Io

Fifth floor

Fourth floor

Third floor

Second floor

First floor

FIGURE 21.18 Performance assessment of frame based on LSP evaluation.

Note: IO = element passing immediate occupancy criteria; LS = component failing IO but passing life safety criteria; CP = component failing LS but passing collapse prevention criteria.

Sixth floor

Fifth floor

Fourth floor

Third floor

Second floor

First floor

FIGURE 21.18 Performance assessment of frame based on LSP evaluation.

Note: IO = element passing immediate occupancy criteria; LS = component failing IO but passing life safety criteria; CP = component failing LS but passing collapse prevention criteria.

desired performance objective has not been met. It is, therefore, necessary to redesign the frame and go through an iterative process till the design objective is satisfied.

21.7.2.2 Method II: Deterministic Assessment — NSP (FEMA-356)

The same frame will now be evaluated using a pushover analysis to determine The building model is subjected to a monotonically increasing inverted triangular till the roof drift reaches the target value. The target roof displacement is estimated coefficients:

C0: 1.42 (From table 3.2 of FEMA-356) Q: 1.0 since Te > TS (from Hazard Spectra) C2: 1.0 (from table 3.3 of FEMA-356) C3: 1.0 for positive postyield stiffness

The spectral acceleration at the fundamental period T: 1.45 s is 0.33g. This results in a target displacement of 260 mm (10.22 in.). When the building model is pushed using an inverted triangular lateral load distribution till the roof displacement reaches this value, none of the elements reach their yield value. This means that the plastic rotation demands are zero and, consequently, all elements (beams and columns) satisfy IO performance levels. This is contrary to the findings using linear static analysis.

21.7.2.3 Method III: Deterministic Assessment — LDP (FEMA-356)

A linear dynamic analysis can be accomplished in two ways: using a response spectrum approach or resorting to a full time-history analysis. In this example, the demands were determined using a response spectrum analysis. The moment demands in each element are tabulated, similar to the summary table described for LSP, and the resulting m-factors are calculated. A sample set of values for all the column elements in the first-story level are shown in Table 21.14. For columns, it is also necessary to compute axial force levels since acceptance criteria for columns are a function of the axial demands in the column (see Table 21.14).

expected demands. lateral load pattern using the following

Performance-Based Seismic Design and Evaluation of Building Structures TABLE 21.14 Peak Demands in Columns on First Story Using LDP

Co-factor

Column no.

0 0

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