A private client wishes to add load

[ANE91]

A private client wishes to add load to their roof. Thus, I am analyzing their most critical monoslope wood truss in RISA3D. The span is 50 feet, and the slope is 1:12. The truss is in service. I documented my own measurements and other truss details for the analysis. Later, I procured the manufacturer’s drawings.

Applying the manufacturer’s load combinations to my model gets me within 5% of their internal forces. This tells me that my model is sound. However, my unity checks are way off. Some of my webs are at 200% DCR, with excessive axial force demand. Since my loads are not the problem, I am digging into the capacities.

Is there a significant difference in truss capacity between the NDS and TPI? RISA3D performs unity checks to ASCE 7 (NDS), not TPI. Where am I going wrong?

 

[IceNine]

Unbraced Lengths?

 

[ANE91]

Thank you for the input.

Bracing was the first thing I checked. Webs are braced out of the truss plane at mid-height. I also set the in-plane effective length as 80% of the web length, per the allowance in TPI.

 

[Tomfh]

Failing how? What check?