Glulam: Engineered Strength. Unsurpassed Versatility. Dependable Quality
By combining engineered strength with the warmth and beauty of wood, structural glued laminated timber (glulam) offers designers a multitude of options for large, open spaces with a minimum number of columns.
Structural glued laminated timber is manufactured by bonding assemblies of high-strength, kiln-dried lumber, with waterproof adhesives. Special bonding techniques allow individual lumber pieces to be joined end-to-end to form long laminations, then face-bonded to form deep timbers.
Glulam is manufactured in both softwood and hardwood species. Popular species include Douglas Fir-Larch, Southern Pine and Alaskan Yellow Cedar. Other species are available upon request. AITC 117, Design Specifications for Structural Glued Laminated Timber of Softwood Species, and AITC 119, Design Specifications for Structural Glued Laminated Timber of Hardwood Species, provide detailed manufacturing and design information.
The laminating process allows timbers to be produced in a variety of shapes from straight beams to graceful, curved arches. This architectural adaptability allows glulam to extend the enduring qualities of wood into applications as varied as individual designers’ imaginations.
Common uses in residential construction include ridge beams, garage door headers, door and window headers, and columns. High strength and stiffness make glulam beams ideal for long-span girders and beams needed for commercial construction. Glulam arch systems and trusses further increase the aesthetic and structural possibilities when using laminated timber construction.
The size of structural glued laminated timber members is limited only by transportation and handling constraints. Widths up to 10-3/4 inches are manufactured using single laminations across the width. Wider sizes are manufactured using two or more laminations across the width of the member. Typical depths range from 5-1/2 inches up to several feet. Standard sizes are described in Standard AITC 113, Standard for Dimensions of Structural Glued Laminated Timber.
Specially graded laminations with high strength and stiffness properties are carefully positioned within timbers to create glulam members with exceptional structural properties. The highest grades of lumber are used in the areas of greatest stress, with lower grades used where strength is not as critical. This layup concept makes very efficient use of the lumber resource. In a typical glulam beam, stresses are highest near the top and bottom of the member, so the highest grades are placed near the surfaces, with lower grades placed in the core.
The high strength and stiffness of laminated timbers enable glulam beams and arches to span large distances without intermediate columns. This translates to larger rooms and more design flexibility than with traditional timber construction.
Structural glued laminated timbers have been used successfully in the United States for more than 70 years. In Europe, glulam has been used successfully for more than 100 years. AITC’s quality program ensures consistent, reliable product performance by inspecting all stages of production for conformance with industry standards. Initially developed in 1961, AITC certification and quality assurance programs are the best in the industry, ensuring safe, long-lasting, high-quality timber. The AITC product mark is the Symbol of Quality™ in engineered timber.AITC’s quality control and inspection system is based on three elements:
For designers and users, AITC brings together all aspects of the engineered timber industry through standards development and technical support activities. AITC standards are recognized by all major building codes in the United States. Standards and technical notes developed by AITC provide guidance to building officials and industry professionals in the design and use of glued laminated timber.
Glulam: Splendid Arches. Custom Designs. Spectacular Structures.
The natural beauty of wood is unsurpassed. Exposed structural glued laminated timber provides structures with a warmth and beauty unrivaled by other building materials. Glulam members may be textured and finished to meet contemporary, traditional or historic buildings’ appearance requirements.
Long, clear spans and majestic soaring arches are no problem for this versatile structural material. The laminating process used to manufacture glulam enables the creation of any number of straight, tapered, and curved shapes. Graceful curved arches and beams are favored for many ecclesiastical designs. The AITC brochure Structural Glued Laminated Timber in Religious Structures showcases several outstanding religious buildings with laminated timber framing.
Glued laminated timber trusses, beams, and arches are used to provide efficient enclosures for expansive areas such as gymnasiums, educational and recreational facilities, indoor pools, auditoriums and shopping centers.
Pressure-treated glulam timbers or timbers manufactured from naturally durable wood species are well suited for creating beautiful and functional bridges and waterfront structures. Wood’s ability to absorb impact forces created by traffic and its natural resistance to chemicals, such as those used for de-icing roadways, make it ideal for these installations. Glulam has been successfully used for pedestrian, forest, highway, and railway bridges.
Experience shows that wood is one of the most suitable materials for construction in and around water. Wood is resilient enough to resist battering by the ocean and docking ships, and it is naturally resistant to the destructiveness of salt water. It doesn’t rust or spall; it is not affected by corrosion.
Where wood is fully exposed to weather, or where protection from the elements is insufficient to ensure a moisture content of less than 20% in the glulam, pressure treatment with preservatives is required. Buildings housing wet processes, or where wood is in direct contact with the ground or water also require preservative pressure treatment. AITC 109, Preservative Treatment of Structural Glued Laminated Timber provides specific recommendations.
Glulam: Readily Available. Cost Effective. Easily Installed.
Frequently used for spans over 100' with no intermediate posts or columns, glulam construction is visually and structurally adaptable, generally reduces the overall cost of a project, and individual glulam are easily modified and installed on site --- no special crews are required.
AITC manufacturing plants are located throughout the United States. Straight beams in common sizes are mass produced and readily available at most building material and lumber distribution centers. Custom timbers may be obtained directly from laminating plants or a local representative, and can be cut-to-length and prefabricated in the laminating plant to arrive at the job site ready for immediate installation.
The beauty of exposed glulam construction does not require the added expense of false ceilings to cover structural framework. Accurate manufacturing reduces the need for on-site fabrication, minimizing waste and labor costs during installation. Equally important, glulam timbers are readily adapted to design changes and minor adjustments during construction. Because glulam may be easily modified in the field to fit existing conditions, renovation projects are also simplified.
The laminating process and use of kiln-dried lumber to manufacture glued laminated timbers minimize wood’s natural propensity to check, twist, warp and shrink in-service.. Installations remain dimensionally stable and beautiful over time, virtually eliminating the need for expensive repairs and call backs.
Smaller glulam members are easily maneuvered manually. Larger timbers and custom configurations can be installed with mobile construction equipment. Conventional hand and power tools are used for modifications and connections.
Standard connection details reduce mistakes and allow for rapid installation. AITC 104 Typical Construction Details provides additional guidance for detailing glulam timbers. The availability of long lengths eliminates the need for splices and reduces construction times. Off-site fabrication of custom laminated timbers further reduces installation time.
Renewable Resource, Sustainable Products
Only one primary building material comes from a renewable resource: wood. As it grows, it cleans the air and water and provides habitat, scenic beauty and opportunities for recreation. As a good environmental steward, the forest products industry practices sustainable forestry practices and efficiently uses harvested material. Every log that is harvested, all under county, state and/or federal forestland management regulations, is nearly 100% utilized.
Of the structural building materials, it has the lowest energy requirements for its manufacture, significantly reducing the use of fossil fuels and pollution of our environment compared to other materials. As part of a structure, wood’s natural insulating properties (many times higher than steel or concrete) reduce the energy required to heat and cool the structure for its lifetime. Wood is reusable, easily recycled, and 100% biodegradable, and unlike the resources for other structural materials, the resource for wood volume has been increasing in U.S. net reserves since 1952, with growth exceeding harvest in the U.S. by more than 30%. Just like its parent material, glulam enjoys all of these natural benefits.
In addition to the great environmental benefits associated with wood, glulam timbers extend the available wood resource by using high grade material only where it is needed in the layup. Glulam technology also uses small dimension lumber to make large structural timbers, utilizing logs from 2nd and 3rd growth forests and timber plantations. As a “green” building material, structural glued laminated timber simply can’t be beat.
Buildings constructed with large structural timbers have excellent fire-resistive qualities. U.S. model building codes recognize this and provide guidelines for ensuring fire resistant timber structures. Two distinct approaches are included in the codes: Heavy Timber Construction and Fire Resistive Construction.
Heavy Timber Construction has long been recognized by the model building codes as fire resistant. To meet the requirements of Heavy Timber Construction, limitations are placed on the minimum size, including depth and thickness, of all load-carrying wood members. Other requirements include the avoidance of concealed spaces under floors and roofs and the use of approved construction details. Minimum sizes for laminated timbers meeting the requirements of Heavy Timber Construction are contained in the building codes and in AITC 113 Standard for Dimensions of Structural Glued Laminated Timber.
The performance of Heavy Timber Construction under fire conditions is markedly superior to most unprotected “non-combustible” construction. Unprotected metals lose strength quickly and collapse suddenly under extreme heat. Steel weakens dramatically as its temperature climbs above 450° Fahrenheit, retaining only 10% of its strength at about 1380°F. The average building fire temperatures range from 1290°F to 1650°F.
In contrast, wood retains a significantly higher percentage of its original strength for a longer period of time, losing strength only as material is lost through surface charring. Fire fighting is safer due to elimination of concealed spaces and the inherent structural integrity of large glued laminated timbers. Additional information is contained in AITC’sSuperior Fire Resistance brochure.
Fire Resistive Construction
Fire resistance is the amount of time a structural member can support its load before collapsing. The goal of fire-resistive construction is to provide adequate fire protection for occupants to evacuate the building safely. o. For example, a one-hour rating means a member or assembly should be capable of supporting its full load without collapsing for at least one hour after a fire starts.
The standard test for measuring fire resistance is the American Society of Materials and Testing (ASTM) Test Method E-119. Ratings of assemblies (including beams, walls, and floors) are determined by test procedures that approximate actual fire conditions.
The results of ASTM fire tests for building assemblies, sponsored jointly by the American Forest Paper Association (AF&PA) and the American Institute of Timber Construction, enable designers to calculate specific fire ratings for glulam members. Calculations are based on a consideration of member size, degree of fire exposure, and loads on the member. Additionally, fire-resistance ratings for glulam beams require layup modifications.
AITC Technical Note 7 Calculation of Fire Resistance of Glued Laminated Timbers and AF&PA Technical Report 10 Calculating the Fire Resistance of Exposed Wood Members provide detailed design methods and layup modifications required for fire-rated glulam construction.