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4.126 CHAPTER FOUR Dead load, w d ϭ (10 ϫ 10) ϩ 36 ϭ 136 lb/ft Total load, w t ϭ 1250 ϩ 136 ϭ 1386 lb/ft Max. moment, fully loaded, M ϭ 80 312 lb/ft, at interior reaction Max. moment, unbalanced loading, M u ϭ 69,790 lb / ft at approximately 10 ft from the outer support of the 23.25 ft span Max. shear, fully loaded, V ϭ 16,795 lb at 24 in. away from the interior reaction, in the 23.25 ft span Max. shear, unbalanced loading, V u ϭ 15,544 lb Max. reaction, R ϭ 37,079 lb at interior support Design: From Table 4.29, a 3 1 ⁄ 2 in. wide beam would exceed the depth limitation, based on shear requirements. Try a 5 in. wide ϫ 23 3 ⁄ 8 in. deep beam. (For purposes of the volume factor, the moment capacity span is the distance between points of zero moment and is approxi- mately 20 ft.) From Tables 4.29 and Eq. (4.1), the allowable moment capacity ϭ 91,065 ϫ 0.9708 ϭ 88,406 lb-ft Ͼ 80,312 lb-ft. The actual beam weight of 29.2 lb/ft is less than the assumed 36 lb/ft—OK. The allowable compression perpendicular to grain, F c Ќ ϭ 740 psi. Minimum bearing length at interior support ϭ 37,079/(740 ϫ 5) ϭ 10 in. Revised design shear, V ϭ 16,867 lb at 23 3 ⁄ 8 in. away from the face of the interior support Ͻ21,038 lb—OK. Max. deflection: total load on longer span, dead load only on shorter span ϭ 0.66 in. ϭ L/425 Ͻ L/240 → OK. Max. deflection: live load on longer span ϭ 0.62 in. ϭ L/454 Ͻ L/360—OK. 4.7.2 Columns Introduction. While glued laminated timbers are typically used as some type of bending member, they are also ideally suited for use as columns. Because glued laminated timber is manufactured with dry lumber having a maximum moisture content at the time of fabrication of 16%, it has excellent dimensional stability. Thus, a glued laminated timber column will not undergo the dimensional changes normally associated with larger solid-sawn sections, which are typically supplied as green timbers. Glued laminated timber will remain straight and true in cross- section. Since glued laminated timber is manufactured with dry lumber, it is also less susceptible to checking and splitting, which often occur with green timbers, and it has better fastener holding capacities. Member Sizes. Like other glued laminated timber shapes, columns can be man- ufactured in virtually any cross-sectional size and length required. However, since they are manufactured using dimension lumber, specifying glued laminated timber column in the typical widths as shown by Table 4.35 will ensure maximum effi- ciency of the resource and product availability. The depths of glued laminated timber columns are normally specified in mul- tiples of 1 1 ⁄ 2 in. for western species and 1 3 ⁄ 8 in. for southern pine. Examples of column sizes are given in Table 4.36 to show the use of typical glued laminated timber width and depth size multiples. Another advantage of glued laminated timber is that any length can be supplied, thereby eliminating the need for costly splices to create long-length columns for multistory applications or high open areas. Availability of specific cross-section dimensions and lengths should be verified with the supplier or manufacturer. STRUCTURAL GLUED LAMINATED TIMBER (GLULAM) 4.127 TABLE 4.35 Typical Glulam Column Widths TABLE 4.36 Typical Glulam Column Sizes TABLE 4.37 Column Lay-up Designations Member Lay-up and Design Stresses. Since compression parallel to grain stresses are distributed uniformly over the cross-section of an axially loaded member, glued laminated timber columns are typically manufactured using a single grade of lumber throughout the depth of the member. Examples of lay-up combinations and some of the associated design stresses for single grade glued laminated timber members are shown in Table 4.37. Two distinct values are provided for F b and F v , depending on which axis the load is applied to, i.e., parallel to the wide or to the narrow face of the member. If a column is going to be loaded as a combined axial and bending member, it may be preferable to specify a bending member lay-up such as a 24F-V8 DF or 24F- V5 SP combination. Such members use a graded lumber lay-up throughout the depth of the member and are more efficient for resisting high bending stresses. For a complete listing of available glued laminated timber layup combinations for both members primarily loaded axially or as bending members, refer to Tables 4.3 and 4.4. Column Design Equations. Until the promulgation of the 1991 NDS, wood col- umns were designed based on a methodology that required classifying the member as a short, intermediate, or long column. This required a trial-and-error solution 4.128 CHAPTER FOUR when it was not obvious which classification applied for a specific design situation, and many designers considered it to be a cumbersome procedure. Based on extensive research conducted at the USDA Forest Products Laboratory and other research institutions, the 1991 NDS was revised to reflect the use of a single column design formula regardless of the length-to-depth (l/d) ratio previ- ously used to classify columns as short, intermediate, or long. This is shown as Eq. (4.18) for a member subjected to concentric axial loads only. 2 1 ϩ (F /F*) 1 ϩ (F /F*) (F /F*) cE c cE c cE c FЈ ϭ F* ϪϪ(4.18) ͭͫͬͮ cc Ί 2c 2cc where ϭFЈ c allowable compression parallel to grain design value ϭF* c tabulated compression parallel to grain design value adjusted for ser- vice conditions (moisture, temperature, load duration) and size effect when applicable F cE ϭ critical buckling design value c ϭ 0.8 for sawn lumber, 0.85 for round timber poles and piles, 0.9 for glued laminated timber and structural composite lumber The critical buckling design value is determined by the well-known Euler col- umn formula: KE Ј cE F ϭ (4.19) cE 2 (L /d) e where EЈ ϭ allowable modulus of elasticity adjusted for service conditions (mois- ture, temperature) d ϭ least unbraced dimension of column L e ϭ effective column length based on unbraced length and end fixity con- ditions K cE ϭ 0.300 for products with the coefficient of variation of MOE, COV E ϭ 0.25, such as visually graded lumber and round timber poles and piles; 0.384 for products with COV E ϭ 0.15, such as machine-evaluated lum- ber (MEL); 0.418 for products with COV E Յ 0.11, such as glued lam- inated timber, machine stress-rated (MSR) lumber, and structural composite lumber The solution of this equation, which determines the allowable compression par- allel to grain stress, is based on the physical dimensions of the column, the pub- lished material properties such as E and F c , and several constants. The two con- stants, c and K cE , are material-dependent, with higher values assigned to wood products with lower variability such as glued laminated timber, thus resulting in higher column capacities. Through the laminating process, naturally occurring strength-reducing charac- teristics in the lumber are randomly distributed throughout the member, resulting in lower variability in mechanical properties for glued laminated timber as com- pared to sawn lumber products. For example, the typical coefficient of variation for the modulus of elasticity of glued laminated timber is about 10%, which is equal to or lower than other comparable wood products. Based on the relative homoge- neity of glued laminated timber and its low variability, the values of c and K cE for glued laminated timber have been established as 0.9 and 0.418, respectively. STRUCTURAL GLUED LAMINATED TIMBER (GLULAM) 4.129 Column Design Tables. Tables 4.38A–4.38F have been generated to provide col- umn capacities for two typical glued laminated timber lay-up combinations for an eccentric condition of load application. These tables are summarized as follows: No. 2 DF Tables 4.38A–4.38C (eccentric loading) No. 47 SP Tables 4.38D–4.38F (eccentric loading) All tables have been truncated at an L/d ratio of 50. For most applications, the No. 2 DF and No. 47 SP combinations will result in the most cost-efficient columns. These permit the use of all L2 laminations for the No. 2 DF and all No. 2 medium grain laminations for the No. 47 SP combinations. For those applications requiring greater capacities, the use of a No. 5 DF (all L1 laminations) or a No. 50 SP (all No. 1 dense laminations) are recommended. For additional tables of glulam columns, see EWS publication Y240A, Design of Structural Glued Laminated Timber Columns. 12 Since wood columns are typically not truly loaded concentrically, Tables 4.38A– 4.38F are provided based on the conservative assumption that the load is applied with an eccentricity of 1 ⁄ 6 of the least dimension of the column. This degree of eccentricity is considered to be representative of many actual in-service column installations such as an end column supporting a beam. As such, it provides a conservative solution based on an allowance for some degree of field framing in- consistencies. It is recommended that these tables be used for those applications where it is desirable to use a simple tabular solution for preliminary design sizing. For applications with greater degrees of eccentricities or side loads, the designer is referred to the NDS 6 for equations that account for these conditions of loading. As with the use of all design tables, it is recommended that the advice of a design professional be obtained to verify the capacity and applicability of any col- umn size provided in Tables 4.38A–4.38F. Where higher capacities are required and it can be ensured that the loads will be applied concentrically, the column may be designed in accordance with Eq. (4.18), as shown in the following example. Column Design Example Determine the size of a glued laminated timber column required to support a 45 kip axial floor load (DOL ϭ 1.0) applied concentrically. Assume the length of the column is 15 ft and that it is in a dry use service condition. Use a Douglas fir combination No. 2. Assume the column is unbraced and that the end conditions are pinned. Tabulated allowable stresses (see Table 4.4): F ϭ 1900 psi c // E ϭ 1,700,000 psi Adjusted allowable stresses: F* ϭ 1900 ϫ 1.0 ϭ 1900 psi c EЈ ϭ E ϭ 1,700,000 psi Try a 6 3 ⁄ 4 in. ϫ 7 1 ⁄ 2 in. section: net area ϭ 6.75 ϫ 7.5 ϭ 50.62 in. 2 Determine effective length (L e ) ϭ 15(12) ϫ 1.0 ϭ 180 in. Determine slenderness ratio ϭ L e /d ϭ 180/6.75 ϭ 26.67 Ͻ 50 4.130 TABLE 4.38A Glulam Column Design Tables ECCENTRIC END LOADS FOR DOUGLAS-FIR COMBINATION NO. 2 GLULAM COLUMNS Allowable axial loads (pounds). Side loads and bracket loads are not permitted. End loads are limited toamaximumeccentricityofeither1/6columnwidthor1/6columndepth. 4.131 TABLE 4.38A Glulam Column Design Tables ECCENTRIC END LOADS FOR DOUGLAS-FIR COMBINATION NO. 2 GLULAM COLUMNS Allowable axial loads (pounds). Side loads and bracket loads are not permitted. End loads are limited to a maximum eccentricity of either 1/6 column width or 1/6 column depth. (Continued) 4.132 TABLE 4.38B Glulam Column Design Tables ECCENTRIC END LOADS FOR DOUGLAS-FIR COMBINATION NO. 2 GLULAM COLUMNS Allowable axial loads (pounds). Side loads and bracket loads are not permitted. End loads are limited to a maximum eccentricity of either 1/6 column width or 1/6 column depth. 4.133 TABLE 4.38B Glulam Column Design Tables ECCENTRIC END LOADS FOR DOUGLAS-FIR COMBINATION NO. 2 GLULAM COLUMNS Allowable axial loads (pounds). Side loads and bracket loads are not permitted. End loads are limited to a maximum eccentricity of either 1/6 column width or 1/6 column depth. (Continued) 4.134 TABLE 4.38C Glulam Column Design Tables ECCENTRIC END LOADS FOR DOUGLAS-FIR COMBINATION NO. 2 GLULAM COLUMNS Allowable axial loads (pounds). Side loads and bracket loads are not permitted. End loads are limited to a maximum eccentricity of either 1/6 column width or 1/6 column depth. 4.135 TABLE 4.38C Glulam Column Design Tables ECCENTRIC END LOADS FOR DOUGLAS-FIR COMBINATION NO. 2 GLULAM COLUMNS Allowable axial loads (pounds). Side loads and bracket loads are not permitted. End loads are limited to a maximum eccentricity of either 1/6 column width or 1/6 column depth. (Continued) [...]... Philadelphia, 1998 3 APA EWS Technical Note S580, Preservative Treatment of Glulam Beams, APA The Engineered Wood Association, Tacoma, WA, 1995 4 APA EWS Technical Note Y 260 , Dimensional Changes in Structural Glued Laminated Timber, APA The Engineered Wood Association, Tacoma, WA, 1998 5 APA EWS Technical Note Y110, Glued Laminated Timber Appearance Classifications for Construction Applications, APA The Engineered. .. parallel to grain design value using Eq (4.18): FcE ϭ (KcEEЈ) (0.418 ϫ 1,700,000) ϭ ϭ 999 psi (Le / d )2 ( 26. 67)2 FcE / F c ϭ * ͭ 999 ϭ 0.5 26 1900 Ίͫ ͬ 2 ͮ 1 ϩ 0.5 26 1 ϩ 0.5 26 0.5 26 Ϫ Ϫ ϭ 914.5 psi 2 ϫ 0.9 2 ϫ 0.9 0.9 Determine allowable axial load ϭ F Ј ϫ A ϭ 914.5 ϫ 50 .62 ϭ 46. 3 kips Ͼ 45 kips c Use a 63 ⁄4 in ϫ 71⁄2 in No 2 Douglas fir glued laminated timber combination F Ј ϭ 1900 c 4.7.3 Substitution of... Madison, WI, 1 962 10 APA EWS Technical Note R 465 , Checking in Glued Laminated Timber, APA The Engineered Wood Association, Tacoma, WA, 1999 11 Faherty, K F., and T G Williamson, Wood Engineering and Construction Handbook, 3d ed., McGraw-Hill, New York, 1999 12 APA EWS Data File Y24A, Design of Structural Glued Laminated Timber Columns, APA The Engineered Wood Association, Tacoma, WA, 1999 13 APA EWS Technical... a maximum eccentricity of either 1 / 6 column width or 1 / 6 column depth 4.1 36 TABLE 4.38D Glulam Column Design Tables ECCENTRIC END LOADS FOR SOUTHERN PINE COMBINATION NO 47 GLULAM COLUMNS Allowable axial loads (pounds) Side loads and bracket loads are not permitted End loads are limited (Continued) to a maximum eccentricity of either 1 / 6 column width or 1 / 6 column depth 4.137 TABLE 4.38E Glulam... 4.39 Typical Net Finished Glulam Widths Nominal width 3 4* 6* 8 10 12 Western species Southern pine 21⁄2 21⁄2 31⁄8 3 51⁄8 5 63 ⁄4 63 ⁄4 83⁄4 81⁄2 103⁄4 101⁄2 * For the 4 in and 6 in nominal widths, glulam may also be available in 31⁄2 in and 51⁄2 in widths respectively These ‘‘full-width’’ members correspond to the dimensions of 2 ϫ 4 and 2 ϫ 6 framing lumber and are supplied with ‘‘hit or miss’’ surfacing... combination should be based on design requirements and section capacities published in Engineered Wood Systems, AITC, or manufacturer’s brochures National Evaluation Report 4 86 and ICBO ES Report ER-5714 provide a tabulation of laminating combinations available from EWS member manufacturers † Appearance classifications are described in Section 4 .6. 1 ‡ When pentachlorophenol in light solvent or waterborne... a maximum eccentricity of either 1 / 6 column width or 1 / 6 column depth 4.138 TABLE 4.38E Glulam Column Design Tables ECCENTRIC END LOADS FOR SOUTHERN PINE COMBINATION NO 47 GLULAM COLUMNS Allowable axial loads (pounds) Side loads and bracket loads are not permitted End loads are limited (Continued) to a maximum eccentricity of either 1 / 6 column width or 1 / 6 column depth 4.139 TABLE 4.38F Glulam... limited to a maximum eccentricity of either 1 / 6 column width or 1 / 6 column depth 4.140 TABLE 4.38F Glulam Column Design Tables ECCENTRIC END LOADS FOR SOUTHERN PINE COMBINATION NO 47 GLULAM COLUMNS Allowable axial loads (pounds) Side loads and bracket loads are not permitted End loads are limited to a maximum eccentricity of either 1 / 6 column width or 1 / 6 column depth (Continued) 4.141 4.142 CHAPTER... permits the use of a variety of species and is suitable for virtually any simple-span beam application • The 26F-E / DF1 and 26F-E / DF1M1 combinations were developed for use in combination with prefabricated wood I-joists and are often referred to as I-joist depth compatible (IJC) lay-ups 4.1 46 CHAPTER FOUR • The 28F-E / SP1, 30F-E / SP1, 30F-E2M2 / SP, and 30F-E2M3 / SP lay-ups are southern pine combinations... design values as shown for normal load duration and dry-use condition.* See Table 4.40 * Dry service condition—moisture content of the member will be below 16% in service; wet service condition—moisture content of the member will be at or above 16% in service When structural glued laminated timber members are to be preservative treated, wet-use adhesives must be specified 4.148 CHAPTER FOUR TABLE 4.40 . psi cE 22 (L / d ) ( 26. 67) e 999 F /F* ϭϭ0.5 26 cE c 1900 2 1 ϩ 0.5 26 1 ϩ 0.5 26 0.5 26 FЈ ϭ 1900 ϪϪϭ914.5 psi ͭͫͬͮ c Ί 2 ϫ 0.9 2 ϫ 0.9 0.9 Determine allowable axial load ϭϫA ϭ 914.5 ϫ 50 .62 ϭ 46. 3 kips Ͼ. psi Try a 6 3 ⁄ 4 in. ϫ 7 1 ⁄ 2 in. section: net area ϭ 6. 75 ϫ 7.5 ϭ 50 .62 in. 2 Determine effective length (L e ) ϭ 15(12) ϫ 1.0 ϭ 180 in. Determine slenderness ratio ϭ L e /d ϭ 180 /6. 75 ϭ 26. 67 Ͻ. 4.1 26 CHAPTER FOUR Dead load, w d ϭ (10 ϫ 10) ϩ 36 ϭ 1 36 lb/ft Total load, w t ϭ 1250 ϩ 1 36 ϭ 13 86 lb/ft Max. moment, fully loaded, M ϭ 80 312 lb/ft,