European experience shows that besides single family housing, Cross-Laminated Timber (CLT) can be competitive in mid-rise and high-rise buildings. Although this system has not been used to the same extent so far in North America, it can be viable wood structural solution for the shift towards sustainable densification of urban and suburban centres. FPInnovations has undertaken a multidisciplinary project on determining the structural properties of a typical CLT construction, including quantifying the seismic resistance and force modification factors of CLT buildings. In this paper, some of the results from a series of quasi-static tests on CLT wall panels are presented as well as preliminary estimates for the force modification factors (R-factors) for seismic design of CLT structures. CLT wall panels with various configurations and connection details were tested. Wall configurations included single panels without openings with three different aspect ratios, panels with openings, as well as multi-panel walls with step joints and fasteners between them. Connections for securing the walls to the foundation included off-the-shelf steel brackets with annular ring nails, spiral nails, and screws; a combination of steel brackets and hold-downs; and custom made brackets with timber rivets. Results from two storey configurations that include two walls and a CLT slab in between are presented and discussed. Finally preliminary estimates and recommendations for the force modification factors (R-factors) for seismic design of CLT structures according to National Building Code of Canada (NBCC) are also made.
The objective of this project was to quantify and compare the environmental impacts associated with alternative designs for a typical North American mid-rise office building. Two scenarios were considered; a traditional cast-in-place, reinforced concrete frame and a laminated timber hybrid design, which utilized engineered wood products (cross-laminated timber (CLT) and glulam). The boundary of the quantitative analysis was cradle-to-construction site gate and encompassed the structural support system and the building enclosure. Floor plans, elevations, material quantities, and structural loads associated with a five-storey concrete-framed building design were obtained from issued-for-construction drawings. A functionally equivalent, laminated timber hybrid design was conceived, based on Canadian Building Code requirements. Design values for locally produced CLT panels were established from in-house material testing. Primary data collected from a pilot-scale manufacturing facility was used to develop the life cycle inventory for CLT, whereas secondary sources were referenced for other construction materials. The TRACI characterization methodology was employed to translate inventory flows into impact indicators. The results indicated that the laminated timber building design offered a lower environmental impact in 10 of 11 assessment categories. The cradle-to-gate process energy was found to be nearly identical in both design scenarios (3.5 GJ/m2), whereas the cumulative embodied energy (feedstock plus process) of construction materials was estimated to be 8.2 and 4.6 GJ/m2 for the timber and concrete designs, respectively; which indicated an increased availability of readily accessible potential energy stored within the building materials of the timber alternative.
This paper examines CLT-steel hybrid systems at three, six, and nine storey heights to increase seismic force resistance compared to a plain wood system. CLT panels are used as infill in a steel moment frame combining the ductility of a steel moment frame system with a stiffness and light weight of CLT panels. This system allows for the combination of high strength and ductility of steel with high stiffness and light weight of timber. This thesis examines the seismic response of this type of hybrid seismic force resisting system (SFRS) in regions with moderate to high seismic hazard indices. A detailed non-linear model of a 2D infilled frame system and compared to the behavior of a similar plain steel frame at each height.
Parametric analysis was performed determining the effect of the panels and the connection configuration, steel frame design, and panel configuration in a multi-bay system. Static pushover loading was applied alongside semi-static cyclic loading to allow a basis of comparison to future experimental tests. Dynamic analysis using ten ground motions linearly scaled to the uniform hazard spectra for Vancouver, Canada with a return period of 2% in 50 years as, 10% in 50 years, and 50% in 50 years to examine the effect of infill panels on the interstorey drift of the three, six, and nine storey. The ultimate and yield strength and drift capacity are determined and used to determine the overstrength and ductility factors as described in the National Building Code of Canada 2010.
A series of 3 cross-laminated timber (CLT) fire-resistance tests were conducted in accordance with ULC S101 standard as required in the National Building Code of Canada.
The first two tests were 3-ply wall assemblies which were 105 mm thick, one unprotected and the other protected with an intumescent coating, FLAMEBLOC® GS 200, on the exposed surface. The walls were loaded to 295 kN/m (20 250 lb./ft.). The unprotected assembly failed structurally after 32 minutes, and the protected assembly failed after 25 minutes.
The third test consisted of a 175 mm thick 5-ply CLT floor assembly which used wood I-joists, resilient channels, insulation and 15.9 mm ( in.) Type X gypsum board protection. A uniform load of 5.07 kPa (106 lb./ft²) was applied. The floor assembly failed after 138 min due to integrity.
In an objective to evaluate the surface burning characteristics of massive timber assemblies such as CLT and SCL, flame spread tests on massive timber assemblies have been conducted in accordance with ULC S102 test method. This study evaluated the flame spread of fully exposed massive timber specimens (i.e. untreated/uncoated) as well as the effect on flame spread by using intumescent coating with CLT. Test results provide low flame spread ratings when compared to those of common combustible interior finish materials provided in Appendix D-3 of NBCC. Specifically, the obtained flame spread ratings of 3-ply CLT assemblies of 105 mm in thickness are 35 and 25 for a fully exposed CLT (untreated) and for a CLT panel protected by intumescent coating respectively. Fully exposed SCL of 89 mm in thickness provided ratings of 35 and 75 for parallel strand lumber (PSL) and laminated strand lumber (LSL) respectively.
Advanced wood building systems form a significant market opportunity for use of wood in taller and larger buildings, which are currently required to be of non-combustible construction in accordance with provisions set forth in Part 3 of Division B of the National Building Code of Canada (NBCC).
In order to evaluate the surface burning characteristics of massive timber assemblies, flame spread tests on CLT assemblies have been conducted in accordance with ULC S102 test method. Three series of 3-ply CLT panels of 99 mm in thickness, V2 stress grade as per ANSI/APA PRG-320 (i.e., manufactured with Spruce-Pine-Fir (SPF) lumber) have been evaluated for flame spread and smoke developed classification. Fully exposed CLT specimens (99 mm) provided much lower flame spread ratings (FSR of 40), when compared to thinner similar products.
The following report provides background information on the standard test method used in Canada to evaluate fire stop systems, ULC S115, “Standard Method of Fire Tests of Firestop Systems” and the regulatory requirements specified in the National Building Code of Canada (NBCC).
A review of research conducted in Europe demonstrates that fire stop systems currently used in reinforced concrete and light-frame construction can be used with success in solid wood construction. While testing conducted in Europe has largely relied on lining the reveal of openings with gypsum board, a limited number of tests indicate that lining methodology using gypsum board may not be necessary in all cases.
The highest priority for facilitating the development and approval of fire stop systems is in wood structures up to 6 storeys tall. This is due to the fact that these buildings are currently permitted in the British Columbia Building Code (BCBC) and are likely to be permitted in other provinces as well as in the 2015 edition of the NBCC.
In order to help the wood industry in moving forward in addressing fire stops issues, three paths are identified and discussed in which the wood industry could facilitate the development of approved fire stop systems for solid wood construction. Ultimately, it is the fire stop manufacturers who must conduct testing in order to seek fire stop listings. Therefore, it is highly recommended that testing be conducted in cooperation with one or more fire stop manufacturers.
Figure 1 shows a floor plan and elevation along with the preliminary shear wall locations for a sixstorey wood-frame building. It is assumed some preliminary calculations have been provided to determine the approximate length of wall required to resist the lateral seismic loads.
If the preliminary design could not meet the drift limit requirement using the base shear obtained based on the actual period, the shear walls should be re-designed until the drift limit requirement is satisfied.
Utilizing Linear Dynamic Analysis (LDA) for designing steel and concrete structures has been common practice over the last 25 years. Once preliminary member sizes have been determined for either steel or concrete, building a model for LDA is generally easy as the member sizes and appropriate stiffness can be easily input into any analysis program. However, performing an LDA for a conventional wood-frame structure has been, until recently, essentially non-existent in practice. The biggest challenge is that the stiffness properties required to perform an LDA for a wood-based system are not as easily determined as they are for concrete or steel structures. This is mostly due to the complexities associated with determining the initial parameters required to perform the analysis.
With the height limit for combustible construction limited to four stories under the National Building Code of Canada, it was uncommon for designers to perform detailed analysis to determine the stiffness of shear walls, distribution of forces, deflections, and inter-storey drifts. It was only in rare situations where one may have opted to check building deflections. With the recent change in allowable building heights for combustible buildings from four to six storeys under an amendment to the 2006 BC Building Code, it has become even more important that designers consider more sophisticated methods for the analysis and design of wood-based shear walls. As height limits increase, engineers should also be more concerned with the assumptions made in determining the relative stiffness of walls, distribution of forces, deflections, and inter-storey drifts to ensure that a building is properly detailed to meet the minimum Code objectives.
Although the use of LDA has not been common practice, the more rigorous analysis, as demonstrated in the APEGBC bulletin on 5- and 6-storey wood-frame residential building projects (APEGBC 2011), could be considered the next step which allows one to perform an LDA. This fact sheet provides a method to assist designers who may want to consider an LDA for analyzing wood-frame structures. It is important to note that while LDA may provide useful information as well as streamline the design of wood-frame structures, it most often will not be necessary.
A research project, Wood and Wood-Hybrid Midrise Buildings, was undertaken to develop information to be used as the basis for alternative/acceptable solutions for mid-rise construction using wood structural elements. One of the Tasks in the project was to investigate the effectiveness of three materials for use as encapsulation materials for combustible structural elements: Type X gypsum board, cement board and gypsum-concrete. Cone calorimeter and intermediate-scale furnace tests were conducted for these materials. The results of the tests on these materials using the cone calorimeter and the intermediate-scale furnace are provided in References 3 and 4, respectively. In addition to the tests for the three encapsulation materials, data from previous NRC fireresistance projects were reviewed for data on the encapsulation time for structural elements afforded by gypsum board in the context of standard fire-resistance testing. In this report, the results of the data-mining from several of NRC’s fire-resistance testing projects are provided.