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At present, there is a lack of research on the influence of different dynamic constitutive models of steel and concrete on the dynamic mechanical properties of concrete-filled steel tubular (CFST) columns under lateral impact. In this paper, A comprehensive numerical study on the effects of different dynamic constitutive models of steel and concrete on the lateral impact response of CFST columns was conducted. The dynamic constitutive models of steel and concrete with different strengths were divided into four categories, namely, normal-strength steel, high-strength steel, normal-strength concrete and high-strength concrete. The established finite element model of CFST columns considering the progressive damage degradation of steel as well as the compressive and tensile damage factors of concrete was verified against published experimental data. Based on the verified FE model, the effects of different dynamic constitutive models of steel and concrete on the impact response of circular CFST columns were analyzed. The analyzed results show that the different dynamic constitutive models of steel have different effects on the impact force and mid-span time-history deflection curves of CFST columns. The analysis result, ignoring the effect of concrete strain rate, is in good agreement with the CEB-FIP model considering the effect of steel strain rate. This is because the largest proportion of the impact energy of CFST members is mainly assimilated by the outer steel tube.

This paper investigates the structural performance of concrete-filled stainless steel tubular (CFSST) columns composed of rectangular and square sections. A fiber-based mathematical model is developed to simulate the nonlinear performance of such columns loaded concentrically accounting for the local buckling of steel tube. An accurate lateral pressure model, as well as a strength degradation parameter are proposed based on the existing test results and incorporated in the mathematical modeling developed. A large test dataset is used to validate the accuracy of the numerical prediction. The mathematical model is employed to study the sensitivities of important column parameters on their axial behavior. The accuracy of the existing confinement model of rectangular CFST columns is evaluated in predicting the performance of CFSST short columns. Furthermore, the accuracy of the existing codified design models as well as and the simplified design model proposed in this study to quantify the ultimate compressive strength of such columns is investigated. An accurate artificial neural network (ANN) model along with the GUI feature is developed for the design engineers as a tool to predict their ultimate axial strengths.

Elliptical concrete-filled stainless steel tubular (CFSST) columns are high-performance composite columns that have the enormous potentiality to be used in composite construction in the near future. However, to date, limited studies on the performance analysis of such columns under axial compression have been performed taking into account the accurate material laws of stainless steel and the confined concrete. This paper presents a mathematical model to investigate the axial performance of elliptical CFSST short columns. Accurate material laws of stainless steel and the confined concrete are incorporated in the numerical modeling to capture their true performance. Independent test results are utilized to validate the accuracy of the mathematical predictions. A parameter study is performed to study the important column parameters on their axial performance. The investigations of the accuracy of the existing design models for CFST columns in designing axially loaded elliptical CFSST columns are performed with the test and numerical predictions.

The accurate prediction of the concrete confinement effects in concrete-filled double-skin steel tubular (CFDST) columns composed of a circular section is vital in stimulating their true structural performance. However, existing concrete confinement models for such columns were developed based on limited studies and may not accurately predict their axial responses under axial loading. In this paper, a numerical model is developed to study the nonlinear performance of axially-loaded short CFDST columns incorporating an accurate concrete confinement model. Herein, a novel expression to calculate the lateral confining pressure on the confined concrete of the CFDST column is proposed considering the influences of a wide range of important column parameters. Furthermore, a reduction factor to accurately predict the post-peak behavior of confined concrete is suggested based on the previous test results. The accuracy of the numerical model incorporating the proposed concrete confinement model is verified against the experimental tests. The accuracy of the existing concrete confinement models is also evaluated and compared with the one proposed in this study. It is demonstrated that the proposed confinement model can yield the axial performance of CFDST columns more accurately. A parameter study is then performed to analyze the impacts of important column parameters on the axial performance of such a column. The applicability of the existing design standards in designing CFDST columns is verified. Lastly, a simple and accurate design equation to quantify the ultimate axial load is proposed.

The existing theoretical models for the analysis of concrete-filled steel tube (CFST) columns are mainly limited to circular specimens. This paper is aimed at developing a unified theoretic...

The column buckling performance of steel circular columns fabricated by submerged arc welding, high-frequency welding and hot-rolled forming was investigated. Nine axially compressed columnar speci...

A finite-element method (FEM) model was used to numerically investigate the overall buckling behaviours of hot-rolled (HR), submerged arc welded (SAW) and high-frequency welded (HFW) steel circular columns under axial compression. A three-dimensional FEM model of circular hollow sections was developed by using shell elements considering material non-linearities, geometric imperfections and residual stress. The FEM model was used to simulate experimental studies carried out by past researchers. Good agreement was found between the numerical and experimental results, which validate the FEM model for further research. The validated FEM model was used to analyse 180 numerically generated HR, SAW and HFW steel circular columns with various section sizes and slenderness values. The numerical results were then compared with existing column design curves in Chinese, European and American codes. To further improve the design efficiency, new column design curves for steel circular columns are recommended ba...

Concrete-filled stainless steel tubes (CFSSTs) are increasingly applied in current composite structures owing to their excellent performance characterized by aesthetic appearance, high corrosion resistance and durability, and ease of maintenance. Compared with austenitic and duplex stainless steels, ferritic stainless steels have not or contain very low nickel content, achieving lower and more stable material costs. This provides a more viable alternative for structural applications. Additionally, it has been used successfully in corrosive marine environment in a few countries, such as South Africa. However, structural applications of concrete-filled ferritic stainless steel tubular (CFFSST) columns are still limited owing to the dearth of performance data and design guidance. To understand their structural behaviour and to include relevant design recommendations in current design specifications, this paper aims at investigating the compressive behaviour of axially loaded rectangular CFFSST short columns using the nonlinear finite element (FE) modelling. The FE models are developed using ABAQUS software, where two different material constitutive models for the flat and corner portions of the rectangular ferritic stainless steel tubes are incorporated. Close agreement is found between the outputs of FE analysis and existing test results with respect to the failure modes, cross-sectional strengths and axial load-shortening curves. Parametric analysis is then conducted to ascertain the impacts of key variables on the compressive behaviour of the studied CFFSST columns. The obtained numerical results as well as available test results are employed to evaluate the feasibility of current design specifications to design the examined CFFSST columns. Finally, a novel strength design model is proposed and shown to achieve a higher degree of accuracy and consistency of the design predictions.

Concrete-filled double-skin steel tubular (CFDST) columns possess lower self-weight, higher ductility and energy absorption than conventional concrete-filled steel tubular (CFST) ones. The use of high-strength concrete (HSC) can further enhance their advantages, such as greater mechanical and economical benefits. However, there is little information on the structural performance of CFDST columns with HSC, especially ones with ultrahigh-strength concrete (UHSC). In this paper, a comprehensive experimental program consisted of 24 specimens was carried out to investigate the compressive behaviour of circular CFDST short columns with HSC and UHSC. The test results show that CFDST columns with higher strength concrete generally achieve higher initial stiffness and axial strengths but lower ductility. Additionally, the axial strengths of CFDST columns are improved as the yield stress and wall thickness of the outer steel tubes increase and as the hollow ratio decreases. A finite element (FE) model was established and verified against the present test results, based on which the interaction of the steel tubes and concrete and the load distribution on components were analysed. A parametric study using the verified FE model was conducted to further ascertain the influences of column variables on the compressive behaviour of the studied CFDST columns. Finally, the applicability of the existing design codes and empirical models to design the CFDST columns was evaluated based on the test results in the present and previous studies. It is shown that European code EN 1994 − 1 − 1 (EC4) achieves better strength predictions than other design models.

This paper presents a numerical finite element model (FEM) investigation on the overall buckling behaviour of hot-rolled (HR), submerged arc welded (SAW) and high-frequency welded (HFW) steel circular columns under axial compression. Three dimensional FEM of circular hollow sections were developed using shell elements considering material nonlinearities, geometric imperfections and residual stress. The established FEM was used to simulate experimental studies conducted by past researchers. Good agreement has been found between numerical analysis and past researchers results, which has validated the reasonability of the FEM to carry out further investigation. Based on the validated FEM, numerical analysis incorporating 180 numerical generated HR, SAW and HFW steel circular columns with various section sizes and slenderness were carried out. The numerical analysis results were compared with the existing column design curves in Chinese, European and American codes. The numerical results showed that the design resistances for hot-rolled and welded steel circular columns calculated based on design curve a in both GB 50017-2003 and Eurocode 3 and the design formula in ANSI/AISC 360-2016 should be accepted. In addition, to further improve the design efficiency, new column design curves for hot-rolled and welded steel circular columns were recommended based on the expressions in GB 50017-2003 and Eurocode 3.

This paper aims to experimentally and numerically investigate the compressive behavior of circular concrete-filled double-skin steel tubular (CFDST) short columns, in which only the sandwiched concrete is under axial compression. In total, 28 CFDST columns were loaded axially, and their axial load-shortening curves, ultimate strength and failure modes were briefly discussed. Results suggest that the wall thickness and yield stress of outer steel tube have a significant effect on the failure modes, while the concrete strength shows an insignificant effect. The tested columns exhibited good ductility concerned by seismic resistant design. The ultimate strength of the columns using STK490 outer steel tubes was about 20–26% than that of ones with STK400 outer steel tubes. With an increase in the concrete strength and wall thickness of outer steel tube, the ultimate strength of the columns was improved by 32% and 43%, respectively. Moreover, finite element (FE) models were established and verified by comparing with the test results, and then an extensive parametric analysis was carried out to ascertain the effects of key variables on the compressive behaviour of the studied CFDST short columns. Finally, based on the numerical and test results, a novel formula was proposed to estimate the ultimate strength of CFDST columns, and high prediction performance was found in the proposed formula. The proposed formula is not only applicable for the strength prediction of CFDST columns, but also for that of steel tube confined concrete (STCC) columns.

The confinement effect of external and internal steel tubes on sandwiched concrete in concrete-filled double-skin circular steel tubular (CFDST) short columns has a significant impact on the compressive strength and ductility of columns. Limited researches on CFDST columns have only considered the influences of a part of column parameters on the confinement effect, leading to the absence of appropriate compressive strength formulas in international standards. To comprehend the compressive behavior of circular CFDST short columns and suitably evaluate their compressive strength for practical engineering design, it is necessary to further launch the experiments on circular CFDST short columns and develop a suitable estimated formula for their compressive strength. The purpose of this paper is to develop a simple and accurate formula for predicting the compressive strength of axially loaded CFDST short circular columns with a wide range of parameters. A total of 24 specimens with outer and inner circular carbon steel tubes that withstand axial compression were tested. A new confinement coefficient reflecting the confinement effect of concrete strength in CFDST columns was proposed on the basis of the test data in the present paper and data collected from literature. Utilizing the proposed confinement coefficient, a novel strength design formula was developed to estimate the compressive strength of CFDST short circular columns. It shows that the proposed confinement coefficient can reasonably reflect the interaction effect between the sandwiched concrete and steel tubes, and the formula suggested in this paper offers better predictions of the compressive strength than current design formulas.

Information extraction of object oriented method was applied to study the land use change, this paper puts forward a kind of application of object oriented remote sensing image classification to extract land change information extraction methods to change the land use, introduces the calculation of object oriented classification, classification of ideas and technology process, automatic extraction of water information in the process of classification to discuss the specific computer.

The performance of acid rain at Nanchang, China was studied in this paper. According to the monitoring data of rain from 2003 to 2012, the time characteristics and causes of the acid rain were analyzed, and the changing trends of the concentration in10 years were described by using Correlation analysis. The result shows that Nanchang air pollutants have the characteristics of obvious inter-annual variability, Rose and diurnal variation.

An analysis of the change regularity of the air pollutant in Nanchang city in this paper. According to the monitoring data of SO2, NO2 and PM10 from 1996 to 2012,the time characteristics and causes of SO2, NO2 and PM10 pollution were analyzed ,and the changing trends of the concentration of SO2, NO2 and PM10 in17 years were described by using Correlation analysis. The result shows that Nanchang air pollutants have the characteristics of obvious inter-annual variability, Rose and diurnal variation.

The performance of atmospheric visibility at Nanchang, China was studied in this paper. The relationship between atmospheric visibility and the meteorological elements was analyzed using statistical method based on those data of Nanchang atmospheric visibility and the observed record of ground meteorological elements from 1990 to 2012. The relationship between the major air pollutants and the atmospheric visibility also was researched according to the air pollutant monitoring data from 2006 to 2012. The result shows that Nanchang atmospheric visibility has the characteristics of obvious inter-annual variability, Rose and diurnal variation; the visibility was significantly negatively correlated to relative humidity; there was weakly negative correlation between the air pollutants SO2, NOx concentration and the visibility.

Circular hollow centrifugal concrete-filled steel tubes (HCCFSTs) are employed widely as structural components, such as power station structures and building foundations, in virtue of their exceedingly good structural performance features. It is essential to comprehend the compressive behavior of circular HCCFST columns and suitably evaluate their compressive strength for practical engineering design. However, limited researches on HCCFST columns have almost not resulted in the development of appropriate design formulae in current international standards. This paper aims to propose a practical formula for estimating the compressive strength of circular HCCFST stub columns that have a wide range of parameters. A new confinement coefficient reflecting the confinement effect of concrete strength in circular HCCFST short columns is proposed, and using the proposed confinement coefficient, a novel strength design formula is developed to estimate the compressive strength of circular HCCFST short columns. The proposed formula is investigated using collected experimental data from literature and finite element analysis results. It is shown that the proposed confinement coefficient can reflect the interaction effect between the steel tube and infilled concrete, and the developed axial capacity formula in this paper offers better predictions of compressive strength than current design formulae.

To investigate and model the residual stress in 345 and 420 MPa normal strength steel (NSS) as well as 690 MPa high-strength steel (HSS) circular tube sections, an experimental study with a total of 45 specimens was conducted using the hole-drilling and sectioning methods. The parameters altered during the experiment included the processing techniques, diameter-to-thickness ratios, steel strengths and welding locations. More than 3064 original test data samples were used to quantify the distribution characteristics of the residual stresses. The results suggest that the magnitudes and distributions of the residual stresses in the welded circular tubes were significantly affected by the processing techniques, steel strengths and welding locations, while no obvious correlation was identified with the diameter-to-thickness ratios. The maximum compressive residual stress ratio gradually decreased with an increase in the steel strength. However, the variation in the tensile residual stress near the weld seam in the middle section was not affected by the variation in the parameters, and its maximum value was in the range of 0.1 π on both sides of the weld seam. Unlike those of the welded approach, the residual stresses along the circumferential direction of the inner or outer surfaces of the hot-rolled seamless circular steel tube sections were almost identical, which is basically consistent with the ECCS’s theoretical model. On the basis of the test results, a distribution model and its simplified forms for NSS were established, and Yang’s distribution model was further validated. The two distribution models can effectively describe the experimental results.

Nonylphenol (NP) is one of the persistent organic pollutants, its key properties are bioaccumulative, poor degradability and three induced impacts including carcinogenic, teratogenic and mutagenic, which have caused high attention by the international academic community. Many deep studies around its biological effect, mechanism of action, environment distribution, organism distribution and metabolism process have been developed and reported. Meanwhile, the studies about its spatial distribution and the enrichment regularity also have been carried out in some typical cities in the shore zone and estuaries. This paper is to summarize the status of nonylphenol pollution in the lotic ecosys-tem refer to those research results before.

As an important influencing factor of global environmental change, land use change has always been the hot issues of geography study. Taking Poyang Lake region as an example the relationship between land use and ecological protection was expounded. Analyzed the comprehensive summarize to the Land use change, retrospected the development history of the Land use change, and also analyzed and depicted the current research field. The exploitation and conservation of the Poyang Lake international importance wetland are of importance for the ecologic environment in Jiangxi province.This paper is to summarize the status of land use change in the Poyang lake region refer to those research results before,finally some effective solutions were proposed.

This paper summarizes the researches of recent years on land use/cover change (LUCC) and carbon cycle in typical wetland ecosystem of Poyang lake. Besides, the developments of carbon cycle in three aspects (carbon fixation, carbon storage and carbon emission) and the characters of LUCC in wetland ecosystem were analyzed. Based on the analysis, this paper discusses the problems that must be resolved to improve the veracity of the forecast results, and points out the direction to the research in the future.

In this paper, we studied the land use/cover change (LUCC) and their driving forces from 1997 to 2005 in Nanchang. The characteristics of land use change in the districts were systematically analyzed in terms of land use quantity, structure and degree. Results showed: 1) The area of cultivated land and grassland were decreasing, the transportation land, and residential and isolated industry land were increasing in recent years; 2) The LUCC in Nanchang was driven by the ratio of rural population to total population, number of village labors, local finance, resident's savings and GDP per capita. LUCC can reflect the socioeconomic developing course. The driving forces of land use changes should be paid more attention in order to draw relevant land use/cover policies.