughly to a Magnitude 6 earthquake whose surface epicenter is 10 km from your building."

 

[JoshPlumSE]

LeeStruct -

I apologize if you took offense. I was just responding light heartedly on the absurdity of your client's question.

The client is perfectly allowed to ask absurd questions. You just have to educate them a bit when you respond. There is nothing wrong with asserting that you know more about structural engineering than they do.

For example, I would politely point out that Richter magnitude is not a good measure of building safety. Instead, you are more interested with the intensity of the shaking.... This is normally measured by the Modified Mercalli Index. Then I'd talk about what level of MMI and ground acceleration I was planning to design the building for.

If you wanted to go the extra mile, then you could then look up the records for that magnitude 6.0 and point out what MMI (and ground accelerations) this town experienced during that earthquake. Then compare that to your chosen design criteria.

If they wanted to up the design criteria at that point, then fine. But, I'm not going to enter into a contract (verbal or written) based on Richter magnitude. Many lawsuits are based as much on contractual mis-understandings rather than on a failure to perform. That's just my opinion.....

 

[rb1957]

yes, but you could interpret the question as meaning "as measured by the siesmograph down the street".

whilst "the customer is god", could you answer "they measure different things" ... the building code works in terms of lateral g, the siesmogrpah works in lateral displacment ... no?

thinking about it, the siesmograph trace shows the lateral displacement on one axis, and time on the other, no? so you could get to lateral acceleration, but doesn't the richter scale work off maximum displacement ?? i don't know, just thinking (often not a good thing ...)

 

[dgillette]

rb1957 - Please refer to the link that asixth provided above for explanation.

Richter magnitude is a rough measure of the total energy released by the earthquake. The newer magnitude scales that have superseded it in engineering and seismology are more directly related to energy.

There are a number of parameters that can be determined at a specific site, and they are better indications of what a structure would be subjected to (Modified Mercalli, peak horizontal acceleration, spectral acceleration, peak velocity, Arias intensity, etc.). You can say "My building is designed to withstand a PGA of 0.6 g with only cosmetic damage," but it doesn't make sense to say it could withstand a M 6.5 unless you also specify a distance (which could be zero if the epicenter is in the town).

DRG