The Design Possibilities of Engineered Wood Products

Transcription

1 The Design Possibilities of Engineered Wood Products INTERNATIONAL Buildingseries NO.7

2 Introduction Wood products have a very long history of providing safe, comfortable shelter. Over the past 60 years, the development of gluing, connection and grading technology has resulted in new engineered wood products that extend even further the possibilities for wood construction. It is estimated that over 90% of existing houses in North America are wood-frame construction For duplexes, row houses and three-storey apartments, about 85% of buildings are wood-frame construction. In addition, many low-rise commercial buildings are built with wood. Engineered wood products (EWPs) open up the possibility of using wood in more of these buildings due to their increased span capability and performance characteristics. 图片 1 Products manufactured to achieve targeted engineering properties are known as engineered wood products. They use manufacturing techniques, mechanical evaluation and special connectors or adhesives to vastly increase the reliable load-carrying capability. The performance of engineered wood products is based on testing and engineering to meet product standards. These standards result in both generic and proprietary products to meet market needs. 2 The use of engineered wood products has grown dramatically over the past 20 years, and is still increasing. Designers and builders are attracted to the strength, quality and reliability of these products, with higher purchase costs offset by ease of construction and increased system performance in span and loadcarrying capacity. The focus of this brochure is on these innovative engineered wood products that are used for structural applications like beams, joists and columns. INTERNATIONAL Buildingseries NO.7 Engineered wood products fi nd use in all types of project: single and multi-family residential, commercial and industrial.

3 Products and Manufacturing To understand the special properties of engineered wood products, it helps to begin with solid-sawn wood products that are still commonly used for joists and beams. Modern saw mills have equipment for scanning logs to select the cuts that will extract the best value and quality from a log, and minimize the effects of naturally occurring knots and grain directions that reduce strength. The logs have a wide range of quality and moisture content that can extend well above 100%, expressed as the ratio of the weight of water to the weight of oven-dry wood fi bre. After sawing, the lumber is typically dried to a moisture content of 19%. Next, the lumber is planed and graded, based on visual observation by a trained grader who, based on strict rules, assigns a grade based on the size and location of knots and other characteristics. Because of variability in the wood material, dimension lumber is assigned a strength value that is well below its average capability. Using lower strength values provides a level of comfort that the material is adequate for a certain application, but does not allow the designer to take maximum advantage of the actual strength each piece would exhibit if it were, for example, proof-tested to determine its actual capability. Engineered wood products are manufactured using high-technology equipment, processes and quality control. Engineered wood products differ from visually graded solid-sawn lumber products in a number of ways. First, the manufacturing processes for engineered wood products generally require the wood have a lower moisture content, usually less than 15%, resulting in a fi nished product that is more dimensionally stable and less prone to shrinkage. Second, the manufacturing processes generally remove strength-reducing characteristics or at least distribute them so that their overall effect is more predictable. Third, EWPs are subject to structural property qualifi cation testing and daily quality control. 3 The Design Possibilities of Engineered Wood Products

4 General Information Engineered wood products are similar to solid sawn wood products in many ways, but there are some fundamental differences that designers and builders must consider. This section provides a brief summary on several topics, and more detailed information is included in the product sections. Product Acceptance All the wood products used for construction are specifi ed for use in one way or another. For small buildings, dimension lumber can be used as prescribed by the applicable Building Code. For larger building applications, engineering design is required to provide assurance of structural adequacy. 4 In the case of engineered wood products, there are several avenues for ensuring their structural adequacy. Some products are covered by generic standards that stipulate manufacturing, quality control and quality assurance procedures that are linked directly to published design values for all such structural products. Other products are proprietary they have company-specifi c design values that are based on both product standards and company procedures, and third-party evaluation services. Structural wood products must use glues that meet stringent water-resistance criteria. This is to ensure that the structural performance of products that are accidentally or unavoidably exposed to rain or moisture will not be adversely affected. This does not mean these structural products are suited for continually wet conditions, but does provide a safety margin in the event of temporary exposure to rain and moisture. INTERNATIONAL Buildingseries NO.7 Fire Safety Buildings are required to provide the code-established degree of fi re safety. The rules for wood use, including engineered wood products, have been established over many years based on experience, research, testing and code development. Fire-resistance rating is the time an assembly resists the passage of heat and fl ames. The building occupancy, the building size, number of exits and the potential use of sprinklers will determine what fi re resistance rating is required. Wood-frame assemblies (using repetitive members like wall studs and fl oor joists and protected by gypsum board) can be constructed to resist the effects of fi re for up to two hours through the use of appropriate materials and construction methods. Engineered wood products have be en evaluated and rated under the same fi re conditions as similar sized members made from solid wood. This evaluation is based on extensive fi re testing to establish the fi re-resistance ratings for assemblies using engineered wood products, taking into account manufacturing processes and adhesives on fi re behavior. Based on test results, the sound and fi re characteristics of many types of fl oor and wall assemblies have been published and recognized in building codes.

5 Connections There are many factors to be taken into account in designing building connections, especially where there is potential exposure to high winds or earthquake loads. In general, the same methods and types of connectors are used for engineered wood products as for sawn lumber. For light-frame construction, nails, screws and metal connectors are used to secure members. Large-dimension EWP applications utilize the same types of hardware used for timber post and beam construction, but design capacities may be proprietary. Storage and Handling All wood products should be stored on a level site on skids that separate them from the ground and covered. In general, even more care is desired for the storage and handling of engineered wood products. Protection from moisture is crucial because part of the product cost and quality is for the energy used to dry the product. Also, engineered wood products may be used in locations where their appearance is on display and therefore it is important to protect them from damage during storage and handling. 5 The Design Possibilities of Engineered Wood Products

6 Special Lumber Products 6 Machine-graded Lumber Most lumber is visually graded by lumber graders who examine each piece and apply visual grading rules to establish its grade, which determines the structural design value. While visual grading still works well, the demand for high-performance lumber has led to enhanced grading techniques. Unlike other engineered wood products that rely on product design to impart engineered qualities, machine-graded lumber is solid sawn lumber that relies on mechanical evaluation to more closely ascertain its engineering properties. As part of this process, each piece of lumber is non-destructively evaluated by equipment designed to measure physical properties. The machine tests each piece of lumber and strength properties are determined from longestablished property relationships verifi ed by daily quality control testing. As lumber is fed continuously into typical mechanical evaluating equipment, stiffness is measured and recorded by a small computer, and strength is assessed by correlation methods. Machine-graded lumber is also visually checked for properties other than stiffness, which might affect the suitability of a given piece. The result is a more precise understanding of the strength distribution of the grade of machine-graded lumber than is possible with visually graded lumber. There are two types of machine-graded lumber: machine stress-rated (MSR) lumber and machine evaluated lumber (MEL). MSR is the more common and traditional lumber product; MEL offers some less traditional grades and properties. The major advantage of machine-graded lumber is that the engineering properties are determined more directly than by visual grading alone, making it possible to use structural lumber elements closer to the limit of their design capacity. Therefore machine-graded lumber is used where higher and more consistent structural properties are required. For example, machine-graded lumber is typically used for wood trusses, where the performance of each member is critical. Machine-graded lumber can be produced for a wide variety of end-use applications. In addition to the grades found in the grade rules, special E-Rated (LAM) laminating stock, and export grades are commonly produced to specifi c customer requirements. INTERNATIONAL Buildingseries NO.7

7 Specifications and Standards Canadian MSR and MEL lumber is manufactured in conformance with the National Lumber Grades Authority (NLGA) Special Product Standard 2 (SPS-2). The MSR and MEL processes and products are accepted by all major building codes in North America and in most overseas countries. The quality control process is key to the reliability of machine-graded lumber. Each manufacturer operates according to an approved plant quality control standard. In addition to the mechanical and visual assessments of the lumber, each producer of MSR lumber adheres to a rigorous set of daily machine calibration checks and mechanical lumber tests. During each production shift, the machines are checked for accuracy and a representative sample of material is selected and proof-tested to verify the grade assignment. Not until the testing is successfully completed can lumber be shipped. All calibration and production records are periodically checked by an independent inspection agency. Machine grading equipment tests each piece of lumber and determines strength values. Photo : Metriguard Inc. 7 Design and Uses Machine-graded lumber can be used anywhere dimension lumber is used, including joists and rafters, and also for special applications, but it is most widely used in the manufacture of wood trusses, where the structural performance and economy of the entire truss is based on the performance of each member, and also as the fl ange stock for some wood I-joists. The Design Possibilities of Engineered Wood Products

8 Finger-joined Lumber Finger-joined lumber is an engineered product manufactured by taking shorter pieces of quality kiln-dried lumber, machining a fi nger profi le in each end of the short-length pieces, adding an appropriate structural adhesive, and bonding the pieces together to produce a longer piece of lumber. Finger-joining is used in several wood product manufacturing processes including the horizontal joints for glulam manufacture. The term fi nger-joined lumber applies to dimension lumber. Two major advantages of this product are its straightness and dimensional stability. The straightness factor is the result of stable short-length pieces of lumber being combined in the manufacturing process. The length of fi nger-joined lumber is not limited by tree size. In fact, the process may result in the production of joists and rafters in lengths of 12m (40 ) or more. Another advantage is the greater value derived from the forest resource since the short-length pieces can be cut out of lower grade lumber, which might otherwise be waste. The fi nger-jointing process allows the removal of strength reducing defects to produce a product with higher engineering properties. The strength of the joints is controlled by stipulating the quality of wood that must be present in the area of the joint. Finger-joined lumber can be used wherever non-fi nger-joined lumber is used. There are two categories of fi nger-joined lumber depending on the intended end use. The fi rst category, sometimes referred to as structural fi nger-joint lumber, uses a thermal-setting structural adhesive such as phenol-resorcinol formaldehyde adhesive, also used in panel products or in glued-laminated timber. This allows the product to be used in either vertical or horizontal load applications. The second category (vertical stud use only), is for vertical use only (wall studs), where bending or tension stresses are rare. Both products may be used interchangeably with solid sawn lumber in terms of strength and end use. A description of both products is provided in 8 INTERNATIONAL Buildingseries NO.7

9 Specifications and Standards Finger-joined lumber must meet the same grading rules as regular sawn lumber. Canadian fi nger-joined lumber must also meet special product standards (Special Product Standards SPS 1 and SPS 3) covering quality control requirements for strength and durability of the joints. Finger-joined lumber meeting these standards is considered equivalent to solid sawn lumber of the same dimension, grade and specie and is recognized by the major North American model-building codes. Other fi nger-jointed and edge-glued products are also available (Special Product Standards SPS 4, 5 and 6). The structural properties are confi rmed through a comprehensive quality assurance program with independent third party verifi cation. Daily structural tests are certifi ed to verify that the product meets the requirements as set out by the North American lumber grading system. Strict tolerances are established for the machining of the fi ngers and for the quality, mixing, and curing of the adhesive. Depending on the type of fi nger-jointed lumber being manufactured, edge and fl at bending tests, and tension tests are performed on each piece to ensure the joint can meet the design value for the lumber. 9 The Design Possibilities of Engineered Wood Products

10 Design and Uses Finger-joined lumber is used in applications where visually graded dimension lumber is used. It is especially specifi ed where longer lengths, or a high degree of straightness is r 图片 19 Finger-jointing relies on precision fi nger profi les and controlled gluing to produce long, straight members. Photo: Doucet Machineries inc. 10 图片 20 Photo FJ 1 Precise machining of the joints is done prior to gluing INTERNATIONAL Buildingseries NO.7

11 Glued-laminated Timber Glued-laminated timber (glulam) is a versatile structural timber product manufactured by gluing together select pieces of dimension lumber to produce much larger sections. The appearance and size attributes of glulam account for its frequent use in large-span applications and where an exposed structure is an important part of a building s architecture. In the manufacture of glulam, the wood pieces are end jointed and arranged in horizontal layers or laminations. Glulam is used for columns and beams and frequently for curved members. Glulam is manufactured at certifi ed plants where standards governing lumber grading, end joining, gluing and fi nishing are used to control quality. Qualifi ed manufacturers can supply a certifi cate of conformance for their products upon request. Glulam photos The lumber used for the manufacture of glulam is a special grade called lamstock. It is dried to a maximum moisture content of 15 percent and it is planed to a closer tolerance than that required for dimension lumber. Canadian glulam may be manufactured in three species combinations: Douglas Fir-Larch, Hem-Fir and Spruce-Pine. Prior to fabrication, all lumber is visually graded for strength properties and mechanically evaluated to determine the modulus of elasticity (E). These two assessments of strength and stiffness are used to determine where a given piece will be situated in a beam or column. For example, high strength pieces are placed in the outermost laminations of a beam where the bending stresses are the greatest. This blending of strength characteristics is known as grade combination and ensures consistent performance of the fi nished product. Small glulam members are used for residential applications. Once graded, the individual pieces of lamstock are end-joined into full-length laminations of constant grade and each endjoint is proof tested. Then, the laminated lengths are arranged according to the required grade combination for the product being manufactured. When gluing and curing is complete, the members are moved to the finishing area where basic surface planing, patching, and end trimming is done. Depending on what the client has ordered, drilling and notching for connections, sanding, and staining and varnishing may also be done. Because of specialized equipment and mass production, these functions can usually be performed in the shop cheaper than at the building site. As a fi nal step, glulam members are wrapped in readiness for shipping. Large glulam arches house a potash storage facility. Large, curved glulam members provide a roof for an indoor ice arena. 11 The Design Possibilities of Engineered Wood Products

12 Specifications and Standards Glulam is an engineered wood product that is manufactured in accordance with CSA Standard O122. Canadian manufacturers of glulam are required to be qualifi ed under CSA Standard This standard sets mandatory guidelines for equipment, manufacturing, testing and record keeping procedures. As a mandatory manufacturing procedure, tests must be routinely performed on several critical manufacturing steps, and recording of test results must be done. For example, representative samples are tested for adequacy of glue bond and all end joints are stress tested to ensure that each joint exceeds the design requirements. Each member fabricated has a quality assurance record indicating glue bond test results, lumber grading, end joint test and laminating conditions for each member fabricated, including glue spread rate, assembly time, curing conditions and curing time. In addition, mandatory quality audits are performed by independent certifi cation agencies to ensure that in-plant procedures meet the requirements of the manufacturing standard. A certifi cate of conformance to manufacturing standards for a given glulam order is available upon request. Design and Uses Canadian glulam is manufactured according to stress grade and appearance grade. The specifi cation of the appropriate stress grade depends on whether the intended end use of a member is for a beam, a column, or a tension member. Glulam can be manufactured to match the specifi c requirements for a given application. For example, some grades are specifi - cally designed for cases where bending members are subjected to stress reversals. In these members the lamination requirements in the tension side are the mirror image of those in the compression side. Similarly, glulam can be optimized for tension members or for compression members. 12 图片 24 In Canada, glulam is manufactured in three appearance grades: Industrial, Commercial, and Quality. Unlike visually graded sawn timbers where there is a correlation between appearance and strength, there is no relationship between the stress grades and the appearance grades of glulam since the exposed surface can be altered or repaired without affecting the strength characteristics. The appearance of glulam is determined by the degree of fi nish work done after laminating and not by the appearance of the individual lamination pieces. INTERNATIONAL Buildingseries NO.7 Glulam is used in a wide variety of applications. It is used for residential construction where beams and columns are required. It is used in commercial and industrial applications, and especially as an architectural feature.

13 Connections There are several types of connection systems used for glulam. The large dimensions means bolts, welded brackets and split rings and shear plates may be required to transfer the large loads that glulam is capable of carrying. Timber rivets <<photo??>>are fasteners originally designed specifi cally for glulam and are convenient because site installation eliminates the pre-drilling and precision required for bolted connections. The type of connection system selected may also depend on whether the glulam and connections are exposed for architectural reasons. In such cases, the colour and size of the connectors can be altered to suit, and the connectors can be concealed inside the glulam members. Heavy Timber Construction Because of the typically large size of glued-laminated timber, it usually meets the minimum size required to qualify it as heavy timber construction to meet fi re-resistance rating requirements of North American building codes. The fi re performance of large dimension engineered wood products is similar to that of solid sawn timber. A char layer develops around the outside of the wood, slowing down the burning process. This means that large sections qualify as heavy timber construction - they can burn for a signifi cant amount of time before their strength is reduced to the point where they can no longer carry their assigned loads. For example, glulam beams having a minimum dimension are considered to be heavy timber construction and have this fi re-resistance capability. 13 The Design Possibilities of Engineered Wood Products

14 Parallel Chord Trusses Trusses are structural components made of triangulated members, including both wood and steel elements. A parallel chord truss has parallel top and bottom chords, essentially making the truss into a beam or joist that can be used for fl oor and roof framing. The space between the webs can be used to accommodate insulation, as well as electrical and mechanical services. Typical wood trusses combine quality lumber and toothed connector plates to produce a wide array of shapes. They are widely used in single- and multi-family residential, institutional, agricultural and commercial construction. Trusses rely on a triangular arrangement of webs and chords to transfer loads to reaction points. This arrangement gives them high strength- to-weight ratios, which permit longer spans than conventional framing, and fast construction. Light frame wood trusses are prefabricated by pressing the toothed connector plates into wood members that are pre-cut and assembled in a jig. Parallel chord truss photo 14 Some parallel-chord trusses are made from fi nger-jointed connections. Other types use toothed connector plates. Photo: Q-WEB Parallel-chord trusses provide long spans and space for services. Photo: Q-WEB INTERNATIONAL Buildingseries NO.7 Parallel-chord trusses are used for fl oors in residential and commercial applications. Photo: Q-WEB

15 Long spans without intermediate supports create large open spaces architects and designers can use with complete freedom. Partitions can be moved without compromising the structural integrity of the building. In addition to fl exibility and cost effectiveness trusses are used for the following reasons: Depending on their depth, typical parallel chord trusses can provide spans up to 11 metres or more (Table 2). 1. Parallel chord trusses are often used to frame vaulted roof spaces such as cathedral roofs. 2. As a testament to their strength, wood trusses are used in concrete formwork, scaffolding and falsework for industrial projects. 3. The open web confi guration of roof and fl oor trusses allows easy placement of plumbing, electrical, mechanical and sanitary services. 4. Wood trusses are very versatile and compatible with other structural products. They can be connected to other trusses (i.e. girder trusses) or be combined with other components, such as glulam, LVL, PSL and steel beams. Residential spans exceeding 6 meters may be governed by vibration criteria 15 The Design Possibilities of Engineered Wood Products

16 Specifications and Standards Design loads for trusses depend on the type of structure as referenced in the building code. In Canada, trusses are designed in accordance with the Truss Plate Institute of Canada s Truss Design Procedures and Specifi cations for Light Metal Plate connected Wood Trusses and the National Building Code. Design and Uses 16 Specifi c loadings and other structural requirements must be clearly identifi ed and documented for proper design of any truss system. In designing the appropriate trusses, the truss manufacturer will incorporate these specifi cations with the architectural requirements. The span capabilities of trusses should be discussed with a truss manufacturer and designer. INTERNATIONAL Buildingseries NO.7

17 Handing, Installation and Bracing Proper storage and handling is important for all structural building materials. By nature, wood trusses are long and slender. Although strong in the vertical plane, they are weak in the horizontal plane until they have been installed, secured and braced. For this reason, trusses must be stored according to manufacturer s instructions and lifting and placement must avoid fl exing the trusses in their weak direction. Bracing is required during erection to: withstand the gravity forces of the weight of the trusses support temporary construction dead loads such as the weight of construction materials keep the trusses plumb and straight assure correct truss spacing Fire Safety Parallel chord trusses have been subjected to testing to assess the fi re and sound resistance of several truss assemblies. A rated roof or fl oor truss assembly includes the truss members, the fl oor or roof sheathing on the upper surface, the ceiling fi nish on the lower surface and insulation material in the cavity. Depending on sheathing, ceiling construction, and insulation, truss assemblies may achieve fi re resistance ratings up to 2 hours. Figure 1 shows a parallel chord truss fl oor assembly that provides a 45 minute fi re-resistance rating (not all truss assemblies require a fi re resistance rating). 17 The Design Possibilities of Engineered Wood Products

18 Structural Composite Lumber Engineering standards in Canada and the United States refer to laminated veneer lumber (LVL) and parallel strand lumber (PSL) together as structural composite lumber (SCL). A third product, laminated strand lumber (LSL) is included here due to similarity of manufacturing methods. Laminated Veneer Lumber Laminated veneer lumber (LVL) is a layered composite of wood veneers and adhesive. It is a solid, highly predictable, uniform lumber product because natural defects such as knots, slope of grain and splits have been dispersed throughout the material or have been removed altogether. The grain of each layer of veneer runs in the same (long) direction with the result that it is strong when edge loaded as a beam or face loaded as a plank. This kind of lamination is called parallel-lamination, and it produces a material with greater uniformity and predictability than the same dimension material made by cross-lamination. 18 In fi nished appearance, LVL resembles plywood on the edge and lumber on the beam face. LVL is fabricated into large billets and then cut at the factory into stock for headers and beams, fl anges for prefabricated wood I-joists, or for other specifi c uses. LVL is used primarily as structural framing for residential and commercial construction and is well suited to applications where open web steel joists and light steel beams might be considered. LVL is mainly a structural material, most often used in applications where the material is concealed and therefore where appearance is not important. Finished or architectural grade appearance is available from some manufacturers, usually at an additional cost. However, when it is desired to use LVL in applications where appearance is important, common wood fi nishing techniques can be used to accent grain and to protect the wood surface. INTERNATIONAL Buildingseries NO.7

19 P arallel Strand Lumber Parallel strand lumber (PSL) is a high strength structural composite lumber product manufactured by gluing strands of wood together under pressure. This results in a product having consistent properties and high load carrying ability. It is available in lengths up to 20 metres and longer if transportation permits. It is a proprietary product marketed under the trade name Parallam. PSL is manufactured to a moisture content of 11 percent, making it less prone to shrinking, warping, cupping, bowing or splitting. PSL is well suited for use as beams and columns for post and beam construction, and for beams, headers, and lintels for light framing construction. It is used for large members in residential construction and as intermediate and large members in commercial building construction. Visually, PSL is suited to applications where fi nished appearance is important. It is also suited to concealed structural applications where appearance is not a factor. PSL readily accepts a very high degree of preservative penetration. Treated PSL should be specifi ed for members that will be directly exposed to high humidity conditions. PSL can be machined, stained, and finished using the techniques applicable to sawn lumber. Differing slightly from the fi nished appearance of sawn lumber or glulam, PSL retains the rich textures displayed by wood products used for exposed structure, as in post and beam construction. 19 The Design Possibilities of Engineered Wood Products

20 Laminated Strand Lumber LSL is the most recent engineered wood product innovation. This revolutionary product is used for a broad range of applications including rim board, studs, millwork and window, door and garage door headers, as well as for many industrial uses. New uses for this product are still evolving, including the use of LSL for vertical members in commercial applications where the framing member heights are long, and the wind loads are high. LSL resembles oriented strandboard (OSB) in appearance because like OSB, LSL is made from long strands coming from fast-growing aspen or poplar trees. The strands are arranged parallel to the axis of the member. Like other structural composite lumber products, LVL offers predictable strength, and dimensional stability that eliminates twist and shrinkage. SCL Photos In residential construction, LVL is used to carry loads over openings. LSL is typically used as a rim joist (outer edge of fl oors) 20 LVL joists are used in this restaurant where extra strength is needed to support concentrated loads. An LVL beam with joist hangers installed is ready for wood-i joist installation. INTERNATIONAL Buildingseries NO.7 Turned PSL columns warm the atrium of a city hall complex.

21 Specifications and Standards LVL, PSL and LSL products are tested and approved for use by the major code and product evaluation agencies in North America and should bear the seal of the certifi cation agency, the manufacturer, date of manufacture, grade and reference to any applicable code or evaluation agency approval numbers. Structural composite lumber used in Canada is evaluated by the Canadian Construction Materials Centre (CCMC) to ensure the product complies with the intent of the National Building Code of Canada. LVL is a proprietary product having engineering properties that are dependent on the materials used in the manufacture and on the product assembly and manufacturing processes. As such, it is assessed using standard evaluation procedures, rather than being designed to meet a common standard of production. Therefore, designers and installers follow the design, use and installation guidelines of a given manufacturer, as confi rmed by an accredited third-party certifi cation agency. PSL is also a proprietary product and designers use the manufacturer s design information that has been evaluated. The PSL manufacturing process includes tight controls on the raw material inputs, product assembly, and fi nished product properties to ensure a consistent, high quality, reliable product. Because the process involves the removal of strength reducing defects from the wood strands, the quality control procedure includes checking for consistent density in the fi nished product. Connections Common wood connectors for structural composite lumber take into account the size and equivalent capacities of the members, as determined through standard tests. Fasteners range from nails and joist hangers for the smallest sections to bolts, split rings, and shear plates for larger sized members. The fastening and connection details for LVL and PSL are similar to those for solid sawn lumber. LSL is usually used as a replacement for dimension lumber and the same types of nailed connections are used for LSL. 21 Fire Safety LVL is a wood-based product and reacts to fi re much the same as a comparable size of solid sawn lumber or a glued-laminated beam. When used in fi rerated fl oor or roof assemblies, the performance of LVL is similar to solid sawn lumber or glued-laminated timber. Research conducted to measure the performance of PSL when exposed to fi re demonstrates that it is appropriate for use in most applications for which solid sawn lumber and timbers are suited. As a result of evaluations, PSL qualifi es for use in Heavy Timber construction when of appropriate cross section. The Design Possibilities of Engineered Wood Products

22 Wood I-joists Wood I-joists are made by gluing solid sawn lumber or laminated veneer lumber (LVL) fl anges to a plywood or oriented strandboard (OSB) panel web to produce a dimensionally stable light-weight member with known engineering properties. The uniform stiffness, strength, and light weight of these prefabricated structural products makes them well suited for longer span joist and rafter applications for both residential and commercial construction. Several different types of wood I-joists are commercially available. Each type features a different combination of fl ange and web materials, and a different connection between the web and the fl anges. The joint between the fl ange and the web is a critical element of member strength and is typically protected by patent by each manufacturer. Builders can expect the following main advantages from their decision to use wood I-joists: 1. Strength: A wood I-joist delivers high strength in relation to the amount of wood it contains. This is because the bulk of the wood fi bre is situated where it is needed most for bending members, in the fl anges. Like a steel I-beam or open web steel joist, this confi guration makes the members very strong along the vertical axis, but relatively weak perpendicular to the vertical axis. 2. Span: Wood I-joists are available in lengths longer than conventional dimension lumber fl oor joists. They are usually manufactured in long or continuous lengths and are trimmed to common market-demanded lengths. 3. Weight: The I shape of these products gives a high strength to weight ratio. For example, wood I-joists 240mm deep and 8m long weigh between 23 and 32 kg, depending on the fl ange size. This means that they can be installed manually, giving advantages in labour and economy Dimensional stability: The plywood or OSB panels used for I-joist webs have a moisture content of about 5%. The moisture content of LVL, if it used for the fl anges, is approximately 8%. If lumber is used for the fl anges, its moisture content is typically less than 16% for fi nger jointing purposes. This means wood I-joists are low in moisture content and are not less prone to shrinking or twisting, which results in quiet, stable fl oors. 5. Electrical and mechanical routing: Wood I-joists have generous allowances for the location and size of holes that can be made in the webs to accommodate electrical and mechanical installations. Manufacturers provide strict guidelines on these allowances, based on the distance from the bearing end, which must not be exceeded. INTERNATIONAL Buildingseries NO.7 6. Floor performance: Wood I-joists are stiff, lightweight, capable of long spans, dimensionally stable and uniform in size, with no crown. Most profi les have a fl ange that provides a larger surface for the nailing, screwing or glued attachment of fl oor sheathing. When built properly, a wood-i joist fl oor should provide strong, quiet performance.

23 Wood I-joists combine lumber or LVL fl anges and a plywood or oriented strandboard web to give light, strong members. Wood I-joists usage is popular for residential construction and for commercial and industrial uses. Modern manufacturing and testing equipment contributes to the consistency of wood I-joists. Wood I-joists can easily be combined with other construction materials, in this case, with an external block wall. Specifications and Standards Wood I-joists are proprietary wood products. This means they are manufactured and quality controlled through a certifi cation agency to increase the reliability of their engineering properties (strength, stiffness etc.). Wood I-joists approved for use in Canada are evaluated by the Canadian Construction Materials Centre (CCMC) to ensure the joists comply with the intent of the National Building Code of Canada. Storage and Handling Wood I-joists are engineered products manufactured to set standards under controlled factory conditions. The investment in quality building materials should encourage builders to store and handle wood I-joists carefully. To a large extent, the quality of the completed job will be directly related to how well the wood I-joist framing members have been handled and stored. Transportation: Wood I-joists must be secured to the truck bed so that they remain fl at and level while being transported. Waterresistant wrapping should be secured in place for transportation to keep the joists protected from rain. 23 Storage: Part of the purchase cost of wood I-joists is the energy expended by the manufacturer to remove moisture from the wood to achieve quality and consistency objectives and to ensure in-place dimensional stability. Store wood I-joists level and away from the ground and standing water. Although the adhesives used to make I-joists are water-resistant, keep the joists dry. Lifting: Lift bundles so that the joists remain straight (unfl exed). Flexing may permanently weaken the joists even if the damage is not visible. Use slings that will not cut into the fl anges. Use spreader bars for lifting long bundles. Long, individual wood I-joists should be moved in the vertical position to minimize fl exing. The Design Possibilities of Engineered Wood Products

24 Installation Although strong once secured in place, wood I-joists are unstable until the fl oor sheathing has been applied and secured. For safety reasons, temporary bracing is recommended. Load Transfer Wood I-joists are most commonly used to replace fl oor joists in residential construction. However, some special installation measures are required for these products (Figure 2). Wood I-joists are designed to carry floor loads. They are not designed to accept loads from bearing walls and column loads above. Therefore, rim framing and squash blocks are used to transfer vertical loads around I-joists rather than through them. Web stiffeners are required when the fl oor load exceeds the capacity of the wood I-joist at supports. Figure 2 Load transfer devices for wood I-joist fl oors 24 INTERNATIONAL Buildingseries NO.7

25 Floor and Roof Assemblies Extensive fi re and sound research resulted in the addition of generic fi re resistance ratings, with corresponding sound transmission classes (STC) and impact insulation class (IIC) for wood I-joist fl oor assemblies. A sample assembly is shown in Figure The Design Possibilities of Engineered Wood Products

26 Conclusion Wood-frame construction has a long history of performance. Woodframe construction is used for the vast majority of residential construction in North America and is attracting substantial attention around the world wherever there is a need for economical, safe and comfortable housing. The addition of the latest engineered wood products provides the building designer with even more fl exibility, strength, performance and reliability. The load-carrying capacity and long-span capability of EWPs are attributes that make wood construction an attractive alternative for commercial, industrial and institutional buildings. Each product has its own particular properties and advantages. Glulam, the heavy workhorse of wood construction, offers beauty and sizes and shapes limited only by transportation constraints. Structural composite lumber products can be acquired in large sections, or can be site assembled into larger sections. And framing members like parallel-chord trusses and wood I-joists offer both residential and non-residential construction fl oors that are strong, quiet, and accommodate services beneath them. The properties of engineered wood products are based on research, testing, standards and quality control. Detailed information about the fi re, acoustic, and thermal performance of engineered wood products is covered in more detail in other International Building Series publications (see the back cover). Engineered wood products are generally manufactured to a lower moisture content than dimension lumber, and to a level that approximates the in-service equilibrium moisture content. This means that buildings made from engineered wood products tend to be dimensionally stable. 26 The many types of engineered wood products provide the designer with unlimited possibilities. In cases where products will be concealed in the structure, lower costs products can be used to provide the required strength. And where exposed wood is part of the structure, the beauty of wood, especially with glulam, can be used to create captivating looks with both straight and curved members. INTERNATIONAL Buildingseries NO.7

27 Contact Canada Wood: For more information please contact our offi ce at: Canada Wood Head Offi ce Website: Canada Wood China Beijing Offi ce Suite 12B10, HanWei Plaza No. 7 Guanghua Road ChaoYang District Beijing, China Tel:(86-10) Fax:(86-10) Shanghai Offi ce 9G29 & 9G31, Shanghai Mart 2299 Yan An Road West Shanghai , China Tel:(86-21) Fax:(86-21) (86-21) Canada Wood Europe12A Place Stéphanie B-1050 Brussels, Belgium Tel: (32-2) Fax: (32-2) info@canadawood.info Canada Wood UK Suite 8, St-Albans House 40 Lynchford Road Farnborough, United Kingdom GU14 6EF Tel: ( ) Fax: ( ) offi ce@canadawooduk.org Canada Wood Japan Tomoecho Annex-11 9F Toranomon Minato-ku Tokyo , Japan Tel: (81-3) Fax: (81-3) The Design Possibilities of Engineered Wood Products

28 Publications in this series 1. Moisture and Wood-Frame Building 2. Wood Trusses Strength, Economy, Versatility 3. Fire Resistance and Sound Transmission in Wood-Frame Residential Buildings 4. Sustainability and Life Cycle Analysis for Residential Buildings 5. Thermal Performance of Light-Frame Assemblies 6. Wood-frame Multi-unit Residences 7. The Design Possibilities of Engineered Wood Products A publication of the Canadian Wood Council. Funding support is provided by Canada Wood Council Canadian Wood Council 99 Bank Street, Suite 400 Ottawa, Ontario K1P 6B9 Canada Tel: Web: Front Cover Surrey City Centre, Surrey, British Columbia Architect: Bing Thom Architects Structural engineer: Fast + Epp Photo: Nic Lehoux Hinton Government Centre Architect: Manasc Isaac Architects Ltd. Photo: Jim Dow