# Formulas for Lattice Girder placement

IMPACT Revit gathers all the values which are specified in Form slab definition, Lattice Girder and properly places the girders. The software respecting all parameters calculates and places the lattice girders accordingly.

To give a thorough insight about the calculations for Lattice Girder placement here you can read about the formulas.

The following pictures contain illustrations about girder calculation which are implemented in IMPACT Revit.

*Figure 1. Setting up Lattice girder in Form Slab definition*

*Figure 2. Form Slab explained*

*Figure 3. Lattice girder definition*

**1.Calculating the length of girders**

The length of the lattice girders we get by extracting from the length of the slab two times the minimum distance to shortside, two time considering the left and right side.

Formula:

*Length of Lattice Girder = the length of the slab - 2* the minimum distance to shortside*

**2. Defining the number of girders**

The number of girder units we get by dividing the length of the girder by the length interval or by C-spacing diagonal bar, if the case when the interval is 0. The software will only insert whole lattice girders units. In the case if the length of the lattice girder will be a value which will not fit, the software automatically generates a value according to the length interval parameter.

Formula:

*Number of girder units = Length of Lattice Girder / length interval*

**3. New length of girder**

Formula:

*New length of girder = Number of girder units * Length interval*

**4.Difference between lengths**

The original lattice girders is calculated with the values specified in the definition, but the new lattice girder length is calculated after the software considers all parameters.

Formula:

*Difference between lengths = Length of Lattice Girder - New length of girder*

**5. Distance to shortside **

Formula:

*Distance to shortside = Minimum distance to shortside + Difference between lengths *