Diaphragms are essential to transfer lateral forces in the plane of the diaphragms to supporting shear walls underneath. As the distribution of lateral force to shear walls is dependent on the relative stiffness/flexibility of diaphragm to the shear walls, it is critical to know the stiffness of both diaphragm and shear walls, so that appropriate lateral force applied on shear walls can be assigned.
In design, diaphragms can be treated as flexible, rigid or semi-rigid. For a diaphragm that is designated as flexible, the in-plane forces can be assumed to be distributed to the shear walls according to the tributary areas associated with each shear wall. For a diaphragm that is designated as rigid, the loads are assumed to be distributed according to the relative stiffness of the shear walls, with consideration of additional shear force due to torsion for seismic design. In reality, diaphragm is neither purely flexible nor completely rigid, and is more realistically to be treated as semi-rigid. In this case, computer analysis using either plate or diagonal strut elements can be used and the load-deflection properties of the diaphragm will result in force distribution somewhere between the flexible and rigid models. However, alternatively envelope approach which takes the highest forces from rigid and flexible assumptions can be used as a conservative estimation in lieu of computer analysis.
Currently, mass timber building designs commonly incorporate a concrete floor topping. This can improve building accoustics by increasing the mass of the assembly, reduce floor vibration and create a smooth flat surface to install finish flooring on. The installation of concrete requires formwork, pouring and finishing the concrete and time to cure which adds to project schedules. One way to address this is to use mass timber elements that are prefabricated with concrete toppings preinstalled. Replaceing the concrete floor toppings wiht dry alternatives, such as cement board, may also reduce construction timelines, while still ensuring adequate acoustic and vibration performance. Cement board needs only to be screwed in place and can be walked on immediately after installation; this reduction in construction time may reduce overall project costs and help make wood buildings more cost competitive than other types of construction.
Interior partition walls for non-residential and high-rise residential construction are an US$8 billion market opportunity in Canada and the United States (Crespell and Poon, 2014). They represent 1.6 billion ft² (150 million m²) of wall area where wood currently has less than 10% market share. To approach this market a new system would be needed to compete against the incumbent system (wood/steel stud plus gypsum). The system would need to have an installed cost before finishing of approximately US$5 per ft² or lower. The system would also need to meet several code requirements for strength, sound transmission and fire resistance (flame spread and burn through). Crespell and Poon further concluded that to be truly transformative, the system would also need to address major trends impacting the building industry including reducing labor, reducing skilled labor, reducing onsite waste, reducing call-backs, and easily recyclable with low environmental impact. A likely market entry point for wood-based interior partition systems may be in taller and larger wood buildings.
Work described in this report investigated the fabrication, installation, acoustic and combustion properties of prototype interior partition wall designs.
Two types of non-structural prototype interior wall panels designated Type A and Type C were installed between two offices in the FPInnovations Vancouver laboratory. Wood sill plates for mounting the prototype panels were fastened to the concrete floor, sides and top of the opening between the two offices to produce a frame for mounting the test panels. Panels were fastened to the frame using dry wall screws. This same method of installation is envisioned in practice. The installation method makes it easy and fast to both install and remove the wall panels.
Acoustic tests showed the difference in ASTC rating measured between a double wall composed of Type A and Type C prototype panels compared with a double wood stud wall with gypsum board faces was approximately 6 ASTC points. A 6 point difference would be clearly noticeable. Although the results of this study are largely qualitative, they suggest that the prototype interior partition panels would have an acoustic advantage compared to stud wall designs.
In a related study summarized in this report, the combustion properties of three prototype interior panel constructions, including Types A and C evaluated in this report, indicated that any of the three types of partition constructions could be used in combustible construction in accordance with Division B of the National Building Code of Canada.
A second related study, also summarized in this report, estimated an installed cost of US$4.07 per ft² including overhead and profit for unfinished panel partitions comparable to panel construction Type C (gypsum/OSB/wood fibre insulation) as evaluated in this study. Thus, there would appear to be potential installed and finished cost advantages for the wood-based panel partitions compared to steel or wood stud walls with gypsum faces.
Other potential advantages of the prototype interior partition panels compared with the most common, currently-used systems (wood/steel stud plus gypsum) include ease and speed of installation, ease and speed of removal, design flexibility, prefabrication including pre-finishing, and easy installation of services.
Based on the positive results of these exploratory studies, further development of wood-based interior partition systems including design, fabrication, installation and in-service performance would appear justified. Knowledge of the products and testing methods developed in these studies would be expected to speed further development.
In the non-residential sector, prescriptive building codes often demand a higher level of fire safety be built into wood-frame buildings than into buildings of non-combustible construction. The extra cost associated with providing this higher level of safety can make wood-frame buildings less economical to build. Even when building code requirements and economics are not impediments, concerns about fire safety often cause designers or insurers to avoid the use of wood. This makes it challenging for the wood industry to capture a larger share of the non-residential market.
Performance-based fire-safety design offers the promise of eliminating the inequitable treatment of wood present in prescriptive codes. Consequently Forintek has taken steps to develop the requisite engineering tools required to undertake performance-based design. With funding from the Natural Sciences and Engineering Research Council (NSERC) and from Forintek, an NSERC Industrial Research Chair in Fire Safety Engineering was created at Carleton University in 2001 with Prof. George Hadjisophocleous as the Chair holder. Since that time, Forintek has engaged in active collaboration with the Chair in delivering his research program, and in educating students and practitioners capable of undertaking or approving performance-based design.
The Chair, Prof. George Hadjisophocleous, has just completed the last year of his five-year term. The product of his research has been the development of CUrisk, a computer model for evaluating the risk from fires in three- and four-storey wood-frame commercial buildings. It is a comprehensive system model that treats the building as a system complete with fire protection systems, building characteristics, occupant characteristics and inherent functions. CUrisk assesses the impact of fires on both life safety and property protection, and enables comparison of the costs and benefits of various design options.
With support from Forintek scientists, the Chair has also set up a strong educational program in fire safety engineering. A Short Course Series for practising engineers has been introduced with the fourth Short Course to be offered in May 2006. Six post-graduate courses are offered regularly on campus and across the country by internet. An Advisory Council has prepared a proposal for creation of a Graduate Level Program in Fire Safety Engineering by 2007.
The Chair has also leveraged support from Forintek and others to attract additional research funding and resources to Carleton University. Most notably, he has leveraged funding from the Canadian Foundation for Innovation and Ontario Innovation Trust to have a $10 million Fire Research Facility constructed for Carleton University. The experimental data obtained from tests carried out in this Facility will be used to develop new and validate existing computer models to evaluate fire safety levels in buildings.
In order to introduce further refinements in CUrisk and to market its use within the design community, Forintek and NSERC have recently agreed to extend the Chair’s for a second five-year term. By supporting development of the requisite design tools, such as CUrisk, and the training of engineers in their use, the wood industry can expect to capture a larger share of the non-residential market.
The wood products industry wants to expand its market share in non-residential buildings. This is a challenging goal because building codes exhibit a bias against the use of wood products, particularly in the construction of non-residential buildings. The move towards adoption of performance-based building codes offers the promise of eliminating such biases. However, in order to be prepared for the introduction of performance-based codes, architects, engineers and building code officials have pointed out the need for engineering tools to assess the fire performance of buildings.
This five-year project was initiated to develop fire-safety design tools for non-residential wood-frame buildings, and to foster development and delivery of educational programs to train students and practitioners in performance-based fire-safety design. In order to achieve these goals an NSERC Industrial Research Chair in Fire Safety Engineering was established at Carleton University in March of 2001. This report summarises the progress towards these goals made by the Chair in his first year of tenure.