The most important parameter used to determine force reduction factors in force-based design procedures adopted in the current seismic codes is the structural ductility. For a structure supported on a flexible foundat...The most important parameter used to determine force reduction factors in force-based design procedures adopted in the current seismic codes is the structural ductility. For a structure supported on a flexible foundation, the ductility factor could be affected by foundation compliances. The ductility factors given in the current codes are mostly assigned ignoring the effect of SSI and therefore the objective of this research is to assess the significance of SSI phenomenon on ductility factors of stack-like structures. The deformed configuration of stack-fike structures is idealized as an assemblage of beam elements considering nonlinear moment-curvature relations, while a linear sway-rocking model was implemented to model the supporting soil. Using a set of artificial records, repeated linear and nonlinear analyses were performed by gradually increasing the intensity of acceleration to a level where the first yielding of steel in linear and nonlinear analyses is observed and a level corresponding to the stack collapse in the nonlinear analysis. The difference between inelastic and elastic resistance in terms of displacement ductility factors has been quantified. The results indicate that foundation flexibility can decrease the ductility of the system and neglecting this phenomenon may lead to erroneous conclusions in the prediction of the seismic performance of flexibly-supported R/C stack-like structures.展开更多
The objective of this study was to assess the contribution of the spatial organization of cropping systems and the physicochemical properties of surface layers of the agricultural zones soils in tropical hydrosystems ...The objective of this study was to assess the contribution of the spatial organization of cropping systems and the physicochemical properties of surface layers of the agricultural zones soils in tropical hydrosystems to the spatial availability of nitrogen and pesticides during the wet season, such as the Béré watershed (BW) in C<span style="white-space:nowrap;">?</span>te d’Ivoire. For this purpose, after mapping the spatial distribution of the BW cropping systems based on the likelihood classification methodology of satellite images of the study area, 27 samples from the 0 - 20 cm horizon of the soil surface layers of the agricultural areas were taken during the wet and agricultural season of the year 2016. The Kjeldahl method has been used to evaluate the total nitrogen concentration and high-performance liquid chromatography (HPLC) chain made it possible for the analysis of pesticide residues in the soil solutions. Geostatistical analysis and processing of spatial data and physicochemical and agrochemical soil parameters revealed that two major agricultural areas stand out in the BW, namely the Béré upstream watershed (BUW) dominated at 32.65% by annual croppings (maize, cotton, rainfed or lowland rice, market gardening, etc.) and the Béré downstream watershed (BDW) by large areas of perennial croppings (cashew nuts, cocoa, etc.), <em>i.e.</em> 21.47%. Agricultural soils in BW are usually of the moderately desaturated ferralitic type with a low acid pH and a quite strong temperature, such as those of tropical soils’ characteristics. However, agricultural soils in the BUW are characterized by higher proportions of sand and coarse sand. The parameters such as total porosity, cation exchange capacity, clay, organic matter, silt, fine silt, coarse silt, and potassium ions, are higher in the soils of the agricultural area of the BDW. Moreover, soils in the agricultural areas of the BUW are less rich in total nitrogen (0.84 g<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>) in contrast to those of the BDW (1.2 g<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>). On the other hand, the median concentrations of total pesticides remain very high in the BUW (193.80 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>) in front of those of the BDW (94.81 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>). In addition, the biological family of herbicides was the most notable in BW. The chemical families of triazines (100% detection;79.37 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>) are the most important in the agricultural area of the BUW with the very significant presence of active molecules of pesticides such as simazine (92.86% detection;13.17 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>). However, in the BDW, urea substitute (100% detection;44.02 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>) dominate, including the active substance chlortoluron (84.62% detection;10.12 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>). The presence and abundance of nitrogen and pesticides in the soils of the agricultural areas of BW are strongly linked to the intensive use of these agrochemicals in cropping systems in recent decades in West African countries, even though most of the active molecules found are forbidden in several countries, especially in European countries. These are applied to tropical agricultural soils with physicochemical characteristics favorable to their retention in wet weather, as confirmed by the case of BW’s agricultural soils. Therefore, the BW’s water resources present worrying risks of contamination during rainy events that deserve to be assessed and monitored. Hence the need to take mitigating measures to this effect in order to preserve the quality of the environment.展开更多
Although pre-Northridge earthquake steel moment resisting frame buildings have been shown to be susceptible to brittle connection failures,they still represent a large fraction of the existing steel buildings in the U...Although pre-Northridge earthquake steel moment resisting frame buildings have been shown to be susceptible to brittle connection failures,they still represent a large fraction of the existing steel buildings in the United States of America.In this study,the performance of the 3-and 9-story Los Angeles pre-Northridge SAC buildings are analyzed considering ductile and brittle beam-column connection failures,and their uncertainty.This paper contributes to understanding the influence of uncertainty associated with connections brittle fracture on building interstory deformation capacity and its impact on bias and variability of fragility functions and loss assessment.The results show that considering brittle connections leads to significantly l arger d rift demands a nd t o h igher r epair costs,particularly under intense ground shaking.New fragility curve parameters are derived that account for the effect of the uncertainty of the strength and deformation capacity of brittle connections.展开更多
为在神光系列激光装置上开展惯性约束聚变（IC F ）带电粒子诊断，通过0.7～10 M eV加速器质子源和241 Am放射性同位素α粒子源完成了CR39探测器的质子和α粒子能量响应实验研究，结合TRIM程序和半经验模型建立了C R39刻蚀动力学模拟程...为在神光系列激光装置上开展惯性约束聚变（IC F ）带电粒子诊断，通过0.7～10 M eV加速器质子源和241 Am放射性同位素α粒子源完成了CR39探测器的质子和α粒子能量响应实验研究，结合TRIM程序和半经验模型建立了C R39刻蚀动力学模拟程序，模拟分析了p、D、T和α粒子在正入射和斜入射条件下C R39的径迹形状与能量响应特征，对多种IC F带电粒子谱仪的C R39探测器单元的设计提出了优化方案。展开更多
文摘The most important parameter used to determine force reduction factors in force-based design procedures adopted in the current seismic codes is the structural ductility. For a structure supported on a flexible foundation, the ductility factor could be affected by foundation compliances. The ductility factors given in the current codes are mostly assigned ignoring the effect of SSI and therefore the objective of this research is to assess the significance of SSI phenomenon on ductility factors of stack-like structures. The deformed configuration of stack-fike structures is idealized as an assemblage of beam elements considering nonlinear moment-curvature relations, while a linear sway-rocking model was implemented to model the supporting soil. Using a set of artificial records, repeated linear and nonlinear analyses were performed by gradually increasing the intensity of acceleration to a level where the first yielding of steel in linear and nonlinear analyses is observed and a level corresponding to the stack collapse in the nonlinear analysis. The difference between inelastic and elastic resistance in terms of displacement ductility factors has been quantified. The results indicate that foundation flexibility can decrease the ductility of the system and neglecting this phenomenon may lead to erroneous conclusions in the prediction of the seismic performance of flexibly-supported R/C stack-like structures.
文摘The objective of this study was to assess the contribution of the spatial organization of cropping systems and the physicochemical properties of surface layers of the agricultural zones soils in tropical hydrosystems to the spatial availability of nitrogen and pesticides during the wet season, such as the Béré watershed (BW) in C<span style="white-space:nowrap;">?</span>te d’Ivoire. For this purpose, after mapping the spatial distribution of the BW cropping systems based on the likelihood classification methodology of satellite images of the study area, 27 samples from the 0 - 20 cm horizon of the soil surface layers of the agricultural areas were taken during the wet and agricultural season of the year 2016. The Kjeldahl method has been used to evaluate the total nitrogen concentration and high-performance liquid chromatography (HPLC) chain made it possible for the analysis of pesticide residues in the soil solutions. Geostatistical analysis and processing of spatial data and physicochemical and agrochemical soil parameters revealed that two major agricultural areas stand out in the BW, namely the Béré upstream watershed (BUW) dominated at 32.65% by annual croppings (maize, cotton, rainfed or lowland rice, market gardening, etc.) and the Béré downstream watershed (BDW) by large areas of perennial croppings (cashew nuts, cocoa, etc.), <em>i.e.</em> 21.47%. Agricultural soils in BW are usually of the moderately desaturated ferralitic type with a low acid pH and a quite strong temperature, such as those of tropical soils’ characteristics. However, agricultural soils in the BUW are characterized by higher proportions of sand and coarse sand. The parameters such as total porosity, cation exchange capacity, clay, organic matter, silt, fine silt, coarse silt, and potassium ions, are higher in the soils of the agricultural area of the BDW. Moreover, soils in the agricultural areas of the BUW are less rich in total nitrogen (0.84 g<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>) in contrast to those of the BDW (1.2 g<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>). On the other hand, the median concentrations of total pesticides remain very high in the BUW (193.80 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>) in front of those of the BDW (94.81 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>). In addition, the biological family of herbicides was the most notable in BW. The chemical families of triazines (100% detection;79.37 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>) are the most important in the agricultural area of the BUW with the very significant presence of active molecules of pesticides such as simazine (92.86% detection;13.17 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>). However, in the BDW, urea substitute (100% detection;44.02 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>) dominate, including the active substance chlortoluron (84.62% detection;10.12 μg<span style="white-space:nowrap;">·</span>kg<sup>-1</sup>). The presence and abundance of nitrogen and pesticides in the soils of the agricultural areas of BW are strongly linked to the intensive use of these agrochemicals in cropping systems in recent decades in West African countries, even though most of the active molecules found are forbidden in several countries, especially in European countries. These are applied to tropical agricultural soils with physicochemical characteristics favorable to their retention in wet weather, as confirmed by the case of BW’s agricultural soils. Therefore, the BW’s water resources present worrying risks of contamination during rainy events that deserve to be assessed and monitored. Hence the need to take mitigating measures to this effect in order to preserve the quality of the environment.
文摘Although pre-Northridge earthquake steel moment resisting frame buildings have been shown to be susceptible to brittle connection failures,they still represent a large fraction of the existing steel buildings in the United States of America.In this study,the performance of the 3-and 9-story Los Angeles pre-Northridge SAC buildings are analyzed considering ductile and brittle beam-column connection failures,and their uncertainty.This paper contributes to understanding the influence of uncertainty associated with connections brittle fracture on building interstory deformation capacity and its impact on bias and variability of fragility functions and loss assessment.The results show that considering brittle connections leads to significantly l arger d rift demands a nd t o h igher r epair costs,particularly under intense ground shaking.New fragility curve parameters are derived that account for the effect of the uncertainty of the strength and deformation capacity of brittle connections.
文摘为在神光系列激光装置上开展惯性约束聚变（IC F ）带电粒子诊断，通过0.7～10 M eV加速器质子源和241 Am放射性同位素α粒子源完成了CR39探测器的质子和α粒子能量响应实验研究，结合TRIM程序和半经验模型建立了C R39刻蚀动力学模拟程序，模拟分析了p、D、T和α粒子在正入射和斜入射条件下C R39的径迹形状与能量响应特征，对多种IC F带电粒子谱仪的C R39探测器单元的设计提出了优化方案。
