It is difficult to solve the structural problems related to agricultural engineering,due to the wide ranges of the means of related variables and complex structural shapes.For these reasons,discrete models are require...It is difficult to solve the structural problems related to agricultural engineering,due to the wide ranges of the means of related variables and complex structural shapes.For these reasons,discrete models are required that are able to replace or simplify solid structure components used in traditional analysis methods.Therefore,the objective of this study was to develop a regular truss structure model that behaves the same way as a solid structure.It was assumed that if a unit element consists of truss elements with each hinge at the end of the element and the size of the element is infinitesimal,the stress distribution and displacement field will be constant throughout the domain of the unit element.Additionally,the behavior of the truss element was assumed to be in a linear state in a two-dimensional plane.The law of energy conservation,based on the theory of elasticity,was applied to determine the equilibrium conditions between discretized and solid elements.The restrictive condition that we obtained revealed that applications are limited to only ideal elastic materials with a Poisson’s ratio of 1 to 3.The volumetric ratio of the equivalent truss to the continuum structures was 3:1,regardless of the size or number of the mesh.To calculate the internal stress and strain of the unit element,the geometric relationships of each truss member,which has its own role against different stress directions,were used.The calculated von Misses stresses were used to verify this model.Stress concentrations,as explained based on Saint Venant’s principle,were also observed in the equivalent truss structure model.The main stress paths,indicating the areas where reinforcement bars should be placed,were successfully shown without the requirement that each element be transformed in the direction of principal stress;this was done by eliminating elements with only compressive and near-zero stresses.展开更多
Aiming at the surrounding rock control problem of mining and preparation entries in Xingdong mine with large mining depth, and the comprehensive control countermeasures including high pre-stress cable truss system, th...Aiming at the surrounding rock control problem of mining and preparation entries in Xingdong mine with large mining depth, and the comprehensive control countermeasures including high pre-stress cable truss system, this study put forward powerful anchor support system and anchor cable adaption technology to surrounding rock deformation. Furthermore, the control measures possess the supporting performance with ‘‘primary rigid-following flexible-new rigid, and primary resistance-following yield-new resistance'', which suits deep roadway surrounding rock control. The mechanical model of truss anchor supporting roof beams was established, and the inverted arch deflection produced by the cable pre-stress with stress increment effect and roof beam deflection were obtained. And then the system working mechanism was illustrated. Finally, the surrounding rock support parameters were determined by means of comprehensive methods, and put into practice. The results show that surrounding rock deformation realized secondary stability after three months. The roadway sides convergence value was less than 245mm, and roof subsidence was less than 124mm. In addition, there was no expansion and renovation during service period.展开更多
基金We acknowledge that this work was supported by the research grant of Chungbuk National University in 2013.
文摘It is difficult to solve the structural problems related to agricultural engineering,due to the wide ranges of the means of related variables and complex structural shapes.For these reasons,discrete models are required that are able to replace or simplify solid structure components used in traditional analysis methods.Therefore,the objective of this study was to develop a regular truss structure model that behaves the same way as a solid structure.It was assumed that if a unit element consists of truss elements with each hinge at the end of the element and the size of the element is infinitesimal,the stress distribution and displacement field will be constant throughout the domain of the unit element.Additionally,the behavior of the truss element was assumed to be in a linear state in a two-dimensional plane.The law of energy conservation,based on the theory of elasticity,was applied to determine the equilibrium conditions between discretized and solid elements.The restrictive condition that we obtained revealed that applications are limited to only ideal elastic materials with a Poisson’s ratio of 1 to 3.The volumetric ratio of the equivalent truss to the continuum structures was 3:1,regardless of the size or number of the mesh.To calculate the internal stress and strain of the unit element,the geometric relationships of each truss member,which has its own role against different stress directions,were used.The calculated von Misses stresses were used to verify this model.Stress concentrations,as explained based on Saint Venant’s principle,were also observed in the equivalent truss structure model.The main stress paths,indicating the areas where reinforcement bars should be placed,were successfully shown without the requirement that each element be transformed in the direction of principal stress;this was done by eliminating elements with only compressive and near-zero stresses.
基金provided by the National Natural Science Foundation of China(No.51234005)National Basic Research Program of China under Grant(No.2010CB226802)Fundamental Research Funds for the Central Universities(No.2010QZ06)
文摘Aiming at the surrounding rock control problem of mining and preparation entries in Xingdong mine with large mining depth, and the comprehensive control countermeasures including high pre-stress cable truss system, this study put forward powerful anchor support system and anchor cable adaption technology to surrounding rock deformation. Furthermore, the control measures possess the supporting performance with ‘‘primary rigid-following flexible-new rigid, and primary resistance-following yield-new resistance'', which suits deep roadway surrounding rock control. The mechanical model of truss anchor supporting roof beams was established, and the inverted arch deflection produced by the cable pre-stress with stress increment effect and roof beam deflection were obtained. And then the system working mechanism was illustrated. Finally, the surrounding rock support parameters were determined by means of comprehensive methods, and put into practice. The results show that surrounding rock deformation realized secondary stability after three months. The roadway sides convergence value was less than 245mm, and roof subsidence was less than 124mm. In addition, there was no expansion and renovation during service period.
