Traditional wooden joinery is the craft of connecting wood pieces for buildings or producing utensils by utilizing only the geometry of the components and material properties of the wood,without other materials such a...Traditional wooden joinery is the craft of connecting wood pieces for buildings or producing utensils by utilizing only the geometry of the components and material properties of the wood,without other materials such as glue or metal connectors.In its thousands of years of tradition,this construction technique has achieved high accomplishment in both East Asian and European architectural civilizations.Although sharing the same basic principles,joinery techniques vary between regions and cultures,rooted in the geographical environment,available wood species and their material properties,characteristics of craftsmanship,tools,and structural systems.Wood framing systems from China,Japan,and Western Europe are selected for comparison to assess the relationship between wood joinery and other aspects of building technology.The main conclusions include:in East Asia,the building tradition pays great attention to the design and execution of joinery(sunmao榫卯),making it responsible for multiple functions including architectural mechanics and the stability of the entire frame,which leads to a broader role meant by the term“joint”itself,while in Europe joinery is treated as the“node”or literally“joint”of the structure.Although in both East Asia and Europe wooden joinery serves as an aesthetic factor of the structure,its expression in East Asia is subtle,veiled,and restrained,while in Europe it is explicit and direct.The most important lesson we learn from the study of traditional joinery technology is that it should be seen in the context of the building process as a whole,taking into account geographical environment,material resources,craftsmanship,tools,construction methods,structural form,and the structural system.展开更多
For a building structure subjected to impulsive loading, particularly shock and impact loading , the response of the critical columns is crucial to the behaviour of the entire system during and after the blast loading...For a building structure subjected to impulsive loading, particularly shock and impact loading , the response of the critical columns is crucial to the behaviour of the entire system during and after the blast loading phase. Therefore, an appropriate evaluation of the column response and damage under short-duration impulsive loading is important in a comprehensive assessment of the performance of a building system. This paper reports a dynamic analysis approach for the response of RC columns subjected to impulsive loading. Considering that the dynamic response of a column in a frame structure can also be affected by the floor movement which relates to the global vibration of the frame system, a generic column-mass model is used, in which a concentrated mass is attached to the column top to simulate the effect of a global vibration. To take into account the high shear effect under impulsive load, the model is formulated using Timoshenko beam theory, and three main nonlinear mechanisms are considered. Two typical scenarios, one under a direct air blast loading, and another under a blast-induced ground excitation, are analyzed and the primary response features are highlighted.展开更多
Natural fibers have recently raised attention for presenting adequate mechanical characteristics for reinforcement of structural elements. The use of both natural fibers, in especial Sisal fibers, in wood laminated be...Natural fibers have recently raised attention for presenting adequate mechanical characteristics for reinforcement of structural elements. The use of both natural fibers, in especial Sisal fibers, in wood laminated beams and also wood from reforestation, is in accordance with the current economic interest and ecological appeal. Specifically, the strengthening of wood laminated beams with Sisal fibers is more effective for structures that require an increase in their structural capacity without a significant increase in height of the cross section. Furthermore, it is recommended that this type of reinforcement is used in wood structural elements where the elastic modulus is at least equal to the Sisal fibers. The composition of Sisal fibers is basically of cellulose, lignin and hemicelluloses. In particular, the amount of cellulose and the angle that the micro-fibers with the axis of the fiber characterize the failure strength and the modulus of elasticity. The average mechanical characteristics of the Sisal fiber are： tensile strength 347 to 378 （MPa） and elastic modulus 15.2 （GPa） whereas these properties are lower for strips of Sisal fibers. In this context, this paper deals with the analysis and the viability of the use of Sisal fibers in wood structures as a reinforced material.展开更多
Timber bridges can provide an economical alternative to concrete and steel structures, particularly in rural areas where vehicle traffic is light to moderate. The wooden components of bridges have historically been pr...Timber bridges can provide an economical alternative to concrete and steel structures, particularly in rural areas where vehicle traffic is light to moderate. The wooden components of bridges have historically been preserved with either an oil type or waterborne preservative system to protect the wood from decay in order to maintain required performance standards for an extended period of time. The focus of this paper is to describe some of the key preservatives, research and case studies that support use of preserved wood, and some important steps to follow for the appropriate and safe use of preserved wood when the planned application will be in or over aquatic and wetland environments. A wealth of scientific information has been collected and analyzed that clearly suggests the use of preserved wood does not present a significant adverse effect on aquatic and wetland environments. This conclusion is based on two decades of empirical research and case study evaluating the environmental fate and effects of preserved wood, level of migration of contaminates into aquatic and marine environments, and the preserved wood environment. This is particularly true when risks are properly assessed on a project site, the appropriate preservative is selected and the wood is preserved to the Western Wood Preservers Institute＇s BMPs （best management practices）, along with properly installing and maintaining the preserved material. To assist with the assessment process, peer-reviewed risk assessment models for 11 commonly used preservatives have been developed that provide for streamlined data entry by users and allow for evaluation of a structure above and below water. A companion preliminary screening level assessment tool is also available. When these measures are properly utilized engineers, biologists and other responsible officials can be confident that the service life of the preserved wood components will more than likely meet the required performance standards in an environmentally safe manner for up to 50 or more years on a majority of timber bridge projects.展开更多
Zircon U-Pb dating, whole-rock geochemical analyses and Hf isotope are undertaken for the monzogranite in Niubiziliang area with the aim of constraining its formation time,petrogenesis and the regional tectonic settin...Zircon U-Pb dating, whole-rock geochemical analyses and Hf isotope are undertaken for the monzogranite in Niubiziliang area with the aim of constraining its formation time,petrogenesis and the regional tectonic setting. The zircons from monzogranite are euhedral-subhedral in shape,and display rhythm growth zoning,indicating a magmatic origin. LA-ICP-MS zircon U-Pb dating indicates the monzogranite formed most probably in the Late Devonian( 359. 0 ± 2. 6 Ma). The monzogranite has Si O2= 74. 69%--76. 11%,Al2O3=12. 07%--12. 81%,Na2 O + K2 O = 8. 24%--8. 70%,Na2 O / K2 O = 0. 60--0. 68,A / CNK > 1,which shows that it belongs to high-Si and high-K weakly peraluminous calc-alkaline series. The monzogranite is enriched in K,Rb,Th( LILEs) and La,Ce,Sm,Nd( LREEs); and depleted in Ba,U( HREEs) and Ta,Nb( HFSEs).Their zircon εHf( t) values range from 1. 21 to 3. 46,in response to their two-stage Hf model ages( TDM2) ranging from 1 034 Ma to 1 159 Ma,respectively,indicating that the primary magma was derived from the young crust in Meso-Neoproterozoic. Combined with the regional geological evolution background,it is considered that the Niubiziliang monzogranite formed the closure of North Qaidam ocean,which was the stretching stage product after the collision between Qaidam block and Qilian block.展开更多
To investigate the charring rate of timber beams exposed to three-side fire, a total of fifteen new and used Douglas-Fir timber beams in four groups exposed to three-side fire were experimentally studied, together wit...To investigate the charring rate of timber beams exposed to three-side fire, a total of fifteen new and used Douglas-Fir timber beams in four groups exposed to three-side fire were experimentally studied, together with the finite element analyses of the temperature distribution in the beam section. The durations of fire exposure were 0 (on a test piece), 10, 15, 20 and 30 min, according to the ISO 834 standard fire curve. The charring depth of each timber beam was calculated by averaging the values at one-third and two-thirds along each cross section to give the charring rate of timber beams. It was found that the timber beam's charring rate reduces as the duration of fire exposure increases and the vertical charring rate is slightly higher than the horizontal one. The areas of beam sections reduce due to charring and the strength and stiffness of the pyrolysis layer near the charring edge decrease owing to the high-temperature. The average horizontal and vertical charring rates are 0.98 and 1.08 mm/min, respectively. To take into account the difference between the test furnace temperature curve and the ISO 834 stand- ard fire curve, some corrections were made for these data to yield the solution for charring rate. With the help of the finite element software ANSYS, the temperature distribution of the wood's cross-section was analyzed. The longer the exposure time is, the greater the effect of density will impose on the distribution of temperature, but the moisture content has no effect.展开更多
In this paper, nonlinear transverse vibrations of axially moving Timoshenko beams with two free ends are investigated. The governing equations and the associated boundary conditions are derived by the extended Hamilto...In this paper, nonlinear transverse vibrations of axially moving Timoshenko beams with two free ends are investigated. The governing equations and the associated boundary conditions are derived by the extended Hamilton principle. The method of multiple scales is applied to analyze the nonlinear partial differential equation. The natural frequencies and modes are investigated by performing the complex mode approach. The effect of natural frequencies with the stiffness and the axial speeds are numerically demonstrated. The solvability conditions are established for the cases of without and with 3:1 internal resonances. The relationships between the nonlinear frequencies and the initial amplitudes at different axial speeds and the nonlinear coefficients are showed for the case of without internal resonances. The effects of the related coefficients are demonstrated for the case of 3:1 internal resonances.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.52008194)。
文摘Traditional wooden joinery is the craft of connecting wood pieces for buildings or producing utensils by utilizing only the geometry of the components and material properties of the wood,without other materials such as glue or metal connectors.In its thousands of years of tradition,this construction technique has achieved high accomplishment in both East Asian and European architectural civilizations.Although sharing the same basic principles,joinery techniques vary between regions and cultures,rooted in the geographical environment,available wood species and their material properties,characteristics of craftsmanship,tools,and structural systems.Wood framing systems from China,Japan,and Western Europe are selected for comparison to assess the relationship between wood joinery and other aspects of building technology.The main conclusions include:in East Asia,the building tradition pays great attention to the design and execution of joinery(sunmao榫卯),making it responsible for multiple functions including architectural mechanics and the stability of the entire frame,which leads to a broader role meant by the term“joint”itself,while in Europe joinery is treated as the“node”or literally“joint”of the structure.Although in both East Asia and Europe wooden joinery serves as an aesthetic factor of the structure,its expression in East Asia is subtle,veiled,and restrained,while in Europe it is explicit and direct.The most important lesson we learn from the study of traditional joinery technology is that it should be seen in the context of the building process as a whole,taking into account geographical environment,material resources,craftsmanship,tools,construction methods,structural form,and the structural system.
文摘For a building structure subjected to impulsive loading, particularly shock and impact loading , the response of the critical columns is crucial to the behaviour of the entire system during and after the blast loading phase. Therefore, an appropriate evaluation of the column response and damage under short-duration impulsive loading is important in a comprehensive assessment of the performance of a building system. This paper reports a dynamic analysis approach for the response of RC columns subjected to impulsive loading. Considering that the dynamic response of a column in a frame structure can also be affected by the floor movement which relates to the global vibration of the frame system, a generic column-mass model is used, in which a concentrated mass is attached to the column top to simulate the effect of a global vibration. To take into account the high shear effect under impulsive load, the model is formulated using Timoshenko beam theory, and three main nonlinear mechanisms are considered. Two typical scenarios, one under a direct air blast loading, and another under a blast-induced ground excitation, are analyzed and the primary response features are highlighted.
文摘Natural fibers have recently raised attention for presenting adequate mechanical characteristics for reinforcement of structural elements. The use of both natural fibers, in especial Sisal fibers, in wood laminated beams and also wood from reforestation, is in accordance with the current economic interest and ecological appeal. Specifically, the strengthening of wood laminated beams with Sisal fibers is more effective for structures that require an increase in their structural capacity without a significant increase in height of the cross section. Furthermore, it is recommended that this type of reinforcement is used in wood structural elements where the elastic modulus is at least equal to the Sisal fibers. The composition of Sisal fibers is basically of cellulose, lignin and hemicelluloses. In particular, the amount of cellulose and the angle that the micro-fibers with the axis of the fiber characterize the failure strength and the modulus of elasticity. The average mechanical characteristics of the Sisal fiber are： tensile strength 347 to 378 （MPa） and elastic modulus 15.2 （GPa） whereas these properties are lower for strips of Sisal fibers. In this context, this paper deals with the analysis and the viability of the use of Sisal fibers in wood structures as a reinforced material.
文摘Timber bridges can provide an economical alternative to concrete and steel structures, particularly in rural areas where vehicle traffic is light to moderate. The wooden components of bridges have historically been preserved with either an oil type or waterborne preservative system to protect the wood from decay in order to maintain required performance standards for an extended period of time. The focus of this paper is to describe some of the key preservatives, research and case studies that support use of preserved wood, and some important steps to follow for the appropriate and safe use of preserved wood when the planned application will be in or over aquatic and wetland environments. A wealth of scientific information has been collected and analyzed that clearly suggests the use of preserved wood does not present a significant adverse effect on aquatic and wetland environments. This conclusion is based on two decades of empirical research and case study evaluating the environmental fate and effects of preserved wood, level of migration of contaminates into aquatic and marine environments, and the preserved wood environment. This is particularly true when risks are properly assessed on a project site, the appropriate preservative is selected and the wood is preserved to the Western Wood Preservers Institute＇s BMPs （best management practices）, along with properly installing and maintaining the preserved material. To assist with the assessment process, peer-reviewed risk assessment models for 11 commonly used preservatives have been developed that provide for streamlined data entry by users and allow for evaluation of a structure above and below water. A companion preliminary screening level assessment tool is also available. When these measures are properly utilized engineers, biologists and other responsible officials can be confident that the service life of the preserved wood components will more than likely meet the required performance standards in an environmentally safe manner for up to 50 or more years on a majority of timber bridge projects.
文摘Zircon U-Pb dating, whole-rock geochemical analyses and Hf isotope are undertaken for the monzogranite in Niubiziliang area with the aim of constraining its formation time,petrogenesis and the regional tectonic setting. The zircons from monzogranite are euhedral-subhedral in shape,and display rhythm growth zoning,indicating a magmatic origin. LA-ICP-MS zircon U-Pb dating indicates the monzogranite formed most probably in the Late Devonian( 359. 0 ± 2. 6 Ma). The monzogranite has Si O2= 74. 69%--76. 11%,Al2O3=12. 07%--12. 81%,Na2 O + K2 O = 8. 24%--8. 70%,Na2 O / K2 O = 0. 60--0. 68,A / CNK > 1,which shows that it belongs to high-Si and high-K weakly peraluminous calc-alkaline series. The monzogranite is enriched in K,Rb,Th( LILEs) and La,Ce,Sm,Nd( LREEs); and depleted in Ba,U( HREEs) and Ta,Nb( HFSEs).Their zircon εHf( t) values range from 1. 21 to 3. 46,in response to their two-stage Hf model ages( TDM2) ranging from 1 034 Ma to 1 159 Ma,respectively,indicating that the primary magma was derived from the young crust in Meso-Neoproterozoic. Combined with the regional geological evolution background,it is considered that the Niubiziliang monzogranite formed the closure of North Qaidam ocean,which was the stretching stage product after the collision between Qaidam block and Qilian block.
基金supported by the National Natural Science Foundation of China (Grant No. 51178115)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘To investigate the charring rate of timber beams exposed to three-side fire, a total of fifteen new and used Douglas-Fir timber beams in four groups exposed to three-side fire were experimentally studied, together with the finite element analyses of the temperature distribution in the beam section. The durations of fire exposure were 0 (on a test piece), 10, 15, 20 and 30 min, according to the ISO 834 standard fire curve. The charring depth of each timber beam was calculated by averaging the values at one-third and two-thirds along each cross section to give the charring rate of timber beams. It was found that the timber beam's charring rate reduces as the duration of fire exposure increases and the vertical charring rate is slightly higher than the horizontal one. The areas of beam sections reduce due to charring and the strength and stiffness of the pyrolysis layer near the charring edge decrease owing to the high-temperature. The average horizontal and vertical charring rates are 0.98 and 1.08 mm/min, respectively. To take into account the difference between the test furnace temperature curve and the ISO 834 stand- ard fire curve, some corrections were made for these data to yield the solution for charring rate. With the help of the finite element software ANSYS, the temperature distribution of the wood's cross-section was analyzed. The longer the exposure time is, the greater the effect of density will impose on the distribution of temperature, but the moisture content has no effect.
基金supported by the National Outstanding Young Scientists Foundation of China (Grant No. 10725209)the National Natural Science Foundation of China (Grant No. 90816001)+3 种基金Shanghai Subject Chief Scientist Project (Grant No. 09XD1401700)Innovation Foundation for Graduates of Shanghai University (Grant No. A.16-0401-08-005)Shanghai Leading Academic Discipline Project (Grant No. S30106)the Program for Changjiang Scholars and Innovative Research Team in University (Grant No. IRT0844)
文摘In this paper, nonlinear transverse vibrations of axially moving Timoshenko beams with two free ends are investigated. The governing equations and the associated boundary conditions are derived by the extended Hamilton principle. The method of multiple scales is applied to analyze the nonlinear partial differential equation. The natural frequencies and modes are investigated by performing the complex mode approach. The effect of natural frequencies with the stiffness and the axial speeds are numerically demonstrated. The solvability conditions are established for the cases of without and with 3:1 internal resonances. The relationships between the nonlinear frequencies and the initial amplitudes at different axial speeds and the nonlinear coefficients are showed for the case of without internal resonances. The effects of the related coefficients are demonstrated for the case of 3:1 internal resonances.
