The instability of functionally graded material(FGM)structures is one of the major threats to their service safety in engineering applications.This paper aims to clarify a long-standing controversy on the thermal inst...The instability of functionally graded material(FGM)structures is one of the major threats to their service safety in engineering applications.This paper aims to clarify a long-standing controversy on the thermal instability type of simply-supported FGM beams.First,based on the Euler-Bernoulli beam theory and von K′arm′an geometric nonlinearity,a nonlinear governing equation of simply-supported FGM beams under uniform thermal loads by Zhang’s two-variable method is formulated.Second,an approximate analytic solution to the nonlinear integro-differential boundary value problem under a thermal-induced inhomogeneous force boundary condition is obtained by using a semiinverse method when the coordinate axis is relocated to the bending axis(physical neutral plane),and then the analytical predictions are verified by the differential quadrature method(DQM).Finally,based on the free energy theorem,it is revealed that the symmetry breaking caused by the material inhomogeneity can make the simply-supported FGM beam under uniform thermal loads occur snap-through postbuckling only in odd modes;furthermore,the nonlinear critical load of thermal buckling varies non-monotonically with the functional gradient index due to the stretching-bending coupling effect.These results are expected to provide new ideas and references for the design and regulation of FGM structures.展开更多
The stability and local bifurcation of a simply-supported flexible beam （Bernoulli- Euler type） carrying a moving mass and subjected to harmonic axial excitation are investigated. In the theoretical analysis, the pa...The stability and local bifurcation of a simply-supported flexible beam （Bernoulli- Euler type） carrying a moving mass and subjected to harmonic axial excitation are investigated. In the theoretical analysis, the partial differential equation of motion with the fifth-order nonlinear term is solved using the method of multiple scales （a perturbation technique）. The stability and local bifurcation of the beam are analyzed for 1/2 sub harmonic resonance. The results show that some of the parameters, especially the velocity of moving mass and external excitation, affect the local bifurcation significantly. Therefore, these parameters play important roles in the system stability.展开更多
桥梁工程是公路建设碳排放的主要环节,T梁桥作为公路项目标准化制造的重要结构形式,掌握其碳排放特征和规律,有助于公路低碳建设和管理。研究采用排放因子法对23座典型T梁桥进行碳排放测算,划定了公路T梁桥建设边界范围,确定了碳排放测...桥梁工程是公路建设碳排放的主要环节,T梁桥作为公路项目标准化制造的重要结构形式,掌握其碳排放特征和规律,有助于公路低碳建设和管理。研究采用排放因子法对23座典型T梁桥进行碳排放测算,划定了公路T梁桥建设边界范围,确定了碳排放测算功能单位,测算了各工程部位的碳排放强度,开展了参数敏感性分析和相关性分析,并提出了基于桥梁长度的桥梁主要结构碳排放估算模型。通过测算结果可知,公路T梁桥建设碳排放强度为8927.13 t CO_(2)e/(km·lane),变化区间为4002.64~9871.74 t CO_(2)e/(km·lane),其中间接碳排放占比为98.28%~99.13%,而直接碳排放为6820.99 t CO_(2)e。桥梁建设约86%碳排放主要集中在预应力T梁和桩基础,碳排放强度分别为1.23 t CO_(2)e/m^(3)、0.68 t CO_(2)e/m^(3);约95%来源于水泥、钢材、回旋钻机和交流电弧焊机。敏感性分析表明,当水泥、钢材、电力、化石燃料碳排放因子变化±(10%~30%)时,碳排放变化分别为±(4.77%~14.32%)、±(4.24%~12.74%)、±(0.57%~1.72%)、±(0.14%~0.43%)。相关性分析表明,桥梁主要工程部位的碳排放受桥梁规模影响较大,可基于桥梁长度快速估算T梁桥整体和各工程部位的碳排放。对此,项目管理者可通过低碳采购等方式降低间接碳排放;可通过优化加工工艺和施工方案等方式,在工程活动中节约材料、降低能耗;可通过降低用量和碳排放因子多种组合方式,对主要材料和能源进行综合减碳。相关结果可为公路建设项目的低碳管理及相关研究提供详实的数据支持和节能降碳措施建议。展开更多
文摘The instability of functionally graded material(FGM)structures is one of the major threats to their service safety in engineering applications.This paper aims to clarify a long-standing controversy on the thermal instability type of simply-supported FGM beams.First,based on the Euler-Bernoulli beam theory and von K′arm′an geometric nonlinearity,a nonlinear governing equation of simply-supported FGM beams under uniform thermal loads by Zhang’s two-variable method is formulated.Second,an approximate analytic solution to the nonlinear integro-differential boundary value problem under a thermal-induced inhomogeneous force boundary condition is obtained by using a semiinverse method when the coordinate axis is relocated to the bending axis(physical neutral plane),and then the analytical predictions are verified by the differential quadrature method(DQM).Finally,based on the free energy theorem,it is revealed that the symmetry breaking caused by the material inhomogeneity can make the simply-supported FGM beam under uniform thermal loads occur snap-through postbuckling only in odd modes;furthermore,the nonlinear critical load of thermal buckling varies non-monotonically with the functional gradient index due to the stretching-bending coupling effect.These results are expected to provide new ideas and references for the design and regulation of FGM structures.
文摘The stability and local bifurcation of a simply-supported flexible beam （Bernoulli- Euler type） carrying a moving mass and subjected to harmonic axial excitation are investigated. In the theoretical analysis, the partial differential equation of motion with the fifth-order nonlinear term is solved using the method of multiple scales （a perturbation technique）. The stability and local bifurcation of the beam are analyzed for 1/2 sub harmonic resonance. The results show that some of the parameters, especially the velocity of moving mass and external excitation, affect the local bifurcation significantly. Therefore, these parameters play important roles in the system stability.
文摘桥梁工程是公路建设碳排放的主要环节,T梁桥作为公路项目标准化制造的重要结构形式,掌握其碳排放特征和规律,有助于公路低碳建设和管理。研究采用排放因子法对23座典型T梁桥进行碳排放测算,划定了公路T梁桥建设边界范围,确定了碳排放测算功能单位,测算了各工程部位的碳排放强度,开展了参数敏感性分析和相关性分析,并提出了基于桥梁长度的桥梁主要结构碳排放估算模型。通过测算结果可知,公路T梁桥建设碳排放强度为8927.13 t CO_(2)e/(km·lane),变化区间为4002.64~9871.74 t CO_(2)e/(km·lane),其中间接碳排放占比为98.28%~99.13%,而直接碳排放为6820.99 t CO_(2)e。桥梁建设约86%碳排放主要集中在预应力T梁和桩基础,碳排放强度分别为1.23 t CO_(2)e/m^(3)、0.68 t CO_(2)e/m^(3);约95%来源于水泥、钢材、回旋钻机和交流电弧焊机。敏感性分析表明,当水泥、钢材、电力、化石燃料碳排放因子变化±(10%~30%)时,碳排放变化分别为±(4.77%~14.32%)、±(4.24%~12.74%)、±(0.57%~1.72%)、±(0.14%~0.43%)。相关性分析表明,桥梁主要工程部位的碳排放受桥梁规模影响较大,可基于桥梁长度快速估算T梁桥整体和各工程部位的碳排放。对此,项目管理者可通过低碳采购等方式降低间接碳排放;可通过优化加工工艺和施工方案等方式,在工程活动中节约材料、降低能耗;可通过降低用量和碳排放因子多种组合方式,对主要材料和能源进行综合减碳。相关结果可为公路建设项目的低碳管理及相关研究提供详实的数据支持和节能降碳措施建议。
