A modified Kelvin impact model for pounding simulation of base-isolated building with adjacent structures

Base isolation can effectively reduce the seismic forces on a superstructure, particularly in lowto medium-rise buildings. However, under strong near-fault ground motions, pounding may occur at the isolation level between the baseisolated building （BIB） and its surrounding retaining walls. To effectively investigate the behavior of the BIB pounding with adjacent structures, after assessing some commonly used impact models, a modified Kelvin impact model is proposed in this paper. Relevant parameters in the modified Kelvin model are theoretically derived and numerically verified through a simple pounding case. At the same time, inelasticity of the isolated superstructure is introduced in order to accurately evaluate the potential damage to the superstructure caused by the pounding of the BIB with adjacent structures. The reliability of the modified Kelvin impact model is validated through numerical comparisons with other impact models. However, the difference between the numerical results from the various impact analytical models is not significant. Many numerical simulations of BIBs are conducted to investigate the influence of various design parameters and conditions on the peak inter-story drifts and floor accelerations during pounding. It is shown that pounding can substantially increase floor accelerations, especially at the ground floor where impacts occur. Higher modes of vibration are excited during poundings, increasing the inter-story drifts instead of keeping a nearly rigid-body motion of the superstructure. Furthermore, higher ductility demands can be imposed on lower floors of the superstructure. Moreover, impact stiffness seems to play a significant role in the acceleration response at the isolation level and the inter-story drifts of lower floors of the superstructure. Finally, the numerical results show that excessive flexibility of the isolation system used to minimize the floor accelerations may cause the BIB to be more susceptible to pounding under a limited seismic gap.

Experimental study of a highway bridge with shape memory alloy restrainers focusing on the mitigation of unseating and pounding

This paper presents an experimental study to investigate the performance of shape memory alloy(SMA) restrainers for mitigating the pounding and unseating of highway bridges when subjected to seismic excitations.Mechanical property tests of the SMA wire used in the restrainers are conducted first to understand the pseudo-elastic characteristics of the material.Then,a series of shaking table tests are carried out on a highway bridge model.The structural responses of the highway bridge model equipped with SMA restrainers,installed in the form of deck-deck and deck-pile connections,are analyzed and compared with the uncontrolled structures.The test results of this study indicate that the SMA restrainers are not only effective in preventing unseating but also in suppressing the seismic-induced pounding of the highway bridge model used in this study.

Implications of seismic pounding on the longitudinal response of multi-span bridges-an analytical perspective

Seismic pounding between adjacent frames in multiple-frame bridges and girder ends in multi-span simply supported bridges has been commonly observed in several recent earthquakes.The consequences of pounding include damage to piers,abutments,shear keys,bearings and restrainers,and possible collapse of deck spans.This paper investigates pounding in bridges from an analytical perspective.A simplified nonlinear model of a multiple-frame bridge is developed including the effects of inelastic frame action and nonlinear hinge behavior,to study the seismic response to longitudinal ground motion.Pounding is implemented using the contact force-based Kelvin model,as well as the momentum-based stereomechanical approach.Parameter studies are conducted to determine the effects of frame period ratio,column hysteretic behavior,energy dissipation during impact and near source ground motions on the pounding response of the bridge.The results indicate that pounding is most critical for highly out-of-phase frames and is not significant for frame period ratios greater than 0.7.Impact models without energy dissipation overestimate the displacement and acceleration amplifications due to impact,especially for elastic behavior of the frames.Representation of stiffness degradation in bridge columns is essential in capturing the accurate response of pounding frames subjected to far field ground motion.Finally,it is shown that strength degradation and pounding can result in significant damage to the stiffer frames of the bridge when subjected to large acceleration pulses from near field ground motion records.

Earthquake induced pounding between adjacent buildings considering soil-structure interaction

Many closely located adjacent buildings have suffered from pounding during past earthquakes because they vibrated out of phase. Furthermore, buildings are usually constructed on soil; hence, there are interactions between the buildings and the underlying soil that should also be considered. This paper examines both the interaction between adjacent buildings due to pounding and the interaction between the buildings through the soil as they affect the buildings＇ seismic responses. The developed model consists of adjacent shear buildings resting on a discrete soil model and a linear visco- elastic contact force model that connects the buildings during pounding. The seismic responses of＇ adjacent buildings due to ground accelerations are obtained for two conditions： fixed-based （FB） and structure-soil-structure interaction （SSSI）. The results indicate that pounding worsens the buildings＇ condition because their seismic responses are amplified after pounding. Moreover, the underlying soil negatively impacts the buildings＇ seismic responses during pounding because the ratio of their seismic response under SSSI conditions with pounding to those without pounding is greater than that of the FB condition.

Dimensional analysis of earthquake-induced pounding between adjacent inelastic MDOF buildings

In this study the seismic pounding response of adjacent multi-degree-of-freedom(MDOF) buildings with bilinear inter-story resistance characteristics is investigated through dimensional analysis. The application of dimensional analysis leads to a condensed presentation of the response, and the remarkable self-similarity property for bilinear MDOF buildings with inelastic collision is uncovered. It is shown that when the response is expressed in the appropriate dimensionless form, response spectra for any intensity of the excitation collapse to a single master curve. The reduced Π set explicitly describes the interaction between the colliding structures. The effect of pounding on the MDOF building’s response is illustrated using three well-divided spectral regions(amplifi ed, de-amplifi ed and unaffected regions). Parametric studies are conducted to investigate the effects of the story stiffness of structures, the story stiffness ratio and mass ratio of adjacent buildings, the structural inelastic characteristics and the gap size values. Results show that(i) the infl uence of system stiffness ratio to the lighter and more fl exible building is more signifi cant in the fi rst spectral region, where the maximum response of the building is amplifi ed because of pounding; and(ii) the velocity and pounding force of the heavier and stiffer building is unexpectedly sensitive to the mass ratio of adjacent buildings.

Underground blast effects on structural pounding

In the present study,actual three-dimensional structures are converted into a stick model of multi degree of-freedom(MDOF)systems for understanding the macro-behavior of structures.The study investigates the performance of three closely spaced,adjacent G+10,fixed-base MDOF systems with the mass aligned at the same levels and subjected to accidental underground blast loading.The acceleration time history of underground blast loading is generated based on past empirical relationships.The blast charge weight varies from 10 to 75 t while keeping the charge distance constant(R=100 m).The entire formulation is solved with the MATLAB solver,using the state space form solution.Three cases are considered,based on changing the position of the three stick systems.The first case considered left building rigid,middle building moderate rigid,and right building flexible.The second assumed left building flexible,middle building rigid,and right building moderate rigid.The third examined the left building as moderate rigid,the middle building as flexible,and the right building rigid.An analysis of the results shows that the arrangement with low stiffness,high stiffness,and moderately stiff buildings placed to the left,middle,and right side,respectively,yields minimum structural response when compared to the other two combinations.

Equivalent Kelvin Impact Model for Seismic Pounding Analysis of Bridges

Based on Hertz contact theory, a method to determine the parameters of Kelvin impact model for seismic pounding analysis of bridges is proposed. The impact stiffness of Kelvin model is determined by the ratio of maximum impact force to maximum contact deformation, which is calculated based on Hertz contact theory with considering the vibration effect. The restitution coefficient which has great influence on the damping coefficient of Kelvin impact model is investigated by numerical analysis. Numerical results indicate that the impact stiffness of Kelvin impact model increases with the increment of the Hertz contact stiffness, approaching velocity or the length ratio of short to long girders. Vibration effect has remarkable influence on the impact stiffness and cannot be neglected. The restitution coefficient decreases when approaching velocity increases or the length ratio of short girder to long girder decreasing. The practical ranges of impact stiffness and restitution coefficient are obtained as 3 × 10^8--6 × 10^8 N/m and 0.6-3.95 respectively.

Nonlinear analysis of pounding between decks of multi-span bridge subjected to multi-support and multi-dimensional earthquake excitation

The nonlinear analysis of pounding between bridge deck segments subjected to multi-support excitations and multi-dimensional earthquake motion was performed.A novel bottom rigid element(BRE)method of the current displacement input model for structural seismic analysis under the multi-support excitations was used to calculate structural dynamic response.In the analysis,pounding between adjacent deck segments was considered.The seismic response of a multi-span bridge subjected to the multi-support excitation,considering not only the traveling-wave effect and partial coherence effect,but also the seismic non-stationary characteristics of multi-support earthquake motion,was simulated using finite element method(FEM).Meanwhile,the seismic response of the bridge under uniform earthquake was also analyzed.Finally,comparative analysis was conducted and some calculation results were shown for pounding effect,under multi-dimensional and multi-support earthquake motion,when performing seismic response analysis of multi-span bridge.Compared with the case of uniform/multi-support/multi-support and multi-dimensional earthquake input,the maximum values of pounding force in the case of multi-support and multi-dimensional earthquake input increase by about 5 8 times;the absolute value of bottom moment and shear force of piers increase by about50%600%and 23.1%900%,respectively.A conclusion can be given that it is very necessary to consider the pounding effect under multi-dimensional and multi-support earthquake motion while performing seismic response analysis of multi-span bridge.

Seismic pounding and collapse behavior of neighboring buildings with different natural periods

Seismic pounding phenomena, particularly the collision of neighboring buildings under long-period ground motion, are becoming a significant issue in Japan. We focused on a specific apartment structure called the Nuevo Leon buildings in the Tlatelolco district of Mexico City, which consisted of three similar buildings built consecutively with narrow expansion joints between the buildings. Two out of the three buildings collapsed completely in the 1985 Mexican earthquake. Using a finite element code based on the adaptively shifted integration (ASI)-Gauss technique, a seismic pounding analysis is performed on a simulated model of the Nuevo Leon buildings to understand the impact and collapse behavior of structures built near each other. The numerical code used in the analysis provides a higher computational efficiency than the conventional code for this type of problem and enables us to address dynamic behavior with strong nonlinearities, including phenomena such as member fracture and elemental contact. Contact release and recontact algorithms are developed and implemented in the code to understand the complex behaviors of structural members during seismic pounding and the collapse sequence. According to the numerical results, the collision of the buildings may be a result of the difference of natural periods between the neighboring buildings. This difference was detected in similar buildings from the damages caused by previous earthquakes. By setting the natural period of the north building to be 25% longer than the other periods, the ground motion, which hada relatively long period of 2 s, first caused the collision between the north and the center buildings. This collision eventually led to the collapse of the centerbuilding, followed by the destruction of the north building.

Elastic and Inelastic Response of Structural Systems in Seismic Pounding

The present paper addresses the comparative study of three adjacent single-degree-of freedom structures for elastic and inelastic system with and without pounding under seismic excitations. For the gap between three adjacent structures, the simulation is done by using linear spring element without damping. The entire numerical simulation is done in time domain by considering the inputs of four real ground motions. The results of the study show that the response of elastic system is much different to that of response of inelastic system in the absence and presence of pounding, especially in lighter or more flexible structures. Elastic structures show much severe pounding response than inelastic structures. Modeling of colliding structures behaving inelastically is really needed in order to obtain the accurate structural pounding involved response under seismic excitation.

Impact analytical models for earthquake-induced pounding simulation

Structural pounding under earthquake has been recently extensively investigated using various impact analytical models.In this paper,a brief review on the commonly used impact analytical models is conducted.Based on this review,the formula used to determine the damping constant related to the impact spring stiffness,coefficient of restitution,and relative approaching velocity in the Hertz model with nonlinear damping is found to be incorrect.To correct this error,a more accurate approximating formula for the damping constant is theoretically derived 5~nd numerically verified.At the same time,a modified Kelvin impact model,which can reasonably account for the physical nature of pounding and conveniently implemented in the earthquake-induced pounding simulation of structural engineering is proposed.

Seasonal Impact of Agricultural Non-point Source Pollution on Water Environment of Dianshan Lake Basin in Shanghai City

Taken the Dalian lake region as the study area,which represents the typical agriculture production mode and agricultural non-point source pollution （ANSP） in Dianshan lake area in Shanghai City,basis on the characteristics of regional ANSP and combing with the seasonal water quality monitoring of Dalian Lake and reaches of its main influents,the laws of seasonal impact on the water environment were investigated.The results showed that,the seasonal change of TN and COD concentration of regional water had no significant correlation with the local ANSP emissions,while the seasonal changes of TP was consistent with seasonal emissions of regional TP pollution,and it had a significant correlation with Chl.a in four seasons,indicating that regional TP pollutant was the constriction factor influenced the eutrophication degree of Dalian lake.Because more than 80% of TP emissions came from the drainage of intensive pounds in winter,summer and fall,TP pollutant control should be adopted as the control target of regional ANSP control.

Seismic behavior of precast segmental column bridges under near-fault forward-directivity ground motions

Precast segmental column bridges exhibit various construction advantages in comparison to traditional monolithic column bridges.However,the lack of cognitions on seismic behaviors has seriously restricted their applications and developments.In this paper,comprehensive investigations are conducted to analyze the dynamic characteristics of precast segmental column bridges under near-fault,forward-directivity ground motions.First,the finite-element models of two comparable bridges with precast segmental columns and monolithic columns are constructed by using OpenSees software,and the nonlinearities of the bridges are considered.Next,three different earthquake loadings are meticulously set up to handle engineering problems,namely recorded near-and far-field ground motions,parameterized pulses,and pulse and residual components extracted from real records.Finally,based on the models and earthquake sets,extensive explorations are carried out.The results show that near-fault forward-directivity ground motions are more threatening than far-field ones;precast segmental column bridges may suffer more pounding impacts than monolithic bridges;the“narrow band”effect caused by near-fault,forward-directivity ground motions may occur in bridges with shorter periods than pulse periods;and pulse and residual components play different roles in seismic responses.

Effects of Bagging with Paper Bags and Non-woven Bags on Flavor Compounds of Feicheng Peach

With Hongli Feicheng Peach as the test material, the effects of bagging with 4 kinds of paper bags and 3 kinds of non-woven bags on the soluble sugar, organic acids and aroma compounds in peach fruits were investigated using headspace solid-phase microextraction （HS-SPME） combined with gas chromatogra- phy-mass spectrometry （GC-MS） and high-performance liquid chromatography （HPLC）. The results showed that there were significant differences in sugar and acids contents of peach fruits between different bagging treatments. The sugar con- tent of peach fruits was increased when bagged with single-layer inner-black outer- yellow paper bags and double-layer inner-white outer-yellow paper bags. The organ- ic acid content in peach fruits bagged with all the types of bags except the single- layer inner-black outer-yellow paper bag was increased greatly. The count and rela- tive content of aroma compounds were all decreased after bagging. Combined with the detection results of soluble sugar, organic acids and aroma compounds, the sin- gle-layer inner-black outer-yellow paper bag was suitable for bagging of Hongli Fe- icheng peach.

A Cultural Analysis of Pound's Mistranslation in the Poem "Blue, blue is the Grass

Ezra Pound is one of the founders of the American Imagist poetry, and Chinese Classic Poetry happened to be a great stimulus as the Renaissance from the Greeks to this poetry movement. Pound, who was deeply fascinated by Chinese poetry, has rendered many into English. Yet due to cultural differences, Pound’s translation has a lot of mistakes. And this paper aims at a cultural analysis of the mistranslation on a certain text to display its influence upon the Imagist Movement in the history of American Poetry.

Seismic Damage to Owner-Built RC Frames in Charikot during the 2015 Nepal Earthquake Sequence

The damage to the masonry-infilled reinforced concrete( RC) frame buildings in Charikot,the capital city of Dolakha district in Nepal,during the 2015 April-to-May Nepal earthquake sequence is reported. Most of these buildings were built by the owners with little governmental inspections regarding their structural design or constructional quality. Although they generally performed better than other structural systems such as stone-masonry houses,the RC frames sustained extensive damage ranging from cracking of infill to complete collapse. In particular,eight of the 72 inspected RC frames alongside an uphill street collapsed in different ways. In addition to the un-engineered nature of these RC frames,their collapse could also be attributed to multiple technical reasons including the effect of terrain, the pounding between adjacent buildings and the accumulative damage in the earthquake sequence.

Stylistic Analysis of Ezra Pound's Cathay

Cathay by Ezra Pound is the masterpiece in modern poetry in the West,and it contains nineteen Chinese poems.Based on literary stylistic theory,Pound’s translation style in Cathay is analyzed from lexical categories,aspects of syntax and figures of speech etc.It is found that the vocabulary and sentences in Cathay are very simple and brief,and the language is rich of images,which is the exact reflection of Pound’s idea of Imagism.

Ezra Pound＇s Conversion to Confucianism

The paper aims to explore Pound＇s early discovery of Confucianism and his conversion to Confucianism. Pound＇s interest in Confucianism coincided with the time when Christianity, already ＂contaminated＂ by ＂historical diseases＂ in Pound＇s view, could not offer a valid vision by which to guide the spiritual life, resulting in losing self in a modem society. Pound discovers three main deficiencies of Christianity： lack of respect for individuality, the decline of ethics, and open attack upon nature, which could not provide solutions to Western problems. Pound turned to Confucianism to search the existence of modem man in the face of society, and nature, which results in Pound＇s Confucian medicine to cure Western moral obtuseness.

Tension in In a Station of a Metro to Explore the Energy in Language

Pound's poem In a Station of a Metro is a masterpiece of imagism. Pound once talked about the energy in language, and American scholar Allen Tate told us that the meaning of poetry is its tension. Based on those two notions, this essay focuses on that how the tension in In a Station of a Metro presented and those tensions form harmony, fully releasing the energy in language in Pound's hand, enabling readers being fascinated for generations in that way.

A Comparison of Pound's Poetic Ideas and Some Chinese Poetic Principles-Using the Translation of "The Jewel Stairs' Grievance" as a Case in Point

The prominent features of Li Bai's "The Jewel Stairs'Grievance" are precise diction;implicit meaning;an absent narrator;and a seamless unity of images and feelings.Pound's translation of it in Cathay reveals some kind of connections between some Chinese poetic principals and Pound's individual poetics.