Computer fire modelling is an important high-tech tool in fire safety engineering and fire science. The movement towards objective-based building codes means that these models will find application in performance-based fire-safety design of wood structures. Accordingly for more than a decade, fire researchers at Forintek strove to develop heat-transfer models for wood-frame assemblies exposed to fire. Then, in 2001 Forintek elected to outsource all future development of these models. This project provides funding, direction and oversight for the outside development of these design tools.
Canadian officials identified construction of wood-frame buildings in Japan as an important market priority. To aid them in their endeavours, in 2002-2003 Forintek contracted the development of a heat transfer model for exterior walls constructed with exterior expanded polystyrene-foam (EPS) insulation and ceramic-siding rains screens when subjected to standard fire exposures on the outside face. In 2003-2004 Forintek contracted to have further refinements made to that heat transfer model so that users would have the option of selecting either exterior EPS insulation or exterior semi-rigid glass-fibre insulation panels. That work was completed and comparisons between the model’s predictions and the results of full-scale tests show good agreement.
A paper describing Forintek’s heat transfer model for exterior walls with exterior insulation and non-combustible rain-screens, and comparisons between the model’s predicted outcomes and the results of full-scale fire tests on such assemblies will be presented later this year at the 8th World Conference on Timber Engineering.
In recent years Japanese building regulations were revised to permit construction of wood-frame (combustible) buildings within the high-density urban centres (Fire Protection Zones) of their larger cities if the major loadbearing elements in those buildings met specific requirements for fireproof construction. Those requirements have been dubbed the “one-plus-three” test requirements because for “low-rise” wood-frame apartment buildings and large houses they include exhibiting one-hour of fire-resistance when tested in accordance with ISO 834, and continued fire resistance without structural collapse when the test assembly is maintained under structural load with the fire-test furnace in-place against the side of the assembly for an additional three hours. Again, to assist in promoting markets for Canadian wood products in Japan, in 2003-2004 Forintek commenced modifying its WALL2D heat transfer model so that it would be capable of predicting the thermal response of walls subjected to the fire (thermal) exposures specified in Japan’s one-plus-three test method, parametric, and “real” fire scenarios. In preparation for that work, a Forintek scientist traveled to Japan to gather more information about the “one-plus-three” testing procedures. Later, Forintek contracted the service of Dr H. Takeda to travel to Japan to obtain thermo-physical property data for the gypsum board products commonly used in construction of wood buildings complying with Japanese specifications for fireproof construction. The information obtained from these two trips indicated that the successful completion of revisions to the WALL2D model would be much more difficult and require much more time than had originally been anticipated.
With the support of Forintek, one of the students enrolled at Carleton University, Steven Craft, chose as the topic for his PhD thesis the reliability of wood-frame floors in fire. One of the tasks that he is carrying out for his thesis is the development of a heat transfer model for floor assemblies constructed with solid-wood joists. Dr Hadjisophocleous, the Chair in Fire Safety Engineering at the university, and Craft’s thesis advisor, submitted a proposal to Materials Manufacturing Ontario (MMO) which would leverage Forintek’s financial support to Craft and enable Hadjisophocleous to build an entire research program around Craft’s thesis research. MMO accepted the proposal.
One of the biggest problems encountered in performance-base fire-safety design of large commercial structures is selecting the proper design or “realistic” fire scenario to be used when modeling fire resistance. For large commercial building with atria, establishing the required fire exposures on the boundaries of the atria from a fire within those tall, large open spaces is a particularly difficult issue. Therefore, in 2003, fire researchers in Australia submitted a proposal to the Australian Research Council (ARC) to study this subject. Forintek will provide some support for the work.
All of these activities will continue in 2004-2005.
Mould growth in buildings is becoming an increasing concern for building owners because of health and aesthetic problems. Mould usually appears as black or greenish-brown patches on surfaces in humid environments and is common in houses. In fact, mould growth is caused by moisture problems. To avoid moisture problems, the most important consideration in ensuring the durability of wood-frame houses is to utilise design features, construction tools and practices that keep wood as dry as possible and promote drying if the wood gets wet. One critical factor in these designs is the accurate estimate of the effects of various temperature and moisture conditions on the rates of fungal attack. The absence of definitive data forces engineers to make extremely conservative estimates of mould growth that may not accurately reflect the risk. This report provides valuable data on mould growth on various wood and fibre products used for the construction of homes in North America.
Sapwood and heartwood of jack pine, white spruce and aspen and heartwood of white cedar, commercial aspen OSB bonded with PF resin, softwood plywood, low-density fibreboard, gypsum board, and fibreglass insulation materials were tested by a modified method of ASTM D 3273-94 standard for mould growth test. Test materials were cut into wafers of 5 cm x 12 cm x 1 cm sample size and were placed in specifically designed incubation containers for 8 weeks. Temperatures were targeted at 20°C and 30°C, and relative humidities (RH) were targeted between 65 and 100% by means of saturated salt solutions. Test samples were inspected weekly for mould growth for 8 weeks. A RCS Biotest air sampler monitored mould spore densities inside containers. Moisture contents (MC) of wood wafers were determined by oven-dry method (105°C) at the beginning and at the end of the test. Volatile organic compounds (VOC) were collected from clean and mouldy samples at the beginning and the end of the test and were analyzed according to the ASTM D5116-97 and EPA TO-17 methods. Thermal Desorption/Gas Chromatograph/Mass Spectrometer (TDU/GC/MS) analytical equipment was used to desorb, characterize and quantify the VOC collected on the sorbent tube. The compounds were identified with the NBS/NIH Mass Spectra database and quantified by extrapolating the chromatogram peak area of each compound with the calibration curve of alpha-Pinene, which was the selected chemical for VOC measurement. Another test was conducted on mould growth on various building materials under fluctuating high and low humidity conditions. In this test, the same materials as those listed above were used. The temperature was controlled in a stable 20°C and the relative humidities were kept one week at a high RH between 85 and 100% and another week at a low RH of 65%. The third test was conducted on the effect of drying/planing process on the mould resistance of solid wood. In this test, one group of samples were planed before drying and another group were planed after drying. The samples were placed in sample containers and inspected weekly for mould growth for 8 weeks.
Results showed that the targeted temperatures were measured as 20°C and 28°C and the targeted relative humidities were measured as 63% to 95%. At 20ºC and 95% RH, mould growth was found as the following: on the sapwood of jack pine and aspen and on fibreboard in the second week of incubation, on the sapwood of white spruce and OSB in the third week, on plywood and gypsum board in the fourth week, and on the heartwood of jack pine and aspen in the fifth week. No mould growth was detected on the heartwood of white spruce and cedar and on fibreglass insulation materials at the end of the in eight- week testing period. Slight mould growth was found on sapwood of white spruce, jack pine and aspen and on 4 types of composite boards after 3 to 8 weeks at 20ºC and 85% RH. Moulds were unable to attack wafer samples at 76% and 73% RH. At 28ºC, a similar mould growth pattern was observed as those tested at 20ºC. No mould growth was detected on any materials tested at 63% and 71% RH. Mould growth was detected on the sapwood of white spruce and aspen, and on plywood and fibreboard at 84% RH for this temperature. At 93% RH, moulds appeared on plywood and fibreboard in the second week of the test. Fungi at the end of the test did not affect the heartwood of white cedar and white spruce and the fibreglass insulation material. For all materials tested, low-density fibreboard was the most susceptible to mould growth, followed by OSB, plywood, gypsum board and the sapwood of all solid wood species. Heartwood of jack pine and aspen was less infested by moulds. Heartwood of white cedar and white spruce and fibreglass insulation material were resistant to mould growth. On most materials, rapid mould growth was found in 4 to 6 weeks of incubation in the favourable environmental conditions.
No mould growth was detected on any sample in containers maintained at a constant RH of 80% and at a fluctuating RH of 85/65%. Slight mould growth was found on sapwood of jack pine and aspen and on heartwood of aspen in container with a fluctuating RH of 95/65%. Heavy mould growth was found on samples of sapwood of aspen and jack pine, followed by the heartwood of aspen and fiberboard in a lesser degree in container with a fluctuating RH of 100/65%. Other samples were not affected by moulds in the 8-week test period. The results of this test showed that at 20ºC with fluctuating RH of 100/65% or 95/65%, sapwood of aspen and jack pine was the most susceptible to mould infection, followed by the heartwood of aspen and fiberboard.
The planing and drying process (planing wood surfaces before or after drying) largely affected severity of mould infections on sapwood but slightly on heartwood samples. The sapwood samples planed after drying were much less affected by moulds than those planed before drying.
Spore densities in incubation containers increased correspondingly with incubation time. More spores were collected from containers maintained above 88% RH than other containers. There was no significant difference of spore density among containers maintained at less than 85% RH. Majority of moulds present on sampling media were identified as Penicillium citrinum, P. vermiculatum and Aspergillus niger.
For all wood materials tested, low-density fibreboard was the most prone to absorb water from air, while cedar heartwood was the least. At 20ºC and 95% RH, fibreboard increased its MC from 4% MC at the beginning of the test to 33% MC at the end of the 8-week test, while cedar heartwood increased its MC from 11% at the beginning to 21.6% at the end. The other wood materials gained their MC from 17.7% to 22% in the same environmental condition.
The VOC profile analysis showed that several compounds were not detected from clean reference samples but only detected from the mouldy samples, which are called microbial VOC. Compounds detected from the mouldy OSB samples were different from those detected from the mouldy fibreboard samples. From the mouldy OSB samples, the predominant detected VOC were 2-, or 3-pentanone and 2-petanol. From the mouldy fibreboard, they were identified as borneol, camphor, 3-cyclohexen-1-ol (4-methyl), pyrazine-methyl and 1-octen-3-ol. These compounds have potential to be used as mould growth indicators on wall materials.
"Buildability" is a concept that refers to the ease of constructing a building that meets end-user needs; as such, it is a measure of the desirability and value of a building. Building "serviceability" is a measure of the ability of a building to serve its intended and normal use and occupancy. It is clear that buildability and serviceability of wood-framed buildings, like other building performance attributes, significantly affect the competitiveness of wood-framed construction. A thorough study of the buildability and serviceability of wood-framed buildings needs multidisciplinary efforts. However, as a pioneer study, this project focuses on the major buildability and serviceability issues in wood-framed floor construction. The issues include the lack of a design method to control vibrations in a broad range of wood-based floors in codes, the lack of a rational method to determining bending and shear stiffness of wood parallel-chord metal-plate connected trusses, the need of a design method for bridging and blocking and the need of system approaches for resolving the conflicting construction solutions such as using concrete topping and/or continuous sub-floor and joists.
This project was designed to cover a three-year period to address these issues. Four tasks were identified:
Task-1 proposing a new design method to control vibration in wood-based floors to code committee;
Task-2 recommendations for a method to determine bending and shear stiffness of wood parallel – chord metal-plate connected trusses;
Task-3: development of design method and design values for various bridging and blocking systems;
Task-4: establishment of a knowledge base on the effects of various construction practices on the serviceability, structural reliance, fire resistance, and sound-transmission performance of wood-framed floors.
In the first two years, Tasks 1- 3 were completed. A new design method to control vibrations in wood-based floors was presented to CSA 086 General Design Sub-Committee. A method to determine true bending and shear stiffness of wood parallel – chord metal-plate connected trusses was proposed based on ASTM D198 method to determine shear and true MOE of wood. An approach to account for the stiffness contribution of bridging/blocking was developed. Test results show that the approach is reasonably accurate even if it is on conservative side and the test method to determine bridging/blocking properties is easy and economical to implement. A study of the impact of the new floor design method on current floor spans was conducted by the wood industry. The results of the impact study have revealed that the new design method is on right track, however, some adjustment may be needed. To make the adjustment with a minimum negative impact to the wood industry, an industry survey of the most common product types, spans and floor construction practises in the marketplace was conducted. The survey results have shown that the constructions of the floors using 9-1/2 inches joists at 16 inches spacing, spanned from 12 to 16.6 feet, or 11-7/8 inches joists at 16 inches spacing, spanned from 15 to 20 feet are the most popular floor systems.
To complete this project in the coming year, the effort will be spent on Task-4 and on the finalization of the design method.
Fibre-reinforced wood systems are light, strong, stiff composites that can efficiently replace larger wood members and can be relied on to provide consistent mechanical properties.
This report is an introduction to fibre-reinforced wood systems for members of the Canadian wood products industry. It provides the motivation for reinforcing wood with synthetic fibres, and surveys the choice of materials and their uses. Numerous examples of current applications are discussed to demonstrate the strong and weak points of various approaches and examine the durability and management of fibre-reinforced wood products, as well as to indicate opportunities that exist for the Canadian wood products industry.
This report is intended to be a useful reference for the Canadian wood products industry, and assist future developments in structural and non-structural applications of fibre-reinforced wood products.