Traditional methods focus on the ultimate bending moment of glulam beams and the fracture failure of materials with defects,which usually depends on empirical parameters.There is no systematic theoretical method to pr...Traditional methods focus on the ultimate bending moment of glulam beams and the fracture failure of materials with defects,which usually depends on empirical parameters.There is no systematic theoretical method to predict the stiffness and shear distribution of glulam beams in elastic-plastic stage,and consequently,the failure of such glulam beams cannot be predicted effectively.To address these issues,an analytical method considering material nonlinearity was proposed for glulam beams,and the calculating equations of deflection and shear stress distribution for different failure modes were established.The proposed method was verified by experiments and numerical models under the corresponding conditions.Results showed that the theoretical calculations were in good agreement with experimental and numerical results,indicating that the equations proposed in this paper were reliable and accurate for such glulam beams with wood material in the elastic-plastic stage ignoring the influence of mechanic properties in radial and tangential directions of wood.Furthermore,the experimental results reported by the previous studies indicated that the method was applicable and could be used as a theoretical reference for predicting the failure of glulam beams.展开更多
A kind of hybrid reliability model is presented to solve the fatigue reliability problems of steel bridges. The cumulative damage model is one kind of the models used in fatigue reliability analysis. The parameter cha...A kind of hybrid reliability model is presented to solve the fatigue reliability problems of steel bridges. The cumulative damage model is one kind of the models used in fatigue reliability analysis. The parameter characteristics of the model can be described as probabilistic and interval. The two-stage hybrid reliability model is given with a theoretical foundation and a solving algorithm to solve the hybrid reliability problems. The theoretical foundation is established by the consistency relationships of interval reliability model and probability reliability model with normally distributed variables in theory. The solving process is combined with the definition of interval reliability index and the probabilistic algorithm. With the consideration of the parameter characteristics of the S-N curve, the cumulative damage model with hybrid variables is given based on the standards from different countries. Lastly, a case of steel structure in the Neville Island Bridge is analyzed to verify the applicability of the hybrid reliability model in fatigue reliability analysis based on the AASHTO.展开更多
Abundance distribution models and diversity-area relationships are tools of biological diversity analysis that have been used by ecologists for decades. In a case study by Ibez et al., these techniques are considered ...Abundance distribution models and diversity-area relationships are tools of biological diversity analysis that have been used by ecologists for decades. In a case study by Ibez et al., these techniques are considered in a mor e general setting, and have been applied to explore notions such as pedodiversity (as an example of geodiversity in a broad sense, including also geomorphic diversity), in order to detect the differences and similarities between both natural resources, biological and non-biological.The discussion has mainly been conducted through the study of the Aegean Islands by the Spanish research team. Standard statistical techniques have been applied to analyze how the pedotaxa-abundance distribution conforms to the abundance distribution models and how pedorichness-area data fit to the diversity-area models.No statistically significant difference has been observed between the abundance distribution models and the diversity-area relationships followed by biodiversity and pedodiversity data in similar situations. Thus, the studied results may suggest that some assumptions underlying biodiversity analysis ought to be carefully re-examined.Since results in ecological literature are usually interpreted in biological terms, the analysis by Ibáez et al. may be relevant to offer some suggestions to the following questions: What are the reasons for the similarities obtained between biotic and soil resources? Should the ecological theory modify some of its constructs once the said similarities have been proven? and what are its implications for environmental management and assessment?展开更多
基金support from High-Level Natural ScienceFoundation of Hainan Province of China (Grant No. 2019RC055)National Natural Science Foundation ofChina (Grant No. 51808176) and the Project Funded by the National First-Class Disciplines (PNFD).
文摘Traditional methods focus on the ultimate bending moment of glulam beams and the fracture failure of materials with defects,which usually depends on empirical parameters.There is no systematic theoretical method to predict the stiffness and shear distribution of glulam beams in elastic-plastic stage,and consequently,the failure of such glulam beams cannot be predicted effectively.To address these issues,an analytical method considering material nonlinearity was proposed for glulam beams,and the calculating equations of deflection and shear stress distribution for different failure modes were established.The proposed method was verified by experiments and numerical models under the corresponding conditions.Results showed that the theoretical calculations were in good agreement with experimental and numerical results,indicating that the equations proposed in this paper were reliable and accurate for such glulam beams with wood material in the elastic-plastic stage ignoring the influence of mechanic properties in radial and tangential directions of wood.Furthermore,the experimental results reported by the previous studies indicated that the method was applicable and could be used as a theoretical reference for predicting the failure of glulam beams.
基金Projects(51178042,51578047)supported by the National Natural Science Foundation of ChinaProject(C14JB00340)supported by the Innovative Research Fund in Beijing Jiaotong University,ChinaProject(2014-ZJKJ-03)supported by Science and Technology Research and Development Fund of the China Communications Construction Co.,LTD
文摘A kind of hybrid reliability model is presented to solve the fatigue reliability problems of steel bridges. The cumulative damage model is one kind of the models used in fatigue reliability analysis. The parameter characteristics of the model can be described as probabilistic and interval. The two-stage hybrid reliability model is given with a theoretical foundation and a solving algorithm to solve the hybrid reliability problems. The theoretical foundation is established by the consistency relationships of interval reliability model and probability reliability model with normally distributed variables in theory. The solving process is combined with the definition of interval reliability index and the probabilistic algorithm. With the consideration of the parameter characteristics of the S-N curve, the cumulative damage model with hybrid variables is given based on the standards from different countries. Lastly, a case of steel structure in the Neville Island Bridge is analyzed to verify the applicability of the hybrid reliability model in fatigue reliability analysis based on the AASHTO.
文摘Abundance distribution models and diversity-area relationships are tools of biological diversity analysis that have been used by ecologists for decades. In a case study by Ibez et al., these techniques are considered in a mor e general setting, and have been applied to explore notions such as pedodiversity (as an example of geodiversity in a broad sense, including also geomorphic diversity), in order to detect the differences and similarities between both natural resources, biological and non-biological.The discussion has mainly been conducted through the study of the Aegean Islands by the Spanish research team. Standard statistical techniques have been applied to analyze how the pedotaxa-abundance distribution conforms to the abundance distribution models and how pedorichness-area data fit to the diversity-area models.No statistically significant difference has been observed between the abundance distribution models and the diversity-area relationships followed by biodiversity and pedodiversity data in similar situations. Thus, the studied results may suggest that some assumptions underlying biodiversity analysis ought to be carefully re-examined.Since results in ecological literature are usually interpreted in biological terms, the analysis by Ibáez et al. may be relevant to offer some suggestions to the following questions: What are the reasons for the similarities obtained between biotic and soil resources? Should the ecological theory modify some of its constructs once the said similarities have been proven? and what are its implications for environmental management and assessment?
