TR.31.2.7 Colombian NSR-98 Seismic Load
This implementation uses a static equivalent approach similar to those outlined by UBC. Depending on this definition, equivalent lateral loads will be generated in horizontal direction(s). The load is based on
The seismic load generator can be used to generate lateral loads in
the X & Z directions for Y up or X & Y for Z up. Y up or Z up is the
vertical axis and the direction of gravity loads (See the
SET Z UP
command in
TR.5 Set Command Specification).
All vertical coordinates of the floors above the base must be positive and the
vertical axis must be perpendicular to the floors.
General Format
DEFINE COLOMBIAN (ACCIDENTAL) LOAD
ZONE f1 ( I f2 S f3)
weight-data
Refer to Common Weight Data for information on how to specify structure weight for seismic loads.
Where:
Parameter | Definition |
---|---|
ZONE f1 | Seismic Risk factor |
I f2 | Soil Site Coefficient |
S f3 | Coefficient of Importance |
Generation of NSR Seismic Load
General format to provide Colombian Seismic load in any load case:
LOAD i
COLOMBIAN LOAD {X | Y | Z} (f4) (ACCIDENTAL f5)
Where:
Parameter | Definition |
---|---|
LOAD i | load case number |
COLUMBIAN LOAD { X | Y | Z } f4 | factor to multiply horizontal seismic load |
ACCIDENTAL f5 | multiplying factor for Accidental Torsion, to be used to multiply the accidental torsion load (default = 1.0). May be negative (otherwise, the default sign for MY is used based on the direction of the generated lateral forces). |
If the
ACCIDENTAL
option is specified, the accidental torsion
will be calculated per the specifications. The value of the accidental torsion
is based on the center of mass for each level. The center of mass is calculated
from the
SELFWEIGHT
,
JOINT WEIGHT
, and
MEMBER WEIGHT
commands specified for this load
definition.
Example
Using NSR-98:
DEFINE COLOMBIAN LOAD
ZONE 0.38 1.0 S 1.5
JOINT WEIGHT
51 56 93 100 WEIGHT 1440
101 106 143 150 WEIGHT 1000
151 156 193 200 WEIGHT 720
LOAD 1 ( SEISMIC LOAD IN X DIRECTION )
COLOMBIAN LOAD X
Methodology for NSR-98
Seismic zone coefficient and parameter values are supplied by the user
through the DEFINE COLOMBIAN LOAD
command.
The program calculates the natural period of building T utilizing clause 1628.2.2 of UBC 1994.
Design spectral coefficient, Sa, is calculated utilizing T as:
Base Shear, Vs is calculated as:
The total lateral seismic load, Vs, is then distributed by the program among different levels as: