混凝土孔结构与渗透性分析

根据混凝土孔的构造特点及混凝土渗透性的试验,通过对混凝土构成材料对孔结构的影响分析,得出了改善混凝土孔结构的条件和可能,提出了混凝土渗透性对混凝土耐久性的影响.     

Modelling of the Indoor Environment – Particle Dispersion and Deposition

Abstract A three-dimensional drift-flux model for particle movements in turbulent airflows in buildings is presented. The interaction between the carrier air and the particles has been treated as a one-way coupling, assuming the effect of particles on air turbulence is negligible due to low solid loadings and comparatively small particle settling velocities. Turbulence effects are modelled with a standard κ-? model. Wall functions are applied at near-wall grid points. Aerosol measurements carried out under turbulent room flow conditions are used to validate the numerical calculations. Several particle size distributions are considered in the simulations. The model is then applied to mixed flow conditions in a room, as well as to homogeneous air supply conditions around a human body. The flow fields and particle distributions are analysed. Close to a standing person, the particle distribution pattern from a downstream point source is strongly dependent on the ventilation air supply rate. This has been confirmed by experiments reported in the literature.     

Expansion of the US wildland–urban interface

For at least two decades, expansion of low-density residential development at the wildland–urban interface has been widely recognized as a primary factor influencing the management of US national forests. We estimate the location, extent, and trends in expansion of the wildland–urban interface (WUI) in the continental United States. We mapped the WUI by determining the intersection of housing density classes computed from refined US Census data with a map of wildfire hazards based on broad forest types using definitions of WUI from the Federal Register. Our methods allowed us to provide a more spatially precise estimation of the WUI that better reflects development patterns of interest to forest land managers. We defined three wildfire hazard classes based on vegetation type. “High” severity applies to vegetation types in which stand-replacing fires dominate both historical and recent fire regimes, e.g., lodgepole pine forest. “Low” severity applies where fuels and climate foster mostly low-intensity fires, e.g., aspen-birch forest. “High (historically low or variable)” applies to vegetation types in which fires historically were of low or variable intensity, but recently have often burned at high intensity because of a century of fire exclusion, e.g., southwestern ponderosa pine forest. In 2000, the WUI that includes a 3.2 km community protection zone occupied 465,614 km², and contained over 12.5 million housing units. This is an expansion of over 52% from 1970, and by 2030 the WUI is likely to expand to at least 513,670 km² with the greatest expansion occurring in the intermountain west states. Roughly 89% of the WUI is privately owned land and about 65% of the WUI occurs in high or high (historically low or variable) severity fire regime classes.     

Analysis of structural interaction in tunnels using the covergence–confinement approach

The rock-support interaction in tunnels is studied through the use of the convergence–confinement method. The equations that characterize the behaviour of the most important support types are given together with a set of conceptual interaction schemes. As far as the behaviour of the support is concerned, reference is made to the ultimate limit state concept, which is widely used in civil engineering. This approach is linked to the classical convergence–confinement method. The interaction between the temporary support system and the final lining is dealt with, and the noteworthy case of presupport ahead of the face, followed by a further internal support (usually steel sets and shotcrete) is also included. Finally, the ‘ground reaction curve of the reinforced tunnel’, which allows one to analyse the interaction between the reinforcement around the tunnel and supports, is introduced.     

A scenario-based approach to assess Ho Chi Minh City’s urban development strategies against the impact of climate change

This paper presents an approach to quantifying current and future city-wide flood risks to Ho Chi Minh City. Here urban planning scenarios linking urban development and climate change explore the main driving forces of future risk. According to the redefined role of urban environmental planning in times of climate change, spatial planning needs to go beyond traditional planning approaches to bring together, draw upon and integrate individual policies for urban adaptation strategies for land-use planning. Our initial research results highlight that the spatiotemporal processes of urban development, together with climate change, are the central driving forces for climate-related impacts. The influence of planned urban developments to the year 2025 on future flood risk is seen to be significantly greater than that of projected sea-level rise to the year 2100. These results aid local decision making in an effort to better understand the nature of future climate change risks to the city and to identify the main driver of urban exposure.     

An analytical approach to free vibration analysis of multi‐outrigger–belt truss‐reinforced tall buildings

This paper deals with a new and simple mathematical model that may be used to determine natural frequencies and mode shapes of a multistory building that consists of a framed tube, a shear core and multi‐outrigger–belt trusses. The effect of outrigger–belt truss and shear core on a framed tube was modeled as a concentrated moment placed at outrigger–belt truss location, which acted in opposite direction of the rotation created by lateral loads. The analysis is based on a continuum approach, in which a tall building structure may be replaced by an idealized cantilevered beam to model the building's structural characteristics. Energy method and Hamilton's principle have been used to develop the governing equations. After applying separation of variables method to time and space variables, the resulting eigensystem was solved to obtain the building's natural modes and frequencies of vibration. A computer program has been developed in MATLAB (Mathworks Inc., CA, USA) environment, and a numerical example has been solved to demonstrate the accuracy of this method. Results obtained from the proposed mathematical model give a good understanding of a structure's dynamic characteristics. The method is simple to use yet reasonably accurate and hence suitable for quick evaluations during preliminary design stages. Copyright © 2011 John Wiley & Sons, Ltd.     

Olfactometric approach for the evaluation of citizens' exposure to industrial emissions in the city of Terni, Italy

Since several years odour nuisance is a serious environmental concern in the city of Terni, whose citizens are repeatedly lamenting the presence of malodours. This paper describes the olfactometric approach adopted for assessing the odour impact on the city of Terni, caused by the co-presence of three important industrial poles: the steel industry pole, the chemical pole and a third industrial pole, comprising different activities for the treatment of wastewaters and solid waste. The combination of analyses by dynamic olfactometry and dispersion modelling allowed the evaluation of the citizens' exposure to the industrial odours, resulting in both the quantification of emissions and the assessment of their impact on the territory. The overall odour emissions were estimated to be equal to 218,000 ou_E s^− 1: 51% from the steel industry pole, 29% from the chemical pole and 20% from the other plants, respectively. The simulation of the emission dispersion shows that the odour impact relevant to all three studied industrial poles is considerable, actually investing almost the whole city of Terni. The study results also enabled the identification of the most problematic odour sources, which turned out to be the primary emissions from the furnace for the steel industry pole, Treofan and the wastewater treatment plant for the chemical pole and the municipal wastewater treatment plant and the pulper incinerator as far as the other plants are concerned.     

Dynamic characteristics and seismic response of frame–core tube structures,considering soil–structure interactions

In order to study the dynamic characteristics and seismic response of high‐rise buildings with a frame–core tube structure, while considering the effect of soil–structure interactions (SSIs), a series of shaking table tests were conducted on test models with two foundation types: fixed‐base (FB), in which the superstructure was directly affixed to the shaking table, and SSI, consisting of a superstructure, pile foundation, and soil. To increase the applicability of the model to the dynamic characteristics of real‐world tall buildings, the superstructure of test models was built at a scale of 1/50. This simulated a 41‐floor high‐rise building with a frame–core tube structure. The mode shape, natural frequency, damping ratio, acceleration and displacement response, story shear, and dynamic strain were determined in each of the test models under the excitation of simulated minor, moderate, and large earthquakes. The SSI effect on frame–core tubes was analyzed by comparing the results of the two test models. The results show that the dynamic characteristics and seismic response of the two systems were significantly different. Finally, these results were verified by performing a numerical analysis on the differences in the seismic responses of the FB and SSI numerical models under various simulated seismic conditions.     

Socio‐economic impacts of the pharmaceuticals detection and activated carbon treatment technology in water management – an example from the Czech Republic

The fast development of laboratory methods has revealed increased amounts of trace concentrations of pharmaceuticals and personal care products (PPCP) in waste waters in the Czech Republic. This paper focuses on the expected costs to solve this problem by quaternary treatment of waste water based on activated carbon filtration. The one‐time investment costs in 155 wastewater treatment plants (WWTPs) with a capacity of over 10 000 population equivalent (PE) would represent an amount of around 300 million EUR. The increase in end‐user operating costs would be 0.4 EUR/m³, which would mean a 15% increase in water and sewage costs. A sociological survey showed that most respondents (65%) would agree with an increase in price but only by 10%. Currently the cost of the quaternary treatment of wastewater is based primarily on estimates. Therefore changes in legislation leading to stricter limits and an increase in the efficiency of wastewater treatment should be preceded by additional applied research.     

Applicability of Mohr–Coulomb and Hoek–Brown strength criteria to the dynamic strength of brittle rock

A series of dynamic uniaxial and triaxial compression, uniaxial tension and unconfined shear tests were conducted on the Bukit Timah granite of Singapore. The results are analyzed in this paper in order to examine the validity and applicability of the Mohr–Coulomb and the Hoek–Brown criteria to the rock material strength properties subjected to dynamic loads. The study indicates that rock material strength under dynamic loads can be approximately described by the Mohr–Coulomb criterion, at low confining pressure range. The change of strength is primarily due to the variation of cohesion with loading rate. The rock material strength under dynamic loads is better described by the Hoek–Brown criterion. Assessment of the Hoek–Brown criterion shows that the uniaxial compressive strength increases with increasing loading rate, and the parameter m appears unaffected by the loading rate.     

Underground disposal of hazardous waste in Israel – Design principles and conceptual approach

The careless or unprofessional handling of hazardous wastes in many places around the world led to severe damage of nature, concurrent with considerable long-term health risks to human beings. This motivated several countries to develop new secure and sustainable waste management strategies in order to enhance the future quality of nature and life. The process of world globalization and the coalescence of its markets increased the importance of formulation and implementation of accepted environmental standards. The rising environmental and ecological awareness in Israel puts the contemporary and common waste handling practices under close scrutiny. An intensive exchange of experiences with other countries is called for, so that the responsible authorities can formulate improved and sustainable waste management strategies, which are specifically tailored to the particular environmental, demographic, economic and political conditions of Israel.The German environmental protection and waste legislation demands an underground disposal of highly contaminated wastes, in order to guarantee that harmful substances are excluded durably from the biosphere. In view of its size and the political situation in Israel, this way of waste disposal seems to be an appropriate waste management strategy aimed at minimising the environmental risks, and the harmful effect of hostile actions against deposits of hazardous wastes. The German waste management policies and practices, which are based on many years of experience, are reviewed first as a guideline for safe long-term underground disposal of hazardous wastes in Israel. Using these guidelines, potentially suitable locations in Israel are selected with special reference to their geohydrological, geological and geomechanical conditions, and then they were evaluated using environmental criteria derived from German standards of waste disposal. The results of this preliminary environmental evaluation, and some relevant geomechanical designs, are presented and discussed. Finally, economic aspects, and further steps, which are needed to safeguard future implementation of the underground disposal system, are considered.     

A systematic approach towards the structural behaviour of a lightweight deck–side shell system

Lightweight structures are increasingly used for high-speed ships. This paper presents a systematic approach to analyse the structural behaviour of a lightweight deck–side shell system using high strength steel. An analytical model of the deck–side shell system was first given, which includes the effects of stiffeners for the deck and side shell, the support conditions of the centreline girder (CL-girder), the influence of transverse beams, and the interaction between the side shell and the lightweight deck as parts of problems to the solution. By changing several geometric parameters, the sensitivity of both overall and local stress and deflection for the deck–side shell system was investigated. The different geometric parameters analysed comprise the influence for variation in the thickness of the web for transverse beams, longitudinal stiffeners and the CL-girder, the thickness of lower flange for the transverse beam and, the thickness for the panel. Furthermore, the influence of the lightweight deck and loads from the deck above on the side shell, the effects of the side shell and loads from top deck on the deck, the support conditions for the CL-girder, and the influence of deck loads on the eigenmodes were also analysed. By evaluating the results obtained from FE simulation, the support conditions of the CL-girder, the thickness of the panels and the lower flange of the transverse beams were found to be the most relevant parameters affecting both the stress and the deflection distribution of the structure. The dynamic characteristics of the structure were also analysed. The FE analysis concerning buckling of the structure was present. The results enable naval architects and structural engineers to design new extreme lightweight deck structure more reliable and economical. And some suggestions for future research are also given.     

An empirical relationship to determine lateral seismic response of mid‐rise building frames under influence of soil–structure interaction

In this study, to determine the elastic and inelastic structural responses of mid‐rise building frames under the influence of soil–structure interaction, three types of mid‐rise moment‐resisting building frames, including 5‐storey, 10‐storey and 15‐storey buildings are selected. In addition, three soil types with the shear wave velocities less than 600 m/s, representing soil classes C_e, D_e and E_e according to AS 1170.4–2007 (Earthquake action in Australia, Australian Standards), having three bedrock depths of 10 m, 20 m and 30 m are adopted. The structural sections are designed after conducting nonlinear time history analysis, on the basis of both elastic method and inelastic procedure considering elastic‐perfectly plastic behaviour of structural elements. The frame sections are modelled and analysed, employing finite difference method adopting FLAC2D software under two different boundary conditions: (a) fixed base (no soil–structure interaction) and (b) considering soil–structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted, and the results in terms of the maximum lateral displacements and base shears for the above mentioned boundary conditions for both elastic and inelastic behaviours of the structural models are obtained, compared and discussed. With the results, a comprehensive empirical relationship is proposed to determine the lateral displacements of the mid‐rise moment‐resisting building frames under earthquake and the influence of soil–structure interaction. Copyright © 2012 John Wiley & Sons, Ltd.     

Parametric study of the use and optimization of tuned mass dampers to control the wind‐ and seismic‐induced responses of a slender monument

Passive energy dissipation devices have been used around the world to mitigate the response of structures under dynamic excitations, such as wind or seismic loading. The use of tuned mass dampers (TMD) in tall and slender buildings to reduce unwanted responses has proved to be very effective. The main purpose of this work is to study the structural behavior of a 115‐m‐height slender monument fitted with TMDs subjected to simulated wind and seismic loading. Turbulent wind forces were calculated based on samples of turbulent wind speed simulated with an auto regressive and moving average (ARMA) model. Ground motions compatible with a seismic site spectrum were also simulated. An optimization approach is suggested to determine the parameters of the TMDs that reduce the structural response to the maximum. The effectiveness of the TMDs for reducing the structural response of the monument is discussed in detail, and the use of optimally tuned TMDs is emphasized.     

A decay function model for the integrity loss of rock when subjected to recurrent cycles of freezing–thawing and heating–cooling

Rocks are used in engineering works as monument or building stone and as architectural covering stone. As a result, they can be subjected to recurrent cycles of freezing and thawing and will be subjected to heating and cooling. They loose some of their integrity under these cyclic temperature variations and the more frequent and severe these cycles, the higher the integrity loss. However, the rates of progressive disintegration is not the same for different rock types, or even within rock types. This paper presents a mathematical model describing the integrity loss process when a rock is subjected to such recurrent cycles. The model postulates a first order process, and provides meaningful parameters for the integrity characteristic of rocks. The validity of the model has been established by an experimental laboratory study carried out on 10 different rock types.     

Static and dynamic stability assessment of slopes or dam foundations using a rigid body–spring element method

A rigid body–spring element method is used to evaluate the static and dynamic stability of slopes or dam foundations. The versatility of the method applies well to both static and dynamic problems for blocks of arbitrary polyhedral shape with various re-entrant surface features. Examples show that the safety factor obtained in this way agrees well with theoretical solutions. The dynamic safety factor determined with this method varies with time, which differentiate it from the results of the limit equilibrium method or the finite element method. The method also makes it possible to search for the most probable sliding mass.     

Overload failure of structural components under random crack propagation and loading – a random process approach

In this paper, the problem of overload failure of a structural component under random loading and under random crack propagation is addressed. The problem is formulated by combining the first passage failure model with stochastic models of crack propagation. Disadvantages of the standard random variable approach to the problem are discussed, and an alternative random process approach is developed. The developed solution addresses both overload and critical crack growth failure modes, requires a single mean crack growth computation, allows the consideration of non-destructive inspections and significantly speeds life-time analysis. The random process approach leads to a first passage problem involving crossings of a random barrier level, which is solved by means of the ensemble up-crossing rate approximation. Limitations of this approximation are addressed and related to typical problem parameters. The concept of barrier failure dominance is discussed, and extended to the case of a barrier-defined failure. Sensitivity studies involving different problem variables are performed, helping to identify the appropriate solution method for specific problems.     

Evaluating environmental impact of STPs situated on streams in the Czech Republic: an integrated approach to biomonitoring the aquatic environment

Sewage water treatment plants (STPs) are frequently associated with the release of xenobiotics and, consequently, with biological responses of fish to these substances. The impact of three STPs situated on small streams was assessed in 2009. Brown trout (Salmo trutta fario L.), captured upstream and downstream of these STPs, were used as biomonitors. The concentrations of 39 organic pollutants (PCBs, OCPs, PBDEs, HBCDs, and MCs), and the biological responses related to oxidative stress (lipid peroxidation and carbonyl protein), and antioxidant responses (superoxide dismutase, glutathione peroxidase and glutathione reductase) were measured. Through chemometrics of these parameters, three groups with 97.62% of the total accumulated variance were distinguished. Integration of the assessed biomarkers using the IBR index, ranked environment impact on sites as: DS Pacov > DS Prachatice > DS Brloh > US Pacov > US Prachatice > US Brloh (most to least affected). STPs are a major source of xenobiotic pollution in streams of the Czech Republic. The combined use of chemical analysis and biological responses is necessary to validate the efficacy of a battery of biomarkers chosen to detect environmental stress due to pollution.     

高层住宅对城市空间形态影响的分析及规划设计对策

本文从城市空间的视角出发,分析高层住宅对城市整体和片区尺度上空间形态的影响,总结高层住宅建设中存在的主要问题,提出城市规划及城市设计应从宏观、中观到微观各个层面对高层住宅空间形态进行控制和引导,且相互统筹协调,并结合实例探讨了规划设计的具体对策与方法。     

An adaptive numerical scheme based on the Craig–Bampton method for the dynamic analysis of tall buildings

A new numerical scheme is proposed to perform a nonlinear dynamic analysis for tall buildings. The structural components (beams and columns) of tall buildings gradually enter the inelastic phase under strong seismic excitation. Because the distribution of nonlinear components is initially unknown due to the randomness of earthquake inputs, a group of linear and nonlinear substructures are automatically figured out during the time‐history analysis of a structure. Then a modified Craig–Bampton method is proposed to condense the DOFs of the linear substructures in modal coordinates at each time step while keeping the governing equation of the nonlinear substructure in physical coordinates. The dominant modes of the linear substructures are selected to capture the main dynamic characteristics of the structure. The time step integration analysis is used to solve the governing equation of the structures in hybrid coordinates. A 20‐story building is employed as the numerical simulation test to validate the feasibility and effectiveness of the proposed numerical scheme. This scheme provides a new method for the nonlinear dynamic analysis of tall buildings with acceptable simulation accuracy and high computational efficiency.