Different values have been assigned to the ratio of the defl ection amplifi cation factor(Cd) to the response modifi cation factor(R) for a specifi ed force-resisting system in the seismic design provisions while the ...Different values have been assigned to the ratio of the defl ection amplifi cation factor(Cd) to the response modifi cation factor(R) for a specifi ed force-resisting system in the seismic design provisions while the same application is defi ned for it. An analytical study of the seismic responses of several reinforced concrete frames subjected to a suite of earthquake records performed in this research indicate that the stories’ overstrength and stiffness distribution along the structural height can affect local defl ections more than global ones. Therefore, the Cd/R ratio is calculated based on the ratio of both maximum inelastic to maximum elastic displacements and interstory drifts. Due to damage concentration in some specifi c stories, the defl ection amplifi cation factor calculated based on inelastic interstory drifts was larger than that of the inelastic displacements. Consequently, a minimum value of 1.0 is recommended for the Cd/R ratio in order to estimate maximum inelastic drifts. The ratio of inelastic to elastic displacement was generally found to increase slightly along the structural height for the studied RC models. In addition, it was detected that the story damage indices of the studied RC frames decrease when the inverted value of inelastic interstory drift ratios are increased through a(negative) power form.展开更多
It is well-known that the responses of a structure are different when subjected to a static load or a sudden step load.The dynamic amplification factor(DAF),which is defined as the ratio of the amplitude of the vibrat...It is well-known that the responses of a structure are different when subjected to a static load or a sudden step load.The dynamic amplification factor(DAF),which is defined as the ratio of the amplitude of the vibratory response to the static response,is normally used to depict the dynamic effect.For a single-degree-of-freedom system(SDOF)subjected to a sudden dynamic load,the maximum value of DAF is 2.Many design guidelines therefore use 2 as an upper bound to consider the dynamic effect.For a civil engineering structure,which is normally a multiple-degrees-of-freedom(MDOF)system,the DAF may exceed 2 in certain circumstances.The adoption of 2 as the upper bond as suggested by the design guidelines therefore may lead to unsafe structural design.Very limited studies systematically investigate the DAF of a MDOF sysCorrespondence to:Bi Kaiming,Centre for Infrastructure Monitoring and Protection,School of Civil and Mechanical Engineering,Curtin University,Kent Street,Bentley WA 6102,Australia Tel:(+61)892665139 E-mail:kaiming.bi@curtin.edu.autem.This study theoretically investigates the DAF of a MDOF system when it is subjected to a step load based on the fundamental theory of structural dynamics.The condition on which the DAF may exceed 2 is defined.Two numerical examples and one experimental study of a cable-stayed bridge subjected to sudden cable loss are presented to illustrate the problem.展开更多
Seismic codes estimate the maximum displacements of building structures under the design-basis earthquakes by amplifying the elastic displacements under the reduced seismic design forces with a deflection amplificatio...Seismic codes estimate the maximum displacements of building structures under the design-basis earthquakes by amplifying the elastic displacements under the reduced seismic design forces with a deflection amplification factor(DAF). The value of DAF is often estimated as ρ× R, where R is the force reduction factor and ρ is the inelastic displacement ratio that accounts for the inelastic action of the structure according to the definition presented by FEMA P695. The purpose of this study is to estimate the ρ-ratio of moment resisting steel frames(MRSFs) designed according to the Egyptian code. This is achieved by conducting a series of elastic and inelastic time-history analyses by two sets of earthquakes on four MRSFs designed according to the Egyptian code and having 2, 4, 8 and 12 stories. The earthquakes are scaled to produce maximum story drift ratios(MSDRs) of 1.0%, 1.5%, 2.0% and 2.5%. The mean values of the ρ-ratio are calculated based on the displacement responses of the investigated frames. The results obtained in this study indicate that the consideration of ρ for both the roof drift ratios(RDRs) and the MSDRs equal to 1.0 is a reasonable estimation for MRSFs designed according to the Egyptian code.展开更多
文摘Different values have been assigned to the ratio of the defl ection amplifi cation factor(Cd) to the response modifi cation factor(R) for a specifi ed force-resisting system in the seismic design provisions while the same application is defi ned for it. An analytical study of the seismic responses of several reinforced concrete frames subjected to a suite of earthquake records performed in this research indicate that the stories’ overstrength and stiffness distribution along the structural height can affect local defl ections more than global ones. Therefore, the Cd/R ratio is calculated based on the ratio of both maximum inelastic to maximum elastic displacements and interstory drifts. Due to damage concentration in some specifi c stories, the defl ection amplifi cation factor calculated based on inelastic interstory drifts was larger than that of the inelastic displacements. Consequently, a minimum value of 1.0 is recommended for the Cd/R ratio in order to estimate maximum inelastic drifts. The ratio of inelastic to elastic displacement was generally found to increase slightly along the structural height for the studied RC models. In addition, it was detected that the story damage indices of the studied RC frames decrease when the inverted value of inelastic interstory drift ratios are increased through a(negative) power form.
基金National Science Foundation of China(NSFC)under Grant No.51508102,China Postdoctoral Science Foundation under Grant No.2018M631292the Beijing Postdoctoral Science Foundation under Grant No.2018-ZZ-032Financial support was also provided by the China Scholarship Council(CSC)under Grant No.201406655012。
文摘It is well-known that the responses of a structure are different when subjected to a static load or a sudden step load.The dynamic amplification factor(DAF),which is defined as the ratio of the amplitude of the vibratory response to the static response,is normally used to depict the dynamic effect.For a single-degree-of-freedom system(SDOF)subjected to a sudden dynamic load,the maximum value of DAF is 2.Many design guidelines therefore use 2 as an upper bound to consider the dynamic effect.For a civil engineering structure,which is normally a multiple-degrees-of-freedom(MDOF)system,the DAF may exceed 2 in certain circumstances.The adoption of 2 as the upper bond as suggested by the design guidelines therefore may lead to unsafe structural design.Very limited studies systematically investigate the DAF of a MDOF sysCorrespondence to:Bi Kaiming,Centre for Infrastructure Monitoring and Protection,School of Civil and Mechanical Engineering,Curtin University,Kent Street,Bentley WA 6102,Australia Tel:(+61)892665139 E-mail:kaiming.bi@curtin.edu.autem.This study theoretically investigates the DAF of a MDOF system when it is subjected to a step load based on the fundamental theory of structural dynamics.The condition on which the DAF may exceed 2 is defined.Two numerical examples and one experimental study of a cable-stayed bridge subjected to sudden cable loss are presented to illustrate the problem.
文摘Seismic codes estimate the maximum displacements of building structures under the design-basis earthquakes by amplifying the elastic displacements under the reduced seismic design forces with a deflection amplification factor(DAF). The value of DAF is often estimated as ρ× R, where R is the force reduction factor and ρ is the inelastic displacement ratio that accounts for the inelastic action of the structure according to the definition presented by FEMA P695. The purpose of this study is to estimate the ρ-ratio of moment resisting steel frames(MRSFs) designed according to the Egyptian code. This is achieved by conducting a series of elastic and inelastic time-history analyses by two sets of earthquakes on four MRSFs designed according to the Egyptian code and having 2, 4, 8 and 12 stories. The earthquakes are scaled to produce maximum story drift ratios(MSDRs) of 1.0%, 1.5%, 2.0% and 2.5%. The mean values of the ρ-ratio are calculated based on the displacement responses of the investigated frames. The results obtained in this study indicate that the consideration of ρ for both the roof drift ratios(RDRs) and the MSDRs equal to 1.0 is a reasonable estimation for MRSFs designed according to the Egyptian code.
