Use of MCER Spectrum in Lieu of Design Response Spectrum

[JGard1985]

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

 

[HTURKAK]

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.)

 

[bones206]

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

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