APA Engineered Wodd Handbooks Episode 4 ppt

4.1 CHAPTER FOUR STRUCTURAL GLUED LAMINATED TIMBER (GLULAM) Borjen Yeh, P.E., PhD Manager, Research and Development, TSD 4.1 INTRODUCTION Structural glued laminated timber (glulam) is a structural member glued up from suitably selected and prepared pieces of laminating lumber or ‘‘laminations’’ either in a straight or curved form with the grain of all pieces parallel to the longitudinal axis of the member. Glued laminated timber members are produced in laminating plants by gluing together dry lumber, normally of 2 in. or 1 in. nominal thickness, under controlled conditions of temperature and pressure. Members with a wide variety of sizes, profiles, and lengths can be produced for superior characteristics of strength, serviceability, and appearance. Glued laminated timber beams are man- ufactured with the strongest laminations on the bottom and top of the beam, where greatest tension and compression stresses occur in bending. This allows a more efficient use of the lumber resource by placing higher grade lumber in zones that have higher stresses and lumber with less structural quality in lower-stressed zones. Glued laminated timber is manufactured from several softwood species, primar- ily Douglas fir-larch, southern pine, hem-fir, spruce-pine-fir, eastern spruce, western woods, Alaska cedar, Durango pine, and California redwood. Several hardwood species, including red oak, red maple, and yellow poplar, are also used. Standard glued laminated timber sizes are given in Section 4.1.2. Any length, subject to the maximum length permitted by transportation and handling restrictions, is available. Glued laminated timber is typically manufactured with kiln-dry lumber having a maximum moisture content at the time of fabrication of 16%. As a result, the allowable design stresses for glued laminated timber are higher than dry (moisture content of 19% or less) or green lumber. The use of kiln-dry laminating lumber also means that the moisture content of glued laminated timber is relatively uniform throughout the member, unlike green sawn timbers, which may have widely varying moisture contents within a given member. This use of uniformly dry lumber gives glued laminated timber excellent dimensional stability. Thus, a glued laminated timber member will not undergo the dimensional changes normally associated with larger solid-sawn green timbers, and will remain straight and true in cross-section. A dry glued laminated timber is also less susceptible to the checking and splitting that is often associated with green timbers. 4.2 CHAPTER FOUR FIGURE 4.2 Disney ICE rink in Anaheim, California, features glulam arches curved to a 75-ft radius to form the ice center’s roof systems. FIGURE 4.1 Glulam beam supports second floor I-joist construction. Glued laminated timber is one of the most versatile of the family of glued engineered wood products and is used in applications ranging from concealed beams and headers in residential construction to structures with large open spaces (see Figs. 4.1 and 4.2). Glued laminated timber has greater strength and stiffness than comparable dimensional lumber. Pound for pound, it is stronger than steel. Because of their composition, large glued laminated timber members can be manu- factured from smaller trees harvested from second- and third-growth forests and plantations. With glued laminated timber, the designer and builder can continue to enjoy the strength and versatility of large wood members without relying on the old growth-dependent solid-sawn timbers. STRUCTURAL GLUED LAMINATED TIMBER (GLULAM) 4.3 4.1.1 100 Years of Glued Laminated Timber In terms of current needs to optimize products from a carefully managed timber resource, glued laminated timber is one of the most resource-efficient approaches to wood building products. It is an engineered product manufactured to meet the most demanding structural requirements. But glued laminated timber is not a new product. The first patents for glued laminated timber were issued in Switzerland and Germany in the late 1890s. A 1906 German patent signaled the true beginning of glued laminated timber construction. One of the first glued laminated timber structures erected in the United States was a research laboratory at the USDA Forest Products Laboratory in Madison, Wisconsin. The structure was erected in 1934 and is still in service today. A significant development in the glued laminated timber industry was the intro- duction of fully water-resistant phenol-resorcinol adhesives in 1942. This allowed glued laminated timber to be used in exposed exterior environments without con- cern of glueline degradation. The first U.S. manufacturing standard for glued lam- inated timber was Commercial Standard CS253-63, which was published by the Department of Commerce in 1963. The most recent standard is ANSI/AITC A190.1-92, 1 which took effect in 1993. 4.1.2 Typical Sizes Individual pieces of laminating lumber used in glued laminated timber manufac- turing are typically 1 3 ⁄ 8 in. thick for southern pine and 1 1 ⁄ 2 in. thick for Western species, although other thicknesses may also be used. Glued laminated timber prod- ucts typically range in net widths from 2 1 ⁄ 2 to 10 3 ⁄ 4 in., although virtually any member width can be custom produced. Glued laminated timber is available in both custom and stock sizes. Stock beams are manufactured in commonly used dimensions and cut to length when the beam is ordered from a distributor or dealer. Typical stock beam widths include 3 1 ⁄ 8 ,3 1 ⁄ 2 , 5 1 ⁄ 8 ,5 1 ⁄ 2 , and 6 3 ⁄ 4 in., which meet the requirements for most residential construction applications. Where long spans, unusually heavy loads, or other circumstances con- trol design, custom members are typically specified. Custom members are available in virtually any size and shape that may be required to meet the design conditions. Some of the common custom shapes that are available include curved beams, pitched and curved beams, radial arches and tudor arches (see Figs. 4.3 and 4.4). 4.1.3 Common Uses Glued laminated timber has a reputation for being used in striking applications such as vaulted ceilings and other designs with soaring open spaces. In churches, schools, restaurants, and other commercial buildings, glued laminated timber is often spec- ified for its beauty as well as its strength for good reason. Glued laminated timber has the classic natural wood appearance that holds a timeless appeal. Aesthetics aside, there are many other applications where the strength and durability of glued laminated timber beams make them the ideal struc- tural choice. Typical uses range from simple purlins, ridge beams, floor beams, and cantilevered beams to complete commercial roof systems. In some instances, ware- house and distribution centers with roof areas exceeding 1 million ft 2 have been constructed using glued laminated timber framing. In large open spaces, glued lam- inated timber beams can span more than 100 ft. 4.4 CHAPTER FOUR FIGURE 4.3 Two-lane highway bridge in Colorado using glulam radial arches. One of the greatest advantages of glued laminated timber is that it can be man- ufactured in a wide range of shapes, sizes, and configurations. In addition to straight prismatic sections, beams can also be produced in a variety of tapered configura- tions, such as single-tapered, double-tapered, and off-centered ridges. Curved shapes range from a simple curved beam to a pitched and tapered curved beam to a complex arch configuration. Spans using glued laminated timber arches are vir- tually unlimited. For example, in reticulated glued laminated timber framed dome structures, arches can span more than 500 ft. Glued laminated timber trusses also take many shapes including simple pitched trusses, complicated scissors configurations, and long-span bowstring trusses with curved upper chords. When designed as space frames, glued laminated timber truss systems can create great clear spans for auditoriums, gymnasiums, and other ap- plications requiring large open floor areas. When manufactured with waterproof phenol resorcinol adhesives, glued laminated timber products can be fully exposed to the environment, provided they are properly pressure-preservative treated. Ex- posed applications include utility poles and cross-arms, marinas, docks, and other waterfront structures and bridges. Bridges represent a growing market for glued laminated timber in pedestrian and light vehicular applications for stream and roadway crossings. Glued laminated timber is also used in secondary highway bridge designs ranging from straight girders to soaring arches. And the railroads are finding glued laminated timber to be a viable structural product for use in their heavily loaded bridge structures. In all of these uses, the strength and stiffness of glued laminated timber give builders and designers more design versatility than they have with other structural products. And, these advantages come at a cost that is competitive with other struc- tural systems. Table 4.1 lists economical spans for selected timber framing systems STRUCTURAL GLUED LAMINATED TIMBER (GLULAM) 4.5 FIGURE 4.4 This 236,000 ft 2 potash storage building in Portland, Oregon, features glulam arches. using glued laminated timber members in buildings. This table may be used for preliminary design purposes to determine the economical span ranges for the se- lected framing systems. However, all systems require a more extensive analysis for final design. 4.1.4 Availability Glued laminated timber members are available in both custom and stock sizes. Custom beams are manufactured to the specifications of a specific project, while stock beams are made in common dimensions, shipped to distribution yards, and cut to length when the beam is ordered. Stock beams are available in virtually every major metropolitan area. Although glued laminated timber members can be custom fabricated to provide a nearly infinite variety of forms and sizes, the best economy is generally realized by using standard-size members. When in doubt, the designer is advised to check with the glued laminated timber suppliers or manufacturers concerning the availability of a specific size glued laminated timber members prior to specification. The following trade associations are available for technical assis- tance: 4.6 CHAPTER FOUR TABLE 4.1 Economical Spans for Glulam Framing Systems Type of framing system Economical spans (ft) Roof Simple-span beams Straight or slightly cambered 10–100 Tapered, double tapered-pitched, or curved 25–105 Cantilevered beams (main span) up to 90 Continuous beams (interior spans) 10–50 Girders 40–100 Three-hinged arches Gothic 40–100 Tudor 40–140 A-frame 20–100 Three-centered, parabolic, or radial 40–250 Two-hinged arches Radial or parabolic 50–200 Trusses (four- or more ply chords) Flat or parallel chord 50–150 Triangular or pitched 50–150 Bowstring (continuous chord) 50–200 Trusses (two- or three-ply chords) Flat or parallel chord 20–75 Triangular or pitched 20–75 Tied arches 50–200 Dome structures 200–500 ϩ Floor Simple span beams 10–40 Continuous beams (individual spans) 10–40 Headers Windows and doors Ͻ10 Garage doors 9–18 APA—The Engineered Wood Association and Engineered Wood Systems (EWS), a related corporation of APA 7011 South 19th Street Tacoma, WA 98466 Phone: (253) 565-6600 Fax: (253) 565-7265 American Institute of Timber Construction 7012 South Revere Parkway, Suite 140 Englewood, CO 80112 Phone: (303) 792-9559 Fax: (303) 792-0669 STRUCTURAL GLUED LAMINATED TIMBER (GLULAM) 4.7 TABLE 4.2 U.S. and Canada Glued Laminated Timber Production 1993 1994 1995 1996 1997 1998 1999 (Million board ft) U.S. Production 241.0 266.1 282.0 309.0 300.0 287.2 315.8 Canada Production NA a NA a 13.0 13.0 15.0 13.0 15.2 North America Total – – 295.0 322.0 315.0 300.2 331.0 a NA, not available; data collection started in 1995. Source: APA—The Engineered Wood Association (April 2000). 4.2 GROWTH OF INDUSTRY Table 4.2 shows the recent history of the glued laminated timber production in North America. Glued laminated timber production is expected to increase steadily in the years to come, as shown in Fig. 4.5. New-generation 30F beams with higher shear strengths are being introduced. A new family of I-joist compatible products is beginning to make market inroads. In addition, fiber-reinforced technology should be more widely available in the near future to help glued laminated timber, and wood construction in general, penetrate the commercial building market. All of these product innovations will be important to the future growth of this industry. Approximately one-half of the glued laminated timber produced in the United States goes to new residential and remodeling uses. The next largest segment is the nonresidential market, as shown in Fig. 4.6. 4.3 STANDARDS 4.3.1 ANSI/AITC A190.1 ANSI/AITC A190.1, the American National Standard for Structural Glued Lami- nated Timber, 1 is a national consensus standard for glued laminated timber manu- facturing. Detailed manufacturing requirements for glued laminated timber are doc- umented in ANSI/AITC A190.1. This standard is recognized in the U.S. model building codes, and a construction specification for glued laminated timber should include reference to this standard. 4.3.2 ASTM D3737 ASTM D 3737, Standard Practice for Establishing Stresses for Structural Glued Laminated Timber, 2 provides a consensus approach in deriving allowable properties for glued laminated timber manufactured in accordance with ANSI A190.1. In the U.S. glued laminated timber industry, two computer programs developed by the major trade associations, APA—The Engineered Wood Association and American Institute for Timber Construction (AITC) are recognized by the model building codes as an alternative to the procedures given in ASTM D3737 for establishing 4.8 CHAPTER FOUR 500 450 400 350 300 250 200 Million Board Feet 2005'04'03'02'01'00'99'98'971996 FIGURE 4.5 Glued laminated timber production in North Amer- ica. (Forecast for 2001 and beyond by APA.) Industrial/Other 2% Residential/R&R 52% International 8% Nonresidential 38% FIGURE 4.6 Glued laminated timber end use in the United States. (2000 production volume per APA.) design properties for glued laminated timber. These associations share the database required for their computer programs on generic laminating lumber grades. 4.4 MECHANICAL PROPERTIES 4.4.1 Lay-up Principles The laminating process used in glued laminated timber manufacturing results in a random dispersion of strength-reducing growth characteristics, such as knots and slope of grain, of lumber throughout the glued laminated timber member. Conse- quently, glued laminated timber has higher mechanical properties with a lower variability than sawn lumber products of comparable sizes. For example, the co- efficient of variation for the modulus of elasticity (E) of glued laminated timber is published as 10%, which is equal to or lower than any other wood product. STRUCTURAL GLUED LAMINATED TIMBER (GLULAM) 4.9 Tension Lam UNBALANCED No. 1 No. 2 No. 3 No. 3 No. 3 No. 2 No. 2 No. 2D Tension Lam BALANCED No. 1 No. 2 No. 3 No. 3 No. 3 No. 2 No. 1 Tension Lam FIGURE 4.7 Unbalanced and balanced lay-up combinations. Single- and Multiple-Grade Lay-ups. Glued laminated timber can be manufac- tured using a single grade or multiple grades of lumber, depending on the intended use. A mixed-species glued laminated timber member is also possible. When the member is intended to be primarily loaded either axially or in bending with the loads acting parallel to the wide faces of the laminations, a single-grade combi- nation is recommended. On the other hand, a multiple-grade combination provides better cost-effectiveness when the member is primarily loaded in bending due to loads applied perpendicular to the wide faces of the laminations. On a multiple-grade combination, a glued laminated timber member can be produced as either a balanced or unbalanced combination, depending on the geo- metrical arrangement of the laminations about the middepth of the member. This is further explained below. Balanced and Unbalanced Lay-ups. Glued laminated timber may be manufac- tured as unbalanced or balanced members, as shown in Fig. 4.7. The most critical zone of a glued laminated timber bending member with respect to controlling strength is the outermost tension zone. In unbalanced beams, the quality of lumber used on the tension side of the beam is higher than the lumber used on the corre- sponding compression side, allowing a more efficient use of the timber resource. Therefore, unbalanced beams have different bending stresses assigned to the com- pression and tension zones and must be installed accordingly. To ensure proper installation of unbalanced beams, the top of the beam is clearly stamped with the word ‘‘TOP’’ (see Fig. 4.8). While the unbalanced combination is primarily for use in simple-span applica- tions, it could also be used for short-cantilever applications (cantilever less than approximately 20% of the back span) or for continuous-span applications when the design is controlled by shear or deflection. If members are inadvertently installed in an improper orientation, i.e., upside down, the allowable bending stress for the compression zone stressed in tension should be used. In this case, the controlling bending stress and the capacity of the beam in this orientation shall be checked to determine if they are still adequate to carry the design loads. Balanced members are symmetrical in lumber quality about the midheight. Bal- anced beams are used in applications such as cantilevers or continuous spans, where 4.10 CHAPTER FOUR FIGURE 4.8 Glued laminated timber with a ‘‘TOP’’ stamp. either the top or bottom of the member may be stressed in tension due to service loads. They can also be used in single-span applications, although an unbalanced beam is more efficient for this use. Visually Graded and E-Rated Lay-ups. Allowable design properties are a key factor in designing glued laminated timber. Bending members are typically specified on the basis of the maximum allowable bending stress of the member. For example, a 24F designation indicates a member with an allowable bending stress of 2400 psi. Similarly, a 20F designation refers to a member with an allowable bending stress of 2000 psi. These different stress levels are achieved by varying the per- centages and grade of higher-quality lumber in the beam lay-up. Use of different species may also result in different stress designations. To identify whether the lumber used in the beam is visually or mechanically graded, the stress combination also includes a second set of designations. For ex- ample, for an unbalanced 24F lay-up using visually graded lumber, the lay-up designation may be identified as a 24F-V4. The ‘‘V’’ indicates that the lay-up uses visually graded lumber. (‘‘E’’ is used for mechanically graded lumber, which is sorted by the modulus of elasticity (MOE) of the laminating lumber.) The number ‘‘4’’ further identifies a specific combination of lumber used to which a full set of design stresses such as horizontal shear, MOE, etc. are assigned. Figure 4.9 shows a typical trademark for a glued laminated timber beam. Horizontally and Vertically Laminated Lay-ups. Glued laminated timber beams are typically installed with the wide face of the laminations perpendicular to the applied load, as shown in Fig. 4.10. These are commonly referred to as horizontally [...]... 24F-V5 26F-V1 26F-V2 26F-V4 1,600 1,550 2,300 2,300 2,300 2 ,40 0 2 ,40 0 E-rated western species 20F-E1 20F-E8 20F-E / SPF1 24F-E10 24F-E11 24F-E 14 24F-E15 24F-E18 24F-E20 24F-E / ES1 26F-E / DF1M1 FcЌx,b psi 650 650 650 650 650 740 650 1.5 1.5 1.6 1.6 1.6 1.8 1.8 E-rated southern pine 255 300 47 0 560 375 560 375 560 350 300 560 1.3 1.3 1.3 1.8 1.6 1.8 1.5 1.7 1.5 1.5 1.8 24F-E1 24F-E4 28F-E1 28F-E2 30F-E1... 20F-V4 20F-V8 20F-V9 20F-V10 20F-V12 24F-V4 24F-V5 24F-V8 24F-V10 24F-1.8E 1,600 1,900 1,600 2,000 1,900 1,950 1,850 2,200 2,100 2,200 2,000 2,000 560 560 560 560 375 375 47 0 560 375 560 375 375 Fbx,a psi Comb symbol 1 ,40 0 1,600 1,600 2,300 2,000 2,300 1,800 2,100 1,800 2,000 2,100 Ex,a 106 psi Visually graded southern pine 1.5 1.5 1 .4 1.6 1.5 1.5 1.3 1.7 1.6 1.7 1.6 1.6 20F-V2 20F-V5 24F-V3 24F-V5... E (E-rated or mechanically graded) The allowable properties given in Tables 4. 3 and 4. 4 should be used in conjunction with the dimensions provided in Section 4. 4 .4 The values for allowable properties given in Tables 4. 3 and 4. 4 are based on use under normal duration of load (10 years) and dry conditions (less than 16% TABLE 4. 3 Design Values for Structural Glued-Laminated Timber Intended Primarily for... of Use1,2,3 (Continued ) 4. 17 TABLE 4. 4 Design Values for Structural Glued-Laminated Timber for Normal Duration of Load and Dry Conditions of Use1,2,3 4. 18 TABLE 4. 4 Design Values for Structural Glued-Laminated Timber for Normal Duration of Load and Dry Conditions of Use1,2,3 (Continued ) 4. 19 4. 20 CHAPTER FOUR moisture content) When used under other conditions, see Section 4. 4.3 for adjustment factors... Laminations1,2 (Continued ) 4. 28 4. 29 TABLE 4. 5 Grade Requirements for Members Stressed Principally in Bending and Loaded Perpendicular to the Wide Faces of Laminations1,2 (Continued ) 4. 30 TABLE 4. 6 Grade Requirements for Members with Two or More Laminations Stressed Principally in Bending Parallel to the Wide Faces of the Laminations1,2,3 ,4 4.31 4. 32 CHAPTER FOUR TABLE 4. 7 Allowable Properties and... following equation: Cc ϭ 1 Ϫ 2000 ͩͪ t R 2 (4. 2) TABLE 4. 12 Exponents for Volume Factor Equation Exponent Exponent symbol Western species Southern pine Hardwoods p 0.10 0.05 0.10 4. 36 CHAPTER FOUR TABLE 4. 13 Flat Use Factor,a Cƒu Member dimensions parallel to wide faces of laminations Cƒu 103 4 or 101⁄2 83 4 or 81⁄2 63 4 51⁄8 or 5 31⁄8 or 3 21⁄2 1.01 1. 04 1.07 1.10 1.16 1.19 a Values for Cƒu are rounded... the Wide Faces of Laminations1,2 (Continued ) 4. 22 TABLE 4. 5 Grade Requirements for Members Stressed Principally in Bending and Loaded Perpendicular to the Wide Faces of Laminations1,2 (Continued ) 4. 23 TABLE 4. 5 Grade Requirements for Members Stressed Principally in Bending and Loaded Perpendicular to the Wide Faces of Laminations1,2 (Continued ) 4. 24 TABLE 4. 5 Grade Requirements for Members Stressed... 4. 3 is not efficient In such cases, the designer should select glued laminated timber combinations from Table 4. 4 Similarly, glued laminated timber combinations in Table 4. 3 are inefficiently utilized if the primary use is not bending about the X–X axis It should be noted that Tables 4. 3 and 4. 4 tabulate the lay-up combinations based on species, whether the combination is for a balanced or unbalanced... laminations of the combination TABLE 4. 8 Allowable Radial Stressesa Radial tension (Frt), psi Species Wind and earthquake Other Loading Radial compression (Frc), psi Alaska cedar California redwood Canadian spruce pine Douglas fir-larch Douglas fir-south Eastern spruce Hem-fir Softwood species (WW) Southern pine 63 42 53 55 55 48 52 47 67 15 42 15 15 15 15 15 15 67 47 0 315 560 560 560 300 375 255 650 a... the Wide Faces of Laminations1,2 (Continued ) 4. 25 TABLE 4. 5 Grade Requirements for Members Stressed Principally in Bending and Loaded Perpendicular to the Wide Faces of Laminations1,2 (Continued ) 4. 26 TABLE 4. 5 Grade Requirements for Members Stressed Principally in Bending and Loaded Perpendicular to the Wide Faces of Laminations1,2 (Continued ) 4. 27 TABLE 4. 5 Grade Requirements for Members Stressed . properties given in Tables 4. 3 and 4. 4 should be used in conjunction with the dimensions provided in Section 4. 4 .4. The values for allowable properties given in Tables 4. 3 and 4. 4 are based on use under. 10 40 Continuous beams (individual spans) 10 40 Headers Windows and doors Ͻ10 Garage doors 9–18 APA The Engineered Wood Association and Engineered Wood Systems (EWS), a related corporation of APA 7011. Use 1,2,3 (Continued) 4. 18 TABLE 4. 4 Design Values for Structural Glued-Laminated Timber for Normal Duration of Load and Dry Conditions of Use 1,2,3 4. 19 (Continued) TABLE 4. 4 Design Values for