risa | inputting the wood adjustment factor, le, in risa-3d

RISA | Inputting the Wood Adjustment Factor, le, in RISA-3D

Do you need to include effective length, le, per NDS Table 3.3.3 for your wood design? 

Yes? While RISA-3D does not automatically follow this le procedure per NDS Table 3.3.3, you as the engineer can input these values once you have them calculated. Inputting the effective length value in RISA-3D allows the program to use the correct value for the Rb calculations.

NDS provisions use an effective length approach to account for different load and support conditions. How does NDS do this?  By calculating the slenderness ratio, Rb using the effective length, le, instead of the unbraced length, lu.

Follow the steps below to calculate and input the effective length into RISA-3D.

STEP 1: Determine your span type and loading condition.

STEP 2: Calculate and determine the effective length values from Table 3.3.3 based on the unbraced length and loading.

lu = 10ft

d = 9.25in = 0.77ft

lu/d = 12.97 > 7, therefore 

le = 1.63lu + 3= 18.61ft

STEP 3: Enter the effective length value calculated into your unbraced length properties section in RISA-3D.


Additional information regarding this topic can be found in our Help file in the Unbraced Lengths section.