TR.31.2.8 Colombian NSR10 Seismic Load
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 2010 (ACCIDENTAL) LOAD
AA f_{1} AV f_{2} FA f_{3} FV f_{4} I f_{5} ( CT f_{6}) ( PX f_{7}) ( PZ f_{8}) ( ALPHA f_{9} )
weightdata
Refer to Common Weight Data for information on how to specify structure weight for seismic loads.
Where:
Generation of NSR Seismic Load
General format to provide Colombian Seismic load in any load case:
LOAD i
COLOMBIAN LOAD {X  Y  Z} (f_{10}) (ACCIDENTAL f_{11})
Where:
Parameter  Description 

LOAD i  load case number 
COLOMBIAN LOAD { X  Y  Z } f10  factor to multiply horizontal seismic load 
ACCIDENTAL f11  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 NSR10:
DEFINE COLOMBIAN 2010 LOAD AA 0.2 AV 0.15 FA 0.85 FV 1.01 I 1.12 JOINT WEIGHT 6 TO 15 21 TO 30 36 TO 45 WEIGHT 10 LOAD 1 COLOMBIAN LOAD X 1.2
Methodology for NSR10
The time period, T, is determined using the Rayleigh method (see section TR.34.1 Rayleigh Frequency Calculation) or specified directly in the X and Z directions with the optional parameters PX and PZ, is used to calculate spectral coefficient, S_{a}, as (refer to Fig. A.2.61 in the code):
=  
=  
=  
=  
=  
= 
Base Shear, Vs is calculated as
V_{s} = S_{a}W 
= 
The horizontal seismic force, F_{x}, at any level x is calculated by the program as:
F_{x} = V_{s}C_{vx} 
=  
=  
=  $k=\begin{array}{c}1.0\phantom{\rule{0ex}{0ex}}\text{when}\phantom{\rule{0ex}{0ex}}T\le 0.5\phantom{\rule{0ex}{0ex}}\mathrm{sec}\\ 0.75+0.5T\phantom{\rule{0ex}{0ex}}\text{when}\phantom{\rule{0ex}{0ex}}0.5\le T2.5\phantom{\rule{0ex}{0ex}}\mathrm{sec}\\ 2.0\phantom{\rule{0ex}{0ex}}\text{when}\phantom{\rule{0ex}{0ex}}2.5\phantom{\rule{0ex}{0ex}}\mathrm{sec}\ge T\end{array}$
