Personne : Ménard, Sylvain
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Université Laval. Département de génie mécanique
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- PublicationAccès libreA parametric study of fire risks of green roofs to adjacent buildings(MDPI AG, 2022-07-07) Ménard, Sylvain; Dagenais, Christian; Gerzhova, Nataliia; Côté, Jean; Blanchet, PierreThe susceptibility of plants to burn raises concerns about fire hazard that green roofs may pose to buildings. Main concerns relate to cases when such roofs are poorly maintained or stressed by drought conditions which leads to drying out of plants and the accumulation of dead organic material, greatly increasing the availability of fuel load. Existing standard safety measures aim to prevent the spread of fire through the vegetation cover. However, fire spread by thermal radiation is not considered. In this study, fire risk of exposure of adjacent buildings to radiant heat flux produced by fire on green roofs was assessed. Based on generally accepted maximum tolerable radiant heat flux to exposed facades of 12.5 kW/m2, the minimum safe separation distances were obtained for different conditions. Wildland fire behavior model was used to determine flame lengths which is the necessary parameter for a radiation model. Several vegetation types, moisture content scenarios and wind speeds were taken as variables. It was found that by providing the vegetation with reasonably high moisture content the fire risk can be greatly reduced, especially for grass-covered roofs. Since wind also has a strong effect on flame size, considering the exposure of a green roof to wind can bring better understanding of fire risk to adjacent buildings. At no-wind condition and at extremely low moisture content separation distances are as short as 3.1 m for dense shrubs and 2.4 m for tall dense grass.
- PublicationAccès libreFinite element study of hyperstructure systems with modular light‐frame construction in high‐rise buildings(MDPI AG, 2022-03-09) Ménard, Sylvain; Oudjene, Marc; Blanchet, Pierre; Labrecque, NicolasTo answer both the growth of the world's urban population and the climate changes, new structural systems with high prefabrication levels and renewable materials need to be developed. A novel structural system that could enable the use of modular light‐frame construction in high‐rise buildings was modeled and analyzed. This system was achieved by having a hyperstructure carrying the loads of four‐story light‐frame superposed substructures. Two 20‐story hyperstructures, one using glulam and another one using reinforced concrete, were designed according to the 2015 National Building Code of Canada and compared. A simplified model for the light‐frame modules according to the CSA O86‐19 was proposed. The interaction between both systems and the impact on the substructures were analyzed. The results of the response spectrum analysis and dynamic wind analysis show that, with a glulam hyperstructure, modules could be connected to the columns and the floors or only to the floors. With a concrete hyperstructure, the modules must be connected to the columns and the cores. For both systems, the design of shearwalls on the short side of the modules is governed by the lateral deformation imposed by seismic forces, while the design of shearwalls on the long side of the modules is governed by the vertical deformation of the primary beams under gravity loads. Standard shearwall assemblies are sufficient to resist the shear induced by gravitational, wind and seismic loads. The analysis indicates that the system could be viable, but more research should be especially performed on the connections between the substructures and the hyperstructure.
- PublicationAccès libreA conceptual framework for modelling the thermal conductivity of dry green roof subsrtates(Dept. of Wood and Paper Science, College of Natural Resources, North Carolina State University, 2019-09-12) Gerzhova, Nataliia; Ménard, Sylvain; Dagenais, Christian; Côté, Jean; Blanchet, PierreThe fire performance of green roofs has never been assessed numerically. In order to simulate its fire behavior, the thermal conductivity of a growing media must be determined as an important input parameter. This study characterized the thermal conductivity of a dry substrate and its prediction as a function of temperature, considering temperature effects on soil organic and inorganic constituents. Experimental measurements were made to provide basic information on thermophysical parameters of the substrate and its components. Thermogravimetric analysis was conducted to consider the decomposition of organic matter. An existing model of the thermal conductivity calculation was then applied. The results of calculated and measured solid thermal conductivity showed close values of 0.9 and 1.07 W/mK, which demonstrates that the model provided a good estimation and may be applied for green roof substrates calculations. The literature data of a temperature effect on soil solids was used to predict thermal conductivity over a range of temperatures. The results showed that thermal conductivity increased and depended on porosity and thermal properties of the soil mineral components. Preliminary validation of obtained temperature-dependent thermal conductivity was performed by experiments and numerical simulation.
- PublicationAccès libreHeat transfer behavior of green roof systems under fire condition : a numerical study(Stamats Communications, 2019-09-19) Gerzhova, Nataliia; Ménard, Sylvain; Dagenais, Christian; Côté, Jean; Blanchet, PierreCurrently, green roof fire risks are not clearly defined. This is because the problem is still not well understood, which raises concerns. The possibility of plants catching fire, especially during drought periods, is one of the reasons for necessary protection measures. The potential fire hazard for roof decks covered with vegetation has not yet been fully explored. The present study analyzes the performance of green roofs in extreme heat conditions by simulating a heat transfer process through the assembly. The main objective of this study was to determine the conditions and time required for the roof deck to reach a critical temperature. The effects of growing medium layer thickness (between 3 and 10 cm), porosity (0.5 to 0.7), and heating intensity (50, 100, 150, and 200 kW/m2) were examined. It was found that a green roof can protect a wooden roof deck from igniting with only 3 cm of soil coverage when exposed to severe heat fluxes for at least 25 minutes. The dependency of failure time on substrate thickness decreases with increasing heating load. It was also found that substrate porosity has a low impact on time to failure, and only at high heating loads.
- PublicationAccès libreFlammability characteristics of green roofs(Stamats Communications, 2020-07-09) Gerzhova, Nataliia; Ménard, Sylvain; Dagenais, Christian; Côté, Jean; Blanchet, PierreAssessing the fire risk of vegetated roofs includes the determination of their possible contribution to fire. Green roof components such as plants and growing media are organic materials and present a fuel that can catch and support the spread of fire. The flammability characteristics of these components were analyzed and compared to a typical roof covering. Growing media with 15% of organic matter were tested using cone calorimeter apparatus. The fuel load and heat release rate of the growing media were measured in both moist (30%) and dry conditions. It was observed that growing media in a moist condition do not present a fire risk, reaching a maximum heat release rate of 33 kW/m2. For dry substrates, a peak heat release rate of 95 kW/m2 was recorded in the first minute, which then rapidly decreased to 29 kW/m2 in the second minute. Compared to a typical bitumen roof membrane, the green roof showed a better fire performance. The literature data report more severe results for plant behavior, reaching peak heat release rates (HRRs) of 397 kW/m2 for dried and 176 kW/m2 for a green material. However, a rapid decrease in HRR to much lower values occurs in less than 2 min. The results also show that extensive and intensive types of green roofs present 22% and 95% of the additional fire load density when installed on a modified bitumen membrane, 19.7 and 85.8 MJ/m2, respectively.