TR.31.2.12 IS:1893 (Part 4) 2015 Codes - LateralSeismic Load
This feature enables one to generate seismic loads per the IS:1893 specifications using a static equivalent approach per Part 4 (2015) for industrial structures.
All industrial (plant and auxiliary) structures like main plants, process plants, water systems, and maintenance workshops are recognized as industrial structures.
SET Z UP
command in
TR.5 Set Command Specification). General Format
DEFINE IS1893 2015 ( ACCIDENTAL ) LOAD PART4
1893-2015-P4-spec
weight-data
Refer to Common Weight Data for information on how to specify structure weight for seismic loads.
where
1893-2015-P4-spec = ZONE f1 RF f2 I f3 { SS f4 | SA f11 } (ST f5) ( { DM f6 | DF f12 } ) (PX f7) (PZ f8)
ACCIDENTAL
option should only be used for ST
4
structures.Parameter | Definition |
---|---|
ZONE f1 | Zone factor based on Table 14 (Clause 7.3.2) FOR 5% damping and Table 15 for Other damping Ratios. |
RF f2 | Response Reduction factor. Refer Table 4 (Clause 8.6). |
I f3 | Importance factor as per Table 3 (Clause 8.5). |
SS f4 |
Soil Type as per Annex B. (Clause 16) (Use if
the SA parameter is not specified).
Note: Use either
SS or
SA to specify site
conditions. If both parameters are specified, SS is
ignored. |
ST f5 |
Structure Type as per Clause 8.1..
|
DM f6 |
Damping ratio to obtain multiplying factor for
calculating Sa/g for different damping. If no damping is
specified 5% damping (default value 0.05) will be considered
corresponding to which multiplying factor is 1.0. Damping is
considered to be 5% for RC structures and 2% for Steel structures (Refer
Table 2). Refer Clause 9.4 of IS:1893(Part 5) -2015.
Note: Use either
DM or
DF to specify
damping. If both parameters are specified, DM is
ignored. This should be a value between 0 (zero) and 1.0, inclusive. For example, 7% damping should be specified as 0.07. |
PX f7 | Optional period of structure (in sec) in X direction. If this is defined this value will be used to calculate Sa/g for generation of seismic load along X direction. |
PZ f8 | Optional period of structure (in sec) in Z direction. If this is defined this value will be used to calculate Sa/g for generation of seismic load along Z direction. |
SA f11 |
Average response spectral acceleration
coefficient corresponding to site specific spectra. Refer to Clause
7.3. Use if SS is not
specified.
|
DF f12 | Multiplying factor for calculating Sa/g. |
Notes
-
If the
ACCIDENTAL
option is specified for anST 4
structure, the accidental torsion will be calculated per the IS 1893 specifications. The value of the accidental torsion is based on the center of mass for each level. The center of mass is calculated from theSELFWEIGHT
,JOINT WEIGHT
, andMEMBER WEIGHT
commands you have specified. TheACCIDENTAL
option is not applicable to other structure types.The
ACCIDENTAL
option along with accidental eccentricity factor (generally 0.05 as per IS 1893 code) needs to be provided in the 1893 seismic primary load case (i.e.,1893 LOAD X / Z f1 ACC f3
). f2 can be negative. See TR.32.12.2 Generation of Seismic Loads -
By default, STAAD.Pro calculates natural periods of the structure in both X and Z directions respectively which are used in calculation for seismic force at each node. If
PX
andPZ
are included, the program will consider these values for calculation of average response acceleration coefficient. IfST
is used instead ofPX
andPZ
values, then the program will calculate natural period using the Rayleigh method.
Example
DEFINE IS1893 2015 LOAD PART4
ZONE 0.36 RF 5 I 1.25 SS 1 ST 1 DM 0.05
JOINT WEIGHT
39 60 80 WEIGHT 100
LOAD 1 LOADTYPE Seismic TITLE SS_(+X)
1893 LOAD X 1
LOAD 2 LOADTYPE Seismic TITLE SS_(+Z)
1893 LOAD Z 1
LOAD 3 LOADTYPE Seismic TITLE SS_(+Y)
1893 LOAD Y 1
Methodology
The seismic force at each node is computed by STAAD.Pro for building structures as per IS: 1893 (Part 4) 2015:
- You provide seismic zone coefficient and desired
1893 specs through the
DEFINE 1893 2015 LOAD PART4
command. - The program calculates the structure period, T using the Rayleigh method.
- The program calculates Sa/g utilizing T.
- Calculate Ah from section 7.3.
- The program calculates V from the
above equation at each node corresponding to the product of the seismic
coefficient and mass at each node. W is obtained from mass table data
entered via
SELFWEIGHT
,JOINT WEIGHT
(s),MEMBER WEIGHT
(S), and/orREFERENCE LOAD
you provide through theDEFINE 1893 2015 LOAD PART4
command.
See TR.32.12 Generation of Loads for additional information.