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Robert D.J.,Monash University | Robert D.J.,RMIT University | Rajeev P.,Monash University | Rajeev P.,Swinburne University of Technology | And 2 more authors.
Canadian Geotechnical Journal | Year: 2016

Pipelines used for water and other services are very important lifelines in modern society. Commonly, these buried pipes are subjected to significant stresses due to external (traffic and earth) and internal (water pressure) loads. As many of these pipelines were laid sometime in the last century or earlier, in most cases their condition has deteriorated primarily by electrochemical and (or) microbiological corrosion. Corrosion activity (internal and external) can manifest in various forms, but in many cases will lead to reduced pipe thickness, which in turn leads to an increase in pipe stresses induced by the external and internal loads. Currently available analytical procedures to estimate pipe stresses are based on oversimplifications such as the two-dimensional (2-D) analysis based on Winkler springs, limiting their application to general pipe burial conditions. This paper describes the application of a three-dimensional (3-D) finite element method to analyse a buried pipe subjected to external and internal loads. Firstly, the finite element model is validated against the data from field tests conducted on the basis of a cast iron pipe that was laid in 1930 at Strathfield, Sydney, Australia. The results of these 3-D finite element analyses are then used to develop a closed-form expression to predict maximum stresses in pipes of different sizes buried in different soil types. Having obtained a good agreement between the proposed model outcomes and the 3-D finite element analysis results, the proposed model has been validated against the field test data under different internal and external loadings. The verified outcomes of the model reveal that it can be used to predict maximum stresses without conducting a full-scale finite element analysis, which often requires specific computational resources and computational skills. Furthermore, the proposed model can be used in probabilistic analyses, where a large number of calculations need to be carried out to account for the uncertainty of the input variables. The applications of the model are also discussed in relation to the assessment of pipe performance and remaining safe life. © the author(s) or their institution(s).

Laucelli D.,University of Bari | Rajani B.,University of Bari | Kleiner Y.,Rajani Consultants Inc. | Giustolisi O.,National Research Council Canada
Journal of Hydroinformatics | Year: 2014

Researchers extensively studied external loads since they are widely recognized as significant contributors to water pipe failures. Physical phenomena that affect pipe bursts, such as pipeenvironment interactions, are very complex and only partially understood. This paper analyses the possible link between pipe bursts and climate-related factors. Many water utilities observed consistent occurrence of peaks in pipe bursts in some periods of the year, during winter or summer. The paper investigates the relationships between climate data (i.e., temperature and precipitationrelated covariates) and pipe bursts recorded during a 24-year period in Scarborough (Ontario, Canada). The Evolutionary Polynomial Regression modelling paradigm is used here. This approach is broader than statistical modelling, implementing a multi-modelling approach, where a multiobjective genetic algorithm is used to get optimal models in terms of parsimony of mathematical expressions vs. fitting to data. The analyses yielded interesting results, in particular for cold seasons, where the discerned models show good accuracy and the most influential explanatory variables are clearly identified. The models discerned for warm seasons show lower accuracy, possibly implying that the overall phenomena that underlay the generation of pipe bursts during warm seasons cannot be thoroughly explained by the available climate-related covariates. © 2014 IWA Publishing.

Rajani B.,Rajani Consultants Inc. | Rajani B.,National Research Council Canada | Abdel-Akher A.,National Research Council Canada
Engineering Structures | Year: 2012

Longitudinal fracture is one predominant observed failure mode in large diameter cast iron pipes installed between 1850 and early 1960s. Some of these failures occur where there is evidence of some corrosion activity. This paper addresses three specific issues, namely, (1) review of expected loads, i.e., internal pressure, earth loads, traffic loads, (2) estimated pipe failure load (pipe resistance), and (3) estimated structural factor of safety. The second and third issues can be equally applicable to non-deteriorated and deteriorated pipes. The procedures described in this paper were motivated by the need to purposefully use the information derived from pipe inspection to assess the margin of safety of deteriorated large diameter cast iron pipes. A mechanistic model that accounts for cast iron material non-linearity is described. The model is validated using data obtained from experimental tests conducted in the mid 1930s on undamaged (new) pipes. The model is subsequently extended to permit the analysis of pipes with corrosion pits or corroded areas. Reliability analysis using Monte Carlo simulations is proposed to account for uncertainties in input data. Illustrative analyses of 16' and 48' diameter pipes subjected to vertical loads and internal pressure showed that significantly high margins of safety exist in cast iron pipes with no damage (due to corrosion and or casting voids) while this margin of safety is meaningfully reduced in the presence of corrosion pits or corroded areas. The methodology described should enable engineers to realistically assess the pipe resistance capacity and hence the corresponding margin of safety of undamaged or damaged cast iron pipes encountered in current operational conditions. © 2012 Elsevier Ltd.

Rajani B.,Rajani Consultants Inc | Kleiner Y.,NRC Institute for Research in Construction
Journal of Infrastructure Systems | Year: 2013

Deterioration in cast iron mains manifests itself in the form of corrosion. External corrosion is typically found to occur in pipes buried in corrosive soils while internal corrosion is dependent on water chemistry and flow characteristics. In the literature, corrosion of cast ron pipes (external and internal) is typically characterized by corrosion pit depth even though corroded area and corroded pit volume as well as pit location may enhance this characterization. Knowledge of these corrosion pit properties permits the assessment of its structural integrity. Typically, internal and external corrosion pits and corroded areas are observed to occur in many irregular shapes and sizes, which make their characterization a challenge. This paper describes extreme value statistical models that can be used to estimate external and internal corrosion pit depths in cast iron pipes using indirect properties or parameters. The goal of these corrosion models is to be able to predict corrosion pit depth based on available data with an acceptable degree of confidence. The external corrosion model is calibrated using external corrosion ata collected by ThamesWater Utilities Ltd (TWUL) and subsequently validated with data obtained from the inspection of four cast iron pipe lengths. The internal corrosion model was calibrated using internal corrosion data but sufficient appropriate data was not available for its validation. © 2013 American Society of Civil Engineers.

Rajani B.,Rajani Consultants Inc. | Rajani B.,NRC Institute for Research in Construction | Dickinson J.,NRC Institute for Research in Construction | Xue H.,NRC Institute for Research in Construction | And 2 more authors.
Journal of Infrastructure Systems | Year: 2014

Cast-iron pipes installed between 1850 and the early 1960s in North America, United Kingdom, and European countries were produced in foundries located near growing urban centers. Their considerable weight, size (especially larger-diameter pipes), and limited transportation facilities made their handling and delivery to the installation site difficult. Historical anecdotal evidence exists to suggest that some cast-iron pipes may have been damaged during delivery. This paper examines different mechanical models to examine what specific conditions may have led to pipe damage during delivery and installation. Analyses show that if pipes did incur damage, then cracks were likely to have occurred on the inside of the pipe bell or spigot ends. Furthermore, it appears that the spigot ends of smaller-diameter pipes had higher risk of damage during delivery, whereas both bell and spigot ends faced increased risk of damage in larger-diameter pipes. Monte Carlo simulations were conducted to account for uncertainties in the parameters that were used in the different models. © 2013 American Society of Civil Engineers.

Rajani B.,Rajani Consultants Inc. | Abdel-Akher A.,NRC Institute for Research in Construction
Engineering Structures | Year: 2013

The annular space between bell and spigot joints for cast iron pipes installed between 1850 and the early 1960s in North America was typically caulked with lead. Lead was caulked unto place using hand-held or pneumatic hammers and special chisels. Historical anecdotal evidence suggests that some bells may have cracked during caulking, especially if the jointer was over zealous in hammering the lead in place or used pneumatic hammers with excessive pressure to produce a tight joint. This paper examines two mechanistic models, one linear and another non-linear, to estimate the levels of hoop stress induced in the bell as a consequence of lead caulking. Illustrative analyses of lead caulking joints in 16" and 48" diameter pipes show that the linear model tends to predict unrealistic high stresses while the non-linear model produced more realistic stresses. Tensile hoop stresses can reach as high as 25% of the tensile strength of cast iron if the joint caulker is over zealous in the hammering action. The non-linear model was also used to reproduce caulking-induced stresses in tests conducted on 20" diameter pipes by Prior in 1935. © 2013.

Rajani B.,Rajani Consultants Inc | Rajani B.,National Research Council Canada
Journal of Engineering Materials and Technology, Transactions of the ASME | Year: 2012

The stress-strain response of cast iron under tension or compression is nonlinear. This paper examines how the hyperbolic constitutive law can be applied to characterize nonlinear stress-strain behavior of cast iron used in water supply networks. Procedures are described to obtain parameters of the hyperbolic constitutive law from either the response (data) obtained from simple uniaxial tensile and compressive tests or from bending tests. To demonstrate its applicability, this hyperbolic constitutive law is first applied to data obtained from uniaxial tensile and compressive tests conducted by Schlick and Moore (1936, Strength and Elastic Properties of Cast Iron in Tension, Compression, Flexure, and Combined Tension and Flexure, Bulletin 127, Iowa Engineering Experiment Station, Ames, IA). In addition, an approach to extract parameters for the hyperbolic constitutive law from bending (beam and pipe rings) tests is proposed and subsequently applied to tests conducted by Talbot (1908, Tests of Cast-Iron and Reinforced Concrete Culvert Pipe, Bulletin No. 22, University of Illinois, Urbana, IL). This latter approach is attractive for practical purposes because the test set up is simple and the test coupons are very easy to prepare. The hyperbolic constitutive law in conjunction with maximum normal strain theory as proposed by St. Venant (Collins, J. A., 1993, Failure of Materials in Mechanical Design: Analysis, Prediction, Prevention, John Wiley, New York, NY) was also used to predict failure loads. © 2012 American Society of Mechanical Engineers.

Rajani B.,National Research Council Canada | Rajani B.,Rajani Consultants Inc. | Lewandowski J.,Case Western Reserve University | Margevicius A.,City of Cleveland
Journal of Failure Analysis and Prevention | Year: 2012

This article describes the failure analyses of a 30"-diameter cast iron main that failed suddenly at the bell-spigot joint in Cleveland, Ohio in March 2008. The main had been operating largely without problems since its installation in 1880. The failure was analyzed using three models developed previously, each of which considered a specific failure mechanism candidate, namely (a) operational load or static analysis, (b) joint failure due to ground movement (settlement), and (c) fatigue failure. Operational load analysis clearly showed that while the factor of safety was significantly reduced in the presence of a concrete vault installed in 2002 just above the pipe, the margin of safety was still sufficient for the main to have performed safely. Ground movement analysis of the jointed pipe showed that the construction of the concrete vault above the joint of the 30"-cast iron main subjected the joint to rotation, which might have ultimately cracked the bell leading to failure. Under this circumstance, two failure scenarios are possible: namely, (a) additional rotation was large enough to cause the bell to split, or (b) additional rotation was sufficient to induce a minor crack in the bell but fatigue (repeated) loading caused the crack to grow over time until the combination of crack length and loading was sufficient to cause the bell to eventually split. The color differences along the fracture surfaces indicated that the fracture occurred in two distinct stages. This observation suggests that the second scenario is more plausible than the first. © ASM International 2012.

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