As of the 2019.a version, CYPECAD and CYPE 3D can take into account the effects of the vertical seismic component by considering them as a percentage of the gravitational effect. Optionally, both programs apply a modification or adjustment coefficient that acts as the sum of the factor of the permanent loads in the seismic force combinations.
This coefficient increases the factor of the permanent loads in seismic combinations for unfavourable gravitational conditions and decreases the factor of the permanent loads for favourable gravitational conditions. In the first case, the gravitational effects are added to the seismic effects. In the latter, the gravitational effects counteract the seismic effects.
Consideration of the effects of the vertical seismic component
In building design, it is usual to calculate a structure to against the horizontal action of the earthquake and neglect the effects of the vertical component. However, in certain cases, it is advisable to consider these effects in the design.
CYPECAD and CYPE 3D apply an alternative procedure to the specification of spectra to consider the vertical seismic action, including its effects in seismic combinations by increasing the effect of the permanent load. This increase takes positive and negative values, due to the reversibility of the seismic action, and increases and decreases the gravitational effects in the combination. By doing so, the effects of vertical movement of the floor in buildings are simulated, such as:
- The variance of the axial force in elements that resist vertical loads.
- The variance in the localised deformation at the top of columns and the deflection at floor slab mid-spans.
- The variance of the total vertical shear force that is transferred between floor slabs and columns.
CYPECAD and CYPE 3D propose a simple calculation for this modification coefficient, which provides a value that adapts to what is established in the standards and that is a function of the seismicity of the site that has been selected by the user. Some codes call it "vertical seismic pseudo-acceleration", but it does not represent the total vertical response, only the part that is combined with the horizontal response and the effects of gravity. The data proposed by the program can be modified by users, since different situations to those usually contemplated by the standards may arise.
In the section of the seismic data dialogue where users can activate whether or not the effects of the vertical seismic component are to be considered, there is a help button where more information on the calculation of the "vertical seismic pseudo-acceleration" coefficient can be found.
