ASCE 37-14 Design Loads on Structures During Construction - Interpretation of Seismic Requirements

[ctb74]

We are tasked with temporarily bracing an existing building during retroftit work. We are getting some push back on what seismic loads to use for the bracing design and want to gain a better understanding of ASCE 37-14 Section 6.5 Earthquake. The project is in California.

Section 6.5.2 states: The mapped values for Ss and S1 may be multiplied by a factor less than 1 to represent the reduced exposure period, but the factor shall not be less than 0.20.
The commentary states C6.5.2: The ground motion response acceleration with a 2% chance of exceedance in one year (a mean recurrence interval of about 50 years) (Ss*) ranges from approximately 5% to 20% of the value mapped as having a 2% chance of being exceeded in a 50-year period (a mean recurrence interval of about 2,475 years). The percentage is in the upper portion of the range in the more seismically active areas. A value of 20% is selected as representative of this ratio...

We interpret this to mean if the structure is relying on the temporary bracing for a year or less, then a 0.20 factor should be applied to the mapped seismic values for Ss and S1. Does anyone know how to go about calculating the reduction factor for a structure that would be relying on the temporary bracing for 2 years? For 3 years? Does anyone have any good references on this subject?

 

[Lomarandil]

I agree with your interpretation for one year -- I'll have to think back to remember about calculating the recurrence interval conversion.