TR.31.2.8 Colombian NSR-10 Seismic Load

Used to define and generate static equivalent seismic loads as the 2010 edition of the Colombian seismic code, NSR-10 Reglamento Colombiano Sismo Resistente.

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 f₁ AV f₂ FA f₃ FV f₄ I f₅ ( CT f₆) ( PX f₇) ( PZ f₈) ( ALPHA f₉ )

weight-data

Refer to Common Weight Data for information on how to specify structure weight for seismic loads.

Where:

Parameter	Description
AA f1	A coefficient representing effective peak horizontal acceleration for design (Table A.2.4-3 NSR-10). Must be within the range of 0 to 0.5 (inclusive) or the output will indicate an error.
AV f2	A coefficient representing the effective peak horizontal velocity for design (Table A.2.4-4 NSR-10). Must be within the range of 0 to 0.5 (inclusive) or the output will indicate an error.
FA f3	The dimensionless amplification factor that affects the acceleration in the short periods due to the effects site (Table A.2.4-3 NSR-10). Must be within the range of 0 to 3.5 (inclusive) or the output will indicate an error.
FV f4	The dimensionless amplification factor that affects the acceleration in the intermediate periods due to site effects (Table A.2.4-4 NSR-10). Must be within the range of 0 to 3.5 (inclusive) or the output will indicate an error.
I f5	The importance factor (Table A.2.5-1 NSR-10). Must be within the range of 1 to 1.5 (inclusive) or the output will indicate an error.
CT f6	Optional CT value to calculate time period. (Table A.4.2-1 NSR-10)
PX f7	Optional Period of structure (in sec) in X-direction to be in lieu of fundamental period of the structure
PZ f8	Optional Period of structure (in sec) in Z-direction to be in lieu of fundamental period of the structure
ALPHA f9	Exponent used in calculating the approximate period, T_a (Table A.4.2-1 NSR-10).

Generation of NSR Seismic Load

General format to provide Colombian Seismic load in any load case:

LOAD i

COLOMBIAN LOAD {X | Y | Z} (f₁₀) (ACCIDENTAL f₁₁)

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.

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-10:

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 NSR-10

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.2.6-1 in the code):

S_{a} = \begin{matrix} 2.5 A_{a} F_{a} I (0.4 + 0.6 \frac{T}{T_{0}}) when T < T_{0} \\ 2.5 A_{a} F_{a} I when T_{0} \leq T < T_{C} \\ 1.2 A_{v} F_{v} \frac{I}{T} when T_{C} \leq T < T_{L} \\ 1.2 A_{v} F_{v} T_{L} \frac{I}{T^{2}} when T > T_{L} \end{matrix}

where

$T_{0}$	=	$0.1 \frac{A_{v} F_{v}}{A_{a} F_{a}}$
$T_{C}$	=	$0.48 \frac{A_{v} F_{v}}{A_{a} F_{a}}$
$T_{L}$	=	$2.4 F_{v}$
A_a	=	Seismic Risk factor
S	=	Soil Site Coefficient
I	=	Coefficient of Importance

Base Shear, Vs is calculated as

V_s = S_aW

where

Total weight on the structure

The horizontal seismic force, F_x, at any level x is calculated by the program as:

F_x = V_sC_vx

where

$C_{v x}$	=	$\frac{W_{x} {F_{x}}^{k}}{Σ (W_{x} {F_{x}}^{k})}$
W_x	=	Weight at the particular level
k	=	the exponent related to the fundamental period, T, of the building; $k = \begin{matrix} 1.0 when T \leq 0.5 \sec \\ 0.75 + 0.5 T when 0.5 \leq T < 2.5 \sec \\ 2.0 when 2.5 \sec \geq T \end{matrix}$

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

Related reference	Related topics
TR.31.2.7 Colombian NSR-98 Seismic Load	V. NSR-10 Static Seismic Short Structure