In conventional modal analysis procedures,usually only a few dominant modes are required to describe the dynamic behavior of multi-degrees-of-freedom buildings.The number of modes needed in the dynamic analysis depend...In conventional modal analysis procedures,usually only a few dominant modes are required to describe the dynamic behavior of multi-degrees-of-freedom buildings.The number of modes needed in the dynamic analysis depends on the higher-mode contribution to the structural response,which is called the higher-mode effect.The modal analysis approach, however,may not be directly applied to the dynamic analysis of viscoelastically damped buildings.This is because the dynamic properties of the viscoelastic dampers depend on their vibration frequency.Therefore,the structural stiffness and damping contributed from those dampers would be different for each mode.In this study,the higher-mode effect is referred to as the response difference induced by the frequency-dependent property of viscoelastic dampers at higher modes.Modal analysis procedures for buildings with viscoelastic dampers distributed proportionally and non-proportionally to the stiffness of the buildings are developed to consider the higher-mode effect.Numerical studies on shear-type viscoelastically damped building models are conducted to examine the accuracy of the proposed procedures and to investigate the significance of the higher-mode effect on their seismic response.Two damper models are used to estimate the peak damper forces in the proposed procedures. Study results reveal that the higher-mode effect is significant for long-period viscoelastically damped buildings.The higher-mode effect on base shear is less significant than on story acceleration response.Maximum difference of the seismic response usually occurs at the top story.Also,the higher-mode effect may not be reduced by decreasing the damping ratio provided by the viscoelastic dampers.For practical application,it is realized that the linear viscous damping model without considering the higher-mode effect may predict larger damper forces and hence,is on the conservative side.展开更多
Rapid urbanization has resulted in increased demand for tall buildings in many large and medium-sized cities around the world.Current code-based standards for seismic design are primarily aimed at minimizing life-safe...Rapid urbanization has resulted in increased demand for tall buildings in many large and medium-sized cities around the world.Current code-based standards for seismic design are primarily aimed at minimizing life-safety risks under major earthquakes.While reinforced concrete(RC)high-rise buildings designed following current code requirements are expected to achieve collapse-prevention,the contribution of higher modes of vibrations to the dynamic response of these structures can produce seismic demands significantly larger than those obtained from prescriptive code-based procedures,causing unexpectedly higher structural and non-structural damage to these buildings.These imply considerable costs associated with the loss of residences and business operations as well as the post-earthquake recovery of cities.This paper presents a concise review of the current state-of-the-art and state of research pertaining to the understanding,estimation and mitigation of higher-mode effects on the seismic response of tall and slender RC structures.The paper is organized into four main foci:(1)analytical studies on understanding and quantifying higher-mode effects,(2)available experimental work on this topic,(3)advances in code practices in accounting for higher-mode effects in seismic design of RC tall buildings,and(4)recent developments in innovative systems intended to mitigate higher-mode effects in RC tall buildings.The paper concludes by briefly summarizing future challenges facing the construction of earthquake-resilient RC tall buildings that are essential in building resilient cities of the future.展开更多
文摘In conventional modal analysis procedures,usually only a few dominant modes are required to describe the dynamic behavior of multi-degrees-of-freedom buildings.The number of modes needed in the dynamic analysis depends on the higher-mode contribution to the structural response,which is called the higher-mode effect.The modal analysis approach, however,may not be directly applied to the dynamic analysis of viscoelastically damped buildings.This is because the dynamic properties of the viscoelastic dampers depend on their vibration frequency.Therefore,the structural stiffness and damping contributed from those dampers would be different for each mode.In this study,the higher-mode effect is referred to as the response difference induced by the frequency-dependent property of viscoelastic dampers at higher modes.Modal analysis procedures for buildings with viscoelastic dampers distributed proportionally and non-proportionally to the stiffness of the buildings are developed to consider the higher-mode effect.Numerical studies on shear-type viscoelastically damped building models are conducted to examine the accuracy of the proposed procedures and to investigate the significance of the higher-mode effect on their seismic response.Two damper models are used to estimate the peak damper forces in the proposed procedures. Study results reveal that the higher-mode effect is significant for long-period viscoelastically damped buildings.The higher-mode effect on base shear is less significant than on story acceleration response.Maximum difference of the seismic response usually occurs at the top story.Also,the higher-mode effect may not be reduced by decreasing the damping ratio provided by the viscoelastic dampers.For practical application,it is realized that the linear viscous damping model without considering the higher-mode effect may predict larger damper forces and hence,is on the conservative side.
基金the financial support of the Nat-ural Sciences and Engineering Research Council of Canada(NSERC).
文摘Rapid urbanization has resulted in increased demand for tall buildings in many large and medium-sized cities around the world.Current code-based standards for seismic design are primarily aimed at minimizing life-safety risks under major earthquakes.While reinforced concrete(RC)high-rise buildings designed following current code requirements are expected to achieve collapse-prevention,the contribution of higher modes of vibrations to the dynamic response of these structures can produce seismic demands significantly larger than those obtained from prescriptive code-based procedures,causing unexpectedly higher structural and non-structural damage to these buildings.These imply considerable costs associated with the loss of residences and business operations as well as the post-earthquake recovery of cities.This paper presents a concise review of the current state-of-the-art and state of research pertaining to the understanding,estimation and mitigation of higher-mode effects on the seismic response of tall and slender RC structures.The paper is organized into four main foci:(1)analytical studies on understanding and quantifying higher-mode effects,(2)available experimental work on this topic,(3)advances in code practices in accounting for higher-mode effects in seismic design of RC tall buildings,and(4)recent developments in innovative systems intended to mitigate higher-mode effects in RC tall buildings.The paper concludes by briefly summarizing future challenges facing the construction of earthquake-resilient RC tall buildings that are essential in building resilient cities of the future.
