b'THE OFFICIAL NFBA MAGAZINEcontinued from page: 29building company, it is indeed scary when some of these individuals start erecting non-engineered buildings. Participating in the erection of engineered buildings does not make one an expert in building design, no more than designing a building makes one an expert in safe and efficient building construction.Very few builders, architects, code officials and nonstructural engineers understand the true RESEARCH & TECHNOLOGYcomplexity of a fully engineered post-frame building system. Several building elements perform multiple functions not apparent or understood by those not actively engaged in post-frame building engineering. In addition to having no idea of the loads to which a componentFigure 2: Shifting of the CLR enables the compression web tobuckle out of the plane of the truss. All trusses to the right of the oneis subjected, builders are not familiar with alllabeled here failed in a progressive manner.methods available to resist applied loads and theyproduced with software developed for trusses do not have the expertise needed to determinespaced less than 4 feet on center (e.g. residential the proper size, support system and connectiontrusses). Using Land/or T-bracing not only saves designs for a building component.lumber and provides greater stability, such braces A prime example of the problems this causes wasare also easier to install (they can be attached on full display in Myrens freestall barn and theon the ground) and do not cause progressive other five failed buildings I visited the same day.collapses. Many of these buildings had seriously under- With a CLR system, when one truss fails, the designed interior columns. As constructed,lateral restraint attached to that truss pulls on the most of these columns would have an allowablesimilarly buckled webs of the two adjacent trusses axial design load of zero (0) which explains(i.e., the trusses located on each side of the failed the classic buckling observed (figure 1). Othertruss). The truss on one side of the failed truss major deficiencies included no column sidewayis helped by this action and does not fail (as its control at connections between interior columnsbowed compressive web is somewhat straightened and trusses, no accounting for additional loadsout). induced by drifting snow and improper truss web bracing. With respect to the latter, all buildingsConversely, the truss on the other side of the failed I inspected with roof trusses utilized continuoustruss becomes more compromised as its buckled lateral restraint (CLR) systems to brace longerweb is pulled further out of alignment. This almost compressive web members. Unfortunately, everyalways snaps the web of that truss, resulting in its CLR system was improperly installed, as none ofcollapse. The collapse of this second truss brings them included diagonal bracing to prevent CLRdown the next truss in a similar fashion. In a shifting. This resulted in web buckling (figure 2)dominolike fashion, trusses continue to fail until and subsequent truss failure. there are no more trusses to pull down. This entire In my view, the more major concern is not thatfailure process explains why this mode of failure is the CLR systems were improperly installed incharacterized by a partial roof collapse that ends these buildings, but that they were used in the firstat a wall.place. In buildings with trusses 6 feet or more on- Misled consumers center, all compression web chords should be T-During my investigation of agricultural building or L-braced. The use by builders of CLR systemsfailures, it has become quite apparent that a vast (instead of L- or Tbracing) results from plansmajority of farmers are under the impression they continued on page: 3230 / FRAME BUILDER - VOL6 5'