Analytical prediction and field validation of transient temperature field in asphalt pavements

This work presented the development and validation of an analytical method to predict the transient temperature field in the asphalt pavement.The governing equation for heat transfer was based on heat conduction radiation and convection.An innovative time-dependent function was proposed to predict the pavement surface temperature with solar radiation and air temperature using dimensional analysis in order to simplify the complex heat exchange on the pavement surface.The parameters for the time-dependent pavement surface temperature function were obtained through the regression analysis of field measurement data.Assuming that the initial pavement temperature distribution was linear and the influence of the base course materials on the temperature of the upper asphalt layers was negligible,a close-form analytical solution of the temperature in asphalt layers was derived using Green's function.Finally,two numerical examples were presented to validate the model solutions with field temperature measurements.Analysis results show that the solution accuracy is in agreement with field data and the relative errors at a shallower depth are greater than those at a deeper one.Although the model is not sensitive to dramatic changes in climatic factors near the pavement surface,it is applicable for predicting pavement temperature field in cloudless days.

Infl uence of structural parameters on dynamic characteristics and wind-induced buffeting responses of a super-long-span cable-stayed bridge

A 3D finite element （FE） model for the Sutong cable-stayed bridge （SCB） is established based on ANSYS. The dynamic characteristics of the bridge are analyzed using a subspace iteration method. Based on recorded wind data, the measured spectra expression is presented using the nonlinear least-squares regression method. Turbulent winds at the bridge site are simulated based on the spectral representation method and the FFT technique. The influence of some key structural parameters and measures on the dynamic characteristics of the bridge are investigated. These parameters include dead load intensity, as well as vertical, lateral and torsional stiffness of the steel box girder. In addition, the influence of elastic stiffness of the connection device employed between the towers and the girder on the vibration mode of the steel box girder is investigated. The analysis shows that all of the vertical, lateral and torsional buffeting displacement responses reduce gradually as the dead load intensity increases. The dynamic characteristics and the structural buffeting displacement response of the SCB are only slightly affected by the vertical and torsional stiffness of the steel box girder, and the lateral and torsional buffeting displacement responses reduce gradually as the lateral stiffness increases. These results provide a reference for dynamic analysis and design of super-long-span cable-stayed bridges.

Physical modeling and visualization of soil liquefaction under high confining stress

The mechanisms of seismically-induced liquefaction of granular soils underhigh confining stresses are still not fully understood.Evaluation of these mechanisms is generallybased on extrapolation of observed behavior at shallow depths.Three centrifuge model tests wereconducted at RPI's experimental facility to investigate the effects of confining stresses on thedynamic response of a deep horizontal deposit of saturated sand.Liquefaction was observed at highconfining stresses in each of the tests.A system identification procedure was used to estimate theassociated shear strain and stress time histories.These histories revealed a response marked byshear strength degradation and dilative patterns.The recorded accelerations and pore pressures wereemployed to generate visual animations of the models.These visualizations revealed a liquefactionfront traveling downward and leading to large shear strains and isolation of upper soil layers.

Modeling and cyclic behavior of segmental bridge column connected with shape memory alloy bars

This paper examines the quasi-static cyclic behavior, lateral strength and equivalent damping capacities of a system of post-tensioned segmental bridge columns tied with large diameter martensitic Shape Memory Alloy （SMA） link-bars. Moment-curvature constitutive relationships are formulated and analysis tools are developed for the PT column, including a modified four-spring model prepared for the SMA bars. The suggested system is exemplified using a column with an aspect ratio of 7.5 and twelve 36.5 mm diameter NiTi martensitic SMA bars. A post-tensioning force of 40% to 60% of the tendon yield strength is applied in order to obtain a self re-centering system, considering the residual stress of the martensitie SMA bars. The cyclic response results show that the lateral strength remains consistently around 10% of the total vertical load and the equivalent viscous damping ratios reach 10%-12% of critical. When large diameter NiTi superelastic SMA bars are incorporated into the column system, the cyclic response varies substantially. The creep behavior of the superelastic SMA bar is accounted for since it affects the re-centering capability of the column. Two examples are presented to emphasize the modeling sensitivities for these special bars and quantify their cyclic behavior effects within the column assembly.

Seismic fragility assessment of existing sub-standard low strength reinforced concrete structures

An analytical seismic fragility assessment framework is presented for the existing low strength reinforced concrete structures more common in the building stock of the developing countries.For realistic modelling of such substandard structures,low strength concrete stress-strain and bond-slip capacity models are included in calibrating material models.Key capacity parameters are generated stochastically to produce building population and cyclic pushover analysis is carried out to capture inelastic behaviour.Secant period values are evaluated corresponding to each displacement step on the capacity curves and used as seismic demand.A modified capacity demand diagram method is adopted for the degrading structures,which is further used to evaluate peak ground acceleration from back analysis considering each point on the capacity curve as performance point.For developing fragility curves,the mean values of peak ground acceleration are evaluated corresponding to each performance point on the series of capacity curves.A suitable probability distribution function is adopted for the secant period scatter at different mean peak ground acceleration values and probability of exceedance of limit states is evaluated.A suitable regression function is used for developing fragility curves and regression coefficients are proposed for different confidence levels.Fragility curves are presented for a low rise pre-seismic code reinforced concrete structure typical of developing countries.

Succession and biodiversity indices in eutrophication process of static landscaping water body in northern China

Many biodiversity indices were used to indicate the biological contamination degree in studies of lake water or seawater. Some were studied on biodiversity comparison for different areas at the same time, or initial structure succession of some aerial lake water systems. The phytoplankton changed with the development of various dominant species. In this study, the dominant species at these stages were Chlorophyta in the beginning stage, Cyanophyta in the second stage, and Xanthophyta in the last stage. Seven of nine biodiversity indices (Margalef's, IE, Shannon-Wiener, Simpson's, McNaughton's, Species and Odds Measure of Diversity) showed their failure to represent the eutrophication trend, and the other two indices (Menhinick's and Monk) exhibited good efficiency to indicate the eutrophication trend for the static landscaping water body.

Removal of Cryptosporidium sized particle under different filtration temperature, flow rate and alum dosing

Recent Cryptosporidium outbreaks have highlighted concerns about filter efficiency and in particular particle breakthrough. It is essential to ascertain the causes of Cryptosporidium sized particle breakthrough for Cryptosporidium cannot be destroyed by conventional chlorine disinfection. This research tried to investigate the influence of temperature, flow rate and chemical dosing on particle breakthrough during filtration. The results showed that higher temperatures and coagulant doses could reduce particle breakthrough. The increase of filtration rate made the residual particle counts become larger. There was an optimal dose in filtration and was well correlated to ζ potential.

Analytical and Numerical Modelling of FRP Debonding from Concrete Substrate under Pure Shearing

External bonding of fiber reinforced polymer （FRP） composites on the concrete structures has been proved to be an effective and efficient way to strengthen concrete structures. For a FRP strengthened concrete beam, it is usually observed that the failure occurs in the concrete and a thin layer of concrete is attached on the surface of the debonded FRP plate. To study the debond behavior between concrete and FRP composites, an analytical model based on the three-parameter model is developed to study the debonding behavior for the FRP-to-concrete joint under pure shearing. Then, nonlinear FEM analysis is conducted to verify the PrOposed analytical model. The FEM results shows good agreement with the results from the model. Finally, with the analytical model, sensitivity analyses are performed to study the effect of the interracial parameters or the ~eometric parameters on the debondin~ behavior.

Whole process reclamation and utilization of wastes produced in the biological fermentation industry

Wastes yielded in the vintage process and the biological fermentation of itaconic acid and sodium gluconate of a winery in Shandong, such as grain stillage, melon lees, cornstarch protein residues, itacanic acid mother liquid, itaconic acid mycelium and sodium gluconate mycelium, were studied. High-activity biological protein feed, foliar fertilizer and irrigation fertilizer were generated from these wastes by applying biological/microbial technologies. Meanwhile, a whole set of technological pathways was put forward. As a result, the optimal economical and social benefits can be obtained with low natural resource consumption and environmental costs by converting wastes into useful matters. In conclusion, through the utilization of limited resources in the whole process of reclamation and utilization of wastes, the harmony promotion can be achieved between the economic system and the natural ecosystem.

Diffraction of anti-plane SH waves by a semi-circular cylindrical hill with an inside concentric semi-circular tunnel

A closed-form analytic solution of two-dimensional scattering and diffraction of plane SH waves by a semi- cylindrical hill with a semi-cylindrical concentric tunnel inside an elastic half-space is presented using the cylindrical wave functions expansion method.The solution is reduced to solving a set of infinite linear algebraic equations.Fourier expansion theorem with the form of complex exponential function and cosine function is used.Numerical solutions are obtained by truncation of the infinite equations.The accuracy of the presented numerical results is carefully verified.

Application of clan member signal method in structural damage detection

It is well known that in most cases, a reference is necessary for structural health diagnosis, and it is very difficult to obtain such a reference for a given structure. In this paper, a clan member signal method （CMSM） is proposed for use in structures consisting of groups （or clans） that have the same geometry, i.e., the same cross section and length, and identical boundary conditions. It is expected that signals measured on any undamaged member in a clan after an event could be used as a reference for any other members in the clan. To verify the applicability of the proposed method, a steel truss model is tested and the results show that the CMSM is very effective in detecting local damage in structures composed of identical slender members.

Seismic behavior of concrete filled steel tubular arch structures

Shaking table tests of a 1:10 scale arch model performed to investigate the seismic behavior and resistance of concrete filled steel tubular (CFT) arch structures are described in this paper. The El-Centro record and Shanghai artificial wave were adopted as the input excitation. The entire test process can be divided into three stages depending on the lateral brace configurations, i.e., fully (five) braced, two braces removed, and all braces removed. A total of 46 tests, starting from the elastic state to failure condition, have been conducted. The natural vibration frequencies, responses of acceleration, displacement and strain were measured. From the test results, it is demonstrated that the CFT arch structures are capable of resisting severe ground motions and that CFT arches offer a credible alternative to reinforced concrete arches, especially in regions of high seismic intensity.

Probabilistic characterization of cyclic shear modulus reduction for normally to moderately over-consolidated clays

Evaluation of the cyclic shear modulus of soils is a crucial but challenging task for many geotechnical earthquake engineering and soil dynamic issues. Improper determination of this property unnecessarily drives up design and maintenance costs or even leads to the construction of unsafe structures. Due to the complexities involved in the direct measurement, empirical curves for estimating the cyclic shear modulus have been commonly adopted in practice for simplicity and economical considerations. However, a systematic and robust approach for formulating a reliable model and empirical curve for cyclic shear modulus prediction for clayey soils is still lacking. In this study, the Bayesian model class selection approach is utilized to identify the most significant soil parameters affecting the normalized cyclic shear modulus and a reliable predictive model for normally to moderately over-consolidated clays is proposed. Results show that the predictability and reliability of the proposed model out performs the well-known empirical models. Finally, a new design chart is established for practical usage.

Performance of BAC process for treatment of micro-polluted water

Biological activated carbon (BAC) has been developed on the granular activated carbon by immobilization of selected and acclimated species of bacteria to treat the micro-polluted water. The BAC removal efficiencies for nitrobenzene, permanganate index, turbidity and ammonia were investigated. Effects of shock loading and SEM (Scanning Electron Microscope) observation on BAC were studied. Backwashing and its intensity of BAC were also discussed. The results showed that BAC took short time to start up and recover to the normal condition after shock loading. The shock loading studies showed that the removal efficiency of BAC was not completely inhibited even at high concentration of nitrobenzene. Backwashing performed once every 10-20 d, or an average of 15 d. Backwashing intensity was 12-14 L/(s·m2) with air and 3-4 L/(s·m2) with water.

Assessment of nutrients and conductivity in the Wachusett Reservoir watershed:An investigation of land use contributions and trends

The quality of drinking water for the Boston Metropolitan Area,supplied by the Quabbin-Wachusett system,is impacted by environmental trends.The objectives of this study are to increase understanding of the role that small streams may play in degradation of reservoir quality by characterizing seasonal constituent patterns from 1998 to 2020 in the Wachusett Reservoir watershed and by developing enhanced modeling frameworks.Previous monitoring(1998–2012)exhibited increased loads due to increasing flows despite declining solute concentration.This present study analyzed seasonal nitrate(NO3)and total phosphorus(TP)concentration and load trends from 2012 to 2020 across 11 tributaries.Specific conductivity(SC)was also assessed to evaluate the impacts of road salt application.From 2012 to 2020,statistical results for mean nutrient concentrations suggest static or declining temporal trends,while SC in all tributaries exhibited increasing trends.Land use data suggest association with altered drainage landscapes as potential sources of increased constituent transport.Subbasins with the highest concentrations of TP,NO3,and SC have the largest percentage of impervious and cultivated areas,two to three times greater than other subbasins.Daily flows were modeled using the airGR hydrological model,subsequently used to calculate loads.Overall,flow magnitude was a more important load driver than long-term nutrient concentrations,thus,showing that stream discharge controlled load variability.On the other hand,persistently high SC levels controlled the increasing SC load trends.Finally,many nutrient reduction management strategies demonstrated an important impact from 1998 to 2020.Despite watershed programs aimed at reducing salt applications,concentrations in streams are increasing,indicating a long-term legacy of salt accumulation.Although smaller tributaries represent a modest portion of the system,addressing these sources has the potential to further reduce the long-term ecological impacts of reservoir constituent loading.

Seismic behavior assessment for design of integral abutment bridges in Illinois

Integral abutment bridges(IABs)minimize deterioration and degradation of the abutment seats and bearings due to water,dirt,and deicing chemicals by eliminating bearings and expansion joints.Although the continuity between superstructure and abutments in an IAB is beneficial for reducing maintenance costs,it leads to more complex behavior under strength and service loading(temperature and traffic)and extreme loading(earthquake).The coupling of superstructure and substructure behavior necessitates system-level analysis of IABs.Prior seismic IAB studies have typically investigated the behavior of individual IAB components,however a gap of knowledge has developed due to the lack of studies and investigation about the behavior of all IAB components and their interactions with each other in a single analysis model.This study uses nonlinear static and dynamic analyses to investigate and assess the seismic behavior of IABs typical to the state of Illinois.The analyses aim to bridge the gap of knowledge by evaluating IABs as a whole and utilizing the results to indicate potential vulnerabilities in the design and construction of IABs in Illinois during design-level and larger seismic events,which could not be identified by component-level IAB analyses alone.

Effect of stress path on the mechanical properties of calcareous sand

Calcareous sand is widely observed in the foundation of off-shore infrastructure.Although a lot of research has been carried out on the mechanical properties of calcareous sand,study into the influence of the stress–strain path on the mechanical behaviour of calcareous sand is very limited.In this study,a series of triaxial tests were performed on calcareous sand under three different stress paths.The particle morphology of calcareous sand before and after the tests,the stress–strain relationship under different stress paths,and the char-acteristics of shear strength and deformation were investigated.The results show that the consolidation pressure and stress path have significant effects on the volume strain,strength,and particle breakage of calcareous sand.In addition,the underlying mechanisms of the different behaviours of calcareous sand observed in this study were discussed.

结构比例柔度矩阵

在环境激励情况下,仅通过测试结构响应不可能获得结构柔度矩阵,因此提出了比例柔度矩阵的概念,该柔度矩阵与结构真正的柔度矩阵仅相差一个比例常数.对于测试自由度完备和非完备两种情况,提出了构建结构比例柔度矩阵的方法,并证明该比例常数近似为结构的第一阶模态质量.经算例验证,比例柔度矩阵的提出和应用可以将基于柔度的损伤识别方法扩展应用到环境激励或外境激励源未知的情况.

泥沙输运模拟综述--现状及其发展趋势

随着流体力学中数值方法的飞速发展,计算模型已经成为研究流体运动,泥沙输运和不同环境(诸如河流,湖泊及沿海地区)中相应污染物归趋过程等方面非常有吸引力的工具,在过去的30多年里,发展了许多计算水动力学/泥沙输运模型.文章追溯当前具有代表性的(一维、二维、三维)模型的发展历程,描述他们各自的特点,优势及局限,力图作为对模型方面感兴趣读者的第一指南,同时也为大家讨论模型的局限性,未来的发展趋势和研究需求方面搭建一个平台.给出了模型的表达,时空特性,水动力学和沉积物的耦合方式,处理非恒定流,推移质和悬移质,泥沙交换过程,泥沙类型(粘性或非粘性)及非均匀泥沙输运的能力.总结了不同模型的应用实例,读者可以运用这些例子作为研究模型设置,模型率定及模型验证的参考.给出了选择泥沙输运模型应遵循的原则,模型输入及率定方面存在的问题及改进的途径.探讨了现有水动力学/泥沙输运模型在处理复杂湍流,泥沙携带,流动与输沙耦合,非均匀泥沙,离散和扩散系数,河岸来沙处理等方面的局限性及改进的方向.最后,对基于多相流思想的泥沙输运模型及其它一些交叉性问题作了评述与展望.