When either of these codes is used in CYPECAD (NSR-10 (Columbia) and NC 46:1999 (Cuba)), there are two options to indicate the value of the Fundamental period of the structure (used to calculate the base shear):
- Based on the code (only possibility in previous versions)
- Specified by the user (implemented in the 2014.d version)
Both options can be selected in the Estimation of the fundamental period of the structure section in the Code for the calculation of seismic loading dialogue box (Job ˃ General data ˃ select “With seismic loading” in the “Loads” section ˃ select Columbia or Cuba as the country and the NSR-10 or NC 46:1999 codes respectively).
The value of the fundamental period of a building must be obtained based on the properties of its seismic resistant system, in the direction under consideration, in accordance with structural dynamics principles. Alternatively, most seismic codes have other procedures to estimate the fundamental period:
- In accordance with empirical formulas provided in their articles
- In accordance with other methods, as long as they are adequately sustained analytically or experimentally
The estimated fundamental period is applied in the static shear analysis at the base of the structure (base shear) to adjust the dynamic results to the minimum values prescribed in the codes, when the dynamic method is applied, and to generate the equivalent static lateral forces when the static method is applied.
The values indicated by the codes are limits that can be applied in the absence of more precise data. If users have fundamental period values, which are more adjusted to their structure (calculated using other methods or with software tools such as CYPECAD, which calculate the fundamental period of the structure in both directions – the values can be consulted after the analysis in the “Justification of seismic action” report: File ˃ Print > Job report) they can specify them using the option Specified by the user located in the Code for the calculation of seismic loading dialogue box.
