The performance of clay-pile-pier system under earthquake shaking was comprehensively examined via three-dimensional finite element analyses,in which the complex stress-strain relationships of a clay and piled pier sy...The performance of clay-pile-pier system under earthquake shaking was comprehensively examined via three-dimensional finite element analyses,in which the complex stress-strain relationships of a clay and piled pier system were depicted by a hyperbolic-hysteretic and an equivalent elastoplastic model,respectively.One hundred twenty ground motions with varying peak accelerations were considered,along with the variations in bridge superstructure mass and pile flexural rigidity.Comprehensive comparison studies suggested that peak pile-cap acceleration and peak pile-cap velocity are the optimal ground motion intensity measures for seismic responses of the pier and the pile,respectively.Furthermore,based on two optimal ground motion intensity measures and using curvature ductility to quantify different damage states,seismic fragility analyses were performed.The pier generally had no evident damage except when the bridge girder mass was equal to 960 t,which seemed to be comparatively insensitive to the varying pile flexural rigidity.In comparison,the pile was found to be more vulnerable to seismic damage and its failure probabilities tended to clearly reduce with the increment of pile flexural rigidity,while the influence of the bridge girder mass was relatively minor.展开更多
This work investigates the correlation between a large number of widely used ground motion intensity measures(IMs) and the corresponding liquefaction potential of a soil deposit during earthquake loading. In order to ...This work investigates the correlation between a large number of widely used ground motion intensity measures(IMs) and the corresponding liquefaction potential of a soil deposit during earthquake loading. In order to accomplish this purpose the seismic responses of 32 sloping liquefiable site models consisting of layered cohesionless soil were subjected to 139 earthquake ground motions. Two sets of ground motions, consisting of 80 ordinary records and 59 pulse-like near-fault records are used in the dynamic analyses. The liquefaction potential of the site is expressed in terms of the the mean pore pressure ratio, the maximum ground settlement, the maximum ground horizontal displacement and the maximum ground horizontal acceleration. For each individual accelerogram, the values of the aforementioned liquefaction potential measures are determined. Then, the correlation between the liquefaction potential measures and the IMs is evaluated. The results reveal that the velocity spectrum intensity(VSI) shows the strongest correlation with the liquefaction potential of sloping site. VSI is also proven to be a sufficient intensity measure with respect to earthquake magnitude and source-to-site distance, and has a good predictability, thus making it a prime candidate for the seismic liquefaction hazard evaluation.展开更多
This paper presents a method for seismic vulnerability analysis of bridge structures based on vector-valued intensity measure （viM）, which predicts the limit-state capacities efficiently with multi-intensity measure...This paper presents a method for seismic vulnerability analysis of bridge structures based on vector-valued intensity measure （viM）, which predicts the limit-state capacities efficiently with multi-intensity measures of seismic event. Accounting for the uncertainties of the bridge model, ten single-bent overpass bridge structures are taken as samples statistically using Latin hypercube sampling approach. 200 earthquake records are chosen randomly for the uncertainties of ground motions according to the site condition of the bridges. The uncertainties of structural capacity and seismic demand are evaluated with the ratios of demand to capacity in different damage state. By comparing the relative importance of different intensity measures, Sa（T1） and Sa（T2） are chosen as viM. Then, the vector-valued fragility functions of different bridge components are developed. Finally, the system-level vulnerability of the bridge based on viM is studied with Duunett- Sobel class correlation matrix which can consider the correlation effects of different bridge components. The study indicates that an increment IMs from a scalar IM to viM results in a significant reduction in the dispersion of fragility functions and in the uncertainties in evaluating earthquake risk. The feasibility and validity of the proposed vulnerability analysis method is validated and the bridge is more vulnerable than any components.展开更多
Application of the artificial neural network （ANN） to predict pseudospectral acceleration or peak ground acceleration is explored in the study. The training of ANN model is carried out using feed-forward backpropaga...Application of the artificial neural network （ANN） to predict pseudospectral acceleration or peak ground acceleration is explored in the study. The training of ANN model is carried out using feed-forward backpropagation method and about 600 records from 39 California earthquakes. The statistics of the residuals or modeling error for the trained ANN-based models are almost the same as those for the parametric ground motion prediction equations, derived through regression analysis; the residual or modeling error can be modeled as a normal variate. The similarity and differences between the predictions by these two approaches are shown. The trained ANN-based models, however, are not robust because the models with almost identical mean square errors do not always lead to the same predictions. This undesirable behaviour for predicting the ground motion measures has not been shown or discussed in the literature; the presented results, at least, serve to raise questions and caution on this problem. A practical approach to ameliorate this problem, perhaps, is to consider several trained ANN models, and to take the average of the predicted values from the trained ANN models as the predicted ground motion measure.展开更多
In this work,an alternative alkali-activated cement(AAC)made of ladle slag precursor mixed with sodium hydroxide and sodium silicate has been developed to enhance the bearing capacity of estuarine soils in coastal con...In this work,an alternative alkali-activated cement(AAC)made of ladle slag precursor mixed with sodium hydroxide and sodium silicate has been developed to enhance the bearing capacity of estuarine soils in coastal conditions via deep soil mixing(DSM).The AAC was optimized to use a low reactivity precursor(ladle slag)and to deal with a contaminated high-water content natural sediment cured under water.The material performance was analysed by comparison to a mixture made with Portland cement and cured in the same conditions.Flexural and unconfined compressive strength tests as well as seismic waves measurements after 3-,7-,14-and 28-d curing were performed to obtain a relationship between elastic stiffness and strength with curing time for both mixtures.Remarkably,the AAC mix demonstrated superior strength results,exhibiting almost double flexural and compressive strengths after 28 d compared to the Portland cement mix.The AAC mix also showed a higher rate of stiffness increase than the Portland cement mix,which has a higher initial stiffness at young ages but lower stiffness evolution.Leachate analysis confirmed that the proposed AAC could effectively immobilise any contaminants from soil or precursors.The effect of curing under stress was analysed in triaxial compression tests and found to be insignificant,indicating that laboratory data obtained without stress curing can represent the material's behaviour in a DSM column,which will cure under the weight of the column.展开更多
基金National Natural Science Foundation of China under Grant Nos.52178353,51808421the Fundamental Research Funds for the Central Universities(WUT:2020III043)。
文摘The performance of clay-pile-pier system under earthquake shaking was comprehensively examined via three-dimensional finite element analyses,in which the complex stress-strain relationships of a clay and piled pier system were depicted by a hyperbolic-hysteretic and an equivalent elastoplastic model,respectively.One hundred twenty ground motions with varying peak accelerations were considered,along with the variations in bridge superstructure mass and pile flexural rigidity.Comprehensive comparison studies suggested that peak pile-cap acceleration and peak pile-cap velocity are the optimal ground motion intensity measures for seismic responses of the pier and the pile,respectively.Furthermore,based on two optimal ground motion intensity measures and using curvature ductility to quantify different damage states,seismic fragility analyses were performed.The pier generally had no evident damage except when the bridge girder mass was equal to 960 t,which seemed to be comparatively insensitive to the varying pile flexural rigidity.In comparison,the pile was found to be more vulnerable to seismic damage and its failure probabilities tended to clearly reduce with the increment of pile flexural rigidity,while the influence of the bridge girder mass was relatively minor.
基金Project(5141001028)supported by International Cooperation and Exchanges of NSFC,ChinaProjects(51308566,51308565,51409025)supported by the National Natural Science Foundation of ChinaProject(CDJZR12200002)supported by the Fundamental Research Funds for the Central Universities,China
文摘This work investigates the correlation between a large number of widely used ground motion intensity measures(IMs) and the corresponding liquefaction potential of a soil deposit during earthquake loading. In order to accomplish this purpose the seismic responses of 32 sloping liquefiable site models consisting of layered cohesionless soil were subjected to 139 earthquake ground motions. Two sets of ground motions, consisting of 80 ordinary records and 59 pulse-like near-fault records are used in the dynamic analyses. The liquefaction potential of the site is expressed in terms of the the mean pore pressure ratio, the maximum ground settlement, the maximum ground horizontal displacement and the maximum ground horizontal acceleration. For each individual accelerogram, the values of the aforementioned liquefaction potential measures are determined. Then, the correlation between the liquefaction potential measures and the IMs is evaluated. The results reveal that the velocity spectrum intensity(VSI) shows the strongest correlation with the liquefaction potential of sloping site. VSI is also proven to be a sufficient intensity measure with respect to earthquake magnitude and source-to-site distance, and has a good predictability, thus making it a prime candidate for the seismic liquefaction hazard evaluation.
基金National Program on Key Basic Research Project of China(973)under Grant No.2011CB013603National Natural Science Foundation of China under Grant Nos.51378341,91315301Tianjin Municipal Natural Science Foundation under Grant No.13JCQNJC07200
文摘This paper presents a method for seismic vulnerability analysis of bridge structures based on vector-valued intensity measure （viM）, which predicts the limit-state capacities efficiently with multi-intensity measures of seismic event. Accounting for the uncertainties of the bridge model, ten single-bent overpass bridge structures are taken as samples statistically using Latin hypercube sampling approach. 200 earthquake records are chosen randomly for the uncertainties of ground motions according to the site condition of the bridges. The uncertainties of structural capacity and seismic demand are evaluated with the ratios of demand to capacity in different damage state. By comparing the relative importance of different intensity measures, Sa（T1） and Sa（T2） are chosen as viM. Then, the vector-valued fragility functions of different bridge components are developed. Finally, the system-level vulnerability of the bridge based on viM is studied with Duunett- Sobel class correlation matrix which can consider the correlation effects of different bridge components. The study indicates that an increment IMs from a scalar IM to viM results in a significant reduction in the dispersion of fragility functions and in the uncertainties in evaluating earthquake risk. The feasibility and validity of the proposed vulnerability analysis method is validated and the bridge is more vulnerable than any components.
基金The financial support received from the Natural Science and Engineering Research Council of Canadathe University of Western Ontario
文摘Application of the artificial neural network （ANN） to predict pseudospectral acceleration or peak ground acceleration is explored in the study. The training of ANN model is carried out using feed-forward backpropagation method and about 600 records from 39 California earthquakes. The statistics of the residuals or modeling error for the trained ANN-based models are almost the same as those for the parametric ground motion prediction equations, derived through regression analysis; the residual or modeling error can be modeled as a normal variate. The similarity and differences between the predictions by these two approaches are shown. The trained ANN-based models, however, are not robust because the models with almost identical mean square errors do not always lead to the same predictions. This undesirable behaviour for predicting the ground motion measures has not been shown or discussed in the literature; the presented results, at least, serve to raise questions and caution on this problem. A practical approach to ameliorate this problem, perhaps, is to consider several trained ANN models, and to take the average of the predicted values from the trained ANN models as the predicted ground motion measure.
基金funding from CNPq(Brazilian council for scientific and technological development)through 201465/2015-9 scholarship of the“Science without borders”programsupport of MCTES/FCT(Portuguese Science and Technology Foundation of Portuguese Ministry of Science and Technology)through CEECIND/04583/2017 grant+1 种基金financially supported by:Base Funding-UIDB/04708/2020 of the CONSTRUCT-Instituto de I&D em Estruturas e Construções-funded by national funds through FCT/MCTES(PIDDAC)A special acknowledgment is also due to the Portuguese National Steel Industry of Maia,part of MEGASA group,for the steel slag supply and to Professor Joaquim Faria for his support in understanding the basic notions of chemistry.
文摘In this work,an alternative alkali-activated cement(AAC)made of ladle slag precursor mixed with sodium hydroxide and sodium silicate has been developed to enhance the bearing capacity of estuarine soils in coastal conditions via deep soil mixing(DSM).The AAC was optimized to use a low reactivity precursor(ladle slag)and to deal with a contaminated high-water content natural sediment cured under water.The material performance was analysed by comparison to a mixture made with Portland cement and cured in the same conditions.Flexural and unconfined compressive strength tests as well as seismic waves measurements after 3-,7-,14-and 28-d curing were performed to obtain a relationship between elastic stiffness and strength with curing time for both mixtures.Remarkably,the AAC mix demonstrated superior strength results,exhibiting almost double flexural and compressive strengths after 28 d compared to the Portland cement mix.The AAC mix also showed a higher rate of stiffness increase than the Portland cement mix,which has a higher initial stiffness at young ages but lower stiffness evolution.Leachate analysis confirmed that the proposed AAC could effectively immobilise any contaminants from soil or precursors.The effect of curing under stress was analysed in triaxial compression tests and found to be insignificant,indicating that laboratory data obtained without stress curing can represent the material's behaviour in a DSM column,which will cure under the weight of the column.
