b'YOUR TOOLKIT FOR BUILDING EXCELLENCEthe building.Extreme wind speeds create eventransfer them into the larger MWFRS systems more extreme load effects on the building. A 10%until they are absorbed entirely and no longer increase in wind speed results in an approximatelycontrol the design.It is important to consider 20% increase in wind load on the building.Athe edge and corner zones as defined in ASCE/buildinglocatedina180mphareamaybeSEI 7 and not skip any steps.Wind-related subjected to a wind load that is two and a half timesfailures in buildings often start with corner and greater than the wind load produced by 115 mphedge surfaces peeling away from the building. winds, while the increase in wind speed is onlyInstalling additional intermediate purlins and girts 57%.To put this in perspective, if the relationshipand extra fasteners in these areas may be necessary. between the wind speed and the wind load effectCollectively, the MWFRS pressures on the building was linear, the wind speed in the latter examplesurfaces create a net lateral load on the building. would be over 280 mph (2.5 times 115 mph).The lateral force resisting system (LFRS) of the post-Additionally, the nature of hurricane winds leads toframe building, typically comprised of embedded a potentially longer duration of exposure and fromcolumns, roof trusses, the roof diaphragm, and more directions than other sources of high wind. shear walls (endwalls and sidewalls), is responsible Constructing a post-frame building that willfor providing a continuous path of load resistance safelyandpredictablywithstandhurricanebetween the load source, the wind, and the source loads cannot be done without an analysis-basedof load resistance, the earth.Each component of design. It is true that many non-engineered post- the LFRS, especially the roof diaphragm, requires frame buildings withstood the test of time.Thecareful detailing to ensure that a continuous load strength and safety of such buildings, however,path is provided.The design and detailing of is an unknown quantity.Building by ear issplices in the diaphragm chords are often omitted. not advisable especially for buildings locatedFigure 2 shows a diaphragm concept where the roof in hurricane regions.Fortunately, the designis separated into two smaller diaphragms, each procedures are the same and are governed by thehaving two diaphragm chords.Other concepts may same design standards as post-frame buildingsuse more or all roof purlins as diaphragm chords located elsewhere in the country.ASCE/SEI 7or use one large diaphragm with structural ridge provides separate provisions for wind pressures on components and cladding (C&C) and wind pressures on the main wind force resisting system (MWFRS).Each component and connection in the buildings envelope, including the cladding material, roof purlins or rafters, and wall girts should be sized and detailed to withstand the calculated local C&C wind pressures. The nearest membersFigure 2: Roof diaphragm with some purlins as chordsand connections of the MWFRS (columns, trusses)cap capable of transferring shear forces between must be designed to receive the localized C&Cthe two smaller diaphragms. Some of the other loads from the cladding members and safelycommonly overlooked areas include blocking continued on page: 14 FRAME BUILDER - FEB2022 / 13'