Seismic Test & Analysis Webinars

This is a work-in-progress…

I am creating a series of webinars with Matlab exercises for seismic testing.

Here are the slides.

Telcordia Technologies Generic Requirements GR-63-CORE:  Bellcore_GR_63_Core.ppt
This unit contains an alternative waveform for VERTEQII.

CEI.IEC 980, Recommended practices for seismic qualification of electrical equipment of the safety system for nuclear generating stations:  CEI/IEC 980: 1989

IEEE Std 693-2005, Recommended Practice for Seismic Design of Substations: IEEE_693_sine_beat.pptx

IEEE Standard for Seismic Qualification of Equipment for Nuclear Power Generating
Stations: IEEE_std_344.ppt

Matlab script: Vibrationdata Signal Analysis Package

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See also:

Cummins Generator Seismic Shaker Test

Earthquake Conference

Seismic Shock

Webinar 47 – Shock Response Spectrum Synthesis, Special Topics

Seismic Peak Ground Acceleration

Some Earthquake Engineering Terminology

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– Tom Irvine

Hypersphere SRS

hsrs

Figure 1. El Centro Earthquake 1940, Peak Pseudo Velocity, 36.4 in/sec
 
Launch vehicle and spacecraft equipment must withstand pyrotechnic shock from stage separation and other flight events. Civil engineering structures and equipment must survive seismic events. There are many other examples where military, automotive, telecommunication and other equipment must be designed and tested to meet shock requirements derived from field or flight data. The specification is commonly given as a shock response spectrum (SRS). An SRS may be calculated for each orthogonal input axis, assuming the availability of triaxial accelerometer data. Each axis may thus have a separate specification. Alternatively, a maximum envelope can be drawn over the three SRS curves and then applied as a uniform specification to each orthogonal axis.

The uniform enveloping method, however, can underestimate the maximum resultant shock when all possible orthogonal axes sets are considered. The purpose of this paper is to introduce a hypersphere method to achieve a true maximum SRS.

Paper link:  hypersphere_SRS

The Matlab script for this calculation is included in the GUI package at:
Vibrationdata Matlab Signal Analysis Package

– Tom Irvine

 

Energy Response Spectrum

My colleagues at Sandia National Laboratories have presented some conference papers recently on energy response spectrum.

Here is a paper that I wrote on this topic:  energy_response_spectrum.pdf

Also, I have added the energy response spectrum as an option for acceleration time histories to the Vibrationdata GUI package.

See also:
Shock Response Spectrum
David O. Smallwood Papers
Temporal Moments

More later …

Tom Irvine

IEEE Std 693-2005, Recommended Practice for Seismic Design of Substations

I am currently researching IEEE Std 693…

One of its recommended shaker test methods for power equipment is to use a “sine beat” acceleration time history. The main frequency is selected as the equipment’s natural frequency.

The minimum number of beats is 5 with a minimum of 10 cycles within each beat pulse. There is also a pause between beat pulses.

A problem with this approach is that the corresponding displacement has a stair-step effect for a whole number of cycles. This offset disappears if an extra half-cycle is added. An example would be to use 10.5 cycles.

Here is a slide presentation:  IEEE_693_sine_beat.pptx

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I have added a function for generating IEEE sine beat time histories to the Vibrationdata GUI package.

Matlab script: Vibrationdata Signal Analysis Package

>> vibrationdata > Miscellaneous > Generate Signal > IEEE std 693 Sine Beat

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The package also has a function for generating the Required Shock Spectrum (RSS) levels.

>> vibrationdata > Import Data to Matlab > SRS Library Array > IEEE std 693 RSS, Various

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References

An Implementation of an Earthquake Test, According to the Sine-Beat Method: Sine_beat.pdf

Seismic Considerations of Circuit Breakers: Seismic_Considerations_of_Circuit_Breakers.pdf

IEEE 693 Seismic Qualificaiton of Composites for Substation High-Voltage Equipment: 13_2306.pdf 

– Tom Irvine

Webinar 47 – Shock Response Spectrum Synthesis, Special Topics

Slides & Video:

webinar_47_SRS_synthesis_special_topics.pptx

A high-range Cummins Generator in a Seismic Shaker Test.mp4

Topics:

1. Shaker Table Seismic Testing of Equipment using Historical Strong Motion Data Scaled to Satisfy a Shock Response Spectrum

2. Temporal Moments

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Matlab script: Vibrationdata Signal Analysis Package

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Reference Papers:

quake_syn.pdf

From SRS to Temporal Moments

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– Tom Irvine

Wisconsin Booms

Clintonville, Wisconsin is an inland community, adjacent to Lake Pigeon.

USA Today reported on March 21, 2012 that a series of mysterious booms have been fraying residents’ nerves.

City administrator Lisa Kuss said the booms have roused people from their beds and into the streets — some in pajamas.

“It startled everyone. They thought something had hit their house or a tree fell on their roof,” Kuss said Wednesday. A police dispatcher took more than 30 calls from concerned residents between 5 a.m. and 7:30 a.m.

Possible explanations for the ruckus have been nearly exhausted, she said.

Residents have said they believe the booms come from underground. City officials have checked and rechecked methane levels at the local landfill, monitored water, sewer and gas lines, contacted the military about any exercises in the area, reviewed mining explosive permits and inspected the Pigeon River dam next to city hall.

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CNN reported on March 23, 2012 that the booms were due to a “swarm” of minor earthquakes amplified by the unique bedrock beneath the state of Wisconsin.

Speaking to Clintonville residents Thursday night, Lisa Kuss said the U.S. Geological Survey has determined that “our community did in fact experience an earthquake that registered 1.5 on the earthquake magnitude scale.” That minor quake was measured on Tuesday night by several mobile earthquake monitoring stations that were dispatched to the region, she said.

USGS geophysicist Paul Caruso said that Tuesday’s 1.5 tremor is only the second recorded earthquake in Wisconsin since 1947.

Caruso explained that the rock underneath Wisconsin and in much of the country east of the Rocky Mountains is “very consolidated” and without fault lines. And that means small quakes are actually felt by residents, unlike in California where the energy is absorbed.

Caruso said all seismic shifts generate noise but these sounds cannot be heard during major quakes.

“When seismic waves travel through the ground, they’re moving … faster than the speed of sound and when they hit the surface,” Caruso explained.

“(It) rattles the ground like a speaker … so it’s common for people to hear what they describe as sonic boom sounds accompanying earthquakes. But usually when there’s a big earthquake, people either don’t hear the sounds because the frequency is lower than the threshold of what humans can hear. Or other sounds going on (like) things falling down.”

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Steve Dutch, a geologist at the University of Wisconsin-Green Bay, said a 1.5 magnitude earthquake produces the energy equivalent of 100 pounds of explosives and could produce loud sounds.

But he was reluctant to describe Tuesday’s event as an earthquake, saying the term is generally used to refer to widespread stress in the earth’s crust. What happened in Wisconsin could be near the surface, perhaps caused by groundwater movement or thermal expansion of underground pipes, he said.

Still, Dutch said it was possible that the event could produce a series of sounds over time.

“If you’ve got something causing a little bit of shifting underground, it may take a while for whatever is causing it to play itself out,” he said.

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Clifford Thurber, a seismologist at the University of Wisconsin-Madison who served as a consultant for the city, is still on the fence.

“I won’t be amazed if it turns out to be earthquakes, but it could also be a near surface event, such as rocks fracturing beneath the surface due to erosion from flowing water.”

So far, the booms have only been heard within in a small, cigar-shaped area that encompasses most of Clintonville, Thurber says, suggesting an origin that is close to the surface, a possibility that falls within the uncertainty of the USGS seismic data.

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David Hill is an emeritus scientist with the U.S. Geological Survey in Menlo Park, California. Hill, who has written about such phenomena, said they have been around for a long time and have been reported all over the world.

“Back before the Industrial Revolution, Indians and early explorers talked about booming sounds in the northeast,” he said.

Powerful booms periodically rattle windows on the North Carolina coast. In upstate New York, residents near Seneca Lake call the phenomena the “Seneca Guns.” In Coastal Belgium, the sounds are called “mistpouffers,” or fog belches, Mr. Hill found. In the Ganges Delta and the Bay of Bengal, they are called “Bansal Guns.” People in the Italian Apennines call them “brontidi” or thunder-like, and residents of Shikoku, Japan, have dubbed them “yan.”

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Update:  March 28, 2012

The booming and shaking continues in Clintonville.

Clintonville police say they received about 65 calls Tuesday night, from people reporting three or four loud booms. Officials say the calls came in from 10:35 until 11:40 p.m.

Authorities say the reports came from the same part of the city that has been experiencing the booms for more than a week. Several callers told police that these booms were stronger than those from last week, but no damage has been reported.

Geophysicist John Bellini says he looked at the nearby seismometers and was unable to detect anything Tuesday night.

Seismic Peak Ground Acceleration

The Iwate-Miyagi Nairiku earthquake struck northeast Honshu, Japan, on 14 June 2008.

This earthquake had a moment magnitude Mw 6.9 according to the USGS.

The peak ground acceleration (PGA) had a maximum vector sum (3 component) value of 4278 cm/sec^2 (4.36 G).

This is the highest ever recorded PGA, although other quakes have had higher moment magnitudes.  The Richter and moment magnitudes are a measure of the total energy released by a quake.

The PGA is measured at a point.  It depends on soil conditions, distance from the hypocenter, and other factors.

Reference:

Masumi Yamada et al (July/August 2010). “Spatially Dense Velocity Structure Exploration in the Source Region of the Iwate-Miyagi Nairiku Earthquake”. Seismological Research Letters v. 81; no. 4;. Seismological Society of America. pp. 597–604. Retrieved 21 March 2011.

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Tohoku, Japan Earthquake 2011

The 2011 earthquake off the Pacific coast of Tōhoku was a magnitude 9.0 (Mw) undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST (05:46 UTC) on Friday 11 March 2011.

The largest peak ground acceleration (PGA) of 2.7 G was recorded in the North-South direction at Miyagi prefecture – MYG04 station.

Reference 1

Reference 2

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The highest PGA for earthquakes in the USA was 1.7 G for the 1994 Northridge, California quake, which had a 6.7 moment magnitude.

Reference:  Lin, Rong-Gong; Allen, Sam (26 February 2011). “New Zealand quake raises questions about L.A. buildings.” Los Angeles Times (Tribune). Retrieved 27 February 2011.

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The peak ground velocity (PGV) has a better correlation with structural damage according to some sources.

The largest recorded ground velocity from the 1994 Northridge earthquake, made at the Rinaldi Receiving station, reached 183 cm/sec (72 in/sec).

Reference:  USGS ShakeMap

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Further information is given at:  Vibrationdata Earthquake Engineering Page

– by Tom Irvine

Some Earthquake Engineering Terminology

Response Spectrum

Response spectrum is a plot of the maximum responses (acceleration, velocity, or displacement) of idealized single-degree-of-freedom oscillators as a function of the natural frequencies of the oscillators for a given damping value. The response spectrum is calculated for a specified vibratory motion input at the oscillators’ supports.

Operational Basis Earthquake (OBE)

OBE is a ground motion with 10% probability of exceedance within 50 year period (475 years return period).  The facility is expected to remain operational after the OBE event without damage.  Reference:  NFPA 59A.

Safe Shutdown Earthquake (SSE)

SSE is a Maximum Considered Earthquake (MCE) ground motion with 2% probability of exceedance within 50 year period. Plastic behavior and significant finite movements and deformations are permissible. The facility is not required to remain operational after the SSE event.   Reference:  NFPA 59A.

SSE & OBE Relationship

SSE is the maximum potential earthquake of the selected site, and the OBE will be decided accordingly.

The OBE acceleration is one-half of the SSE value in some regulatory standards.

The OBE acceleration may be less than one-third the SSE value in other references.

Damping

The U.S. Nuclear Regulatory Commission, Regulatory Guide 1.61 gives different damping values for SSE & OBE analysis.  The damping values are higher for the SSE case.

Note that damping is non-linear for seismic response due to joint slipping and other factors.  Higher damping is expected for higher input excitation.

Further information is at:  Vibrationdata Earthquake Engineering Page

– Tom Irvine