b'THE OFFICIAL NFBA MAGAZINEcontinued from page: 21Table 5:Comparison of resultsload combinations are applied while Building ID Number Building Size Knee Brace (KB)condition Effective Shear Modulusof Roofing/SidingNumber of Bays Diaphragm HorizontalShear Stiffness Endwall Stiffness Interior Frame Stiffness Eave Load Restraining Force atMax Deflection Max. HorizontalDisplacement at Eave Deflection at EndwallsShear Load at Endwalls Max. Internal HorizontalDiaphragm Load the truss designer must incorporate the load impact of the knee brace into the component design.3.In all buildings with knee braces, posts were subjected to additional G eff C h k e k R Q max e V e V max,d(ft) (lb/in) %%%%%%%%%bending stresses under gravity loads. No KB This behavior was more pronounced 1 40x80 KB no slip 1260 no change 431% 45% -21% -12% -8% -8% -14% in buildings with long truss spans RESEARCH & TECHNOLOGY Building ID Number Building Size Knee Brace (KB)condition Effective Shear Modulus ofRoofing/SidingMax. Axial CompressionLoad in Knee Brace Max. Axial Tension Loadin Knee Brace Max. Shear at Grade inWindward Post Max. Moment at Grade inWindward Post Max. Shear at Grade inLeeward Post Max. Moment Grade inLeeward Post Stress Unity for WindwardPost Below Grade Stress Unity for WindwardPost Above Grade Stress Unity for LeewardPost Below Grade Stress Unity for LeewardPost Above GradeKB w/ slip 383% 40% -20% -11% -7% -7% -13%No KB (Buildings #4 and #5).2 40x80 KB no slip 2210 no change 431% 45% -3% 4% 7% 7% 2%KB w/ slip 383% 40% -3% 3% 6% 6% 2% 4.Knee braces should not be added No KB3 40x80 KB no slip 6200 no change 431% 45% 22% 26% 27% 27% 25% to a building if knee braces are not KB w/ slip 383% 40% 20% 23% 24% 24% 22% specified in the design documents. No KB4 60x80 KB no slip 2210 no change 429% 45% 9% 14% 16% 16% 13% Knee braces should not be specified KB w/ slip 381% 40% 8% 13% 14% 14% 11% in the design documents unless No KB5 80x160 KB no slip 2210 no change 374% 38% -55% -38% -28% -28% -33% their effects on the building are KB w/ slip 274% 28% -46% -33% -24% -24% -28% considered by structural analysis.5.Kneebracesmaybenefit buildings with certain geometrical configurationsandloading conditionswherediaphragm action alone is not enough. It is G eff P k,comp P k,ten V G,Wind M G,Wind V G,Leew M G,Leew recommended that the building (ft) (lb/in) %%%%%%%%%%designer first check the need for No KB kneebracingwhendiaphragm 1 40x80 KB no slip 1260 n/a -4% -8% 6% 4% -7% -13% 5% 1% action is included in the design. KB w/ slip -4% -7% 6% 4% -6% -12% 5% 0%No KB In the buildings analyzed herein, 2 40x80 KB no slip 2210 n/a -11% -14% -1% -1% -13% -16% 0% -1% however,kneebracesdidnot KB w/ slip -10% -13% -1% -1% -12% -17% 0% -3%No KB produceaconsistentadvantage 3 40x80 KB no slip 6200 n/a -14% -33% -14% -17% -30% -1% -17% 11% in any of the relevant metrics of KB w/ slip -20% -29% -13% -17% -27% -12% -17% 0% design. The stiffer frames did not No KB4 60x80 KB no slip 2210 n/a -18% -24% -3% 10% -20% 47% 13% 57% consistently translate to a stronger KB w/ slip -16% -22% -3% 7% -20% 32% 10% 41% or more efficient design. The results No KB were mixed and highly dependent 5 80x160 KB no slip 2210 n/a -1% -18% 39% 17% -6% 104% 25% 113%KB w/ slip 1% -14% 24% 7% -12% 54% 15% 61% on relative stiffness of the primary Conclusions and Recommendations frame and diaphragm. The following key points can be withdrawn from the analysis: References:1.In the 5 buildings analyzed in this study, use of kneeANSI/AITC A190.1 (2012). American National Standard: braces produced inconsistent results. Knee braces mayStandard for Wood ProductsStructural Glued Laminated increase or decrease horizontal eave deflection, loadTimberdemand on the diaphragm and end walls, load demandANSI/ASABE EP559.1 (R2014) Design Requirements and on the foundation, and stress unity in the posts. Bending Properties for Mechanically-Laminated Wood Assemblies2.Modeling knee bracing within a post-frame building isANSI/ASAE EP484.3 (2017) Diaphragm Design of Metal-complex. The complexity extends to the roof-truss designClad, Wood-Frame Rectangular Buildingsbecause the truss design must include the knee braceANSI/ASAEEP486.3(2017)ShallowPostandPier reaction forces.The building designer is responsibleFoundation Designfor reviewing truss drawings and verify that knee brace loads are applied correctly, and that correct governingANSI/AWC NDS-2018 National Design Specification (NDS) 22 / FRAME BUILDER - MAY2023'