Field Notching and Drilling of Laminated Veneer Lumber

Transcription

1 T E C H N I C A L N O T E Fiel Notching an Drilling of Laminate Veneer Lumber EWS G535A June 2010 INTRODUCTION Laminate veneer lumber (LVL) is an engineere woo prouct manufacture from specially selecte veneers of varying strength an stiffness properties. LVL proucts are often specifie where a certain span, strength an/or stiffness is require. As such, LVL proucts are generally esigne for an use in applications where they will be highly stresse uner esign loas. For this reason, fiel moifications, such as notching, tapering or rilling, not shown on the esign or shop rawings, shoul be avoie an never one without a thorough unerstaning of the effects on the structural integrity of a member. Most LVL proucts are use as beams an heaers loae parallel to the gluelines. Any rilling, tapering or notching that takes place in LVL reuces the net section an may introuce stress concentrations at the notching or rilling location. Therefore, it is easy to see why a cautious approach to fiel moifications is vital. This Technical Note provies recommenations for fiel notching, tapering an rilling LVL beams. NOTC HING Notching of LVL beams shoul be avoie whenever possible, especially on the tension sie of a member. Tensionsie notching of LVL beams is not recommene except at en bearings an then only uner specific conitions. The notching of LVL beams on the tension sie results in ecrease strength cause by stress concentrations that evelop aroun the notch an a reuction of the net cross section resisting the bening an shear forces. Such notches inuce perpenicular-to-grain tensile stresses which, in conjunction with horizontal shear forces, can cause splitting along the grain, typically starting at the insie corner of the notch. Stress concentrations, ue to notches, can be reuce by using a graually tapere notch configuration in lieu of a square-cornere notch. Rouning the square corner of a notch with a raius of approximately 1/2 inch is also recommene to reuce stress concentrations in these areas. LVL beams illustrate in Figure 1 are assume to be simple span subjecte to uniform loas. All equations an notching guielines are presente using the same assumptions. If this information is applie to continuous or cantilevere beams, it shoul be use with extreme caution an only after careful analysis base on soun engineering jugment. Where LVL beams are notche at the ens for bearing over a support, the notch epth is recommene to not excee 1/10 of the beam epth (Figure 1(e)). Within the limitation given above, the shear stress at the notch can be calculate in accorance with Figure 1(e). For notches on the compression sie, a less severe conition exists an equations for the analysis of the effects of these notches are also given in Figure 1. The equations given are empirical in nature an were evelope for the conitions shown.

2 Fiel Notching an Drilling of Laminate Veneer Lumber 2 FIGURE 1 SHEAR DESIGN EQUATIONS FOR NOTCHED AND TAPERED LVL BEAMS Compression sie Compression sie f v = 2b f v = 2b (a) Square En Bearing (b) Slope En Bearing Maximum 1/3 of the span e 0.4 max. Maximum 1/3 of the span e e 0.6 e 0.6 When e e, f v = 2b ( e) e e When e > e, f v = 2be (c) Slope En Cut for Roof Drainage When e e, f v When e > e, f v = 2be () Compression-sie Notch = 2b ( e) e e e max. ( ) 2 f v = 2b e e (e) Tension-sie Notch f v = shear stress (psi) V = shear force at notch location (lbf) b = with of beam (in.) = epth of beam (in.) e = effective epth as shown (in.) e = length of notch as shown (in.) Form No. EWS G535A 2010 APA The Engineere Woo Association

3 Fiel Notching an Drilling of Laminate Veneer Lumber 3 As the notching provisions given in this Technical Note are limite to uniformly loae simple-span beams, the notches shown in Figure 1 occur in areas of high shear an lower moment. For this reason, the esign equations given are shear equations. When necessary to cut a small notch in the top of an LVL beam (in the compression sie) to provie passage for small-iameter pipe or conuit, the cut shoul be mae in an area of the beam stresse to less than 50 percent of the allowable bening stress. The net section in this area shoul be checke for shear an bening stresses to ensure aequate performance. All fiel notches shoul be accurately cut. It is important to unerstan that improperly cut fiel notches may reuce the capacity of a beam an cause serious structural failure. Avoi over-cutting at the corners of the notch. Drilling a pilot hole in a member at the interior corner of a notch as a stop point for the saw blae provies both a roune corner an minimizes over-cutting at the corner. It shoul be recognize that the top of an LVL beam might not always be stresse in compression an the bottom of an LVL beam might not always be stresse in tension. For example, if the LVL beam is esigne for win uplift, the top of the LVL will be stresse in tension an the bottom of the LVL will be stresse in compression. In this case, the recommenations given above shoul be applie accoringly. Furthermore, when evaluating the effect of notching, the shear force within a istance from supports equal to the beam epth shoul not be neglecte, as typically permitte by the esign of rectangular woo members in accorance with the National Design Specification for Woo Construction (NDS) in the U.S. an the Woo Design Manual in Canaa. HOLES Horizontal Holes Like notches, holes in an LVL beam reuce the net section of the beam at the hole location an introuce stress concentrations. This causes a reuction in the beam capacity. For this reason, horizontal holes in LVL are limite in size an location to maintain the structural integrity of the beam. Figure 2 shows the zones of a uniformly loae beam in simple or multiple spans, where the fiel rilling of holes may be consiere. The requirements given consier the effect of the horizontal hole on the shear an moment capacities of an LVL beam, an may be applie to multiplepiece built-up LVL beams. FIGURE 2 PERMISSABLE HORIZONTAL ROUND HOLE LOCATIONS FOR LVL BEAMS UNDER UNIFORM LOADS Uniform loa ω (plf) 1/3 1/3 1/3 Minimum horizontal spacing = 2 x iameter of the largest hole 1/3 span 1/3 span 1/3 span = Zones where horizontal holes are permitte for passage of wires, conuit, etc. For beam epth of 3-1/2, 5-1/2, an 7-1/4 inches, the maximum hole iameter is 3/4, 1-1/8, an 1-1/2 inches, respectively. For eeper beams, the maximum hole iameter is 2 inches. The maximum number of holes for each span is limite to 3. Holes shoul not be cut in cantilevers. Form No. EWS G535A 2010 APA The Engineere Woo Association

4 Fiel Notching an Drilling of Laminate Veneer Lumber 4 A 1-inch-iameter or smaller hole may be cut at the mile 1/3 of the beam epth anywhere along the span, except for the area that is within 6 inches of clear istance between the face of the support an the nearest ege of the hole (see Figure 3), provie the following conitions are all met: 1. the beam is at least 7-1/4 inches in epth, 2. the beam is subject to uniform loas only, 3. the span-to-epth ratio (l/) is at least 11, 4. the maximum number of holes for each span is limite to three, 5. the horizontal spacing must be a minimum of two iameters clear istance between ajacent holes base on the iameter of the larger hole, an 6. the hole must not be cut in cantilevers. If l/ of the beam is less than 11, the 1-inch iameter or smaller hole may be cut in accorance with the provisions liste above except that the location of the hole must maintain a clear istance between the face of the support an the nearest ege of the hole of at least 1/6 of the span. Beam epth, (in.) Span when l/ = /4 6'-8" 7-1/2 6'-11" 9-1/4 8'-6" 9-1/2 8'-9" 11-1/4 10'-4" 11-7/8 10'-11" 14 12'-10" 16 14'-8" 18 16'-6" 20 18'-4" 22 20'-2" 24 22'-0" FIGURE 3 ZONES WHERE 1-INCH OR SMALLER DIAMETER HORIZONTAL HOLES ARE PERMITTED IN A UNIFORMLY LOADED BEAM ( 7-1/4 inches) Uniform loa ω (plf) 1/3 1/3 1/3 λ Minimum 2 x iameter of the larger hole λ λ l Zones where 1-inch or smaller iameter horizontal holes are permitte for passage of wires, conuit, etc. a) the maximum number of holes for each span shall not excee 3 an b) the hole must not be cut in cantilevers. λ = 6 inches minimum when l/ 11, or l/6 minimum when l/ < 11. Fiel-rille horizontal holes shoul be use for access only an shoul not be use as attachment points for brackets or other loa bearing harware unless specifically esigne as such by an engineer or esigner. Examples of access holes inclue those use for the passage of wires, electrical conuit, small-iameter sprinkler pipes, fiber-optic cables an other small, lightweight materials. For LVL beams that have been over-size, the guielines given above may be relaxe base on an engineering analysis. When holes are require to be rille outsie the allowable zones, an engineering analysis shoul be conucte an approve by an engineer or architect qualifie in woo esign. Regarless of the hole location, holes rille horizontally through a member shoul be positione an size with the unerstaning that the beam will eflect (creep) more over a perio of time uner in-service loaing conitions. This eflection coul overstress supporte equipment or piping unless properly consiere. Form No. EWS G535A 2010 APA The Engineere Woo Association

5 Fiel Notching an Drilling of Laminate Veneer Lumber 5 Vertical Holes Whenever possible, avoi rilling vertical holes through LVL beams unless the beam with is at least 3-1/2 inches. Prior to rilling any vertical holes, an engineer or architect qualifie in woo esign shoul be consulte. Use a rill guie to minimize wanering of the bit as it passes through knots or material of varying ensity an to insure a true alignment of the hole through the epth of the beam. The vertical hole shoul be centere in the beam with. As a rule of thumb, vertical holes rille through the epth of an LVL beam cause a reuction in the capacity at that location irectly proportional to the ratio of 1-1/2 times the iameter of the hole to the with of the beam. For example, a 1/2-inch hole rille in a 3-1/2-inch-wie LVL beam woul reuce the beam capacity at that section by approximately 21 percent [(1/2 x 1-1/2)/3-1/2 = 21%]. Holes for Support of Suspene Equipment Heavy equipment or piping suspene from LVL beams shoul be attache such that the loa is applie to the top of the beam to avoi inucing tension perpenicular-to-grain stresses. Any horizontal holes require for support of significant weight, such as suspene heating an cooling units or main water lines, shoul be locate above the neutral axis of the beam an in a zone stresse to less than 50 percent of the allowable bening stress. The beam capacity shoul be checke for all such loas to ensure proper performance. Protection of Fiel-Cut Notches an Holes Frequently, LVL beams are provie by the manufacturer with the ens seale by a protective coating. This sealer is applie to the en grain of the LVL to retar the migration of moisture in an out of the beam ens uring transit an job site storage. Fiel cutting a notch at the en of a beam can change the moisture absorption characteristics of LVL at the notch location. This can result in localize splitting at the corners of the notch. To minimize this possibility, all notches shoul be seale with a water-repellent sealer immeiately after cutting. Sealing other fiel cuts as well as fiel-rille holes is also recommene. These sealers can be applie with a brush, swab, roller or spray gun. Form No. EWS G535A 2010 APA The Engineere Woo Association

6 Fiel Notching an Drilling of Laminate Veneer Lumber We have fiel representatives in many major U.S. cities an in Canaa who can help answer questions involving APA traemarke proucts. For aitional assistance in specifying engineere woo proucts, contact us: APA HEADQUARTERS 7011 So. 19th St. Tacoma, Washington (253) Fax: (253) PRODUCT SUPPORT HELP DESK (253) Aress: DISCLAIMER The information containe herein is base on APA The Engineere Woo Association s continuing programs of laboratory testing, prouct research an comprehensive fiel experience. Neither APA, nor its members make any warranty, expresse or implie, or assume any legal liability or responsibility for the use, application of, an/or reference to opinions, finings, conclusions or recommenations inclue in this publication. Consult your local jurisiction or esign professional to assure compliance with coe, construction an performance requirements. Because APA has no control over quality of workmanship or the conitions uner which engineere woo proucts are use, it cannot accept responsibility for prouct performance or esigns as actually constructe. Form No. EWS G535A/Revise June 2010