Parametric study of frost-induced bending moments in buried cast iron water pipes

While the features of frost susceptible soils have been examined in various studies, the mechanisms by which volume changes due to ground freezing can influence cast iron water pipes buried below the frost line have not been explained, and the hypothesis that frost-induced ground deformations can induce ring fractures due to longitudinal bending of these pipes has not been proven. Therefore, a parametric study employing three dimensional finite element analysis is reported, where the soil–pipe interaction associated with a pipe crossing under an intersection of a major arterial road with a residential street are examined. The arterial road is modeled as having non-frost susceptible sub-base and the local street is represented as having a lower grade pavement with frost susceptible sub-base. One specific frost loading case featuring both isotropic pore water expansion and orthotropic ice lens formation is modeled.The analysis demonstrates how volume changes due to ground freezing in soil strata above the buried pipe can induce bending moments sufficient to cause ring fracture. Changes in the relative axial stiffness of the pipe were found to have only a small effect on pipe moments. Decreases in the relative flexural stiffness of the pipe resulting from reductions in pipe modulus also had only a small effect on pipe deflections and normalized moments. Changes due to soil modulus had a significant effect on deformations, but little influence on moments. Decreases in pavement stiffness decrease pipe deflections and moments. Trench backfill conditions greatly affect deflection and moment. Reduction in burial depth from 2 m to 1.5 m increases deflections, and increases moments beyond the failure capacity of the grey, cast iron pipe considered in the study, and this computational result is directly supported by field evidence.     

Structural performance of buried prestressed concrete cylinder pipes with harnessed joints interaction using numerical modeling

Broken prestressing wire wraps are the main cause of failure in buried prestressed concrete cylinder pipes (PCCP), which form the backbone of water and wastewater infrastructure networks in North America. Advanced numerical modeling using non-linear finite elements is used to model the effect of the number and location of broken wire wraps on the structural performance of Class 125-14, 96-in. PCCP. The modeling technique used is unique in that it considers full interaction between adjacent pipes with harnessed joints, as well as combined internal and external loading with full soil–pipe interaction. Performance indicators in the various components of PCCP are monitored as internal pressure is increased. A sensitivity analysis is presented for how manipulating the severity of the damage affects the failure pressure of the pipe. The results show that the internal fluid pressure required to cause failure can be as much as 34% lower when the damage is at the barrel of the pipe, and that the internal pressure that causes yielding of the wire wraps decreases by 66% as the damage worsens from 5 to 100 wire breaks.     

Experimental evaluation of bursting capacity of corroded grey cast iron water pipeline

Cast iron was used in the water industry prior to 1970 and a large number of cast iron pipes still remain as trunk mains. These pipes have been subjected to different levels of corrosion and variety of loading conditions. This leads cast iron pipes to fail in the field without prior warning. Water utilities are seeking solutions to optimise cast iron pipe renewal and rehabilitation programs for critical water mains (diameter ≥ 300 mm). A new experimental set-up has been developed at Monash University in order to perform burst testing of large diameter cast iron pipes (diameter ≥ 300 mm). A section of cast iron pipe, extracted during maintenance in Sydney, was laser scanned to determine the remaining thickness of the pipe (minimum of 7–8 mm at the most critical patches). Although the pipe was pressurised to 3.6 MPa, catastrophic failure did not occur. Water leakage from the two critically corroded patches was observed at around 3.25–3.45 MPa internal pressure. Strain results on the outer pipe surface were greater than the strain measured during tensile testing of the same pipe material. A 3-D finite element model using the scanned pipe dimensions was able to predict the maximum pressure at pipe failure (~3.7 MPa) within the range of leaking water pressure level observed in the experiment.     

边坡的弹塑性有限元可靠度分析

以弹塑性有限元理论和可靠度理论为基础,基于偏微分技术及增量初应力法,对采用Mohr-Coulomb屈服准则的边坡土体进行了弹塑性随机有限元可靠度分析,比较了基于强度折减法和基于滑面应力分析的弹塑性随机有限元分析法的异同:前者编程简单,可利用现有大型有限元计算软件计算边坡的整体可靠指标,但不能确定边坡中相应的潜在滑动面的位置,计算量较大,运算速度较慢;后者可以同时求出边坡的整体可靠指标及潜在滑动面的位置,运算速度快,但编程复杂。文中还研究了基于滑面应力分析的弹塑性随机有限元可靠度分析方法中滑面可靠指标的4种计算方法,比较了不同功能函数形式对边坡可靠指标及滑面位置的影响,指出采用考虑滑面方向的功能函数形式来求解可靠指标的方法3与基于强度折减法的可靠度分析本质相同,较为合理。     

边坡稳定的非线性随机有限元加速收敛算法的研究

基于滑面应力分析的边坡稳定随机有限元可靠度分析方法,边坡整体可靠指标的求解包含多重循环,如可靠指标的迭代求解循环、非线性随机有限元迭代求解循环、滑面最小可靠指标的搜索循环等。因此,改进非线性随机有限元的迭代计算方法、减少其迭代计算次数对于提高整个程序的运行速度具有重要意义。本文以增量切线刚度法为基础,详细推导了基于修正的Aitken加速法的非线性随机有限元加速迭代公式,并将之应用于边坡稳定的可靠度分析。其中,可靠指标的迭代求解方法是有限步长迭代法。算例表明,本文方法合理可行;采用加速算法可明显减少随机有限元的迭代次数,加速程序的运行效率;若中心点法与有限步长迭代法所求的可靠指标值相差较大,则其对应的滑面位置也相差较大;反之,若中心点法与有限步长迭代法所求的可靠指标值很接近,则其对应的滑面位置也基本一致。     

Spatial time-dependent reliability analysis of corroding pretensioned prestressed concrete bridge girders

Accelerated pitting corrosion tests have been performed to obtain spatial and temporal maximum pit-depth data for prestressing wires. This data is then used to develop probabilistic models of pitting corrosion and strength capacity of 7-wire strands. The probabilistic model of pitting corrosion for strands is then combined with a non-linear Finite Element Analysis and probabilistic models of corrosion initiation and propagation to study the spatial and temporal effects of pitting corrosion on a typical pretensioned prestressed concrete bridge girder. The limit states considered are flexural strength and serviceability. The spatial time-dependent reliability analysis takes into account the uncertainties and variabilities related to material properties, dimensions, loads and corrosion parameters as well as the spatial variability of pitting corrosion of prestressing strands. Including the spatial variability of pitting corrosion in the reliability analysis increased both the probability of strength and serviceability failure when compared with a mid-span sectional analysis.     

基于ANSYS的穿透裂纹三维板数值分析

以承受均匀表面压力的中心穿透裂纹三维板为例,运用ANSYS有限元软件,使用KCALC命令和J积分方法计算其应力强度因子,并与解析解进行比较,结果具有相当高的精度,为三维构件裂纹扩展分析提供数值依据。     

氯氧镁水泥钢筋混凝土通电锈蚀的断裂性能分析

为了得到氯氧镁水泥钢筋混凝土开裂时的临界锈胀力,基于断裂力学研究了氯氧镁水泥钢筋混凝土在通电锈蚀试验下的断裂性能.根据Glinka-Shen权函数法,利用已知参考荷载下的裂纹尖端应力强度因子,得到孔边单裂纹方形板的权函数;然后推导出孔边单裂纹方形板的裂纹尖端应力强度因子计算公式;最后,由混凝土断裂准则给出通电锈蚀下混凝土开裂时临界锈胀力的计算公式及变化规律.结果表明:随着裂纹长度的增加,裂纹尖端应力强度因子增加,临界锈胀力减小;随着钢筋直径的增加,裂纹尖端应力强度因子减小.     

再生水水质综合评价的主成分分析方法

采用主成分分析方法评价再生水综合水质,利用R软件强大的统计功能,对某再生水厂供水实测数据进行了定量化评价。结果表明,主成分分析方法是一种切实可行的水质综合评价方法,值得进一步研究,并能为其他相关行业的质量评价提供参考。     

输电线路采用高柱桩基础的可行性分析

介绍了我国输电线路工程中不断涌现出的基础形式,阐述了高柱桩基础具有铁塔根部斜材不易被盗、非专业人员不易攀登、可提高铁塔抗腐蚀能力的优点,从技术与经济方面对高柱桩基础在我国输电线路中的应用进行了可行性分析.     

Finite element reliability and sensitivity analysis of structures using the multiplicative dimensional reduction method

Finite element reliability analysis (FERA) has been used to evaluate the reliability of structures. In FERA, approximate methods are commonly used to estimate the mean and variance of the structural response, while its probability distribution is primarily derived based on the Monte Carlo simulation (MCS) method. This paper advances FERA by combining it with the multiplicative dimensional reduction method (M-DRM). The proposed M-DRM allows fairly accurate estimation of the statistical moments, as well as the probability distribution of the structural response. The distribution of the response is obtained using fractional moments, which are calculated from the M-DRM, along with the maximum entropy principle. The variance of the response, based on global sensitivity measures, is obtained as a by-product of the analysis. The proposed approach is integrated with the OpenSees software and is illustrated through examples of nonlinear finite element analyses of reinforced concrete and steel frames. The paper shows that the proposed approach is an accurate and efficient alternative for FERA.     

Two-dimensional stability analysis of a soil slope using the finite element method and the limit equilibrium principle

A slope stability analysis method using the finite element method and the limit equilibrium principle is presented in this paper to determine the critical slip surface and to calculate the minimum safety factor based on the stress field produced by a numerical simulation. This method assumes a cutting export and makes good use of geometric combination to reduce the search range during the calculation process. The proposed method was validated using two classical benchmark slopes and an engineering slope; it was also compared with other conventional limit equilibrium methods. The error between the proposed method and the limit equilibrium method was relatively small. The proposed method resolved several limitations of the traditional methods, and a comparison of the benchmark slopes showed that the proposed method exhibited good accuracy and efficiency. The proposed method can thus analyse both the stability of a natural slope and the stability of a soil slope under seismic loading conditions.     

Stability analysis of large-scale stope using stage subsequent filling mining method in Sijiaying iron mine

To improve mining production capacity, a stage subsequent filling mining(SSFM) method is employed for Sijiaying iron mine. The height of the stage stope is approximately 100 m. As there are farmlands and villages on the surface of the mine, the surface deformation should be controlled when the ore is mined out for the purpose of stope stability and minimizing surface subsidence. In this paper, according to the site-specificgeological conditions, the self-stability of the stagefi lling body was analyzed, and the failure mechanism of back filling body was defined. Thus the relationship between the exposed height of filling body and the required strength was obtained. Next, the stability of back filling body and the characteristics of surface subsidence due to mining of 450 m level were analyzed using physical modeling.Finally, a three-dimensional numerical model was established using FLAC3 D, with which the surface subsidence and the stability of stope were achieved. The results show that the stope basically remains stable during the two-step recovery process. The maximum magnitude of the incline is 10.99 mm/m, a little larger than the permissible value of 10 mm/m, and the horizontal deformation is 5.9 mm/m,approaching the critical value of 6.0 mm/m, suggesting that the mine design is feasible for safety mining.     

Nonlinear inelastic response history analysis of steel frame structures using plastic-zone method

A beam–column element formulation and solution procedure for nonlinear inelastic analysis of planar steel frame structures under dynamic loadings is presented. The spread of plasticity is considered by tracing the uniaxial stress–strain relationship of each fiber on the cross section of sub-elements. An elastic perfectly-plastic material model with linear strain hardening is employed for deriving a nonlinear elemental stiffness matrix, which directly takes into account geometric nonlinearity and gradual yielding. A solution procedure based on the combination of the Hilber–Hughes–Taylor method and the Newton–Raphson method is proposed for solving nonlinear equations of motion. The nonlinear inelastic time-history responses predicted by the proposed program compare well with those given by the commercial finite element package known as ABAQUS. Shaking table tests of a two-story steel frame were carried out with an aim to clarify the inelastic behavior of the frame subjected to earthquakes generated by the proposed program. A more practical analysis method for seismic design can be developed by comparing it with the presented frames for verification.     

Finite element model updating of a large structure using multi-setup stochastic subspace identification method and bees optimization algorithm

In the present contribution, operational modal analysis in conjunction with bees optimization algorithm are utilized to update the finite element model of a solar power plant structure. The physical parameters which required to be updated are uncertain parameters including geometry, material properties and boundary conditions of the aforementioned structure. To determine these uncertain parameters, local and global sensitivity analyses are performed to increase the solution accuracy. An objective function is determined using the sum of the squared errors between the natural frequencies calculated by finite element method and operational modal analysis, which is optimized using bees optimization algorithm. The natural frequencies of the solar power plant structure are estimated by multi-setup stochastic subspace identification method which is considered as a strong and efficient method in operational modal analysis. The proposed algorithm is efficiently implemented on the solar power plant structure located in Shahid Chamran university of Ahvaz, Iran, to update parameters of its finite element model. Moreover, computed natural frequencies by numerical method are compared with those of the operational modal analysis. The results indicate that, bees optimization algorithm leads accurate results with fast convergence.     

Analysis of virtual water consumption in China: using factor decomposition analysis based on a weighted average decomposition model

Exploring the cause‐and‐effect relationship between economic sectors and water resources is important to China. This study implemented a factor decomposition analysis by weighted average decomposition (WAD) model on the changes of Chinese virtual water (VW) consumption between 2002 and 2007, which includes both direct water consumption (consumed to produce final products) and indirect water consumption (consumed to produce intermediate products). The change in VW consumption is decomposed into three determinant factors: technological effect, economic structural effect and the products' scale effect. The results show that the volume of VW consumption in China has decreased from 5.92 × 10¹¹ m³ in 2002 to 5.17 × 10¹¹ m³ in 2007, which is mainly because of the technological effect (?5.48 × 10¹¹ m³). The increase in net VW exports is mainly due to the economic structure effect (6.19 × 10⁹ m³) and the fast growth of exports (3.49 × 10¹⁰ m³).     

Assessment of roof stability in a room and pillar coal mine in the U.S. using three-dimensional distinct element method

This paper examines the effect of different geological and mining factors on roof stability in underground coal mines by combining field observations, laboratory testing, and numerical modeling. An underground coal mine in western Pennsylvania is selected as a case study mine to investigate the underlying causes of roof falls in this mine. Three-dimensional distinct element analyses were performed to evaluate the effect of different parameters, such as the variation of immediate roof rock mass strength properties, variation of discontinuity mechanical properties, orientations and magnitudes of the horizontal in-situ stresses, and the size of pillars and excavations on stability of the immediate roof. The research conducted in this paper showed that the bedding planes play an important role on the geo-mechanical behavior of roofs in underground excavations. Therefore, an appropriate numerical modeling technique which incorporates the effect of discontinuities should be employed to simulate the realistic behavior of the discontinuous rock masses such as the layered materials in roof strata of the underground coal mines. The three-dimensional distinct element method used in this research showed the capability of this technique in capturing the important geo-mechanical behavior around underground excavations.     

Identifying fouling events in a membrane-based drinking water treatment process using principal component analysis of fluorescence excitation-emission matrices

The identification of key foulants and the provision of early warning of high fouling events for drinking water treatment membrane processes is crucial for the development of effective countermeasures to membrane fouling, such as pretreatment. Principal foulants include organic, colloidal and particulate matter present in the membrane feed water. In this research, principal component analysis (PCA) of fluorescence excitation-emission matrices (EEMs) was identified as a viable tool for monitoring the performance of pre-treatment stages (in this case biological filtration), as well as ultrafiltration (UF) and nanofiltration (NF) membrane systems. In addition, fluorescence EEM-based principal component (PC) score plots, generated using the fluorescence EEMs obtained after just 1 hour of UF or NF operation, could be related to high fouling events likely caused by elevated levels of particulate/colloid-like material in the biofilter effluents. The fluorescence EEM-based PCA approach presented here is sensitive enough to be used at low organic carbon levels and has potential as an early detection method to identify high fouling events, allowing appropriate operational countermeasures to be taken.