b'YOUR TOOLKIT FOR BUILDING EXCELLENCEMOST FARMERS DONT KNOW THEIR OWN (BARNS) STRENGTHA dairy farmer from Jackson County, Wisconsin called me this winter with some structural concerns about his Freestall dairy barn.Specifically, he observed some truss web members bowing out of plane by an estimated 6 to 8 (YIKES!).Aaron Halberg, P.E.Professional Engineer and NFBA Editorial Committee ChairA fter some phone discussions and a reviewExposed (C e= 1.0), Building Category: I (I s= of his truss design drawing from the 20140.8), Thermal Condition: attic ventilated (C t= drawings, we determined the trouble was1.1), Unobstructed Slippery surface.Using these because the web lateral restraints did not includefactors and ASCE 7 equations results in a Roof any diagonal bracing which is required to makeSnow Load ( P ) of 20 psf, about the equivalent s them effective against bowing.It was obvious toof 1ft of nominal density snow (snow density me that adding diagonal bracing to meet BCSIvaries widely).and TPI guidelines would be required, but he alsoWhen I explained that the truss design loads wanted to gain more confidence in the situation, soapplied several reductions to the Ground Snow he hired me to visit his barn to make sure we hadLoad, the farmer was immediately concerned: correctly identified the extent of the problem andWhat do you mean, reductions?!?I explained to ensure he knew how repairs should be made. such adjustments can be legitimately used in the Before visiting, I noticed there was likely a problemdesign process, but the reality is the truss design with the truss design loads.The truss designincluded some technically allowed adjustments drawing included the information shown in thisI did not agree with.More importantly, this box: discussion should have taken place with his builder psf is Pounds per Square Foot.and building designer when the design process first Loading (psf) began. He should have also had some education GSLisGroundSnowLoad.GSL:35 on the factors and been given input on which TCDL and BCDL are Top /TCDL:5 adjustments are used for his building.After all, Bottom Chord Dead Load.TheBCDL:5 it ends up being a roof over HIS head and HIS immediate concern for me waslivelihood if something goes wrong.the appearance of Ground Snow Load, not Roof Snow Load or Top Chord Live Load, so I suspectedDespite some disagreement with the adjustments, right away that this truss was likely designed forthe starting point is the Ground Snow Load, and something much less than 45psf total load (35 +the 35psf starting point for this project should 5 + 5). have been 50psf for this location (see Figure 1). The truss design notes stated the truss was designedThe builder may have requested a 35psf truss with user defined input: 35psf ground snow load,(intending roof snow load), but the request appears Terrain Category C, Exposure Category: Partiallyto have been supplied as 35psf Ground snow load, transformed to 20psf roof snow load.Any continued on page: 28 FRAME BUILDER - JUN2021 / 27'