Introducing the long period parameter in ibc2012

[zthaer]

Hello,
Im wondering why is the long period parameter Tl introduced in ibc2012 ? And what's the effect of not considering it in design response spectrum ,?

Thank you .

[huffte]

TL defines the period at which spectral acceleration transitions from a function of 1/T (constant spectral velocity) to a function of 1/T^2 (constant spectral displacement). This is important in displacement based seismic design because the parameter TL determines the maximum possible spectral displacement. If it is ignored in design and the effective (not initial, but effective) period is larger than TL, you will overestimate deflections, possibly by a large amount.

I leave it to the administrators to determine if the is forum is the proper place for non-SeismoSoft-related seismic questions.

I hope this answer helps clear it up zthaer. Best of luck with your work. Kind regards. - Tim

[zthaer]

Hay tim ,
Well i think its totally related to our subject in get most of the software and interpret the results , on the other hand i m asking about the origin of it , does the new response spectrum represent anew parameter by introducing Tl , in addition to all others factors , seems the ductility plays a great role in that portion of the curve

Thanks

[huffte]

Hi zthaer. For periods up to TL, there is no change in the spectral shape. For periods longer than TL there is a distinct and significant decrease in the spectrum. This is more in line with true behavior of ground shaking during earthquakes. In fact, there are additional periods still undefined in the codes - (a) the period at which spectral displacement begins to descend from its maximum, and (b) the period at which spectral displacement becomes equal to PGD, the maximum ground displacement.

For my region TL is 12 seconds currently. So the effect is probably nil. However, for regions where TL is 4 seconds or similar, then the effect is more pronounced.

Yes. You are correct, zthaer. The parameter is very important for structures responding inelastically. TL is identical to the 'corner period' referred to in direct displacement based design (DDBD) procedures.

Enjoy what's left of 2014, zthaer.

[zthaer]

Hay Tim ,
Well explained friend , and i think maybe re analysing the attenuation relationships with in more and test related accurate manner gives anew factors such what's you mentioned .

And about the joy, sure i will , searching for a good plans any suggestions [8D],

Best of wishes