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3.1 CHAPTER THREE WOOD STRUCTURAL PANELS IN STRUCTURAL COMPONENTS H. Fulton Desler Senior Engineer, TSD 3.1 INTRODUCTION* The structural components included in this chapter are box beams, stressed-skin panels, and structural insulated panels (SIPs). These are composed of a combination of wood structural panels and lumber, or structural composite lumber, although flanges, stiffeners, and splices may also be composed of wood structural panels with little or no sawn lumber products required. Components made of wood structural panels and lumber are often major struc- tural members, which depend on the glued or mechanically fastened joints to com- bine the separate pieces into an efficient structural unit capable of carrying the design loads. Materials in these components may be stressed to an appreciably higher level than in nonengineered construction. Since improperly designed or fabricated components could constitute a hazard to life safety and property damage, it is strongly recommended that they be designed by qualified design professionals, using recognized design and fabrication methods, and that adequate quality control be maintained during manufacture. To ensure that such quality control has been carefully maintained, it is recom- mended that the services of an independent third-party testing agency be employed. A requirement that each unit bear the trademark of an approved agency will ensure adequate independent inspection. Working design capacities for wood structural panels are given in Chapter 2. References are also made to the American Forest and Paper Association publication National Design Specification for Wood Construction (NDS) 1 for other wood prod- ucts. Presentation of these specific design methods is not intended to preclude further innovation. Therefore, where adequate test data are available, the design provisions *Caution on the use of equations: Metric equivalents are frequently given in this chapter. Many of the equations contain constants or variables that are intended to permit the use of mixed units and may make these equations incapable of being used by directly substituting equivalent metric units. 3.2 CHAPTER THREE may be appropriately modified. If they are modified, any such change should be noted when cross-referencing the design procedure to those presented in this Hand- book. Quality of workmanship and the conditions under which wood structural panels are used vary widely. Because the authors and publisher of this Handbook have no control over those elements, they cannot accept responsibility for wood structural panel or lumber performance or designs as actually constructed. 3.1.1 Growth of Industry and History There is little if any actual box beam industry in the United States. These com- ponents are often built on-site, for residential construction, using nails. Nailed box beams are most-often used by do-it-yourselfers since the time spent in fabrication has less value to the builder than the cost of buying a ready-made alternative, such as a glulam or LVL beam. Factory-built beams may be fastened together mechanically with nails or staples or with a structural adhesive such as resorcinol. Best estimates put the size of the industry at about 2,000,000 ft 2 ( 3 ⁄ 8 in. [9.5 mm] basis). Because of the availability of alternative engineered wood products, the use of wood structural panels in box beams is not expected to grow. Of the different fabricated-component industries utilizing wood structural panels, the structural insulated panel (SIP) industry is the major user. Here the usage is in the neighborhood of 100,000,000 ft 2 ( 3 ⁄ 8 in. [9.5 mm] basis) and is growing steadily as designers and users recognize the benefits of using SIPs. SIPs are used in both residential and nonresidential construction. They are built to specification in a fac- tory for rapid installation at the job site. Stressed-skin panels are assemblies that have wood structural panel faces and backs with framing lumber or ribs in between. No statistics on utilization of wood structural panels for use in stressed-skin panels are available. Their use has declined in recent years, but they are still occasionally used in floors and roofs in the man- ufactured housing industry. 3.2 DESIGN OF GLUED PANEL LUMBER BOX BEAMS 3.2.1 General This design method applies only to box beams with joints glued with structural adhesive. Design of mechanically fastened box beams is covered in Section 3.3. The primary difference in analysis between the two methods of fastening box beam components together is in the analysis of rolling shear stresses. With glued beam components, rolling shear must be considered in the design. With mechanically fastened box-beam components, planar (rolling) shear is seldom a consideration. Beam Behavior. In wood structural panel box beams, the lumber flanges carry most of the bending, and one or more panel webs carry the shear. Joints between them transfer stresses between components. Vertical stiffeners set between flanges distribute concentrated loads and resist web buckling. Deflection resulting from shear is usually significant and must be WOOD STRUCTURAL PANELS IN STRUCTURAL COMPONENTS 3.3 added to the bending deflection. Lateral restraint is often required to maintain sta- bility. End joints in flange laminations and webs may require splicing. Shape. Loads, spans, and allowable stresses, as well as desired appearance, de- termine the beam proportions. The depth and cross section may be varied along the length of the beam to fit design requirements, provided the resisting moments and shears at all sections are adequate. Typical cross sections are shown in Fig. 3.1. 3.2.2 Design Considerations Design Loads. Live loads are typically those that are caused by objects moved into the structure after it is completed, including the occupants and their equipment and possessions. Snow, wind, and earthquake are special cases of live loads. The design live loads should not be less than required by the governing building code. Dead loads are those that will remain in place for 10 years or more. Dead load is the actual weight of the members and the permanent elements it supports. Allow- ance should be made for any temporary erection (construction) loads, or moving concentrated loads, such as cranes. Allowable Working Capacities. Working capacities are determined as described in Chapter 2, with due regard for duration of loading. For symmetrical sections, the design should be based on the allowable stress in axial tension or compression, whichever is less. When butt joints occur in the tension flange, the design should be based on 0.8 of the allowable tensile stress. Values for compression and tension parallel with lumber grain depend on spe- cies, grade, number of laminations, slope of scarf joints, and moisture condition. Values are applied as outlined in Chapter 2. Allowable stresses for stress-grade lumber flanges shall not exceed those given in the latest edition of the NDS. 1 Allowable stress level at any point in the flanges must be determined based on the number of laminations continuous at that point. Any lamination with a butt joint within 10 times the lamination thickness of the point under investigation is considered discontinuous. Allowable Deflection. Deflection should not exceed that allowed by the applicable building code. Maximum deflections recommended, shown in Table 3.1, are the proportions of the span, L, in inches. More severe limitations may be required for special conditions, such as for supporting vibrating machinery, long spans, or beams over large glass windows or sliding doors. Camber. Camber may be provided opposite to the direction of anticipated deflec- tion for purposes of appearance or utility. It will have no effect on strength or actual stiffness. Where roof and floor beams are cambered, a recommended amount is 1.5 times the deflection due to dead load only. This will provide a nearly level beam under conditions of long-term dead load application. Additional camber may be introduced as desired to provide for drainage or appearance. Members used in low-slope roof applications must be designed to pre- vent ponding of water. This may be done either by cambering or by providing slope or stiffness such that ponding will not occur. 3.4 Typical Section at Beam Ends (High Shear) (If extra webs are outside) (If extra webs are inside) Typical Section in Center Portion of Span FIGURE 3.1 Typical beam sections. WOOD STRUCTURAL PANELS IN STRUCTURAL COMPONENTS 3.5 TABLE 3.1 Standard Allowable Deflections for Beams Floor beams Live load only L/360 Dead plus live load L/240 Roof beams Live load only L/240 Dead plus live load L/180 3.2.3 Trial Section The first step in the actual design of a wood-structural-panel box beam is the selection of a trial section. Suitable beam depths vary somewhat, ranging generally from 1 ⁄ 8 to 1 ⁄ 12 of the span (although ratios up to 1 ⁄ 22 have been successfully used). The depth should ordinarily be equal to an available width of wood structural panel, such that waste is minimized. As a rule, the flange depth should be equal to at least four times the adjoining wood-structural-panel web thickness in order to have suf- ficient contact area between the flange and web for gluing. Selection from Table. Table 3.2 lists preliminary bending and shear capacities for typical glued box beams with two webs. First, determine the design requirements in terms of maximum moment and shear. A cross section that meets the design requirements may then be selected directly from the table. Tabular maximums, however, may also be subject to a number of adjustments based on duration of load, allowable flange tension stress (grade of lumber), and web thickness and grade. Note that further adjustment will be necessary when butt joints are allowed in lumber flanges. For example, it may be necessary to add a lamination to those shown in the table. The final design must then take into account provisions of Section 3.6.6. Lumber Flanges Symmetrical Sections. Symmetrical cross sections are generally used in wood- structural-panel beams for several practical reasons. These practical considerations usually outweigh the savings in material that theoretically can be achieved with unsymmetrical sections. The design stresses for flanges are those for allowable stress in axial tension and axial compression. With symmetrical sections, the lower of these allowable stresses will limit the flange design. The equations in this section assume a sym- metrical section. Allowance for Surfacing. To allow for resurfacing of flange laminations for gluing, each lamination should be considered 1 ⁄ 8 in. (3 mm) smaller in dimension perpendicular to gluing surfaces ( 1 ⁄ 16 in. per surface) (2 mm) than its standard, net lumber size. Beams should be designed for an actual depth, h, slightly less than their nominal depth, to allow for resurfacing, which may occur for the sake of appearance or uniformity of depth. Actual depth of beams under 24 in. (610 mm) deep should be considered 3 ⁄ 8 in. (10 mm) less than nominal; for beams 24 in. (610 mm) and deeper, actual depth 3.6 CHAPTER THREE TABLE 3.2 Preliminary Maximum Moments and Shears for Glued Box Beams Preliminary selection estimates a Table basis DOL ϭ 1.00 Panel webs Thickness ϭ 15 ⁄ 32 in. Span rating ϭ 32/16 Grade ϭ Rated Sheathing—Structural I EA ϭ 4,150,000 lb /ft of width, each web F v t v ϭ 62 lb/in., each web F s (Ib/Q) ϭ 210 lb/in., each web Lumber flanges Species and Grade: Douglas fir-larch Select Structural F t ϭ 1,000 psi, unadjusted for size factor E ϭ 1,900,000 psi Beam depth, in. Flange Lams Size Max. moment, ft-lb M f M w M t Max. shear, lb V h V s Stiffness, lb-in. 2 EI 12 1 2 ϫ 4 3,563 512 4,076 1,055 2,091 405,359,633 12 2 2 ϫ 4 7,126 512 7,639 1,068 1,857 720,168,009 12 3 2 ϫ 4 10,690 512 11,202 1,073 1,779 1,034,976,385 16 1 2 ϫ 4 5,657 926 6,583 1,486 3,105 891,656,921 16 2 2 ϫ 4 11,314 926 12,240 1,519 2,722 1,563,438,930 16 3 2 ϫ 4 16,971 926 17,897 1,532 2,594 2,235,220,938 16 1 2 ϫ 6 5,863 802 6,665 1,369 4,253 1,023,152,754 16 2 2 ϫ 6 11,725 802 12,527 1,379 3,796 1,826,430,596 16 3 2 ϫ 6 17,588 802 18,390 1,383 3,644 2,629,708,438 20 1 2 ϫ 4 7,826 1,460 9,286 1,913 4,213 1,602,875,041 20 2 2 ϫ 4 15,652 1,460 17,112 1,969 3,640 2,770,093,183 20 3 2 ϫ 4 23,477 1,460 24,938 1,992 3,449 3,937,311,325 20 1 2 ϫ 6 8,639 1,266 9,905 1,798 5,758 1,922,470,875 20 2 2 ϫ 6 17,279 1,266 18,545 1,823 5,106 3,409,284,850 20 3 2 ϫ 6 25,918 1,266 27,184 1,833 4,888 4,896,098,825 20 1 2 ϫ 8 8,632 1,168 9,800 1,700 6,979 2,044,959,026 20 2 2 ϫ 8 17,264 1,168 18,432 1,709 6,235 3,654,261,152 20 3 2 ϫ 8 25,896 1,168 27,064 1,713 5,987 5,263,563,278 24 1 2 ϫ 4 9,831 2,094 11,925 2,322 5,301 2,503,820,790 24 2 2 ϫ 4 19,662 2,094 21,756 2,404 4,509 4,259,611,285 24 3 2 ϫ 4 29,493 2,094 31,587 2,440 4,245 6,015,401,780 24 1 2 ϫ 6 11,389 1,815 13,204 2,220 7,271 3,095,116,623 24 2 2 ϫ 6 22,779 1,815 24,594 2,264 6,392 5,442,202,951 24 3 2 ϫ 6 34,168 1,815 35,983 2,282 6,099 7,789,289,280 24 1 2 ϫ 8 11,820 1,675 13,495 2,114 8,800 3,386,764,149 24 2 2 ϫ 8 23,639 1,675 25,315 2,138 7,828 6,025,498,003 24 3 2 ϫ 8 35,459 1,675 37,134 2,147 7,504 8,664,231,858 24 1 2 ϫ 10 11,452 1,536 12,988 2,010 10,458 3,537,200,608 24 2 2 ϫ 10 22,905 1,536 24,440 2,018 9,352 6,326,370,920 24 3 2 ϫ 10 34,357 1,536 35,893 2,022 8,984 9,115,541,233 30 2 2 ϫ 4 26,229 3,300 29,529 3,061 6,010 7,360,192,535 30 3 2 ϫ 4 39,343 3,300 42,643 3,119 5,607 10,300,425,217 30 4 2 ϫ 4 52,457 3,300 55,757 3,151 5,406 13,240,657,899 30 2 2 ϫ 6 31,666 2,860 34,526 2,940 8,549 9,671,384,201 30 3 2 ϫ 6 47,498 2,860 50,358 2,973 8,113 13,767,212,717 WOOD STRUCTURAL PANELS IN STRUCTURAL COMPONENTS 3.7 TABLE 3.2 Preliminary Maximum Moments and Shears for Glued Box Beams (Continued) Beam depth, in. Flange Lams Size Max. moment, ft-lb M f M w M t Max. shear, lb V h V s Stiffness, lb-in. 2 EI 30 4 2 ϫ 6 63,331 2,860 66,191 2,991 7,895 17,863,041,233 30 2 2 ϫ 8 34,101 2,640 36,741 2,812 10,514 11,036,469,878 30 3 2 ϫ 8 51,151 2,640 53,791 2,832 10,044 15,814,841,233 30 4 2 ϫ 8 68,202 2,640 70,842 2,843 9,809 20,593,212,587 30 2 2 ϫ 10 34,397 2,420 36,817 2,669 12,543 11,995,692,795 30 3 2 ϫ 10 51,595 2,420 54,015 2,680 12,027 17,253,675,608 30 4 2 ϫ 10 68,793 2,420 71,213 2,686 11,769 22,511,658,420 30 2 2 ϫ 12 32,693 2,200 34,893 2,549 14,454 12,474,215,712 30 3 2 ϫ 12 49,039 2,200 51,239 2,554 13,882 17,971,459,983 30 4 2 ϫ 12 65,385 2,200 67,585 2,556 13,596 23,468,704,253 36 2 2 ϫ 4 32,842 4,779 37,621 3,706 7,603 11,439,373,785 36 3 2 ϫ 4 49,262 4,779 54,041 3,787 7,032 15,869,711,155 36 4 2 ϫ 4 65,683 4,779 70,462 3,834 6,746 20,300,048,524 36 2 2 ϫ 6 40,721 4,142 44,862 3,611 10,810 15,255,365,451 36 3 2 ϫ 6 61,081 4,142 65,223 3,661 10,201 21,593,698,655 36 4 2 ϫ 6 81,441 4,142 85,583 3,690 9,896 27,932,031,858 36 2 2 ϫ 8 44,930 3,823 48,753 3,489 13,336 17,731,416,753 36 3 2 ϫ 8 67,395 3,823 71,218 3,523 12,690 25,307,775,608 36 4 2 ϫ 8 89,860 3,823 93,684 3,542 12,366 32,884,134,462 36 2 2 ϫ 10 46,605 3,505 50,110 3,341 15,955 19,725,189,670 36 3 2 ϫ 10 69,908 3,505 73,412 3,362 15,260 28,298,434,983 36 4 2 ϫ 10 93,210 3,505 96,715 3,374 14,912 36,871,680,295 36 2 2 ϫ 12 45,487 3,186 48,673 3,201 18,362 20,987,462,587 36 3 2 ϫ 12 68,231 3,186 71,417 3,213 17,610 30,191,844,358 36 4 2 ϫ 12 90,975 3,186 94,161 3,220 17,234 39,396,226,128 42 2 2 ϫ 6 49,871 5,660 55,531 4,274 13,168 22,268,846,701 42 3 2 ϫ 6 74,806 5,660 80,467 4,344 12,356 31,343,447,092 42 4 2 ϫ 6 99,742 5,660 105,402 4,384 11,950 40,418,047,483 42 2 2 ϫ 8 55,968 5,225 61,193 4,164 16,269 26,185,038,628 42 3 2 ϫ 8 83,952 5,225 89,177 4,214 15,416 37,217,734,983 42 4 2 ϫ 8 111,936 5,225 117,161 4,241 14,989 48,250,431,337 42 2 2 ϫ 10 59,220 4,789 64,009 4,018 19,516 29,589,561,545 42 3 2 ϫ 10 88,830 4,789 93,619 4,052 18,610 42,324,519,358 42 4 2 ϫ 10 118,440 4,789 123,229 4,071 18,157 55,059,477,170 42 2 2 ϫ 12 58,956 4,354 63,310 3,871 22,498 32,011,784,462 42 3 2 ϫ 12 88,434 4,354 92,788 3,894 21,533 45,957,853,733 42 4 2 ϫ 12 117,912 4,354 122,266 3,906 21,050 59,903,923,003 48 2 2 ϫ 6 59,080 7,415 66,495 4,929 15,619 30,786,527,951 48 3 2 ϫ 6 88,621 7,415 96,036 5,020 14,575 43,091,158,030 48 4 2 ϫ 6 118,161 7,415 125,576 5,073 14,052 55,395,788,108 48 2 2 ϫ 8 67,135 6,845 73,980 4,833 19,304 36,472,035,503 48 3 2 ϫ 8 100,703 6,845 107,547 4,901 18,214 51,619,419,358 48 4 2 ϫ 8 134,270 6,845 141,115 4,939 17,669 66,766,803,212 48 2 2 ϫ 10 72,087 6,274 78,361 4,695 23,197 41,663,508,420 48 3 2 ϫ 10 108,130 6,274 114,404 4,744 22,050 59,406,628,733 48 4 2 ϫ 10 144,173 6,274 150,447 4,770 21,477 77,149,749,045 48 2 2 ϫ 12 72,843 5,704 78,547 4,548 26,792 45,621,881,337 48 3 2 ϫ 12 109,265 5,704 114,969 4,582 25,583 65,344,188,108 48 4 2 ϫ 12 145,686 5,704 151,390 4,600 24,979 85,066,494,878 3.8 CHAPTER THREE TABLE 3.2 Preliminary Maximum Moments and Shears for Glued Box Beams (Continued) a Bases and adjustments: 1. Basis: normal duration of load (C D ): 1.00 Adjustments: 0.90 for permanent load (over 50 years) 1.15 for 2 months, as for snow 1.25 for 7 days 1.6 for 10 minutes, as for wind or earthquake 2.00 for impact 2. Basis: F t of flange ϭ 1000 psi, (6,895 kPa) corrected by C F (Douglas fir-larch select structural, 1997 NDS) 1 2 ϫ 4 ϭ 1,000 ϫ 1.5 ϭ 1,500 psi 2 ϫ 6 ϭ 1,000 ϫ 1.3 ϭ 1,300 psi 2 ϫ 8 ϭ 1,000 ϫ 1.2 ϭ 1,200 psi 2 ϫ 10 ϭ 1,000 ϫ 1.1 ϭ 1,100 psi 2 ϫ 12 ϭ 1,000 ϫ 1.0 ϭ 1,000 psi Adjustment: for other tabulated tension stresses F t 1000 (C F in numerator and denominator cancel when flanges are same width.) 3. Basis: one web effective in bending because web joints are assumed to be unspliced. Adjustment: 2.0 for web splices should be considered 1 ⁄ 2 in. (13 mm) less than nominal. This resurfacing also results in reduced flange dimensions. Bending Moment—Symmetrical Sections. In a symmetrical section allowable bending moment may be calculated by the formula M ϭ FЈS (3.1) tT where M ϭ allowable bending moment (lb-in. or lb-ft) ϭFЈ t allowable controlling working tensile stress of the flange lumber after all permissible/required adjustments (psi) I T S ϭ (3.2) T c where S ϭ section modulus of beam cross section I T ϭ total moment of inertia of beam cross section c ϭ distance from beam neutral axis to outermost fiber Unsymmetrical Sections. When the cross section is not symmetrical about its center, the resisting moment may be calculated as above, except that the distance from the neutral axis to the extreme fiber of each flange is used in place of the value 0.5h and the moment of inertia is calculated with due regard for the location of the neutral axis. The location of the neutral axis is computed based on the total cross section, without reduction for butt joints. Net Moment of Inertia (I n ). The net moment of inertia, I n , is the sum of I of the flanges plus the sum of all effective web material. I n is used in determining the beam’s allowable bending moment and deflections. Wood Structural Panel Webs. When calculating moment of inertia of the wood structural panel webs, consider only effective material parallel to the span. The effective thickness, t Ј,is 1 ⁄ 12 of the appropriate area, A. The effective area, A,is derived from the axial stiffness, AEC G , of the panel. AEC G is obtained from Chapter 2, where it is in units of lb/ft of panel width. Dividing by E gives the designer the WOOD STRUCTURAL PANELS IN STRUCTURAL COMPONENTS 3.9 TABLE 3.3 Effective Area of Flange Laminations Butt joint Spacing (t ϭ lamination thickness) Effective factor 30t 90% 20t 80% 10t 60% panel area in in. 2 /ft of width. Dividing by E lumber gives the effective area of the panel transformed by the E of the lumber. (For a more detailed discussion of trans- formed sections see below, Transformed Section, under Section 3.4.1.) Dividing this by 12 in./ft of width gives the effective thickness, t Ј, of panel transformed by E lumber . The equation is: AEC G tЈ ϭ (3.3) 12 ϫ E lumber for tension and compression where AE ϭ panel stiffness capacity, from Chapter 2 C G ϭ adjustment to stiffness capacity, from Chapter 2 E lumber ϭ modulus of elasticity for lumber flanges Butt joints in wood structural panel webs are usually spliced to transmit shear only, with a splice plate only as deep as the clear distance between flanges. If such butt joints in webs are staggered 24 in. (610 mm) or more, only one web need be disregarded in computing moment of inertia for bending stress. When unequal web thicknesses are used, use the most critical condition for computing I n , unless the location of butt joints is specified in the design. For joints closer than 24 in. (610 mm), the contribution of the webs should be neglected in computing I n . When webs are spliced full-depth to carry direct flange stresses, they may all be included in computing the moment of inertia from allowable section capacities as given in Chapter 2. Flange Lumber. Butt joints in the lumber flanges are required by the Fabrica- tion Specification (Section 3.2.4) to be spaced at least 30 times the lamination thickness in adjoining laminations. Adjoining laminations refers to multiple-ply lumber flanges that are in direct face-to-face contact such as shown in Fig. 3.1. Butt joints in the lumber flanges are required to be spaced at least 10 times the lamination thickness in nonadjoining laminations (where web material separates multiple flanges), if not otherwise stipulated in the design. Ignore any panel material between laminations. If butt-joint location is not otherwise stipulated by the designer, the net moment of inertia of flanges in which butt joints occur may be calculated by ignoring one lamination and 10% of the two adjoining laminations. The effective area of such adjoining laminations shall be computed by multiplying their gross area by the percentages in Table 3.3. Butt joints spaced closer than 10t (t ϭ lamination thick- ness) shall be considered as occurring in the same section. Wood Structural Panel Webs. Webs are primarily stressed in shear through their thickness, although they may also carry bending moment, if individual panels are properly spliced to transmit both types of stresses. In addition, sufficient contact 3.10 CHAPTER THREE area with the flanges must be provided to transmit the stresses between web and flange. The number and thickness of the webs may be varied along the beam length in proportion to the shear requirements considering both shear through the panel thick- ness at the neutral axis and planar/rolling shear between flange and web. Where web joints result in a change of beam thickness, wood structural panel or lumber shims may be glued to the flanges to maintain beam width as required for appear- ance or for gluing pressure. When the depth of a beam is tapered, the net vertical component of the direct forces in the flanges should be considered in determining the net shear to be resisted by the webs and the flange-web joints. This vertical component may add to or subtract from the external shear. It is equal to M/L 1 , where M is the bending moment acting on the section and L 1 is the horizontal distance from the section to the intersection of the flange centerlines. Horizontal Shear. The allowable horizontal shear on a section can be calculated by the following formula: Ft ЈCIN vv GT V ϭ (3.4) h Q T where V h ϭ allowable total horizontal shear (through the panel thickness) on sec- tion (lb). ϭFtЈ vv allowable shear capacity through the panel thickness (lb/in.), as given in Chapter 2, with adjustments such as duration of load, if applicable. Note that per Plywood Design Specification, Section 3.9.1, 3 F v , and by extension F v t v , can commonly be increased by 19% for plywood and 33% for marine-grade plywood. C G ϭ adjustment factor, depending on panel type, as given in Chapter 2 I T ϭ total moment of inertia of all flanges and webs about the neutral axis regardless of any butt joints (in. 4 ). N ϭ number of webs effective in shear (typically the same as the number of webs). Q T ϭ statical moment about the neutral axis of all flanges and webs, regard- less of any butt joints, lying above (or below) the neutral axis (in. 3 ). End Joints for Tension or Bending. End joints across the face grain shall be considered capable of transmitting the following stresses parallel with the face plies (normal duration of load). Scarf Joints and Finger Joints. Scarf joints 1 in 8 or flatter shall be considered as transmitting full allowable stress in tension or flexure. Scarf joints 1 in 5 shall be considered as transmitting 75% of the allowable stress. Scarf joints steeper than 1 in 5 shall not be used. Finger joints are acceptable, at design levels supported by adequate test data. Butt Joints. When backed with a glued wood-structural-panel splice plate on one side having its strength axis perpendicular to the joint, the same width as the panels spliced, of a grade and span rating the same as the panel itself, joints may be considered capable of transmitting tensile or flexural stresses as in Table 3.4 (normal duration of loading). Splices are to be at least 14 in. long on each side of the joint. With adequately supported test data, it may be possible to make splices shorter. Mated faces of glued joints must be clean and free of oils and waxes prior to application of the adhesive. [...]... IT ϭ 36 63 ϩ 419 .3 ϭ 4082 .3 in.4 (6.802 ϫ 106 mm4) (3. 34) WOOD STRUCTURAL PANELS IN STRUCTURAL COMPONENTS QT ϭ Qflange ϩ Qwebs Qflange ϭ A Qflange ϭ 3( 5.5) ͩ ͪ (3. 35) ͩ ͪ h d Ϫ 2 2 (3. 36) 24 3 Ϫ ϭ 1 73. 25 in .3 (2 839 ϫ 1 03 mm3) 2 2 Qweb ϭ Qweb ϭ 3. 33 ͩ ͩ ͪ A h h Ϫ 2 2 4 ͪ (3. 37) (0.182)(24) 24 24 Ϫ ϭ 13. 1 in .3 (214 ϫ 1 03 mm3) 2 2 4 Qwebs ϭ NQweb (3. 38) Qwebs ϭ 2( 13. 1) ϭ 26.2 in (429 ϫ 10 mm ) 3 3 3 QT... 1000(1 .3) 130 0 psi (8.96 MPa) FЈ flanges ϭ FtCf CD ϭ 130 0(1.15) ϭ 1495 psi (10 .31 MPa) t I Sflanges ϭ flanges (in .3) c Iflanges ϭ b[h3 Ϫ (h Ϫ 2d )3) ] (in.4) 12 c ϭ distance from neutral axis to outermost fiber ϭ ϭ 12 in (30 5 mm) (3. 31) h 24 ϭ 2 2 3. 32 CHAPTER THREE d ϭ depth of flange (in.) ͭ ͮ 24 Ϫ [24 Ϫ (2) (3) ]3 ϭ 36 63 in.4 (1524 ϫ 106 mm4) 12 Iflanges ϭ 5.5 3 Sflanges ϭ I 36 63 ϭ ϭ 30 5.25 in .3 (5002... neutral axis to outermost fiber ϭ D 23. 5 ϭ ϭ 11.75 in (298 mm) 2 2 Sflange ϭ 2470.6 ϭ 210 .3 in .3 (34 46 ϫ 1 03 mm3) 11.75 196.8 ϭ 16.8 in .3 (275 ϫ 1 03 mm3) 11.75 Sweb ϭ Section Moment Capacity MT ϭ FtЈS ϭ (FЈS)total t FЈ(CD)S ϭ 130 0 ϫ 1.15 ϫ (210 .3 ϩ 16.8) t ϭ 33 9,514 lb-in / ft (125.85 kN-m / ft) Ft(CD)S ϭ 33 9,514 12 ϭ 28,292 lb-ft (38 ,35 9 N-m) ഡ 28,420 lb-ft (38 , 532 N-m) OK Note that the use of five-ply,... 1.5 ϭ 1200 psi (8.27 MPa) 3. 20 CHAPTER THREE d= 3. 25 c h= 23. 5 c b= 2.75 FIGURE 3. 3 Assumed Section: Trial 1 Iflange Iweb ϩ c c (3. 13) bh3 b 3 3 ϭ (h Ϫ d 1) 12 12 (3. 14) Sflanges ϩ Swebs ϭ Iflange ϭ h ϭ net depth of beam ϭ 24 in Ϫ 0.5 in ϭ 23. 5 in (595 mm) d ϭ net depth of flanges ϭ 3. 5 in Ϫ ͩ ͪ 0.5 ϭ 3. 25 in (85 mm) 2 d1 ϭ net beam depth Ϫ 2(d) ϭ 23. 5 Ϫ 2 (3. 25) ϭ 17 in ( 430 mm) b ϭ net width of flanges... (Aflange) d ϭ depth of flange (in.) Qflange ϭ 5.25(2.75) ͩ ͪ ͩ ͪ h d Ϫ 2 2 (3. 20) 23. 5 5.25 Ϫ ϭ 131 .7 in .3 (2158 ϫ 1 03 mm3) 2 2 Qweb ϭ (Aweb) ͩ ͪ h c Ϫ 2 2 (3. 21) c ϭ distance from neutral axis to outermost fiber Qweb ϭ 23. 5(0.182) ϭ ͩ ͪ 23. 5 11.75 Ϫ ϭ 25.1 in .3 (411 ϫ 1 03 mm3) 2 2 QT ϭ 131 .7 ϩ 25.1 ϭ 156.9 in .3 (2571 ϫ 1 03 mm3) Vh ϭ 169.7(2864.2)2 ϭ 6196 lb Ͼ 4060 lb 156.9 OK Check Panel Shear in the.. .3. 11 WOOD STRUCTURAL PANELS IN STRUCTURAL COMPONENTS TABLE 3. 4 Panel Butt Joints—Tension or Flexure (Minimum splice length ϭ 16 in on each side of joint) Maximum stress Span rating 24 / 0 24 / 16 32 / 16 40 / 20 48 / 24 16 oc 20 oc 24 oc Thickness (in.) 3 ⁄8 ⁄16 15 32 19 32 23 32 19 32 19 32 23 32 7 Ft ACG psi A Structural I grades Regular grades 3 ply 4 ply 5 ply OSB 3 ply 4 ply... ϫ 1.15 ϫ (157 .3 ϩ 24.9) ϭ 251, 436 lb-in t Converting to lb-ft: Ft(CD)STotal ϭ 251, 436 12 ϭ 20,9 53 lb-ft (28,408 N-m) Ͻ 28,420 lb-ft (38 , 532 N-m) OK Trial 1 Summary Section Properties (transformed) Inet (in.4) Flanges Webs Total Igross (in.4) Snet (in .3) Moment capacity (lb-ft) 1848.2 2 93. 1 2141 .3 1848.2 586.2 2 434 .4 157 .3 24.9 182.2 — — 20,9 53 Because this is considerably less moment capacity than required,... ͪ (0.271)( 23. 5 )3 ϭ 2 93. 1 in.4 (122 ϫ 106 mm4) 12 Note that only a single web is used in calculating bending strength because the webs are not spliced for bending in this example Find Sϭ I c where c ϭ distance from neutral axis to outermost fiber 23. 5 ϭ ϭ 11.75 in (298 mm) 2 1848.2 Sflange ϭ ϭ 157 .3 in .3 (2578 ϫ 1 03 mm3) 11.75 2 93. 1 Sweb ϭ ϭ 24.9 in .3 (408 ϫ 1 03 mm3) 11.75 Section moment capacity: (FЈS)total... ϭ Net depth of beam ϭ 24 in Ϫ 0.5 in ϭ 23. 5 in (597 mm) 0.5 d ϭ Net depth of flanges ϭ 5.5 in Ϫ ϭ 5.25 in ( 133 mm) 2 ͩ ͪ d1 ϭ 23. 5 Ϫ 2(5.25) ϭ 13 in (33 0 mm) Iflange ϭ 2.75 [( 23. 5 )3 Ϫ ( 13) 3] ϭ 2470.6 in.4 (1028 ϫ 106 mm4) 12 tweb ϭ tweb ϭ Iweb ϭ ͩ EAwebCG 12Elumber 4,150,000(1.0) ϭ 0.182 in (5 mm) 12(1,900,000) ͪ (0.182)( 23. 5)2 ϭ 196.8 in.4 (81.91 ϫ 106 mm4) 12 3. 24 CHAPTER THREE Section Modulus of Beam... flanges ϭ 1,900,000 psi ( 13. 1 GPa) FtCF ϭ allowable tensile stress in flanges ϭ 1000 ϫ 1 .3 ϭ 130 0 psi (8.96 MPa) where Ft ϭ tabulated tensile stress (psi) CF ϭ size factor (NDS1) Moment of Inertia (I ) of Beam Components IT ϭ ͩ ͪ bh3 12 Iϭ flanges ϩ ͩ ͪ bh3 12 b 3 3 (h Ϫ d 1) 12 webs (3. 17) WOOD STRUCTURAL PANELS IN STRUCTURAL COMPONENTS 3. 23 Y d= 5.25 h= 23. 5 X X b= 2.75 Y FIGURE 3. 4 Assumed Section: Trial . 34 ,35 7 1, 536 35 ,8 93 2,022 8,984 9,115,541, 233 30 2 2 ϫ 4 26,229 3, 300 29,529 3, 061 6,010 7 ,36 0,192, 535 30 3 2 ϫ 4 39 ,34 3 3, 300 42,6 43 3,119 5,607 10 ,30 0,425,217 30 4 2 ϫ 4 52,457 3, 300 55,757 3, 151. 17, 731 ,416,7 53 36 3 2 ϫ 8 67 ,39 5 3, 8 23 71,218 3, 5 23 12,690 25 ,30 7,775,608 36 4 2 ϫ 8 89,860 3, 8 23 93, 684 3, 542 12 ,36 6 32 ,884, 134 ,462 36 2 2 ϫ 10 46,605 3, 505 50,110 3, 341 15,955 19,725,189,670 36 . 44,862 3, 611 10,810 15,255 ,36 5,451 36 3 2 ϫ 6 61,081 4,142 65,2 23 3,661 10,201 21,5 93, 698,655 36 4 2 ϫ 6 81,441 4,142 85,5 83 3,690 9,896 27, 932 , 031 ,858 36 2 2 ϫ 8 44, 930 3, 8 23 48,7 53 3,489 13, 336