Seismic Spectrum - NPR 9998 NL



The Dutch Standardization Institute (NEN) has published on December 18, 2015 the latest Dutch Practice NPR 9998 with regards to earthquake resistant buildings. This NPR contains details for the definition of the seismic spectrum.

SCIA Engineer 16.1 enlarged the seismic load library with enhancements regarding the seismic spectrum according with this NPR. The seismic spectrum has been added into the library and it can be easily input by the definition of few primary parameters: geotechnical parameters of the site, structure parameters, spectrum type (elastic or design), PGA component (direction of the earthquake: vertical and horizontal) and behaviour factor q.

In the NEN-NE 1998 and NPR 9998 are defined 2 linear calculation method that can be used for the determination of seismic loads on a structure:

  • Calculation according with “Equivalent Lateral Forces-method” (applicable to regular buildings) based on static analysis
  • Calculation according with “Modal Response Spectrum” (applicable to all buildings) based on dynamic analysis

Both methods are provided by SCIA Engineer.

Seismic load definition

SCIA Engineer 16.1 brings new possibility for definition of the seismic spectrum according with the latest Dutch Practice NPR 9998 for earthquake resistant building on December 18, 2015 published by the Dutch Standardization Institute (NEN).

The seismic loads are determinated by size acceleration PGA and response surface vibration (response spectrum).

SCIA Engineer extended the load library with NPR - Netherlands standards. The user is enable to input the spectrum by definition of code parameters.

Code parameters taken into account for the definition of the spectrum
Coeff accel. agref

reference value of peak ground acceleration from seismic map ( Figure 3.1)

Definition of the spectrum Elastic / Design
q - factor behaviour factor (only for design spectrum)
direction of the load Vertical / Horizontal
x (%) Damping of spectrum
consequence class classes of structure based on the risk associated with a collapse of the structure (Table 2.1)
Subsoil type  
Limit state

Degree of damage of the building structure: NC (near collapse) - SD (significant damage) - DL (damage limitation)

k ag

dimensionless factor depending on the result class (Consequence Class CC) according to Table 2.1 and Table 2.2.

gM partial factor for material properties
TLS,ref repetition time of the reference seismic load, depending on the considered limit state
Tref reference period as defined in BS EN 1990 or BS 8700
b reliability index (according to Table 2.1 and Table 2.2)

Access to the “seismic load”

  1. Project data: activate Seismic into Functionality > Dynamics
  2. Define the spectrum: Libraries > Loads > Seismic spectrum
  3. Into Seismic spectrum library define the Input type as “NPR 9998 – Netherlands standards
  4. Update Code parameters