b'YOUR TOOLKIT FOR BUILDING EXCELENCEWinds truss plates at the ridge of animal confinement buildings. Not Wind forces tend to be the most destructive environmentalonly are the plates subjected to repeated moisture cycling and load for most buildings. This is largely due to their cyclicextreme temperature swings, but they are also exposed to the nature, directional variability, and frequent (daily) presence.corrosive effects of manure gases (i.e., hydrogen sulfide (HS) To this end, rural America is replete with old timberand ammonia (NH)) as they vent out of the facility. Figure frame barns which have succumbed to wind forces. In10 shows metal connector plate deterioration at a building many of these buildings, the joints in timber frame bentsridge. Many designers avoid this problem by using engineered become loose after years of moisture content cycling andlumber rafters in place of metal-plate-connected trusses.racking by wind. A telltale sign of loose joints is a barnEquipment Induced Vibrationnoticeably out-of-plumb. Unfortunately, even when theStructural integrity can be compromised by vibrations visible signs of distress become obvious, many owners dothat cause material fatigue and also loosen bolts, screws, not take steps to brace, reinforce and repair the frames,nails, and other mechanical connections.Such vibrations which inevitably results in partial or total building collapse. are induced by power equipment (e.g., HVAC systems) in Ventilationdirect contact with building components, or by equipment While ventilation is essential for indoor air quality, it canthat generates fluctuating air pressures (i.e., sounds) that result in the unwanted transport of moist air and water intoin turn vibrate surrounding components.Vibrations areas where it can enhance decay, corrosion, and mold growth.are minimized by using passive and active vibration isolation mountings, attaching equipment directly to Ventilation systems in cold weather regions are generallyconcrete slabs or other large masses, and by surrounding negative pressure systems. This prevents moist indoornoisyequipmentwithsoundabsorbingmaterials.air from entering cracks in the exterior envelope, whereSummaryit will form ice during sub-freezing weather, and freeze shut doors and windows. One downside of negativeTo varying degrees, all buildings are under continual pressure systems is that they may draw exterior waterassault by the damaging effects of photodegradation, into unsealed joints between cladding components andwood decay fungi, animals, corrosion, water condensation around doors and windowsa problem that can beand deposition, cold weather, temperature fluctuations, compoundedbypositiveexteriorwindpressures. winds, ventilation, and equipment induced vibrations. Natural ventilation systems in animal confinement facilitiesWith an acute awareness of how these siege forces damage are characterized by large wall openings and frequentlybuildings, architects and engineers can improve building by ridge openings which expose indoor componentsdesigns.This in turn can lower repair and maintenance to precipitation that will shorten their functional life.costs, reduce the likelihood of a catastrophic building loss, Particularly problematic is the complete exposure of metalenhance building resale value, and extend building life.Abouttheauthor:DavidR.Bohnhoff isa registered professional engineer and emeritus professorofBiologicalSystemsEngineering attheUniversityofWisconsin-Madison. This article was subjected to a peer review processconductedbytheNFBAEditorial Committee, which consists of at least 10 members from engineering and academic organizations throughout the United States who are each knowledgeable about Post-Frame construction.FIGURE 10. CORRODED METAL TRUSS PLATE UNDER AN OPEN RIDGE IN A DAIRY FREESTALL BARN. FRAME BUILDER - JAN2023 / 19'