Wood and Fiber Science (E-Journal)
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RECENT DEVELOPMENT IN CLT CONNECTIONS PART II: IN-PLANE SHEAR CONNECTIONS FOR CLT BRACING ELEMENTS UNDER CYCLIC LOADS
Full text linkBecause of their high shear strength and stiffness, cross-laminated timber (CLT) members are especially suited for in-plane loads. However, the ductility and energy dissipation capacity of a CLT structure is mainly determined by properties of the mechanical connections such as dowel-type fasteners. Unfortunately, the load-slip behavior of these typical timber-to-timber connections shows pinched hysteresis loops and impairment of strength. For seismic loads, highly dissipative connections with stable dissipation properties are desirable. A new type of connection was developed avoiding the pinching of hysteresis loops while showing high energy dissipation. An experimental investigation and a design proposal of a highly dissipative steel plate connection for CLT shear walls is presented as a result of the work.
Fire Safety of Mass timber Buildings with CLT in USA
Full text linkMultistory buildings using mass timber and cross-laminated timber (CLT) as the primary structural elements are being planned and constructed globally, with interest starting to gather momentum in the United States. Model building codes in the United States limit timber construction to a building height of 85 ft (25.9 m) because of concerns over fire safety and structural performance. Up to 85 ft, the mass timber can be exposed. Architects and developers in the United States are pushing boundaries, requesting mass timber structures are constructed as high-rises and that load-bearing mass timber such as CLT be exposed and not fully protected. This provides an opportunity for the application of recent fire research and fire testing on exposed CLT to be applied, and existing methods of analyzing the impact of fire on engineered timber structures to be developed further. Fire testing has shown that exposing large areas of CLT significantly impacts the heat release rate and fire duration. This article provides an overview of the code requirements for timber construction in the United States, provides methods for building approval for a high-rise timber structure, and summarizes recent CLT compartment fire testing that is informing the fire engineering process. Methods for solutions are also discussed
BENDING STRENGTH AND STIFFNESS OF NO. 2 GRADE SOUTHERN PINE LUMBER
Full text linkSouthern pine is the most important species group planted and used for lumber products in the United States. Most southern pine trees come from managed forests, with relatively short rotations and excellent growth yields. The accelerated growth volume allows trees to reach merchantable size in 16- 22 yr. However, these trees may contain large amounts of juvenile wood which can negatively impact the bending properties of lumber. In 2010, the Southern Pine Inspection Bureau (SPIB) began to reevaluate the mechanical properties of southern pine lumber, which resulted in changes in design values. The objective of the study herein was to summarize the growth characteristics and bending properties of No. 2 grade 24, 26, 28, and 210 samples collected from across the geographical growing range (southern United States). Each piece met the requirements for No. 2 grade southern pine lumber. Overall, 34.5% of the sample contained pith, averaged 4.6 rings per inch, and contained 43.8% latewood. The sample’s average specific gravity,MOE, and MOR were 0.54, 10.1 GPa, and 41.7 MPa, respectively. The mean MOE found in this study was higher than the current design value required for No. 2 southern pine lumber. For allowable design bending strength (Fb), the results showed that, as dimension stock size increased, the Fb decreased from 11.2 MPa for 2 4 s to 7.1MPa for 2 10 s. The Fb values determined herein exceeded the new published design value and also met the previous SPIB design values. These results suggest that the timber resource quality might have increased since the housing crisis of 2008-2010
Relationship between static and cyclic front to back load capacity of wooden chairs and evaluation of the strength values according to acceptable design values
Full text linkTests were carried out to investigate the relationship between static and cyclic strength of wooden chairs. Furthermore, cyclic front to back load performance of chairs were compared with acceptable design loads that were given in the American Library Association (ALA) specifications. For this purpose, 90 chair frames were constructed of Turkish beech (Fagus orientalis L.) with round edge mortise and tenon joints, with tenons that varied from 30, 40, and 50 mm in width and 30, 40, and 50 mm in length. All joints were assembled with 65% solid polyvinyl acetate adhesive. Half of the chairs were subjected to “cyclic” loads and the other half were subjected to “static” loads based on the ALA specifications. In conclusion, it was recommended that the cyclic strength could be taken as the 56% of the static strength. According to the results, the chairs constructed with any size of tenons could meet the light-duty service (domestic usage), except for the chairs constructed with 30 by 30 mm tenons. The chairs constructed with 50 by 50 mm tenons could meet the heavy-duty service, whereas the chairs constructed with 30 by 50 mm tenons could meet the medium-duty service
FIRE SAFETY OF CLT BUILDINGS IN CANADA
Full text linkThis article provides an overview of the code requirements pertinent to large cross-laminated timber (CLT) buildings and the methods for meeting the requirements in Canada. Canadian building codes are objective-based. Compliance with the code is achieved by directly applying the acceptable solutions up to certain prescriptive building sizes (height and area) or by developing alternative solutions beyond the height and area limits. The fire safety design for a CLT building larger than the prescriptive limit must demonstrate that the building will achieve at least the minimum level of performance afforded by noncombustible construction in limiting the structural involvement in fire and contribution to the growth and spread of fire during the time required for occupant evacuation and emergency responses.
EXPERIMENTAL STUDY OF THE BENDING PERFORMANCE OF HOLLOW GLULAM BEAMS
Full text linkHollow glulam beam has some advantages that the traditional solid glulam beam does not have, such as the convenience for wiring construction and comparably light weight. Four-point bending tests of three solid glulam beams and 15 hollow glulam beams with various sizes of rectangular holes produced from small-diameter larch timber were conducted to investigate the influence of the hollow ratio and wall thickness on bending stiffness and load capacity. The midspan deflection, cross-section strain, and ultimate load were obtained from the tests, and the detailed failure modes and apparent MOE for all specimens are reported. Hollow glulam beams with the hollow ratio ranged from 25% to 40%, and the wall thickness greater than 20 mm after the assumption of plane section under bending moment. The apparent bending stiffness and ductility of hollow glulam beam were less than those of solid glulam beam, and the apparent MOE is 0.86 times the elastic modulus value calculated by theory of elasticity. In addition, a calculation formula for the ultimate bending moment is proposed.
LIFE-CYCLE ASSESSMENT OF ACTIVATED CARBON FROM WOODY BIOMASS
Full text linkActivated carbon (AC) developed and marketed for water and gas purification is traditionally made from hard coals (fossil-based materials). However, increasing awareness of environmental impacts caused by fossil fuel consumption and fossil-based products has provided a market opportunity for renewable and low-impact biobased products as alternatives including AC. The huge volumes of woody biomass generated from forest management activities could be used as feedstocks for these new bioproducts. These new bioproducts require evaluation to determine if they are low impact. To aid in quantifying environmental impacts of a new bioproduct (such as AC), this study developed the cradle-to-gate life cycle inventory (LCI) data for the carbon activation of biochar in a rotary calciner by collecting operational and direct emission data while conforming to the internationally accepted life cycle assessmentmethod. The LCI datawere then modeled to develop the life cycle impact assessment profile of biochar-based carbon activation and compared with commercial coal-based carbon activation. The results showed about 35% less cradle-to-product gate cumulative energy demand for the biochar AC system compared with the coal AC system. Consequentially, the greenhouse gas emissions for biochar AC production were less than half that of coal AC production (8.60 kg CO2 eq vs 18.28 kg CO2 eq per kg of AC produced). This was because of both lower energy consumption and the biogenic carbon benefit from using woody biomass for both feedstock and processing. To ensure substitution of the two ACs, the physical properties for the AC from biochar and coal were compared for their Brunauer–Emmett–Teller surface area and iodine number, which showed that both indicators were superior for biochar AC compared with coal AC. Therefore, biochar AC results from this study suggest a potential high-value market for woody biomass derived from forest restoration and wildfire suppression activities.
DESIGN APPROACHES FOR CLT CONNECTIONS
Full text linkVarious design approaches for establishing the resistance of connections in cross-laminated timber (CLT) structures have been developed and adopted in timber design standards worldwide. Although the fundamental principles are similar, the new design provisions for CLT connections have been aligned in some standards with the existing design philosophy and format adopted for sawn timber and glulam using traditional fasteners such as dowels, nails, and wood screws for consistency and simplicity, in the other standards, alternate approaches have been developed. This article presents a snap shot of the various design approaches for connections in CLT adopted in Europe, Canada, the United States, and New Zealand. The intent is for the reader to have a better knowledge of the underpinning assumptions, principles, and the adopted design rules in each of these standards
Ability of finger-jointed lumber to maintain load at elevated temperatures
Full text linkThis article presents a test method that was developed to screen adhesive formulations for finger-jointed lumber. The goal was to develop a small-scale test that could be used to predict whether an adhesive would pass a full-scale ASTM E119 wall assembly test. The method involved loading a 38-mm square finger-jointed sample in a four-point bending test inside of an oven with a target sample temperature of 204°C. The deformation (creep) was examined as a function of time. It was found that samples fingerjointed with melamine formaldehyde and phenol resorcinol formaldehyde adhesives had the same creep behavior as solid wood. One-component polyurethane and polyvinyl acetate adhesives could not maintain the load at the target temperature measured middepth of the sample, and several different types of creep behavior were observed before failure. This method showed that the creep performance of the one-component adhesives may be quite different than the performance from short-term load deformation curves collected at high temperatures. The importance of creep performance of adhesives in the fire resistance of engineered wood is discussed.
MASS TIMBER CONSTRUCTION IN AUSTRALIA AND NEW ZEALAND—STATUS, AND ECONOMIC AND ENVIRONMENTAL INFLUENCES ON ADOPTION
Full text linkMass timber construction in Australia and New Zealand uses three main materials—laminated veneer lumber, glue laminated timber and cross-laminated timber (CLT). This article focuses on the use of mass timber in nonresidential construction—the use in single-family homes and apartments is not considered. In Australia and New Zealand, mass timber building technology has moved from being technologically possible to being a feasible alternative to reinforced concrete and steel construction. It has not taken over a large market share in either market and, as such, has not been a disruptive technology. The major changes in this market in the past 5-10 yr in Australia and New Zealand have been the development of new industrial capacity in CLT and the acquisition of computer controlled machining equipment to facilitate prefabrication of wooden building components. The development of new codes and standards and design guides is underway. The drivers of future growth in market share are expected to include more clients putting a higher weight on the various environmental benefits of building in wood, reduction in the real and perceived professional risk for builders and architects specifying mass timber construction, and fuller participation in the supply chain for timber buildings (from design to construction) by timber building specialists. Government policies to encourage the use of timber may also be helpful. Engineers and architects will continue to learn—through experience—how to optimize building construction methods to take advantage of the specific features and qualities of timber as a construction method.