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Use of MCER Spectrum in Lieu of Design Response Spectrum

Use of MCER Spectrum in Lieu of Design Response Spectrum

Use of MCER Spectrum in Lieu of Design Response Spectrum

(OP)
ASCE 7-16 states:

11.4.7 Risk-Targeted Maximum Considered Earthquake (MCER) Response Spectrum. Where an MCER response spectrum is required, it shall be determined by multiplying the design response spectrum by 1.5.


My Question:
Recognizing that the design response spectrum is 2/3 the MCER response spectrum; my question is how/when is the MCER response spectrum (Section 11.4.7) specified for design in ASCE 7-16? E.g. what other design conditions drive you to 11.4.7? Most of what I notice is that MCER response involves non-linear, base isolated and damped building response.

I'm performing a response spectrum analysis of a non-building structure, Risk Category III

Looking at Figure C11.5-1 "Expected Performance as Related to Risk Category and Level of Ground Motion" it makes sense that the higher the risk category the better the performance for the MCE. I was under the impression that a higher seismic capacity for essential structures was addressed by scaling up the design spectra using the importance factor.


Thank you




RE: Use of MCER Spectrum in Lieu of Design Response Spectrum

Quote (JGard1985

My Question:
Recognizing that the design response spectrum is 2/3 the MCER response spectrum; my question is how/when is the MCER response spectrum (Section 11.4.7) specified for design in ASCE 7-16? E.g. what other design conditions drive you to 11.4.7? Most of what I notice is that MCER response involves non-linear, base isolated and damped building response.

I'm performing a response spectrum analysis of a non-building structure, Risk Category III

Looking at Figure C11.5-1 "Expected Performance as Related to Risk Category and Level of Ground Motion" it makes sense that the higher the risk category the better the performance for the MCE. I was under the impression that a higher seismic capacity for essential structures was addressed by scaling up the design spectra using the importance factor.)


DEAR JGard1985,

I will try to respond your questions as per ASCE 7-16 and FEMA documents,

- The MCER is an event with a 2% probability of exceedance within a 50-year period , and recurrence interval is 2500 yrs
- The design earthquake ground motions is ( IMO,with a wishful thinking ) 2/3 of the corresponding MCER ground motions.This is an event having a 10% probability of exceedance in 50 years with a recurrence interval of 475 years.
- The design design earthquake ground motion ( 475 years event ) is assumed reasonable for the bldgs with importance I=1.0
- If the importance factor Ie=1.5, we multiply MCER with 2/3 to get design design earthquake ground motion , then multiply with ( Ie) ,1.5 to get the same figure.

In you case, if Risk Category III , you are expected to use Ie=1.25 ( refer to table 1.5-2 Importance Factors by Risk Category of Buildings and Other Structures for Snow, Ice, and Earthquake Loads ).

I will suggest you to look C11.5 thru C11.8..

If this respond does not answer to your question, you may provide more info ( for the bldg structure,SDC, seismicity, site etc.)

RE: Use of MCER Spectrum in Lieu of Design Response Spectrum

There happens to be an article in this month’s Structure magazine that delves into this topic.

https://www.structuremag.org/?p=18799

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