G. Performance Objective 3B (Immediate Occupancy for Essential Facility)
(See Flow Chart in Figure 4-4)
Using the mathematical model of the building developed for Performance Objective 1A,
perform a 3D spectral response analysis using Ground Motion B (3/4 x MCE).
para. 5-4e (5) and (6)
Using only fundamental mode responses, calculate combined load effects, displacement of
center of mass at roof level, and base shear.
Calculate DCR' for the structural elements and identify element with highest DCR and any
other elements within 10% of that value.
Determine necessary reduction in seismic effects to reduce highest DCR to 1.0. Reduce the
seismic effects ,base shear, and roof displacement by the seismic effects reduction. Plot base
shear vs. roof displacement.
Modify elements identified in Step 4 by inserting plastic hinges at the yielding ends in the
Repeat the analyses, add the new seismic effects to the reduced seismic effects from the prior
analyses, and repeat Steps 2 and 3.
Determine necessary reduction in the new seismic effects to reduce highest DCR to 1.0.
Reduce the new seismic effects, base shear, and roof displacement by the reduction in the new
seismic effects. Plot the new increment of base shear and roof displacement by superposition
on prior plot.
Repeat Steps 5,6,and 7 until plot results in undesirable response or failure of critical elements.
Idealize the plot to determine Vy, 0.6Vy, and Ke.
Obtain the elastic fundamental period Ti, from step 2 and calculate the effective fundamental
period, Τe , by Τe = Τi Ki /Ke
Determine appropriate values for coefficients C0, C1, C2, and C3 and for spectral acceleration
Calculate target displacement, δ by δ= C0 C1 C2 C3 Sa
Table 4-7 Step-by-Step Procedure for Enhanced Performance Objective
with Nonlinear Elastic Static Analysis
Sheet 1 of 2