Influence of Seismic Scale Factor

DOE-STD-1020-2002

The differences in seismic evaluation criteria among categories in terms of load and

importance factors, limits on inelastic behavior, and other factors by this standard are

summarized below:

From PC 1 to PC 2, seismic design forces are increased. All other factors are held

1.PC 1 and PC 2

the same.

From PC 2 to PC 3, load and importance factors are eliminated, damping is

generally increased, and limits on inelastic behavior are significantly reduced. All

2.PC 2 and PC 3

other factors are essentially the same, although static force evaluation methods are

allowed for PC 2 SSCs and dynamic analysis is required for PC 3 SSCs.

From PC 3 to PC 4, seismic hazard exceedance probability is lowered and a seismic

3.PC 3 and PC 4

scale factor is used. All other factors are held the same.

The basic intention of the deterministic seismic evaluation and acceptance criteria presented in

Chapter 2 is to achieve less than a 10% probability of unacceptable performance for a structure,

system, or component (SSC) subjected to a Scaled Design/Evaluation Basis Earthquake (SDBE)

defined by:

SDBE = (1.5SF) (DBE)

(C-2)

where SF is the appropriate seismic scale factor (SF is 0.9 for PC 3 and 1.25 for PC 4). The

seismic evaluation and acceptance criteria presented in this standard has intentional and

controlled conservatism such that the required risk reduction ratios, RR, and target performance

goals are achieved. The amount of intentional conservatism has been evaluated in Reference

C-20 as that there should be less than 10% probability of unacceptable performance at input

ground motion defined by a scale factor of 1.5SF times the DBE. Equation C-2 is useful for

developing alternative evaluation and acceptance criteria which are also based on the target

performance goals.

It is permissible to substitute alternate acceptance criteria for those criteria defined in Chapter 2

so long as these alternate criteria will also reasonably achieve less than about a 10% probability

of unacceptable performance for the combination of the SDBE defined by Equation C-2 with the

best-estimate of the concurrent non-seismic loads. This relief is permitted to enable one to

define more sophisticated alternate acceptance criteria than those presented in Chapter 2 when

one has a sufficient basis to develop and defend this alternate criteria.

C.2.2

Influence of Seismic Scale Factor

The target performance goals are the basis of the seismic design and evaluation criteria

presented in this standard. For PC 3 and PC 4, target performance goals, PF, of 1x10-4 and

1x10-5, respectively, are met in a more approximate manner as illustrated in this section. The

variability in performance goal achievement can be most significantly attributed to the

uncertainty in the slopes of seismic hazard curves from which DBE ground motion is

determined.

C-8