C M AProgressive dverti$er A
Th e
omponent
anufacturing
Don’t Forget!
ReseaRch
+
September 1 , 2016 Technology st
roof Progressive Roof Collapse Progressive CollaPse Dueroof to CollaPse Due to to CLR Shifting Clr Due shifting Clr shifting You Saw it in the
dverti$er
#09206 Page #67
by DaviD R. bohnhoff, PhD, PE
This article appeared in the August 2016 issue of Frame Overview Building News. Reprinted with permission. byProgressive DaviD R. bohnhoff, PhD, PE roof collapse is a roof collapse in which the failure of a single structural component triggers a chain reaction of Overview failures that result in a large portion of a roof collapsing onto roof collapse is a roof collapse inlateral which restraint the failtheProgressive contents below. The shifting of continuous ure of a single structural component triggers a chain reaction of is well known as a leading cause of progressive roof collapse. failures that result in a large portion of a roof collapsing onto Within post-frame buildings, CLR is commonly used to laterthe The shifting of continuous lateral restraint ally contents brace topbelow. and bottom truss chords, compression web memis well known as a leading cause of progressive roof collapse. bers, interior and exterior posts and post-to-truss connections. Within CLRreduced is commonly used toattachlaterFailurespost-frame due to CLRbuildings, shifting are by properly ally brace top and bottom truss chords, compression web meming and anchoring CLR, ensuring that the CLR itself does not bers, interior and exterior and post-to-truss connections. buckle and using framingposts elements that do not require CLR. Failures due to CLR shifting are reduced by properly attaching and anchoring CLR, ensuring that the CLR itself does not Preventing Buckling with buckle and using framing elements that doCLR not require CLR. CLR is a continuous line of bracing used to provide lateral support to a series of structural elements. preventing lateral Preventing Buckling withByCLR movement, CLR reduces the effective length of a member it CLR thereby is a continuous linethe ofamount bracing of used lateral braces, increasing loadtoitprovide would take to support to member. a series ofUse structural elements. By preventing buckle the of a single row of CLR to brace alateral series movement, CLR reduces the effective length of a member it braces, thereby increasing the amount of load it would take to buckle the member. Use of a single row of CLR to brace a series
Figure 1. Web member CLR with a diagonal brace for prevention of shifting
Figure 1. Web member CLR with a diagonal brace for prevention of shifting www.FrameBuildingNews.com
PHONE: 800-289-5627
www.FrameBuildingNews.com
of compressive web members is shown in Figure 1. For a pinned-end component, the relationship between the component’s length and the load required to buckle the compoof compressive members is shown in Figure 1. nent is given byweb Euler’s equation as 2 relationship between the For •E•I•π2 / L2component, = 9.87•E•I/Lthe Pc =an2pinned-end e component’s length and the load required to buckle the component given by Euler’s equation as or forispinned-end rectangular components as 2 •E•I•π2 / L22 = 29.87•E•I/L 2 2 P = n Pcc = 0.822•E•A•d /Le = 0.822•E•A/(L e e /d) or for pinned-end rectangular components as where 2 /L 2 = 0.822•E•A/(L /d)2 P = 0.822•E•A•d Pcc is critical buckling component, e load for a pinned-end e n is the number of uniform-length, buckled segments within where the component, P critical buckling load for a pinned-end component, Ecisismodulus of elasticity, n is the number of uniform-length, buckled segments within L is component length, theL component, e is component effective length or L/n, E modulusofofinertia elasticity, I isismoment about the buckling axis, L length, A is is component cross-sectional area, L component effective length ordirection L/n, d eisisdepth of the component in the of buckling, and ILis/dmoment of inertia about the buckling axis, is slenderness ratio. e A is cross-sectional area, dEuler’s is depth of the component in the direction buckling, and equation sets an upper limit on theofaxial compresLeload /d is that slenderness ratio. to a long member that is not subsive can be applied jected to any other loads. In accordance with the equation, the Euler’sofequation sets an upper limittoonbuckle the axial compresamount compressive load it takes a component sive load that can be applied to a long member that is not subjected to any other loads. In accordance with the equation, the amount of compressive load it takes to buckle a component
Figure 2. Cut the effective length in half, and the load required to cause buckling quadruples. Figure 2. Cut the effective length in half, and the load required to cause 1 buckling quadruples.
Read/Subscribe online at www.componentadvertiser.com
FAX: 800-524-4982 1