Floor Acc. Histories for Shake Table Testing

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rashid
Posts: 26
Joined: 05 Apr 2014, 16:27
Location: Christchurch, New Zealand

Floor Acc. Histories for Shake Table Testing

Post by rashid » 18 Jan 2019, 03:22

Hi everyone,

I want to generate artificial floor acceleration response histories for shake table testing of non-structural elements. My target response spectrum is from ICC- AC -156, which establishes acceptance criteria for seismic qualification testing of NSEs.

1. The ICC 156 requires a build, hold, and decay of 5, 15 and 10 seconds. Is the trapezoidal function, in SeismoArtif, the correct choice to address this requirement?

2. A survey of literature on testing of NSEs shows that the Artificial Accelerogram Generation (Gasparini & Vanmarcke) is mostly used. Any recommendations regarding the options in SeismoArtif for this specific job?

Best regards,
Rashid

huffte
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Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: Floor Acc. Histories for Shake Table Testing

Post by huffte » 18 Jan 2019, 12:58

Hi rashid. Without a knowledge of your governing document, I cannot attest to the definitions of rise, hold, and decay times. However, it appears that the trapezoidal, the compound (Jennings), and the trigonometric options would all permit you to define rise, hold, and decay.

You may have to try all three options and pick the one which gives the most appropriate results. Frequency domain matching can be difficult, particularly over a wide period range. Always examine the integrated velocity and displacement histories to see if they look realistic - sometimes they won't look at all like typical real histories, having almost harmonic characteristics.

If your criteria limits you to artificial records with the rise, hold, and decay times given, then you are somewhat limited in options. As before, it would be advisable to try all three options for envelope functions. Try to use as narrow a period range for the matching as your criteria will permit. This will increase your chances of success. If there are provisions in your criteria which permit options other than artificial records, SeismoArtif will also produce (a) synthetic generation and adjustment or (b) real accelerogram adjustment to the target spectrum. These would be worth exploring if permitted by the design criteria. Judge success by match to spectral shape over the desired period range, appearance of velocity and displacement histories, and any other criteria requirements.

Interesting work rashid. Best of luck.
Tim Huff

rashid
Posts: 26
Joined: 05 Apr 2014, 16:27
Location: Christchurch, New Zealand

Re: Floor Acc. Histories for Shake Table Testing

Post by rashid » 20 Jan 2019, 23:58

Hi Tim,

Thanks for the detailed response and guidance.

The Rise-Hold-Decay is used to simulate the non-stationary nature of an earthquake event. The standard accepts a linear approximation of the envelope. I'll look into the differences that result from the three options in SeismoArtif. The artificial floor spectra should match the target spectrum over the frequency range of 1.3 Hz to 33.3 Hz or 0.03s to 0.77s (It also mentions a maximum-one-sixth octave bandwidth resolution).

I cannot opt for synthetic motions as that requires parameters like M & R and linking floor motions all the way down to M & R is very complicated.

Thanks.
Rashid

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