Triggering Threshold Value For Earthquake Detection System

[JoeH78]

Dear ALL,

I'm a structural engineer and I've been asked to provide the threshold value of earthquake to be feeded to the earthquake detection system. I will appreciate the hepl of those who has previous experience on that.

As you know in order to simulate the earthquake and forces excited on structure we normally calculate the earthquake as equivalent base shear or as ground shaking acceleration as function of weight of structure. But how to correlate that to provide the input for the earthquake detection system. I'll appreciate your guidance.

 

[r13]

Are you using sensor to detect motion, then feed the info to the control system? Remember, during real event, the motion is random, within a short seconds, you shall see stress reversal in both horizontal and vertical directions. The info is more useful, if your detector is under interior column that without direct influence from wind.

 

[WARose]

What is the purpose of this detection system? The answer to that question has a big impact on the setting.

 

[JoeH78]

Are you using sensor to detect motion, then feed the info to the control system? Remember, during real event, the motion is random, within a short seconds, you shall see stress reversal in both horizontal and vertical directions. The info is more useful, if your detector is under interior column that without direct influence from wind.

Yes they will use the sensors and they said that they already installed that system and waiting for my input. It is R.C. sturdy structure ( industrial building) and I believe that wind loading is not the governing case when compared to the other equipment loads. IMHO I think that instead of stress I have to use ground motion and the PGA ( Peak ground acceleration Value ) should be enough for that purpose, definitely I will observe the drastical change of acceleration from direction to the other, but it should be normal to the nature of quake.

P.S. I'm planing to pay a visit to site to see that sensor as well.

 

[JoeH78]

What is the purpose of this detection system? The answer to that question has a big impact on the setting.

They said they will use to put the elevator in out of order mode in case of earthquake. If detector detects an earthquake then elevator will reach to its closest floor level to stop and then it will open its doors and will not function any more as long as not being interefered by operator.

 

[3DDave]

This looked interesting; it's not a drop in product and the design of the building dictates the level allowable:

https://hackaday.com/2019/07/06/earthquake-detection-on-a-chip/#comments

Give the chip maker a call and it's likely they have made contacts that can help with particular questions and any companies looking to sell a solution.

 

[JoeH78]

This looked interesting; it's not a drop in product and the design of the building dictates the level allowable:

https://hackaday.com/2019/07/06/earthquake-detecti...

Give the chip maker a call and it's likely they have made contacts that can help with particular questions and any companies looking to sell a solution.

In either way it will require an input from structural engineer.

I have the 0.387g PGA for one of the principal axes when designing the structure, IMHO any value which excceeds that should be set for the triggering value.

 

[r13]

I think you need to determine in what magnitude the device should be activated/triggered, not at the peak, but little above initial motion.

Peak ground acceleration provides a measurement of instrumental intensity, that is, ground shaking recorded by seismic instruments. Other intensity scales measure felt intensity, based on eyewitness reports, felt shaking, and observed damage. There is correlation between these scales, but not always absolute agreement since experiences and damage can be affected by many other factors, including the quality of earthquake engineering.

Generally speaking,
0.001 g (0.01 m/s²) – perceptible by people
0.02 g (0.2 m/s²) – people lose their balance
0.50 g – very high; well-designed buildings can survive if the duration is short.

 

[wannabeSE]

If the seismic detection system is for elevator safety, the threshold should be based on the elevator design, not the building's design. In the USA, ASME A17.1 governs elevator design and seismic switch requirements. These switches activate with 0.15g vertical acceleration and the elevators are also equipped with counterweight derailment sensors. The standard also prescribes the switch's response frequency. These values are coordinated with all of the ASME A17.1's structural and operational requirements.

Bottom line - the earthquake detection system needs to coordinated with the specific building or equipment it serves. There isn't a generic answer or simple equation.

 

[WARose]

Like wannabeSE said, you need to get with the elevator manufacturer. Find out what movement they consider tolerable. Then work backwards to a ground acceleration that could make that happen.