Fire Resistance of Glulam Structures
Glulam structures act as an effective collective defense system against fire spread, providing extra time for evacuation and improving safety.
The thermal mass and carbon coatings found on glulam columns help prevent hot spots and slow heat transfer, making them safer alternatives to steel structures.
1. Structural integrity
Glulam is a wood product composed of lumber boards arranged in a cross-laminated pattern and glued together under pressure, producing an extremely durable timber element. As its multi-layer construction ensures fire resistance through their charring process, glulam structures also serve to mitigate fire spread by blocking flame penetration of inner structure while protecting lumber beneath from excessive heat levels, giving time for material to cool off before spreading further.
The char layer acts as a thermal barrier and absorbs and disseminates heat slowly, further mitigating sudden temperature swings. Furthermore, timber’s lower thermal conductivity than other materials helps limit fire spread while decreasing potential structural damage risks.
Glulam differs from steel and concrete in that it does not combust easily, maintaining its strength and shape for extended periods during a fire. This allows engineers to design buildings out of glulam in such a way that maximizes its fire-resistance rating.
As part of designing a building, it’s crucial to keep pedestrian and vehicular safety as well as seismic performance top of mind when creating its design. To meet these criteria, structures must be capable of withstanding large loads without collapsing, something which requires extensive finite element modeling to verify.
In order to ascertain the effects of W/D cycles and aging on glulam’s bending strength, six specimens from „reference”, „6 months inside”, and „6 months outer loaded” sets were subjected to 4-point bending tests in 4-point mode. Results demonstrated that instantaneous bending strength decreased over time with ageing of the material, particularly where glue joints exist due to increased hygromechanical coupling occurring there.
2. Ignitability
When exposed to standard fire conditions, glulam will char, but remains noncombustible. The char layer acts as a buffer that slows fire spread while providing time for evacuation and extinguishment procedures. Furthermore, its multilayer structure and carbon crust help it remain structurally sound for some time post fire exposure, unlike steel which loses strength rapidly as it burns.
Charring of wood reduces thermal conductivity, slowing heat transfer and mitigating fire spread to nearby members, which in turn helps preserve structural integrity in glulam columns during and after fire outbreaks as well as limit fire spreading further throughout a building or structure.
Char layer has an exceptional resistance to re-ignition. This property is particularly important as re-ignition can significantly decrease residual bearing capacity of a glulam column, necessitating an additional thick char depth to avoid structural failure of such columns.
Well-documented lab measurements of char layers allow researchers to calculate fire resistance of glulam members; however, this calculation method suffers from uncertainty due to differences between actual material properties of each glulam, such as exact locations and dimensions of knots, weak sections and finger joints as well as density and strength properties of small cells.
This research investigates how integrated sensors into glulam can monitor durability indicators like moisture variations and deformations during W/D cycles and medium-term external climate exposure tests such as shear and 4-point bending tests (shear/4 point bend). Engineers and architects will be able to use this monitoring data when specifying pre-tested connection assemblies which meet fire test requirements outlined by International Building Code.
3. Flame spread
Glulam stands up well against fire compared to steel, which weakens quickly under high temperatures and loses its load-bearing capacity. Its layered structure composed of solid wood elements bound by resilient adhesives acts as an effective protection from high heat levels – delaying combustion while giving time for evacuation. Furthermore, fireproof treatments and coatings available for glulam further increase its ability to resist flame propagation and heat transfer.
Numerous factors, including wood species and adhesive type, can impact the structural fire resistance of glulam. A recent study conducted at the University of Alberta by a team of researchers concluded that wood species with increased moisture content and lower abrasiveness tend to exhibit greater fire resistance; they also noted how glued joints with rough joints or preservative chemicals present can speed the rate of spread in beams made of this material.
A separate investigation by the same team investigated glulam columns during and after fire damage. To characterize these specimens from MTDFTP and conduct compression tests postfire load demands were identified using an effective cross-section method prescribed by CSA O86 Engineering Design in Wood [18].
Experimental results indicated that on average, axial capacities obtained through testing results were 33% lower than those calculated with respect to CSA O86 provisions. This discrepancy can be explained by higher-than-expected experimental char depth and visual degradation layer depth compared with what would be acceptable according to code calculations (note: equivalent coefficients can be found within EN 1995-1-2; these terms refer to reduction coefficients d1 and d2). These findings highlight the necessity of including empirical data about charred glulam material properties when comparing design results with testing results when making comparisons between design and testing results when making comparisons of their results between designs and tests results.
4. Heat transfer
Fire safety is of utmost importance when building commercial structures, so understanding how different materials perform is vital. Glulam is an excellent material choice for many purposes due to its inherent resistance to fire’s effects and ensures safe evacuation while safeguarding structural integrity – this is particularly advantageous in wood frame high rise buildings; unlike steel it does not collapse under fire pressure, maintaining load-bearing capacity through its duration.
Glulam is a composite material composed of kiln-dried, stress-graded lumber which has been finger-jointed and then secured using weatherproof glue. These lams can be customized into straight, curved or arched members according to need, with typical species such as Douglas-fir, spruce-pine-fir (SPF), western hemlock or redwood being utilized as building material.
Manufacturing allows for larger and longer length glulam members than could be made with solid sawn timber, leading to greater strength per unit of section than would otherwise be achievable with individual pieces of timber. Furthermore, glulam’s dimensional stability reduces risk due to changes in moisture content levels.
Glulam is highly resistant to abrasion and chemical corrosion, making it the ideal material for use in harsh environments like animal hide curing facilities and fertilizer storage facilities. In addition, due to its aesthetic appeal and durability it’s often employed in modern low-rise mass timber buildings for structural elements or decorative touches.
5. Residual bearing capacity
Glulam construction involves glueing together wood lamellas to form a structural beam with grain running parallel with its length. This versatile timber can be purchased custom or stock sizes and finished using any one of four appearance classifications: premium, architectural, industrial and framing. In addition to providing structural integrity and aesthetic value, glulam also stands up well against fire resistance while remaining load bearing while other materials break down.
Loss of load-bearing capacity is one of the primary contributors to structural failure during fires in buildings and bridges, especially long span glulam structures whose failure can result in significant lateral displacement and impact safety concerns. Therefore, fire resistance of glulam structures should be an integral consideration when designing them.
Numerous studies have evaluated the performance of glulam under different fire conditions. Experimental and numerical analyses have demonstrated that its flexural behavior remains stable under design loads for up to 30 minutes at design loads with only 20% loss in original strength, decreasing as temperature rises up to 50% at 210degC.
Integrity of timber members is another key element in glulam fire resistance. To achieve this goal, a zero-strength layer must be created which lowers both tensile and compressive strengths of timber below its yield strength, then adhered securely to prevent delamination.
Research has demonstrated that for effective fire resistance, zero-strength layer thickness must be increased from 7 mm as specified in EN 1995-1-2 to achieve sufficient fireproofing. Furthermore, a new method has been devised which accounts for loss of strength and stiffness within the pyrolysis zone called the effective cross section method and will be included in any future revision of EN 1995-1-2.