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)
RSPEC	`RID`	`DCOMB`	`MCOMB`	`CLOSE`	`MMASS`	`RIGRESP`
	`DTISPEC1`	`SCALE1`	`X11`	`X12`	`X13`	`ZPA1`	`FA1`	`FB1`
	`DTISPEC2`	`SCALE2`	`X21`	`X22`	`X23`	`ZPA2`	`FA2`	`FB2`
	`DTISPEC3`	`SCALE3`	`X31`	`X32`	`X33`	`ZPA3`	`FA2`	`FB2`

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)
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)
`MMASS`	Keyword indicating missing mass response is used. Default = blank
`RIGRESP`	Keyword specifying which rigid response method is applied. GUPTA Gupta rigid response method is applied. LINDLEY Lindley-Yow rigid response method is applied. Default = blank
`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
`ZPAi`	Zero Period Acceleration value. 4 No default (Real ≥ 0.0)
`FAi`, `FBi`	Frequency limits indicating a pure periodic response or a pure rigid response. 4 No default (Real ≥ 0.0, `FBi` ≥ `FAi`)

Comments

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.
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.
$F (i + 1) < C L O S E * F (i)$
Where, $F (i)$ and $F (i + 1)$ 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.
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.

ZPAi must be defined for missing mass response or rigid response with Lindley-Yow Method. Missing mass response can be used together with both rigid response methods.

When RIGRESP option is active, the response is divided into periodic part and rigid part in modal combinations. A variable α is introduced as the ratio of the rigid part to the modal response of mode i, hence providing an estimate of the proportion of rigid part of the response.

Rigid part:

R_{r i} = α_{i} R_{i}

Periodic part:

R_{p i} = \sqrt{1 - α_{i}^{2}} R_{i}

Gupta method calculates α based on the frequency. When the frequency is less than FA, it is pure periodic response, so α = 0; When the frequency is greater than FB, it is pure rigid response, so α = 1; When the frequency is between FA and FB, a value [0,1] is adopted for α in the transition range.

Lindley-Yow method calculates α based on the acceleration response spectrum value. When the spectrum value is equal to ZPA, it is pure rigid response, so α = 1; When the spectrum value is less than ZPA it is pure periodic response, so α = 0; When the spectrum value is greater than ZPA, a value [0,1] is adopted for α in the transition range. It is optional to define FA in Lindley-Yow method, and α is 0 as long as the frequency is less than FA.


	ZPA	FA	FB
MMASS	Required
GUPTA		Required	Required
LINDLEY	Required	Optional

Refer to Response Spectrum Analysis in the User Guide for more details.