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Researchers keep trying to find a way to reduce the requirement knowledge of Multivariate Process for performance assessments. Till now, the knowledge of interactor matrix or first several Markov parameter matrices are at least required to obtain the minimum variance benchmark in the performance assessment of Multivariate Process. In this paper, a novel minimum variance performance assessment technique is proposed for multivariate processes. Under the condition that the time delay indicator matrix can be written as row echelon form by row or/and column shift operations, the delay order is determined and the minimum variance (MV) benchmark can be straightforward obtained when the knowledge of time delay matrix is available. Comparing with the traditional approaches, the first several Markov parameter matrices and the knowledge of the plant are both not necessary required based on the proposed technique. It has been proved that the proposed technique can directly solve the problem of the performance assessment of Multivariate Process. The validity of the proposed algorithm will be verified through numerical examples, which include the practical industrial model - ‘Shell’ oil fractionator process.

Rational design of electrocatalysts with unique morphological structures and chemical compositions is crucial for electrochemical performance and energy storage capacity. In this work, an Fe-doped NiCoP hybrid hollow nanocage (denoted as Fe-NiCoP) was synthesized through the phosphorization of the product from [Fe(CN)6]3−-intercalated NiCo-LDH (layered double hydroxide), where the original ZIF-67-Co was used as the template. Because of the hollow nanostructure and the synergistic effect between multiple components, the Fe-NiCoP catalyst exhibited promising hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities in 1.0 M KOH with low overpotentials of 147 and 235 mV at 10 mA cm−2, respectively. Furthermore, the Fe-NiCoP catalyst only achieved a current density of 10 mA cm−2 at the voltage of 1.60 V. Inspired by the excellent OER performance of the Fe-NiCoP catalyst, a Zn–air battery was built to explore the Fe-NiCoP catalyst for practical application. After 900 successive cycles, the Fe-NiCoP + Pt/C catalysts exhibited excellent cycling stability at 5 mA cm−2, which was a much stronger performance than that of the RuO2 + Pt/C catalysts. This work provides a practical strategy for the synthesis of high-performance and low-cost electrocatalysts.

Ammonia-water hybrid absorption-compression heat pump (HACHP) based on Osenbruck cycle is a promising high-temperature heating technology. However, in the case of large temperature rise, the HACHP is faced with the problem that the compressor discharge temperature is too high, which greatly limits its application. In order to solve this problem, this paper introduces three two-stage HACHP cycles and thermodynamic analysis is conducted respectively. Results show that under the constraints of high pressure of 5000 kPa, compressor discharge temperature of 180 °C and vapor water mass fraction of 5%, the single-stage HACHP cycle cannot meet the heating requirement with the temperature lift of 40K, while three two-stage HACHP cycles can easily meet the needs of heating with the temperature lift of 40 K. When HACHP with flash tank intercooler is especially used, the heating with the temperature lift of 50 K can be achieved. Furthermore, this paper gives some typical combinations of ammonia mass fraction and circulation ratio for realizing high-temperature heating.

An accurate structural assessment of rails under combined effect of fatigue and corrosion prevents a phenomenal disaster, also saves millions of dollars and people’s lives. Recent studies which are...

The time to cover cracking is widely used as a service life indicator in the assessment of deterioration of corrosion-affected reinforced concrete structures. This paper presents a general probabilistic procedure for prediction of time to cover cracking. Within this procedure, the response surface method (RSM) is employed to calibrate a new model for calculating of radial displacement required for cover cracking based on the results obtained from the finite element (FE) analysis. By taking advantage of the central limit theorem (CLT), simple but accurate probabilistic models for prediction of time to cover cracking that only rely on the knowledge of first and second moments of basic random variables are derived. Rigorous simulation analysis has proved the accuracy of these models. It is shown in the paper that using this probabilistic procedure, factors affecting randomness of time to cover cracking can be easily identified. It is also shown that the time to cover cracking is highly variable with the concrete cover, tensile strength of concrete, corrosion current density, and the model error as the most influential factors on its randomness.

A rare opportunity has been seized to study the corrosion effect on fatigue strength of steel after service for 128 years. This paper presents a comprehensive experiment on degradation of fatigue strength of steel under simultaneous natural corrosion and service loading. Fatigue tests, tensile tests and microstructural analysis are carried out, and the mechanism of degradation of fatigue strength of corroded steel is examined fundamentally. Relationship between fatigue strength, corrosion and tensile strength are developed. It is found in this study that corrosion can reduce the fatigue strength by altering the microstructure of corroded steel. It is also found that the effect of corrosion on degradation of fatigue strength can be overestimated with accelerated corrosion, and more importantly, it can be underestimated without considering the simultaneous cyclic load effect during the corrosion. The significance of this study is that it not only quantifies the effect of corrosion on degradation of fatigue strength but also provides a more accurate understanding of cause-effect relationships among corrosion, fatigue strength and microstructural characteristics of steel in the most common environment (atmospheric) and loading applications (traffic loads), thereby contributing to the body of knowledge of corrosion science of steel.

Corrosion of steel is now a worldwide issue, threatening the safety of steel structures. Literature suggests that little research has been conducted on the prediction of fatigue failures of connect...

This paper presents analytical models for evaluating effective hydraulic conductivity, diffusivity and sorptivity of concrete considering the properties of the Interfacial Transition Zone (ITZ) and the aggregate size distribution. Results of the proposed models compare well with the experimental results and those obtained from rigorous numerical Finite Element (FE) analysis. It is also found that a change of Interfacial Transition Zone (ITZ) properties has more influence on the effective hydraulic conductivity than it has on the effective hydraulic sorptivity. The significance of the proposed models is that they can estimate the hydraulic sorptivity and diffusivity of concrete by only knowing the hydraulic properties of mortar, effectively extricating the need for sophisticated and time-consuming FE analysis required for estimation of the effective hydraulic conductivity of concrete at the meso-scale. Furthermore, these models offer scientific insight into the effect of different components of concrete on its effective hydraulic properties.

This paper presents a theoretical framework for developing a risk–cost optimised maintenance strategy for structures during their whole service life. A time-dependent reliability method is employed to determine the probability of structural failure and a generic form of stochastic model is developed for structural responses. To facilitate practical application of the proposed framework, a general algorithm is developed and programmed in a user-friendly manner. The merit of the proposed framework is that, in predicting when, where and what maintenance is required for the structure, all structural components and multi-failure modes are considered. It is found in the paper that, to ensure the safe and serviceable operation of the structure as a whole, some components need maintenance multiple times for different failure modes, whilst other components need “do nothing”. It is also found that ignorance of correlation amongst structural components and failure modes would underestimate the risk of structural failures in longer term and that the components with higher cost of structural failures require more maintenance actions. The paper concludes that the proposed framework can equip structural engineers, operators and asset managers with a tool for developing a risk–cost optimal maintenance strategy for structures under their management.

Practical experience and observation suggest that corrosion-affected reinforced concrete structures are highly susceptible to cracking. This paper presents an analytical time to corrosion-induced concrete cracking model based on fracture mechanics. The concrete cover load-bearing capacity is proposed and is used as a fracture criterion for concrete cracking. An accelerated corrosion test has been undertaken to produce data on time to corrosion-induced concrete cracking and crack width over time. A comparison between the analytical model and experimental results on time to concrete cracking and on crack width over time shows reasonable agreement. It is found that the distribution and size of the porous zone are non-uniform which is one of the main causes for discrepancy between results. The larger the porous zone is the longer it takes for concrete cover to crack due to corrosion. Although the experimental and model results exhibit similar trend, it is also found that assuming only a single propagating crack in analytical model results in an overestimation of corrosion-induced crack width. The models presented in this paper can serve as useful tool for serviceability and durability assessment of corrosion-affected reinforced concrete structures.

Corrosion of ferrous metals and its effects on degradation of mechanical properties and the remaining service life of metal structures have been a serious challenge to research community globally. ...

The intention of this paper is to investigate the degradation of mechanical properties of corroded water pipes after long service. The mechanical tests are conducted to quantify the degrada...

Accurate knowledge of the optical turbulence ( C n 2 ) in the atmospheric surface layer is of great significance for the applications of various ground-based optical systems (e.g., astronomical observation, laser communication and target detection), however, many methods using instruments to measure C n 2 are limited spatially and temporally and they are more difficult and expensive in severe environments, which makes estimations a less expensive and convenient alternative. This study introduces a method where the products of Weather Research and Forecasting (WRF) model coupled with Monin–Obukhov similarity (MOS) theory is used to estimate the value of C n 2 in the surface layer, and the performance of this method is evaluated against the corresponding C n 2 dataset from the in-situ micro-thermometer during a campaign over south-west China. The variance between the estimated C n 2 and measured C n 2 is found to be comparable to the observed variance of the temporal due to temporal and spatial variations of the atmospheric turbulence. Evaluation against direct observations shows that this approach can well estimate C n 2 time series with some error in some time periods, and both the estimated C n 2 and the measured C n 2 are more consistent in trend and magnitude in general. Given these validated results, this method has the potential to be a useful tool in a wide range of ground-based optical applications.

Steel structures are usually subjected to simultaneous corrosion and service loads which are cyclic in nature. This paper proposes a new methodology for prediction of fatigue failure of steel structures subjected to simultaneous corrosion and fatigue stresses. A model is developed to determine the effect of corrosion on S-N curve of steel subjected to corrosion and fatigue and verified with experimental results. The fatigue damage to steel is modelled as a stochastic process allowing for corrosion effects on both stress range and S-N curve. The first-passage probability method is employed to determine the time-dependent probability of fatigue failure of the steel structure subjected to corrosion and fatigue stresses. A worked example is provided to demonstrate the application of the proposed methodology. It is found in the paper that neglecting corrosion effect on S-N curve can lead to 90.43% reduction of the probability of fatigue failure of steel structures subjected to corrosion and fatigue stresses in 120 years, which can be catastrophic. The methodology proposed in this paper can help structural engineers and asset managers to predict the fatigue failure of steel structures when they are subjected to simultaneous corrosion and fatigue stresses.

State of charge (SOC) estimation has always been a hot topic in the field of both power battery and new energy vehicle (electric vehicle (EV), plug-in electric vehicle (PHEV) and so on). In this work, aiming at the contradiction problem between the exact requirements of EKF (extended Kalman filter) algorithm for the battery model and the dynamic requirements of battery mode in life cycle or a charge and discharge period, a completely data-driven SOC estimation algorithm based on EKF algorithm is proposed. The innovation of this algorithm lies in that the EKF algorithm is used to get the SOC accurate estimate of the power battery online with using the observable voltage and current data information of the power battery and without knowing the internal parameter variation of the power battery. Through the combination of data-based and model-based SOC estimation method, the new method can avoid high accumulated error of traditional data-driven SOC algorithms and high dependence on battery model of most of the existing model-based SOC estimation methods, and is more suitable for the life cycle SOC estimation of the power battery operating in a complex and ever-changing environment (such as in an EV or PHEV). A series of simulation experiments illustrate better robustness and practicability of the proposed algorithm.

Porous band at the steel-concrete interface in reinforced concrete can significantly affect the corrosion-induced cracking process of concrete. The quantification of this porous band is of great significance for accurate prediction of service life of corrosion affected concrete structures. In this paper, the effects of concrete design parameters, namely water to cement ratio, aggregate size and concrete cover, on the thickness of porous band at the steel-concrete interface are quantitatively investigated using the technique of Backscattered electron imaging. The results show that the porous band is not uniformly distributed around the steel bar at the steel-concrete interface with the thickness ranging from few microns to a hundred microns. The results also show that the water to cement ratio and concrete cover affect the thickness of porous band proportionally. The significance of these findings is that they can provide guidance on the design of reinforced concrete with a view to alleviating porous band at the steel-concrete interface.

This paper presents a methodology for determining the probability of system failure of corrosion affected steel pipelines with multiple failure modes. The failure modes include fracture, strength failure, deflection and buckling and they are all modelled as stochastic processes with correlations among them. The first passage probability theory is employed to quantify the probability of pipe failure. A case study is presented to illustrate the proposed methodology, followed by a sensitivity analysis to investigate the effects of key random variables on the probability of pipe failure. It is found that correlation of the load effect process at different points in time and the correlation among different failure modes have a considerable effect on the probability of failure for each failure mode and probability of system failure respectively. It is also found that the corrosion model and pipe thickness are most influential with positive and negative indices respectively on the probability of pipe failure for all failure modes. The methodology presented in this paper can help pipe engineers and asset managers develop a risk-informed maintenance strategy for corrosion-affected steel pipelines.

This paper presents the discovery of the most severe form of corrosion induced degradation of steel – delamination. The causes and effects of preferred corrosion of steel are quantitatively determined through a comprehensive experimental program and detailed analysis of steel microstructure. A large number of simulated corrosion tests are conducted by immersing steel in acidic solutions to acquire new understanding of the corrosion process of continuously cast steel. Three microstructural characteristics that affect the corrosion resistance of steel are quantified: grain size, phase composition and distribution of impurities. The results and their analyses presented in the paper indicate that preferred corrosion occurs at locations of steel where the grain size is larger; there is less cementite and more impurities. The analysis of causes and effects of the preferred corrosion provides insight into the prevention of preferred corrosion from the steel making process through to the delamination of steel in structures. This information could be used to predict, mitigate or avoid catastrophic failures of structures made of steel, potentially saving lives and resources, whilst advancing the knowledge in corrosion science of steel and improving the manufacturing process of steel.

The existing high-density distributed distribution network single-phase earth fault interval location method has the disadvantage of long positioning time. Hence, a single-phase earth fault interval positioning method for high-density distributed distribution network is proposed to solve this problem. In order to accurately locate the single-phase earth fault interval of distribution network, zero-order equivalent model of distribution network is built at first. Next the clustering algorithm is used to extract the single-phase earth fault characteristics, while the single-phase earth fault phase current increment is calculated by using the analysis method to obtain the single-phase earth fault phase current increment law. Then a fault-maximum interval T-shaped structure is built to divide the potential fault interval. Finally, the S-transformation is applied to accurately locate the single-phase earth fault interval, and the localization of the single-phase earth fault interval of the high-density distributed distribution network is achieved. The experimental results show that comparing with the existing high-density distributed distribution network single-phase earth fault interval positioning method, the proposed high-density distributed distribution network single-phase earth fault interval positioning method dramatically reduces the positioning time. It is fully explained that the proposed method in this article has a better positioning effect.

In this paper, a new analytical formula is proposed to determine the mean outcrossing rate of nonstationary non-Gaussian performance functions. The performance function is firstly transform...

Unloading compliance (UC) method and normalization method (NM) are two of the most commonly used methods for determining the fracture toughness of materials. However, considerable differences often exist in the fracture toughness determined by these two methods, which solicits a new method to determine the fracture toughness accurately. In this paper, the compliance of crack length differences as measured by the crack length difference ratio Si is discovered, analysed and verified by experiments. Based on this compliance, a new accurate method, known as AJR, is developed and verified by test results. Factors that exhibit the advantages of the developed new AJR method are also investigated. It is found that the J-R curves determined by the new AJR method are more accurate than those determined by UC and NM. The new AJR method should be the first choice for steels with a small strain hardening ratio and low effective yield strength, and thicker CT specimens with shallower initial crack length. This is because the disagreement between UC and NM is unacceptably large. The developed new AJR method and the results presented in this paper can assist engineers and researchers to determine J-R curves and fracture toughness of steels more accurately and can contribute to the body of knowledge of fracture mechanics.

Surface cracks have been recognized as major causes of their potential failures. This paper intends to determine a normalized fully plastic J-integral solution to mixed-mode fracture caused by inclined surface cracks in pressurized ductile metal pipes. A combined J-integral and finite element method is developed to evaluate the J-integral for inclined surface cracks. A set of predictive formulas for the normalized fully plastic J-integral are developed. It is found in this paper that an increase of strain hardening exponent can increase the difference of normalized fully plastic J-integrals in pipes with different wall thicknesses and the normalized fully plastic J-integral increases with the decrease of crack inclination angle and aspect ratios and the increase of strain hardening exponent. It is also found that the critical locations of crack propagation occur between the surface point and the deepest point of cracks when the inclination angle is relatively small and that the developed formulas can accurately predict the normalized fully plastic J-integrals along the front of inclined surface cracks. The results of this paper enable researchers and practitioners to predict the mixed-mode fracture failure of pressurized pipes subject to inclined surface cracks.

Permeability of concrete is usually measured in laboratory conditions without loading, which can be completely different from that in service. This paper presents a new method to determine ...

In determining structural responses under random excitation using the Monte Carlo method, simulation of non-Gaussian processes is always a challenge. Various methods have been developed to ...

There has been limited research in the past on the effect of varying soil’s acidity measured as pH and saturation measured as moisture content on the fracture toughness of buried cast iron ...

Normalization method is a practical method for determining the J-R curves and fracture toughness of steels. There is some concern, however, about the performance of this method on steels with small strain hardening exponent and yield strength due mainly to the assumption of infinite strain hardening exponent (n). This paper intends to analytically modify the normalization method by removing this assumption and incorporating the strain hardening in calculating the blunting corrected crack length. This modification enables the normalization method to be applied to steels with small strain hardening exponent and yield strength. Experiments are undertaken to prove the underperformance of the normalization method for steels with small strain hardening exponent and yield strength and to verify the modified normalization method (CNM). A comparison of fracture toughness determined by CNM with that by the unloading compliance method and normalization method corroborates the improved accuracy of the developed CNM. It is found in the paper that the developed CNM performs very well for materials with small strain hardening exponent and yield strength and performs better for specimens with smaller thickness and in accordance with all standards. The paper concludes that the developed CNM overcomes the deficiency of the normalization method for steels with small strain hardening exponent and yield strength.

The vertical distributions of optical turbulence ( C n 2 profiles) are a major factor in defining the capabilities of ground-based telescopes and interferometers. As site-testing campaigns are extremely expensive and instruments only provide the local atmospheric parameter, atmospheric modeling might represent an advance prediction result in astronomical sites. The key meteorological parameters and the integrated astroclimatic parameters (Fried parameter r0, seeing ɛ, isoplanatic angle θAO and wavefront coherence time τAO) related to the C n 2 profiles above the Tibetan Plateau are investigated for astronomical applications by using the Weather Research and Forecasting (WRF) model. Radiosonde measurements from a field campaign at Lhasa station above the Tibetan Plateau are used to quantify the ability of this model. The results show that the C n 2 profile decreases rapidly in the surface layer, increasing with height from the boundary layer to low stratosphere, and decreases gradually in the high free atmosphere. From the whole campaign measurements above the Tibetan Plateau, the mean r0 is 8.64 cm, the mean ɛ is 1.55′′, the mean θAO is 0.42′′ and the mean τAO is 1.89 ms, and the comparison with the other world’s leading observatory sites have been presented. In addition, such as the bias and the root-mean-squared error are used to quantify the performance of the WRF model. In spite of the model performance in reconstructing the meteorological parameters is reasonable in general, the uncertainty in quantifying the C n 2 profiles and the integrated parameters are not negligible in some cases. The main results of this study tell us that the WRF model could provide a useful resource to design, monitor the performance of, and even optimize the operation of sophisticated Adaptive Optics (AO) systems.

Deterioration of reinforced concrete (RC) structures is unavoidable after their long time in service, with corrosion being the major mechanism of deterioration. In order to ensure safety of deteriorated structures, an effective rehabilitation plan is essential. Although considerable research on strengthening of RC structures using fibre-reinforced polymers (FRPs) composites has been undertaken, more is on the methods of strengthening and effects of corrosion on strength of RC columns than that on the prediction of optimum strengthening time. This paper presents a methodology for determining the optimal strengthening time and the required number of FRP layers for corrosion-affected RC structures with application to columns. The methodology is based on the time-dependent reliability method and the renewal theory. An example is provided to illustrate the application of the proposed methodology. It is found in this study that an optimum point for the formulated objective function exists, and that outcomes of optimisation problem, i.e. strengthening time and number of required FRP layers, are sensitive to corrosion rate. The significance of the proposed methodology is that it provides guidance for practitioners and asset managers to decide when and how to strengthen deteriorated structural members.

Corrosion-induced deterioration of reinforced concrete (RC) structures results in premature failure of the RC structures. In practice concrete crack width is one of the most important criteria for the assessment of the serviceability of RC structures. It is therefore desirable to predict the growth of the crack width over time so that better informed decisions can be made concerning the repairs due to concrete cracking. Literature review shows that little research has been undertaken on numerical prediction of concrete crack width. The intention of this study was to develop a numerical method to predict concrete crack width for corrosion-affected concrete structures. A cohesive crack model for concrete is implemented in the numerical formulation to simulate crack initiation and propagation in concrete. Choices for evaluating the parameters of cohesive elements are extensively discussed which is a key for developing a plausible model employing cohesive elements. The surface crack width is obtained as a function of service time. Accurate prediction of crack width can allow timely maintenance which prolongs the service life of the reinforced concrete structures.

Research on quantification of the size and porosity of the interface between the reinforcing steel and concrete is limited in the current published literature. This paper presents a reliable and accurate method for quantification of steel-concrete interface using the technique of Backscattered Electron (BSE) imaging. Details of sample preparation procedure designed to minimize the damage to the steel-concrete interface due to grinding and polishing are presented. A new thresholding method to separate porous band at the interface from steel and cement pastes is proposed. It is found that there is a relatively wide porous band with large pores and voids near the steel-concrete interface. It is also found that the size of porous band around the steel bar is not uniform, and that the water to cement ratio can significantly affect the size and distribution of porous band at the interface. Quantification of steel-concrete interface as proposed in this paper is of importance in crack prediction of corrosion-affected reinforced concrete structures.

As a composite material, hydraulic conductivity of concrete depends on conductivity of its components that are the mortar, aggregates and the Interfacial Transition Zone (ITZ). Since hydraulic conduction is analogous to heat and electrical conduction, analytical models from these analogous areas relating effective conductivity of composite to conductivity of its components can be used to find the effective hydraulic conductivity of concrete as a function of properties of its components, i.e., aggregate, mortar and the ITZ. However, effect of the conduction in the ITZ has not been considered in these models. This paper presents an analytical solution for the hydraulic conductivity of concrete as a three-phase composite material. The solution is an extension to the model originally proposed for conduction of composite media with randomly suspended spheres. Results of the proposed model compare well against the experimental results and those obtained from rigorous numerical analysis using the Finite Element (FE) method. The principal significance of this study lies in the development of a versatile analytical model that can be employed as a quick tool for assessment of hydraulic conductivity of concrete without the need for sophisticated FE models at the meso-scale level. It offers more insight into effect of different components of concrete on its overall conductivity.

Concrete permeability is usually determined by testing unstressed, non-damaged specimens in laboratories as a constant. In reality, however, concrete is subjected to various operational loads in the time span of its service life. Therefore, the permeability of stressed concrete can be time-variant and completely different from that of unstressed conditions. This paper intends to develop a new methodology to determine the permeability of stressed concrete over time, based on the damage mechanics of concrete meso-structure in conjunction with Monte Carlo simulation and finite element analysis. It is found in this study that the permeability of concrete starts to increase when the applied stress in concrete reaches a certain threshold value for the given aggregate fraction. It is also found that the aggregate fraction is the most influential factor for permeability degradation of concrete. The significance of the developed methodology is that it can determine the permeability degradation of concrete with different mechanical properties and geometries of constituent materials under various applied loads over time, which would be otherwise impractical experimentally.

This paper investigates the effect of corrosion on degradation of mechanical properties of G250 mild steel. Corrosion tests are conducted by immersing steel into hydrochloride acid solutions, with acidity ranging from 0.00001 M to 3 M. Both macro analysis and micro analysis are undertaken to investigate the mechanism of corrosion induced degradation of mechanical properties. Intergranular corrosion is found for mild steel during corrosion. Results indicate that there is considerable reduction in mechanical properties due to corrosion, which is attributed to a combined effect of hydrogen embrittlement, changes in element composition, grain size and phase composition, and the residual stress concentration at corrosion pits.

Corrosion of steel in reinforced concrete structures has been a major worldwide problem. The time to cover cracking plays a key role in assessment of serviceability of reinforced concrete structures subjected to corrosion. A large number of analytical, numerical, and empirical models have been developed to predict the time to time to cover cracking. In addition, extensive experiments have been conducted in order to verify the developed models. In this paper, an overview of the existing models is presented. A large experimental database of reported data on time to cover cracking is collated. Performance of four analytical models taken from the available literature is then examined using the established experimental database. Sensitivity analysis followed by a probabilistic study is carried out to identify the factors affecting time to cover cracking as a service life indicator by means of the selected models. The results from sensitivity analysis show that the porous zone and the properties of rust are the most influential factors for time to cover cracking. It is also shown that there is high uncertainty in predicting service life of reinforced concrete structures based on time to cover cracking.

The flow of water into a tunnel, through the surrounding rock mass and the tunnel lining, has important implications for tunnel design and tunnel condition assessment. The hydraulic conductivity of the lining is a major controlling factor on the water inflow rate. Previous work had been mainly based on the assumption of constant hydraulic conductivity of the lining. In this work, the existing analytical models of water flow through a tunnel lining under steady-state, saturated conditions are extended to incorporate a linear variation of hydraulic conductivity with distance from the tunnel wall. The inhomogeneity of a lining is shown to have a significant impact on water inflow rate and water pressure distribution according to the model. The relation between lining inhomogeneity and other hydraulic parameters was established. This model can be used to predict the hydraulic pressure and crack condition at the outer face of the lining based on measured water inflow rate and the crack condition at the inner face, with significantly increased accuracy compared with the existing models based on constant hydraulic conductivity. Design charts are also developed for engineering applications.

The fracture resistance of elasto-plastic materials varies significantly depending on the mode mixities, i.e., the loading combinations. This paper aims to experimentally investigate the fracture resistance and behaviour of two grades of mild steel under various in-plane loading combinations. A loading fixture with high loading capacity and modified compact tension shear (CTS) specimen are designed to conduct fracture tests on elasto-plastic materials under various mode mixities. A digital image correlation (DIC) technique-based method is developed and verified to detect the fracture initiation. It is found in the paper that the sensitivity of the fracture resistance of steel to mode mixity is attributed to the strain hardening capacity and the impurities in chemical composition of the steel. It is also found that the plastic strain concentration, crack tip blunting and fracture mechanism lead to different fracture resistance of both types of steel under various mixed mode loading combinations. The contribution of the paper is that an additional method to determine the fracture initiation under non-mode I loading is developed. The test results show the necessity of considering the mode mixity effect under the mode II loading dominance in practical engineering applications.

Ageing and deterioration of underground tunnels is inevitable after their long-time in service. This necessitates a rigorous assessment of the probability of failure due to deterioration with a vie...

Mixed mode fractures can be triggered by either multi-axial stresses or inclined cracks or both. Little research has been undertaken on J-integral for inclined surface cracks in plates under biaxial loading. This paper intends to determine the elastic and fully plastic J-integral for mixed mode fracture induced by inclined surface cracks in plates under biaxial loading conditions, using three-dimensional finite element method. Various geometries, biaxiality and material properties of cracked plates, including crack depth to plate thickness ratios, inclination angles, strain hardening exponents and biaxiality ratios, are considered. From numerical results, it is found that for elastic analysis, the equivalent influence coefficients increases with the increase of the relative crack depth and the magnitude of the biaxiality ratios. It is also found that for a given crack and plate geometry, the values of normalized fully plastic J-integral h1 decrease along the whole crack front for different strain hardening exponents n with the increase of the inclination angles from 0 ° to 45 ° for uniaxial loading. It can be concluded that the method presented in the paper can determine the J-integral for inclined surface cracks in plates with reasonable accuracy. The results presented in the paper can equip practitioners for more accurate prediction of plate failures under various loads.

Passive building technology belongs to the near-zero-energy building technology system, which maximizes the utilization of free energy from the ambient environment to reduce building energy consumption. In recent years, it has been widely recognized and developed rapidly. This paper takes a lot of effort to review the advances in the research and development of passive buildings in China, including the development status, representative projects and emerging technologies, design tools, benefit analysis and applied research in various climate zones. It also examines the policies and barriers for the development of passive buildings in China, including local incentive mechanisms, laws and regulations, etc. Finally, the application prospects of passive buildings in China are analyzed and recommendations are made for future development.

This study performed design optimization on a building with integrated photovoltaic, Trombe wall and phase change material based on building life cycle cost (LCC) and indoor thermal comfort. A total of thirty-four design variables were considered as the optimization variables. The optimization process consists of four steps. Firstly, Monte Carlo Method was used to generate a set of design samples, and the LCC and indoor discomfort degree hour were obtained through computer simulation. Secondly, stepwise linear regression (SLR) and artificial neural network (ANN) models were developed as the prediction models. ANN models exhibited better prediction performance with errors of less than 6%. Thirdly, six optimization algorithms were selected to couple with the ANN models for design optimization and the Strength Pareto Evolutionary Algorithm II (SPEA II) presented the best performance. Finally, optimization with different groups of design variables were conducted by using the SPEA II algorithm. Compared with the reference building, the optimal solutions reduce life cycle cost up to 45.51% and improve thermal comfort level up to 43.81%. The recommended heating and cooling temperature setpoint is around 18 °C and 24 °C, respectively. The PCM type convergence value is BioPCM M182/Q21, and the east and west window-to-wall ratios are around 10%.

A disparity in the distribution and quality of urban parks has been widely recognized as an important environmental justice issue. There is currently inconsistent evidence focusing on park distribution in high-density cities that can shed light on socioeconomic inequalities in park quality. To address this issue from an environmental justice perspective, the current study aimed to examine the associations between the quantity and quality of urban parks and neighborhood-level socioeconomic deprivation and ethnic minorities in Hong Kong, as an example of a high-density city. A total of 102 urban parks from 209 Tertiary Planning Units (TPUs) were included in this study. Quantity and quality of the 102 urban parks were objectively measured using Geographic Information Systems and the Community Park Audit Tool from April to June 2018. Findings of the current study demonstrated that the quantity of parks, quality of amenities, park safety, and park aesthetics were not associated with socioeconomic deprivation or ethnic minorities. However, compared to the TPUs with low deprivation values, a greater quantity and diversity of active facilities were observed in the moderate and high deprived TPUs. Moreover, the TPUs with a higher percentage of ethnic minorities were associated with parks with fewer active facilities, as well as less diversity of active facilities and supporting amenities. The current study provides key evidence of distributional injustice for urban parks in high-density cities and contributes to the development of urban planning strategies to address these issues.

Efficient genome editing with Cas9–sgRNA in vivo has required the use of viral delivery systems, which have limitations for clinical applications. Translational efforts to develop other RNA therapeutics have shown that judicious chemical modification of RNAs can improve therapeutic efficacy by reducing susceptibility to nuclease degradation. Guided by the structure of the Cas9–sgRNA complex, we identify regions of sgRNA that can be modified while maintaining or enhancing genome-editing activity, and we develop an optimal set of chemical modifications for in vivo applications. Using lipid nanoparticle formulations of these enhanced sgRNAs (e-sgRNA) and mRNA encoding Cas9, we show that a single intravenous injection into mice induces >80% editing of Pcsk9 in the liver. Serum Pcsk9 is reduced to undetectable levels, and cholesterol levels are significantly lowered about 35% to 40% in animals. This strategy may enable non-viral, Cas9-based genome editing in the liver in clinical settings.

This article focuses in the development of high thermal resistant, fireproof, and durable expanded perlite based lightweight aggregate composites with a good balance between the thermal and mechanical properties. The thermal insulation boards were prepared with expanded perlite, coal fly ash, and aluminum dihydrogen phosphate by the process of mixing, molding, demolding, and calcinations, and surface treatment with an organic silicon abhorred agent. Coal fly ash is used to obtain an appropriate mechanical strength. The mechanical strength, thermal properties, and porosity structure of the designed composites are studied. The aggregate composites are well satisfied the Chinese expanded perlite insulation standard GB/T 10303-2001, can be used as insulation materials, with the bulk densities 253 kg m−3–305 kg m−3, the compressive strengths 0.428 MPa–0.462 MPa, and the heat conductivities 0.073 W m−1 K−1–0.082 W m−1 K−1, and could be applied in high-rise building instead of normally used organic insulation materials. © 2017 American Institute of Chemical Engineers Environ Prog, 2017

Underground pipes are essential infrastructure for water, oil and gas transport. The presence of localized pitting corrosion has been identified as one of the main deterioration mechanisms for metal pipes, which, when exposed to external loadings, can easily fail due to intensified stresses at the corrosion pit. The assessment of such an intensified stress field around the pit has been a key focus for decades since it is a major mode of pipe failures. Although stress intensity factors for structures with surface cracks have been extensively studied in literature, there is little study essentially relating the stress intensity factors of pipes with different levels of pitting corrosion. In the present study, a three-dimensional geometrical model for corrosion pits is proposed and a J -integral based finite element method is employed to derive the solutions for stress intensity factors for various pit and pipe geometries. Attempt is also made to derive formulas of maximum stress intensity factors by use of the evolutionary polynomial regression method. It has been found that the maximum stress intensity factor for corrosion pits with high aspect ratio occurs at a different position from those with low aspect ratio. It has also been found that idealization of corrosion pits as surface cracks rather than three-dimensional pits will cause an inaccurate estimate of stress intensity factors for pipes. The results of this study provide a fundamental basis for safety evaluation and life prediction of buried cast iron pipelines.

As an essential infrastructure tunnels play an important role in transport network. The functionality of this infrastructure depends on its structural and durability performance. In the climate of an increasing scarcity of resources, infrastructure maintenance is becoming increasingly important. This paper aims to develop a maintenance strategy for tunnels, which determines when, where and what to maintain, to ensure the safe and serviceable operation of tunnel structure with the intention to minimise the total risk. Application of the proposal is presented in a numerical example of a practical case study. It was found that an optimum solution, which can predict when, where and what to maintain for tunnel structure to ensure its safe and serviceable operation during its lifespan, exists. The paper concludes that the proposed framework can equip tunnel operators and asset managers with a tool in developing a risk cost optimised maintenance strategy for tunnels under their management.

Linear elastic fracture mechanics has been widely employed for fracture analysis of cracked pipes. For ductile metal pipes, the existence of plasticity eases the stress concentration at the crack front, which increases the fracture toughness of the pipe. Therefore, when using linear elastic fracture mechanics to predict the fracture failure of ductile pipes, the plastic portion of the fracture toughness should be excluded. This paper intends to derive an analytical model of elastic fracture toughness for ductile metal pipes with circumferential external surface cracks under combined axial tension and bending. The derived elastic fracture toughness is a function of crack geometry, material properties and loading conditions of the cracked pipe. The significance of the derived model is that the well established linear elastic fracture mechanics can be used for ductile materials in predicting the fracture failure. It is found in the paper that, the elastic fracture toughness increases with the increase of the internal pressure of the pipe and that an increase in fracture toughness and yield strength of the pipe materials will result in a more ductile and brittle pipe failure respectively. The derived analytical model enables more accurate prediction of fracture failure of ductile metal pipes with circumferential external cracks.

Mixed mode fractures can be triggered by either multi-axial stresses or inclined cracks or both. Little research has been undertaken on stress intensity factors for inclined cracks in pipes under axial tension and bending. This paper intends to determine stress intensity factors for mixed mode fracture induced by inclined external surface cracks in pipes under axial tension and bending, using a combined J integral and 3 dimensional finite element method. Formulae for the influence coefficients of stress intensity factors are developed. To predict the fracture failure of the pipe, the propagation of inclined cracks in pipes is also investigated. From numerical results, it is found in the paper that, for given wall thickness to internal radius ratio and crack depth to half crack length ratio, the absolute values of the influence coefficients of all three modes I, II and III stress intensity factors along the whole crack front increase with the increase of the relative depth for all inclination angles of the surface cracks. It is also found that the crack propagation angles in depth of the inclined cracks increases in magnitude along the whole crack front with the decrease of the crack inclination angle defined as the angle between the crack and pipe axial direction. The results presented in the paper can equip practitioners for more accurate prediction of pipe failures under various loads.

The microstructures and mechanical properties of TiAl alloys are directly linked to micro-segregation which cannot be avoided during solidification. So a thorough understanding of the micro-segregation should be a great help to further enhance the mechanical properties of the cast products. Theoretical analysis and experiments have been used to predict the micro-segregation, but it is very difficult to observe and determine the dendritic segregation in the micro region. Phase-field method has been employed for the simulation of dendritic growth. However, due to the complicated quasi-sub regular solution model for Ti-45Al(at.%) alloy, the classic phase-field models have difficulty to deal with the free energy. In this work, a phase-field model by linking thermodynamic calculation was used to simulate solidification dendritic segregation of Ti-45Al alloy for Liquid→Liquid+β(Ti). The free energies of solid phase and liquid phase for Ti-45Al alloy were calculated by Thermo-Calc and then coupled with the phase-field equations. The simulation results show the dendritic morphology and Al content variations between liquid and growing solid phase for Ti-45Al alloy. With the growth of the β(Ti), dendritic segregation is formed in the liquid and solid phases due to the solute partitioning and rejection into the liquid. As a result, the dendrite arms are depleted of Al element, while the inter-dendrites are enriched. The dendritic tip growth velocity decreases with the progress of solidification, whereas the segregation ratio increases.

Previous studies have seldom investigated the effects of direct emissions at different stages of a building construction. This study aims to estimate and compare direct and indirect emissions and environmental impacts at foundation and structure construction stages of a building using a case study. The case study is multi-storey commercial building construction with concrete framing. A process based methodology is developed to estimate emissions from seven sources that contribute to both greenhouse gas (GHG) and non-GHG emissions. An impact assessment is also carried out to compare the environmental impacts for different stages of construction from global, regional and local perspectives. The results highlight an overpowering indirect GHG contribution of 89% from material embodied emissions at the structure construction stage. Direct GHG emissions at the foundation construction are prominent with a contribution of 12.7% and 13.4% for emissions from equipment usage and transportation respectively. Nitrous Oxides (NOx) and Carbon Monoxides (CO) are recorded as the most prominent non-GHG emissions. The results were further analysed based on four scenarios corresponding to direct and indirect emissions. The results signified a GHG emission reduction of 12% can be achieved by adopting sustainable materials such as fly ash and blast furnace concrete. The impact assessment results illustrate a large contribution to global warming potential (GWP) with a value of over 98% for the construction stage from the global perspective. This large contribution from GWP is reduced to 60% and 57% with relative high contributions from Photochemical Oxidation Potential (POFP) with 26% and 34% at regional and local levels. The scenario analyses on direct emissions highlight the importance of resource utilisation in reducing impacts at local level. The results indicate that identification of the significant emission sources and impact categories at different construction stages, prior to implementing emission reduction opportunities such as usage of sustainable materials and operational optimisation of construction equipment and transportation vehicles is key to minimising impacts at building construction.