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TR.31.2.7 Colombian NSR-98 Seismic Load

Used to define and generate static equivalent seismic loads as the 1998 edition of the Colombian seismic code, Reglamento Colombiano de Construcción Sismo Resistente (NSR-98),Normas Colombianas de Diseño y Construcción, 1998, Asociación Colombiana de Ingeniería Sísmica.

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:

ParameterDescription
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:

ParameterDescription
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.

Note: For additional details on the application of a seismic load definition used to generate loads, refer to TR.32.12.2 Generation of Seismic Loads.

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:

S a = { A a I ( 1.0 + 5.0 T )  when  0 ≤ T ≤ 0.3  sec 2.5 A a I  when  0.3 < T ≤ 0.48  sec 1.2 A a S I T  when  0.48 < T < 2.4  sec A a I / 2  when  2.4 sec < T
where
Aa
=
Seismic Risk factor
S
=
Soil Site Coefficient
I
=
Coefficient of Importance

Base Shear, Vs is calculated as:

Vs = W × Sa

where
W
=
Total weight on the structur

The total lateral seismic load, Vs, is then distributed by the program among different levels as:

Fx = Cvx × Vs

where
Cvx
=
W x h x K ∑ i = 1 n ( W x h x K )
Wx
=
Weight at the particular level
hx
=
Height of that particular level
K
=
1.0 when T ≤ 0.5 sec

0.75 + 0.5T when 0.5 < T ≤ 2.5 sec

2.0 when T > 2.5 sec

Parent topic: TR.31.2 Definitions for Static Force Procedures for Seismic Analysis
Related conceptsRelated reference