In this study,a novel rotational damper called a Rotational Friction Viscoelastic Damper(RFVD) is introduced.Some viscoelastic pads are added to the Rotational Friction Damper(RFD) in addition to the friction discs us...In this study,a novel rotational damper called a Rotational Friction Viscoelastic Damper(RFVD) is introduced.Some viscoelastic pads are added to the Rotational Friction Damper(RFD) in addition to the friction discs used in this conventional device.Consequently,the amount of energy dissipated by the damper increases in low excitation frequencies.In fact,the input energy to the structure is simultaneously dissipated in the form of friction and heat by frictional discs and viscoelastic pads.In order to compare the performance of this novel damper with the earlier types,a set of experiments were carried out.According to the test results,the RFVD showed a better performance in dissipating input energy to the structure when compared to the RFD.The seismic behavior of steel frames equipped with these dampers was also numerically evaluated based on a nonlinear time history analysis.The numerical results verifi ed the performance of the dampers in increasing the energy dissipation and decreasing the energy input to the structural elements.In order to achieve the maximum dissipated energy,the dampers need to be installed in certain places called critical points in the structure.An appropriate approach is presented to properly fi nd these points.Finally,the performance of the RFVDs installed at these critical points was investigated in comparison to some other confi gurations and the validity of the suggested method in increasing the energy dissipation was confi rmed.展开更多
Exact calculations of the static earth pressure from a thick alluvium require accurate/Co values. These calculations influence the sinking cost and the safety of the freezing method. The static earth pressure coeffici...Exact calculations of the static earth pressure from a thick alluvium require accurate/Co values. These calculations influence the sinking cost and the safety of the freezing method. The static earth pressure coefficient （K0） of thick and deep soil was analyzed using laboratory tests. The results show that the static earth pressure coefficient of thick and deep soils is nonlinear and different from that of superficial soils. The constant of superficial soils is usually invariant and the total stress or incremental stress definitions used in traditional geo-meehanics give the same value. The influence of load increments when calculating for superficial soil is ignored. The difference in values of K0 for thick alluvium defimed by the total stress or the incremental stress methods is over 10%. The effects of the thick alluvium on K0 should be considered during the design of frozen shaft projects. Such things as the frozen shaft thickness and the excavated section height should be chosen to assure the rationality of the design and to avoid potential faults and accidents.展开更多
People started posting textual tweets on Twitter as soon as the novel coronavirus(COVID-19)emerged.Analyzing these tweets can assist institutions in better decision-making and prioritizing their tasks.Therefore,this s...People started posting textual tweets on Twitter as soon as the novel coronavirus(COVID-19)emerged.Analyzing these tweets can assist institutions in better decision-making and prioritizing their tasks.Therefore,this study aimed to analyze 43 million tweets collected between March 22 and March 30,2020 and describe the trend of public attention given to the topics related to the COVID-19 epidemic using evolutionary clustering analysis.The results indicated that unigram terms were trended more frequently than bigram and trigram terms.A large number of tweets about the COVID-19 were disseminated and received widespread public attention during the epidemic.The high-frequency words such as“death”,“test”,“spread”,and“lockdown”suggest that people fear of being infected,and those who got infection are afraid of death.The results also showed that people agreed to stay at home due to the fear of the spread,and they were calling for social distancing since they become aware of the COVID-19.It can be suggested that social media posts may affect human psychology and behavior.These results may help governments and health organizations to better understand the psychology of the public,and thereby,better communicate with them to prevent and manage the panic.展开更多
This paper reports a computational study on the seismic response of a three-span highway bridge system incorporating conventional and novel substructure details for improved seismic performance.The bridge has three co...This paper reports a computational study on the seismic response of a three-span highway bridge system incorporating conventional and novel substructure details for improved seismic performance.The bridge has three continuous spans supported by two single-column piers and integral abutments founded on drilled shafts.It will be the first full-scale highway bridge to use superelastic shape memory alloy bars (SMA)and engineered cementitious composite (ECC)to mitigate column plastic hinge damage and minimize residual displacements after a strong earthquake. A three-dimensional computational model capturing the nonlinear constitutive response of the novel materials and the effects of dynamic soil-structure interaction was developed to assess the seismic response of the bridge in finite-element software OpenSees.Two versions of the same bridge were analyzed and compared,one with conventional cast-in-place reinforced concrete columns,and the other with top plastic hinges incorporating Nickel-Titanium (NiTi)SMA reinforcing bars and ECC.The novel SMA/ECC plastic hinges were found to substantially reduce damage and post-earthquake residual displacements in the bridge substructure,but led to larger maximum drifts relative to the bridge with conventional reinforced concrete plastic hinges.The analysis results suggested that the novel plastic hinges could lead to improved post-earthquake serviceability of bridges after intense earthquakes.展开更多
Wind-related disasters are one of the most frequent disasters in Indonesia.It can cause severe damages of residential construction,especially in the world's most populated island of Java.Understanding the characte...Wind-related disasters are one of the most frequent disasters in Indonesia.It can cause severe damages of residential construction,especially in the world's most populated island of Java.Understanding the characteristics of extreme winds is crucial for mitigating the disasters and for defining structural design standards.This study investigated the spatiotemporal variations of extreme winds and pioneered a design wind map in Indonesia by focusing on western Java.Based on gust data observed in recent years from 24 stations,the extreme winds exhibit a clear annual cycle where northwestern and southeastern sides of western Java show out-of-phase relationship due to reversal monsoons.Meanwhile,extreme wind occurrences are mostly affected by small-scale weather systems,regardless of seasons and locations.To build the wind map,we used bias-corrected gust from ERA5 and applied the Gumbel method to predict extreme winds with different return periods.The wind map highlights some drawbacks of the current national design standards,which use single wind speed values regardless of location and return period.Beside a fundamental improvement for wind design,this study will benefit disaster risk mapping and other applications that require extreme wind speed distribution.展开更多
文摘In this study,a novel rotational damper called a Rotational Friction Viscoelastic Damper(RFVD) is introduced.Some viscoelastic pads are added to the Rotational Friction Damper(RFD) in addition to the friction discs used in this conventional device.Consequently,the amount of energy dissipated by the damper increases in low excitation frequencies.In fact,the input energy to the structure is simultaneously dissipated in the form of friction and heat by frictional discs and viscoelastic pads.In order to compare the performance of this novel damper with the earlier types,a set of experiments were carried out.According to the test results,the RFVD showed a better performance in dissipating input energy to the structure when compared to the RFD.The seismic behavior of steel frames equipped with these dampers was also numerically evaluated based on a nonlinear time history analysis.The numerical results verifi ed the performance of the dampers in increasing the energy dissipation and decreasing the energy input to the structural elements.In order to achieve the maximum dissipated energy,the dampers need to be installed in certain places called critical points in the structure.An appropriate approach is presented to properly fi nd these points.Finally,the performance of the RFVDs installed at these critical points was investigated in comparison to some other confi gurations and the validity of the suggested method in increasing the energy dissipation was confi rmed.
基金Project BK2007040 supported by the Provincial Natural Science Foundation of Jiangsu, China
文摘Exact calculations of the static earth pressure from a thick alluvium require accurate/Co values. These calculations influence the sinking cost and the safety of the freezing method. The static earth pressure coefficient （K0） of thick and deep soil was analyzed using laboratory tests. The results show that the static earth pressure coefficient of thick and deep soils is nonlinear and different from that of superficial soils. The constant of superficial soils is usually invariant and the total stress or incremental stress definitions used in traditional geo-meehanics give the same value. The influence of load increments when calculating for superficial soil is ignored. The difference in values of K0 for thick alluvium defimed by the total stress or the incremental stress methods is over 10%. The effects of the thick alluvium on K0 should be considered during the design of frozen shaft projects. Such things as the frozen shaft thickness and the excavated section height should be chosen to assure the rationality of the design and to avoid potential faults and accidents.
文摘People started posting textual tweets on Twitter as soon as the novel coronavirus(COVID-19)emerged.Analyzing these tweets can assist institutions in better decision-making and prioritizing their tasks.Therefore,this study aimed to analyze 43 million tweets collected between March 22 and March 30,2020 and describe the trend of public attention given to the topics related to the COVID-19 epidemic using evolutionary clustering analysis.The results indicated that unigram terms were trended more frequently than bigram and trigram terms.A large number of tweets about the COVID-19 were disseminated and received widespread public attention during the epidemic.The high-frequency words such as“death”,“test”,“spread”,and“lockdown”suggest that people fear of being infected,and those who got infection are afraid of death.The results also showed that people agreed to stay at home due to the fear of the spread,and they were calling for social distancing since they become aware of the COVID-19.It can be suggested that social media posts may affect human psychology and behavior.These results may help governments and health organizations to better understand the psychology of the public,and thereby,better communicate with them to prevent and manage the panic.
基金Shanghai Municipal Education Commission and the National Natural Science Foundation of China under Research Grant No.51408360 during his stay at University of Nevada,Reno.
文摘This paper reports a computational study on the seismic response of a three-span highway bridge system incorporating conventional and novel substructure details for improved seismic performance.The bridge has three continuous spans supported by two single-column piers and integral abutments founded on drilled shafts.It will be the first full-scale highway bridge to use superelastic shape memory alloy bars (SMA)and engineered cementitious composite (ECC)to mitigate column plastic hinge damage and minimize residual displacements after a strong earthquake. A three-dimensional computational model capturing the nonlinear constitutive response of the novel materials and the effects of dynamic soil-structure interaction was developed to assess the seismic response of the bridge in finite-element software OpenSees.Two versions of the same bridge were analyzed and compared,one with conventional cast-in-place reinforced concrete columns,and the other with top plastic hinges incorporating Nickel-Titanium (NiTi)SMA reinforcing bars and ECC.The novel SMA/ECC plastic hinges were found to substantially reduce damage and post-earthquake residual displacements in the bridge substructure,but led to larger maximum drifts relative to the bridge with conventional reinforced concrete plastic hinges.The analysis results suggested that the novel plastic hinges could lead to improved post-earthquake serviceability of bridges after intense earthquakes.
基金funded by the Institute of Research and Community Service,Institut Teknologi Bandungfunded by the Newton Fund of the UKRI Natural Environment Research Council(NERC)。
文摘Wind-related disasters are one of the most frequent disasters in Indonesia.It can cause severe damages of residential construction,especially in the world's most populated island of Java.Understanding the characteristics of extreme winds is crucial for mitigating the disasters and for defining structural design standards.This study investigated the spatiotemporal variations of extreme winds and pioneered a design wind map in Indonesia by focusing on western Java.Based on gust data observed in recent years from 24 stations,the extreme winds exhibit a clear annual cycle where northwestern and southeastern sides of western Java show out-of-phase relationship due to reversal monsoons.Meanwhile,extreme wind occurrences are mostly affected by small-scale weather systems,regardless of seasons and locations.To build the wind map,we used bias-corrected gust from ERA5 and applied the Gumbel method to predict extreme winds with different return periods.The wind map highlights some drawbacks of the current national design standards,which use single wind speed values regardless of location and return period.Beside a fundamental improvement for wind design,this study will benefit disaster risk mapping and other applications that require extreme wind speed distribution.
