# Determination of Base Shear Scale Factor (4.8.4.1)

If V

_{tx }^{(X)}<γ_{E}* V_{tE }^{(X)}for any earthquake direction^{(X)}, all reduced internal force and displacement magnitudes obtained by the modal calculation method applied according to**4.8.2**or**4.8.3**, The equivalent base shear force given by**Eq. (4.31)**is automatically increased by multiplying it by the magnification factor β_{tE }^{(X)}.

**If**at least one of the**A1**,**B2**or**B3**type irregularities defined in**Table 3.6**is found in the building, γ_{E}= 0.90 is automatically taken.

**If**none of the irregularities defined in**Table 3.6**are found in the building, γ_{E}= 0.80 is taken automatically.

According to the definition given in

**3.3.1**, in buildings with basements surrounded by rigid walls from the outside, the equivalent base shear force magnification coefficient is automatically calculated only for the upper part above the basement floors of the building.

**ICONS**

* V _{tE }^{(X)}* = (X) total equivalent earthquake load (base shear force) acting on the entire building in the earthquake direction

*= Maximum total earthquake load obtained in the x direction with the modal combination method*

**V**_{tx }^{(X)}*= Equivalent base Shear force amplification coefficient*

**β**_{tE }^{(X)}*= Empirical coefficient used in determining the equivalent base shear amplification coefficient*

**γ**_{E }*=Total mass ofthe*

**m**_{t }*upper part*of the building above the basements

*= Reduced design spectral acceleration*

**S**_{aR}(T)From a mathematical point of view, Mode Combination Method is considered as a more precise method than Equivalent Earthquake Load Method. However, considering the stiffness of the elements of the carrier system, uncertainties in their behavior as well as the assumptions made in determining the spectrum curve, this method includes approximation. For this reason, the regulation demands that the results determined in the mode combination are compared with the results determined in the Equivalent earthquake load method and increased where necessary.

According to the logic of equivalent earthquake load method, this coefficient may be higher than 1 in regular and low-rise buildings that can be represented with 1.mod, while it is calculated less than 1, especially in random and high-rise buildings. This situation comes from the philosophy of modal combination method in determining dynamic effects by using single degree of freedom equations of motion for multiple modes. In short, it is because of the large number of modes taken into account in determining the earthquake behavior of the building. According to the regulation, the magnification factor can be at least 1.

**Calculation of Total Equivalent Earthquake Load**

Total Equivalent Earthquake Load (base shear force) for any * _{direction }^{(X)}* ,

*V*, to Equivalent Earthquake Load Method, Equivalent Lateral Force Method, according to

_{tE }^{(X)}**TBDY Equation 4.19**.

In this equation, *m _{t}* corresponds to the total mass of the building calculated considering the live load participation ratio .

*S*shows the Reduced Design Spectral Acceleration calculated by taking into account the dominant natural vibration period of the building,

_{aR }^{(X)}(T_{p})*T*, in the direction of the considered (X) earthquake .

_{p }^{(X)}In the earthquake parameters table of the dynamic analysis report, the values used in the calculation for the relevant direction and the magnification coefficient obtained as a result of the calculation are given. In the Modal Base Shear Forces section of the earthquake regulation report, the base shear forces combined with the base shear force of each mode determined as a result of the modal analysis for each direction are given. Again, in the irregularities section of the earthquake regulation report, the coefficient γ _{E} is *automatically* determined according to the presence of any of the A1, B2 and B3 irregularities .

The magnification factor according to the equivalent earthquake load is *automatically* applied only for * the upper section* elements

*according to the regulation . Quantities such as internal force, displacement and relative displacement determined only under the*

**above the basement floor in Basement Structures***of*

**effect***multiplied by this coefficient.*

**horizontal earthquakes are**automatically