Wooden constructions are on the rise again – encouraged by a strong trend towards sustainable and resource efficient buildings. Load-bearing timber-glass composite elements – a novel concept to use the in-plane loadbearing potential of glass – could contribute to a more efficient use of materials in façades. The current study relates to...
Southern Pine (SP) is one of the fastest growing softwood species in the Southern Forest of United States. With its high strength to weight ratio, SP becomes an ideal candidate for manufacturing engineered wood products such as cross laminated timber (CLT). Two batches of CLT panels were manufactured using visually graded SP lumbers in this study: pilot-scale panels in a laboratory setting and full-size panels in a manufacturing plant environment. The first batch of pilot-scale CLT panels was manufactured at Clemson University. The second batch of full-scale CLT panels (3m x 12.2m) was produced and CNC-sized by Structurlam in Penticton, Canada and shipped to Clemson University for testing. Four types of structural wood adhesives were selected in the panel production, namely Melamine Formaldehyde (MF), Phenol Resorcinol Formaldehyde (PRF), Polyurethane (PUR) and Emulsion Polymer Isocyanate (EPI). This paper presents the manufacturing process of SP CLT in a laboratory setting as well as structural performance verification of 3- ply SP CLT in terms of rolling shear and bending properties. The obtained performance data of 3-ply CLT in both major and minor strength directions is verified against PRG-320 Standard for Performance Rated Cross Laminated Timber. Tested results are presented and discussed.
This article outlines the structural design approach used for the Brock Commons Student Residence project, an 18-storey wood building at the University of British Columbia in Vancouver, Canada. When completed in summer 2017, it will be the tallest mass timber hybrid building in the world at 53 meters high. Fast + Epp are the structural engineers, working in conjunction with Acton Ostry Architects and Hermann Kaufmann Architekten. Total project costs, inclusive of fees, permits etc. are $51.5M CAD.
This thesis deals with the shear design of Cross Laminated Timber (CLT) elements stressed by concentrated loads which are locally reinforced by means of self-tapping screws with continuous threads. A simplified model is presented using an effective width for the calculation of the shear stresses in the vicinity of point supports or concentrated loads. Laboratory tests supply material-mechanical principles to determine the interaction of rolling shear stresses and compression perpendicular to the grain. In addition to experimental tests theoretical models are developed to examine the load bearing behaviour of CLT-elements reinforced by self-tapping screws. Preliminary tests with plate elements provide initial experience with these reinforcements under biaxial load transfer. Finally a design concept validated by means of the test results is proposed.
In timber construction, curved timber components have been used repeatedly. Yet the use of curved CLT elements is a relatively recent phenomenon. To obtain a European Technical Approval (ETA) for so-called radius timber (single curved CLT elements), Holzbau Unterrainer GmbH commissioned the accredited testing institution TVFA – Innsbruck to carry out the tests required for this purpose. To this end, overall 158 tests were performed in building component dimensions from December 2013 to May 2014, and several laboratory tests were carried out to monitor adhesive joint quality. Due to the single curved shape of radius timber elements, it is key to particularly focus on possible implications on load bearing capacity due to pre-stress of the slats and to the tensile stress perpendicular to grain resulting from deflection forces. To comply with the criteria laid down in the semi-probabilistic safety concept used in Eurocode 5, the impact caused by these pre-curvatures on strength, rigidity and gross density must be known.
The cross-laminated timber (CLT) technology is also perceived as a potential for utilization of lumber oflower grades and underused species, because the core layers perpendicular to the principle loading direction transferloads through rolling shear, which is not correlated to the grade of lumber. Current the product standard however specifies the minimum grade requirements for all lumber to be used as CLT laminations. In this study the effect of the presence of knots in the transverse core layer of CLT billets was examined in matched CLT samples where the heavy presence of knots in the transverse core layer was the only variable compared to knot free reference. All samples were tested as short-beams in three point bending and all failed in rolling shear in the transverse core layer. The presence of knots had no measurable effect on the shear capacity expressed as nominal MOR of the tested CLT beam samples
Wood as building material is gaining more and more attention in the 21st century due to its positive attributes such as light weight, renewability, low carbon footprint and fast construction period. Cross-laminated timber (CLT), as one of the new engineered wood products, requires more research emphasis since its mechanical performance can allow CLT to be utilized in massive timber structures. This thesis focuses on revealing one of the key failure mechanisms of CLT, which is usually referred to as the rolling shear failure. The scientific research conducted in this thesis combined both analytical modelling and experimental material testing. The stresses in CLT cross-layers obtained from a finite-element model were analyzed to differentiate various failure modes possible. Tension perpendicular to grain stress was found to cause cross-layer failure in combined with the rolling shear stress. Experimentally, specimens prepared from 5-layer CLT panels were tested under center-point bending condition. Detailed failure mechanism of CLT cross-layers were recorded with high speed camera to capture the instant when initial failure happened. It is evident that some of the specimens failed in tension perpendicular to grain which verified the modelling results. Variables such as the rate of loading and the manufacturing clamping pressure were designed in experiments to compare their influence to the failure of CLT specimens. In this research, the failure of CLT cross-layer was updated to a combined consequence of both rolling shear stress and tension perpendicular to grain stress. Future research topics and product improvement potentials were given by the end of this thesis.
Project contact is Erica Fischer, Oregon State University
Previous large-scale fire testing of mass timber buildings has occurred on a single floor of a building. The data collected from these experiments were used to demonstrate the fire performance of cross-laminated timber (CLT) buildings and to change the International Building Code (IBC) prescriptive fire protection design provisions for mass timber buildings. The scope of the tests was limited to compartment fires with varying levels of encapsulation. However, multi-story mass timber buildings are being constructed in the United States and fire science experts understand that fire threats can move beyond compartment fires and into travelling (moving fires) and vertical fire spread. In addition, many buildings are being proposed outside of the scope of the IBC prescriptive fire protection design approach (i.e. open floor plans), thereby requiring the employment of performance-based structural fire engineering. Performance-based structural fire engineering requires quantifying fire demands within the structure and calculating the resistance of the structure throughout the fire to provide safety to the occupants during egress, safety to fire fighters during and after the fire, and to ensure the building will not collapse introducing a threat of fire spread and damage to the surrounding buildings. To date, engineers are employing performance-based structural fire engineering on mass timber buildings; however, engineers are typically forced to make simplifications, be very conservative, and/or frequently use unproven assumptions. These simplifications and assumptions need to be tested experimentally to ensure that engineers are providing adequate levels of safety. Some of these assumptions include exterior wall and façade details that can prevent vertical fire spread, and detailing by engineers that considers the effects of charring during the decay phase of the fire.
The PIs have an opportunity to perform large-scale fire tests on a multi-story mass timber building in Corvallis, OR. Future large-scale fire tests will utilize a portion of the 10-story building being tested as a part of the Natural Hazards Engineering Research Infrastructure (NHERI) Tall Wood project (http://nheritallwood.mines.edu/). After the seismic testing of the 10-story building, the top four stories will be demolished and not utilized. Therefore, the research team will transport these floors to Corvallis to be re-assembled at the Corvallis Fire Training Center. In this preliminary stage, a multi-disciplinary team will perform computer simulation modeling of the fire tests, fully develop the scope of the tests and create a detailed experimental plan for the large-scale fire tests. The tests will be designed with considerations for the ability to address the following questions. These questions are consistent with future research needs that were identified by the Forest Products Laboratory  and the recent National Fire Protection Association (NFPA) Fire Safety in Tall Timber Buildings Workshop.
(1) How does the façade detailing of a mass timber building influence the vertical fire spread behavior?
(2) How can engineers better design mass timber buildings to enhance the safety for firefighters?
(3) How do glulam beam-to-column connections perform in real fires?
(4) What engineering solutions can be implemented within mass timber buildings to account for the behavior of the mass timber during the decay phase of the fire in the case that suppression is not available?
(5) How can engineers better design mass timber buildings to enhance the safety for fire fighters during the firefight and during overhaul/investigation?