# Natural Fundemantal Period Determination (4.7.3) • The natural vibration period of the building is determined automatically by modal calculation methods. • The dominant natural vibration period of the building is compared and reported with the automatically calculated T pA value in Equation 4.27 .

Symbols

A t = Equivalent area used in the empirical natural vibration period calculation [m2]
A wj = Body cross-section area of ​​the jth curtain [m2]
C t = Coefficient used in the empirical natural vibration period calculation
d fi (X) = (X) The displacement of the fictitious load on the i'th floor in the calculation of the natural vibration period [m]
F fi (X) = (X) the fictitious load imposed on the i'th floor in the calculation of the dominant natural vibration period of the building in the direction of the earthquake [kN]
H N = Total height of the upper part of the building above the basement floors [m]
l wj = Length of the curtain in plan [m]
S aR (T) = Reduced design spectral acceleration [g]
S DS = Short period design spectral acceleration coefficient [dimensionless]
T = Natural vibration period [s]
T pA = Dominant natural vibration period calculated empirically [s]
T p (X) = (X) dominant natural vibration period of the building in the direction of the earthquake [s]

Tp (X), which represents the dominant natural vibration period of the building in the direction of the earthquake (X) taken into consideration in Equation (4.19) in all buildings where the 'Equivalent Earthquake Load Method' is applied, Eq. (4.26) will be calculated with. ' It is calculated automatically for comparison and compared with the dominant vibration period obtained as a result of modal analysis. The dynamic analysis report is given in detail in the parameters used in the calculation in the earthquake parameters section.

According to TBDY (2018), the maximum value of the dominant natural vibration period T p (X) calculated with Rayleigh's formula will not be more than 1.4 times the period T pA empirically defined below . H N in the equation denotes the height of the building. By definition, it is calculated from the floor above the basement floor in buildings with rigid basement floors.

In buildings carrier system consisting of concrete frame C t = 0.1, or from steel braced frame in buildings with steel frame C t = 0.08, all other buildings C t = 0.07 automatically received. In buildings where all earthquake effects are covered by reinforced concrete curtains, the C t coefficient is calculated automatically with Equation (4.28a) .

• Curtain clean opening is used in A t calculation.  JavaScript errors detected