# RSPEC

Bulk Data Entry Specifies directional combination method, modal combination method, excitation direction(s), response spectra and scale factors for Response Spectrum Analysis.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
RSPEC RID DCOMB MCOMB CLOSE
DTISPEC1 SCALE1 X11 X12 X13
DTISPEC2 SCALE2 X21 X22 X23
DTISPEC3 SCALE3 X31 X32 X33

## Example 1

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
RSPEC 35 ALG SRSS 1.0
7 1.3 0.5 0.5 -1.

## Example 2

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
RSPEC 35 SRSS CQC 0.0
7 1.3 0.5 0.5 -1.
4 2.0 -2 -0.0 -1.
2 17. 0.5 -2.5 -1.

## Definitions

Field Contents SI Unit Example
RID RSPEC identification number. Must be unique.

No default (Integer > 0)

DCOMB Directional combination method.
ALG (Default)
Algebraic.
SRSS
Square root of sum of squares.
MCOMB Modal combination method.
ABS (Default)
Absolute sum.
SRSS
Square root of sum of squares. 2
CQC
Complete quadratic combination.
NRL
Navy Research Laboratory's SRSS.
CLOSE Modal frequency closeness parameter. 2

Default = 1.0 (Real ≥ 1.0)

DTISPECi Response spectrum reference. Identification number of the DTI,SPECSEL entry.

No default (Integer > 0)

SCALEi Scale factor for excitation.

No default (Real <> 0.0)

Xij Components of a vector representing ground excitation i, j = 1..3

## Comments

1. DTISPEC2/SCALE2/X21/X22/X23 and DTISPEC3/SCALE3/X31/X32/X33 are optional ground excitations for multi-directional excitation. The directions of excitation have to be orthogonal to each other and will be reported as error otherwise.
2. When MCOMB = SRSS or NRL, natural frequencies that are close will be summed by the ABS method. The close frequencies are determined using the inequality.
$F\left(i+1\right)

Where, $F\left(i\right)$ and $F\left(i+1\right)$ are successive natural frequencies.

Then, they are combined with other modal contributions in accordance with the specified MCOMB option. Since natural frequencies are in ascending order, CLOSE values should be greater than or equal to 1.0.

3. Response spectra values are defined as a table of frequencies in the X axis and the response spectra in the Y axis in a TABLED1 entry referenced by the DTI,SPECSEL entry. For any modes extracted during the response spectrum analysis that lie within or outside the range of the frequencies defined by the TABLED1 entry, linear interpolation or extrapolation is carried out to determine the corresponding spectral values associated with such modes.
4. Refer to Response Spectrum Analysis in the User Guide for more details.