Rasko P. Ojdrovic

RISK ANALYSIS OF PRESTRESSED CONCRETE CYLINDER PIPE WITH BROKEN WIRES

The paper reviews the significant impact that the development of Remote Field Eddy Current/Transformer Coupling (RFEC/TC) technology for inspection of Prestressed Concrete Cylinder Pipe (PCCP) has made on the condition assessment of the PCCP lines. The paper presents a summary of results of the research effort that had the following scope: hydrostatic pressure testing of PCCP with broken wires; field investigation of the condition of PCCP with broken wires away from broken wire zones; finite element analyses of the cracking process and of the ultimate failure of PCCP with cracked core; and development of simplified approach for risk analysis.

CONCRETE CREEP AND SHRINKAGE PREDICTION FROM SHORT-TERM TESTS

This paper presents a method for predicting the ultimate creep and shrinkage from the results of short-term standard creep and shrinkage tests on 15-cm-diameter cylinders. Short-term tests are defined as those performed during a time period not exceeding 28 days after exposure. The paper uses both Bazant-Panula (BP-KX) and American Concrete Institute (ACI) 209 models to predict the ultimate concrete creep and shrinkage from the short-term test results. Predictions are compared with the results of long-term creep and shrinkage tests. Results show that the accuracy of prediction of the ultimate creep and shrinkage increases significantly when short-term tests results are used to adjust the models. Relative to both test-adjusted BP-KX and ACI model predictions, the coefficient of variation of long-term measured shrinkage strains is less than 20 percent, and the coefficient of variation of long-term measured instantaneous plus creep strains is typically less than 7 percent.

Seismic damage evaluation of a steel building using stress triaxiality

This paper presents a procedure for the evaluation of the seismic damage in steel moment frame buildings. The rotational capacities, of typical connections of a building in the Los Angeles area, which suffered extensive damage during the Northridge earthquake, were determined using stress triaxiality as an indicator for fracture. The rotational demands of the same connections were obtained from a three-dimensional finite element analysis of the building model. Comparisons of the rotational demands at several locations in the building to the rotational capacities determined by the stress triaxiality analysis showed that fracture of steel moment connections of the building are governed by the triaxiality of stresses. Based on a number of moment connections analyzed, the paper suggests a moment capacity equation for the pre-Northridge welded steel moment connections taking into account the fracture incidence due to stress triaxiality effect. The moment capacity of such connections as dictated by stress triaxiality compared favorably to FEMA-350 requirements.

Prestressed Concrete Cylinder Pipe Condition Assessment What Works, What Doesn't, What's Next

This paper presents a summary of the research performed for Water Research Foundation on the evaluation of condition assessment and remaining service life prediction/failure margin analysis technologies in use for prestressed concrete cylinder pipe (PCCP). The project involved a literature review, an industry survey, and a workshop. The literature review integrated the published experiences with all condition assessment and monitoring technologies. The industry survey included design, distribution, and compilation of responses to a questionnaire sent to water utilities, technology stakeholders, and consultants to document their experiences. The workshop provided a venue to discuss utility experiences and utility needs. The results of the literature review, industry survey, and workshop were used to develop a Best Practices Guidance Manual that identifies a method of prioritizing pipelines for condition assessment; condition assessment, monitoring, and failure margin analysis technologies that are in existence or near deployment; benefits and limitations of existing technologies; gaps in knowledge; what works and what does not work in management of a pipeline; and further research and field work needed to improve condition assessment and pipeline management.

CONDITION ASSESSMENT AND PERFORMANCE OF 50-YEAR OLD LCP

The paper describes the conditioning assessment of the water distribution system in Cheyenne, Wisconsin that includes four prestressed concrete cylinder pipelines. The multidisciplinary condition assessment performed included the following: collection and review of data on pipeline and operational history and all available data related to the pipelines; electromagnetic soil conductivity survey along the pipeline alignment; soil and groundwater testing; external inspection of pipe coating, prestressing wires and steel cylinder, and sampling of coating and soil; material testing including petrographic analysis and testing of mortar coating and testing of prestressing wires, steel cylinder, and concrete core; hydraulic transient analysis, structural analysis; and evaluation of high risk areas along the four pipelines.

Quality Assurance Procedures for Repair of Concrete Pressure Pipes with CFRP Composites

This paper proposes quality assurance procedures to be followed prior to, during, and after repair of concrete pressure pipes with carbon fiber reinforced polymer (CFRP) liners. A design framework for such repairs was recently proposed (Zarghamee et al. 2010). In this paper, the importance of and requirements for prequalification of the engineer, manufacturer, installer, and inspector; on-site verification of quality of construction, including material preparation, installation, curing, and post-installation inspection; and testing of CFRP are presented. The available guidelines for CFRP repair of other concrete structures are reviewed, existing requirements that are particularly important for repair of pipelines are highlighted, and modifications and additions to these requirements are discussed. Required physical and mechanical tests on the CFRP liner and associated testing standards are listed, and evaluation of the test results is presented.

VERIFICATION OF PCCP FAILURE MARGIN AND RISK CURVES

Failure margin analysis of prestressed concrete cylinder pipe (PCCP) evaluates the effect of broken prestressing wires on performance of the pipe and its margin to failure using the risk curves technology. The risk curves technology is based on structural analysis calibrated and verified by hydrostatic pressure testing of pipes with broken wires to failure, nonlinear finite element analysis that simulates the behavior of distressed pipe to failure, and external inspection of pipes with broken wires. This paper compares the observed levels of distress from external inspection of failed or highly distressed pipes to those predicted using the risk curves technology with the observed number of broken wires and expected internal pressure.

Cure Behavior of Epoxies Used for CFRP Repair of Pipelines

This paper presents the results of a laboratory testing program on the curing behavior of one impregnating epoxy (Tyfo S) and one thickened epoxy (Tyfo WS) that are most commonly used in carbon fiber reinforced polymer (CFRP) repair of pipelines, including progression of cure at various temperatures; relative humidities and relationships between the degree of cure and properties such as hardness, glass transition temperature, and long-term water absorption of these epoxies; and tensile properties of the CFRP. Based on the tests performed, curing schedules can be established to achieve a minimum degree of cure of 85%, which is typically used in practice for newly installed CFRP liners prior to refilling of pipelines. Quality assurance procedures are proposed for verification of the degree of cure achieved in the field, including a project example where the proposed procedures have been used.

ANALYSIS OF BLAST EFFECTS ON PCCP PIPELINE

The goal of this paper is to formulate guidelines that determine acceptable and safe blasting criteria for the prestressed concrete cylinder pipe (PCCP) lines near a quarry. The proposed approach for the analysis of blast effects includes three components that relate maximum strain waves in the soil that result from blasting to damage limit states of a particular type in its present condition. The three components are: field inspection of pipes; site characterization based on analysis of blast data; and, evaluation of PCCP limit states.

Analysis and Performance of PCCP Mortar Coating

The aggressive nature of the soil surrounding prestressed concrete cylinder pipes (PCCP) has been identified as causing pipe failures related to deterioration of mortar coatings used to protect the prestressing wires. This paper presents a discussion of the degradation mechanisms and methods that can be useful for evaluating the condition of mortar coating and assessing its remaining useful life.