# Seismic Analysis Using Equivalent Lateral Force Method for Structures with Basement (4.7.5)

Equivalent earthquake load method is used only in irregularity calculations and these checks are made automatically.

**Symbols**

* D =* Resistance excess coefficient

*building importance factor*

**I =***Move the behavior factor*

**R =***Move applied to the lower part of the building system behavior factor*

**R**_{sub}=*Move applied to the upper part of the building the behavior factor*

**R**_{top}=**(**

*applied to the lower part of the building of Static Reduction Coefficient*

**R**_{a})_{bottom}=*Natural vibration period*

**T =**In buildings with basements surrounded by rigid curtains from the outside, the upper part of the building and the lower part with basement will be modeled together as a single carrier system. In buildings with basement, the upper part and the lower part (basement floors), which is relatively rigid in terms of horizontal rigidity, have very different properties in terms of dynamic behavior and strength. In the approximate two-load case calculation approach, the upper part of the building and the lower part with basement are modeled together as a single carrier system, but because the upper part and the lower part vibrate in very distant modes, the earthquake calculation is made separately as two load cases:

In the first stage of the calculation, using only the masses of the upper part, the calculation is made according to the equivalent earthquake load method. For the analysis in the calculation, the R and D parameters selected from Table 4.1 according to the carrier system type are used.

In the second stage, analysis is made using only the masses of the lower section. (R

_{alt}/ I) = 2.5 and D_{alt}= 1.5 are used in the calculation. However, since T = 0 assumption is made , the earthquake load reduction coefficient calculated from**TBDY Equation (4.1)**for the**subsection**will always be (R_{a})_{sub}= D_{alt}= 1.5. As a result of the calculation for the second loading case, the reduced internal forces in the lower section are obtained.ideCAD Statik uses this account

*automatically*only for irregularity calculations .

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