Thermal degradation modeling of flexural strength of wood after exposure to elevated temperatures

Abstract

Wood is being used heavily in single-family residential dwellings. Therefore, it is important to categorize their response when exposed to elevated temperatures for a sustained period of time. An important aspect of structural fire design is to assess postfire residual strength of existing structures. This study addresses this issue by developing models to predict strength degradation of wood after exposure to elevated temperature. The objectives were to (a) study the effect of exposure time on bending strength [Modulus of Rupture (MOR)] of wood at elevated temperatures, (b) interpret any relationships between different temperature and time of exposure using kinetics and a statistical approach, and (c) compare the two approaches. Two hundred thirty-two samples in total were tested in flexure as a function of exposure time and several temperatures. MOR of wood decreased as a function of temperature and exposure time. Rate of degradation was higher at higher temperatures. These results were fit to a simple kinetics model, based on the assumption of degradation kinetics following an Arrhenius activation energy model with apparent activation energy of 37.4 kJ/mol. A regression-based statistical model was also developed. The kinetics-based model fit the data better with one less parameter and predictions consistently matched the observed values, making the model preferred over the regression approach.     

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高职电子商务专业“工学并行”人才培养模式的探索

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东风农场橡胶树施肥GIS数据模型的建立和数据处理

基于GIS技术,建立了东风农场橡胶树施肥空间数据模型和属性数据模型,收集并整理了橡胶树施肥GIS数据,为数据库的建立和橡胶树施肥信息管理系统的开发应用奠定基础。     

高校图书馆新管理模式影响因子初探

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夏大豆植株干物质积累数学模拟研究

对夏大豆濉科8号、中黄13两个品种从出苗至成熟共15次测定了植株质量,建立了数学模型。结果表明:植株、茎叶质量呈"慢—快—慢—降"的单峰变化趋势,而籽粒质量呈"慢—快—慢"的S形曲线变化趋势,单株粒重、百粒重则随生育时期呈直线增长趋势。y=ef(t)真实的反映了出苗、始花、终花至成熟期植株、茎叶质量变化。     

Application of the Cropping System Model (CSM)‐CROPGRO‐Soybean for Determining Optimum Management Strategies for Soybean in Tropical Environments

The determination of optimum crop management practices for increasing soybean production can provide valuable information for strategic planning in the tropics. However, this process is time consuming and expensive. The use of a dynamic crop simulation model can be an alternative option to help estimate yield levels under various growing conditions. The objectives of this study were to evaluate the performance of the Cropping System Model (CSM)‐CROPGRO‐Soybean and to determine optimum management practices for soybean for growing conditions in the Phu Pha Man district, Thailand. Data from two soybean experiments that were conducted in 1991 at Chiang Mai University and in 2003 at Khon Kaen University were used to determine the cultivar coefficients for the cultivars CM 60 and SJ 5. The CSM‐CROPGRO‐Soybean model was evaluated with data from two experiments that were conducted at Chiang Mai University. The observed data sets from farmers’ fields located in the Phu Pha Man district were also used for model evaluation. Simulations for different management scenarios were conducted with soil property information for seven different soil series and historical weather data for the period 1972–2003 to predict the optimum crop management practices for soybean production in the Phu Pha Man district. The results of this study indicated that the cultivar coefficients of the two soybean cultivars resulted in simulated growth and development parameters that were in good agreement with almost all observed parameters. Model evaluation showed a good agreement between simulated and observed data for phenology and growth of soybean, and demonstrated the potential of the CSM‐CROPGRO‐Soybean model to simulate growth and yield for local environments, including farmers’ fields, in Thailand. The CSM‐CROPGRO‐Soybean simulations indicated that the optimum planting dates from June 15 to July 15 produced maximum soybean yield in a rainfed environment. However, the planting date December 15 produced the highest yield under quality irrigation. Soybean yield was slightly improved by applying nitrogen at a rate of 30 kg N ha^?1 at planting. Soybean yield also improved when the plant density was increased from 20 to 40 plants m^?2. The results from this study suggest that the CSM‐CROPGRO‐Soybean model can be a valuable tool in assisting with determining optimum management practices for soybean cropping systems in the Phu Pha Man district and might be applicable to other agricultural production areas in Thailand and southeast Asia.