In Europe, computation of displacement demand for seismic assessment of existing buildings is essentially based on a simplified formulation of the N2 method as prescribed by Eurocode 8(EC8). However, a lack of accurac...In Europe, computation of displacement demand for seismic assessment of existing buildings is essentially based on a simplified formulation of the N2 method as prescribed by Eurocode 8(EC8). However, a lack of accuracy of the N2 method in certain conditions has been pointed out by several studies. This paper addresses the assessment of effectiveness of the N2 method in seismic displacement demand determination in non-linear domain. The objective of this work is to investigate the accuracy of the N2 method through comparison with displacement demands computed using non-linear timehistory analysis(NLTHA). Results show that the original N2 method may lead to overestimation or underestimation of displacement demand predictions. This may affect results of mechanical model-based assessment of seismic vulnerability at an urban scale. Hence, the second part of this paper addresses an improvement of the N2 method formula by empirical evaluation of NLTHA results based on EC8 ground-classes. This task is formulated as a mathematical programming problem in which coefficients are obtained by minimizing the overall discrepancy between NLTHA and modified formula results. Various settings of the mathematical programming problem have been solved using a global optimization metaheuristic. An extensive comparison between the original N2 method formulation and optimized formulae highlights benefits of the strategy.展开更多
The mechanism for the decomposition of 2-mercaptoethyl O-ester was theoretically investigated.The mecha-nism that 2-mercaptoethyl O-ester undergoes an S_(N)2 displacement of the O atom by the S atom onα-C is much fa-...The mechanism for the decomposition of 2-mercaptoethyl O-ester was theoretically investigated.The mecha-nism that 2-mercaptoethyl O-ester undergoes an S_(N)2 displacement of the O atom by the S atom onα-C is much fa-vored over the mechanism of N-to-S acyl transfer.The length of the alcohol moiety has large effects on the decom-position efficiency of thiol-substituted alkyl O-esters.The reactivities of these esters are controlled by distortion en-ergies.Only 2-mercaptoethyl O-ester can undergo the decomposition at room temperature due to the low distortion energy to achieve the transition state geometry.If the thiol group of 2-mercaptoethyl O-ester is replaced by an amino group,the N-to-N acyl transfer mechanism is more favored than the S_(N)2 displacement mechanism.展开更多
文摘In Europe, computation of displacement demand for seismic assessment of existing buildings is essentially based on a simplified formulation of the N2 method as prescribed by Eurocode 8(EC8). However, a lack of accuracy of the N2 method in certain conditions has been pointed out by several studies. This paper addresses the assessment of effectiveness of the N2 method in seismic displacement demand determination in non-linear domain. The objective of this work is to investigate the accuracy of the N2 method through comparison with displacement demands computed using non-linear timehistory analysis(NLTHA). Results show that the original N2 method may lead to overestimation or underestimation of displacement demand predictions. This may affect results of mechanical model-based assessment of seismic vulnerability at an urban scale. Hence, the second part of this paper addresses an improvement of the N2 method formula by empirical evaluation of NLTHA results based on EC8 ground-classes. This task is formulated as a mathematical programming problem in which coefficients are obtained by minimizing the overall discrepancy between NLTHA and modified formula results. Various settings of the mathematical programming problem have been solved using a global optimization metaheuristic. An extensive comparison between the original N2 method formulation and optimized formulae highlights benefits of the strategy.
基金We thank the National Natural Science Foundation of China(No.21202102)for the financial support.
文摘The mechanism for the decomposition of 2-mercaptoethyl O-ester was theoretically investigated.The mecha-nism that 2-mercaptoethyl O-ester undergoes an S_(N)2 displacement of the O atom by the S atom onα-C is much fa-vored over the mechanism of N-to-S acyl transfer.The length of the alcohol moiety has large effects on the decom-position efficiency of thiol-substituted alkyl O-esters.The reactivities of these esters are controlled by distortion en-ergies.Only 2-mercaptoethyl O-ester can undergo the decomposition at room temperature due to the low distortion energy to achieve the transition state geometry.If the thiol group of 2-mercaptoethyl O-ester is replaced by an amino group,the N-to-N acyl transfer mechanism is more favored than the S_(N)2 displacement mechanism.
