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Response Spectra Analysis

Site Class (Section 11.4.3)

Site class A, B, C, D, and E are considered in this implementation.

Site Coefficients and Risk-Targeted Maximum Considered Earthquake (MCER) Spectral Response Acceleration Parameters (Section 11.4.4)

The MCER spectral response acceleration parameters for short periods (SMS) and at 1 s (SM1), adjusted for Site Class effects, are calculated from the following:

SMS = FαSs (11.4-1)

SM1 = FvS1 (11.4-2)

where
Ss
=
the mapped MCER spectral response acceleration parameter at short periods as determined in accordance with Section 11.4.2 (user input)
S1
=
the mapped MCER spectral response acceleration parameter at a period of 1 second as determined in accordance with Section 11.4.2 (user input)

Site coefficientsFα and Fv are given in Table 11.4-1 and 11.4-2, respectively.

If soil properties are unknown in sufficient details, Site class D (subject to the requirements of Section 11.4.4) can be used. If this is the case, the value of Fα cannot be less than 1.20 (see Section 1.4.4).

Table 1. Short-Period Site Coefficient, Fa ( Table 11.4-1)
Site Class Ss ≤ 0.25 Ss = 0.5 Ss = 0.75 Ss = 1.0 Ss = 1.25 Ss ≥ 1.75
A 0.8 0.8 0.8 0.8 0.8 0.8
B 0.9 0.9 0.9 0.9 0.9 0.9
C 1.3 1.3 1.2 1.2 1.2 1.2
D 1.6 1.4 1.2 1.1 1.0 1.0
E 2.4 1.7 1.3 See Section 11.4.8 See Section 11.4.8 See Section 11.4.8
Site Class S1 ≤ 0.1 S1 = 0.2 S1 = 0.3 S1 = 0.4 S1 = 0.5 S1 ≥ 0.6
A 0.8 0.8 0.8 0.8 0.8 0.8
B 0.8 0.8 0.8 0.8 0.8 0.8
C 1.5 1.5 1.5 1.5 1.5 1.5
D 2.4 2.2 a 2.0 a 1.9 a 1.8 a 1.7 a
E 4.2 See Section 11.4.8 See Section 11.4.8 See Section 11.4.8 See Section 11.4.8 See Section 11.4.8

aSee requirements of site-specific ground motions in Section 11.4.8

Two options are available for calculation of design spectral acceleration parameters (i.e., SDS and SD1, see Section 11.4.5):
  • Calculate from Site Properties: Site Class, SS and S1 are required (user-input). In this case, the following conditions are assumed:
    • Short-Period Site Coefficient, Fα:
      • If SS ≥ 1.0 for site class E, coefficient Fα is taken as equal to that of Site Class C (See EXCEPTION 1 in Section 11.4.8).
      • For other cases, the values in Table 11.4-1 are used in calculation of Fα
    • Long-Period Site Coefficient, Fv:
      • If S1 ≥ 0.2 for site class D, use the values given in the table
      • If S1 ≥ 0.1 for site class E, response spectra analysis is not allowed.
      • For other cases, the values in Table 11.4-2 are used in calculation of
  • You can directly enter the values of SMS and SM1. In this case, no need to calculate Fα and Fv

Design Spectral Acceleration Parameters (Section 11.4.5)

Design earthquake spectral response acceleration parameter at short period SDS and at 1 s period SD1 are calculated from the following equations:

S D S =   2 3 S M S (11.4-3)
S D 1 = 2 3 S M 1 (11.4-4)

Design Spectral Acceleration Parameters (Section 11.4.6)

The design response spectrum curve is constructed as follows:
S a = { S D S ( 0.4 + 0.6 T T 0 ) T < T 0 S D S T 0 ≤ T ≤ T S S D 1 T T S < T ≤ T L S D 1 T L T 2 T ≥ T L
where
SDS
=
the design spectral response acceleration parameter at short periods (Eq. 11.4-3)
SD1
=
the design spectral response acceleration parameter at 1-s period (Eq. 11.4-4)
T
=
the fundamental period of the structure, S D 1 S D S
TL
=
long-period transition period provided by the engineer
To
=
0.2 S D 1 S D S
Ts
=
SD1SDS

ASCE 7-16 Design Spectrum Curve

Parent topic: ASCE 7-16