# Determination of Equivalent Lateral Force Acting on Stories per ASCE 7-16 with ideCAD

**How does ideCAD calculate the equivalent lateral force acting on stories according to ASCE 7-16?**

The seismic force to the effect on the floors for each direction is calculated automatically using

**Equations 12.8-11**and**12.8-12**.

The Equivalent Lateral Force Method is only used to determine structural irregularities.

**Symbols**

* F_{i} = *The portion of the seismic base shear (V) [kip (kN)] induced at level i

*= vertical distribution factor*

**C**_{vx}*total design lateral force or shear at the base of the structure [kip (kN)]*

**V =***portion of the total effective seismic weight of the structure (W) located or assigned to level i or x;*

**w**and_{i}**w**_{x}=*height [ft (m)] from the base to level i or x; and*

**h**and_{i}**h**_{x}=*an exponent related to the structure period*

**k =**The peak load is used to approximate the effect of the high modes neglected in this method. The following equation calculates the total equivalent lateral force (Base shear force).

The part of the total equivalent lateral force other than the peak load is automatically distributed to the building floors, including the N^{th} floor, by accepting the mode shape of the dominant mode as an inverted triangle.

* k* = an exponent related to the structure period as follows:

for structures that have a period of 0.5 s or less, k = 1;

for structures that have a period of 2.5 s or more, k = 2; and

for structures that have a period between 0.5 and 2.5 s, k shall be 2 or shall be determined by linear

interpolation between 1 and 2.