Polder R.B.,TNO |
Polder R.B.,Technical University of Delft |
Angst U.M.,ETH Zurich |
Pacheco J.,CTLgroup |
Concrete Solutions - Proceedings of Concrete Solutions, 6th International Conference on Concrete Repair, 2016 | Year: 2016
Where exposed to an aggressive environment, concrete structures will develop reinforcement corrosion at some point in their life. Chloride ions from de-icing salt or sea water induce pitting corrosion. Local cross section reduction may occur relatively quickly and expansion due to corrosion products precipitating may crack and spall concrete cover and reduce steel-concrete bond. With the aging of the existing stock, questions arise about the effects of corrosion on their structural behaviour, safety and reliability.TNOhas started a four-year programme to investigate this subject. One project concerns modelling of pitting corrosion from electrochemical principles, aimed at prediction of cross section loss with time and, in a next stage, corrosion product formation. Existing models for pitting corrosion are highly simplified and essentially two-dimensional, while pitting is clearly a three-dimensional phenomenon. The difference may have serious consequences for structural safety. New approaches are needed, including new conceptual models and addressing uncertainties on several levels. The paper presents some conceptual models for pitting corrosion and reports preliminary results of numerical (finite element) modelling of pitting corrosion, based on solving potential and current distributions and resulting in cross section loss as a function of time. Further work including experimental validation is foreseen. © 2016 Taylor & Francis Group, London.
Mehrabi A.B.,P.O. Box 1565 |
Ligozio C.A.,CTLGroup |
Ciolko A.T.,CTLGroup |
Journal of Bridge Engineering | Year: 2010
The Hale Boggs Bridge opened to traffic on October 5, 1983. At the time, it was the first U.S. cable-stayed crossing over the Mississippi River. The PE (polyethylene) protective sheathing was damaged in many of the cables before and during installation, and after the opening of the bridge to traffic. Repairs were attempted to correct the defects in cable sheathing. Many of the repairs performed poorly and failed to protect the main tension element. The condition of 39 out of 72 cables indicated a critical need for repair and timely action was recommended. To address these damages, and to assure the structural integrity of the bridge structure, several strategies involving a range of repair and replacement options were evaluated using life cycle cost analysis. It was concluded that the strategy to replace all cables presents the best value among evaluated alternatives. The design of the complete 72 cable array replacement is the first occasion on which this process is attempted in North America. The final design of the replacement cables is heavily influenced by the geometric restrictions of the existing anchorage locations. The replacement cables are being designed for a 75-year design life and incorporated with the latest advancements in corrosion protection and vibration control. Maintenance of traffic design is an essential part of the project. The bridge is a critical regional link and constitutes a hurricane evacuation route. Traffic maintenance during cable replacement was designed to be as unobtrusive to the public and commerce as practical. This paper describes efforts associated with cable condition assessment, rehabilitation strategy, and design considerations and concepts, undertaken by the writers since 2002 to improve the condition of this major river crossing. © 2010 ASCE.
McCann D.M.,CTLGroup |
Viz M.J.,Exponent, Inc.
Structures Congress 2015 - Proceedings of the 2015 Structures Congress | Year: 2015
Day-to-day environmental and operational conditions that lead to deterioration of in-service structures are most often addressed through prescriptive inspection routines or handled on an ad-hoc basis. These approaches lack effectiveness if inspections are untimely or efforts are misdirected. Gains may be realized by following risk-based inspection paradigms in civil infrastructure. Related industries, such as the oil and gas, chemical process, energy and commercial aerospace sectors have long been applying risk-based methods to perform hazard assessments and to then prioritize the inspection and maintenance of structures and systems. These risk-based methods are used to identify, evaluate and control hazards, many of which involve more typical day-to-day deterioration hazards in addition to rare, high-consequence hazards. This paper will serve to highlight hazard assessment techniques and risk-based inspection methods from related industries and suggest how analogous methods may be used for civil infrastructure.
Murphy M.,CTLGroup |
Belarbi A.,University of Houston |
Bae S.-W.,Texas Tech University
PCI Journal | Year: 2012
This paper investigates the behavior of full-scale prestressed concrete girders strengthened in shear with externally bonded carbon-fiber-reinforced polymer (CFRP) sheets. The study is aimed at identifying the failure modes and effects on ultimate bearing capacity associated with the application of CFRP laminates as externally bonded shear reinforcement for prestressed concrete I-girders. A total of 16 full-scale prestressed concrete girder tests are reported. Test parameters include the cross-sectional shape, effects of preexisting damage, CFRP strengthening scheme, different anchorage systems, and transverse steel reinforcement ratio. The test results show that the failure modes are complex and can vary considerably with respect to the test parameters. The test results also show that the application of externally bonded CFRP reinforcement for shear may not yield an increase in the load-carrying capacity of a girder compared with a reference member that is not strengthened with CFRP.
Lim M.K.,Universal Construction Testing |
Construction and Building Materials | Year: 2013
The uses of different nondestructive testing techniques have been well documented over the past decade or so. The techniques provide the opportunity to obtain the problem without having to chip into the test member. Many times, an NDT practitioner uses only one nondestructive test method to perform the evaluation. If the scope of work is straight forward, using a single test method is acceptable. However, there are times when a single test method does not provide enough information on the problem, and thereby combining different methods is essential. Knowing the advantages and limitation of each test method is key to applying the right combination of test methods to the evaluation. This paper provides insight into the different test methods and also provide case history whereby combining different nondestructive test methods were used in the evaluation. © 2012 Elsevier Ltd. All rights reserved.
Sheehan M.J.,CTLGroup |
Forensic Engineering 2012: Gateway to a Better Tomorrow - Proceedings of the 6th Congress on Forensic Engineering | Year: 2013
The expansion of an entertainment complex in the eastern US was under constructed in 2003 when a portion of a multi-story parking garage collapsed during an 8th level concrete floor pour. This investigation was initiated to determine the cause of progressive collapse. Garage construction generally consisted of stay-in-place, precast, prestressed concrete formwork and cast-in-place composite floor system connected with mild steel reinforcing to cast-in-place concrete columns and shear walls. The collapse of an approximate 50 by 180 ft. area of the garage occurred during placement of cast-in-place floor system concrete at an upper level of the parking garage. A progressive failure of multiple levels of the stay-in-place precast formwork and cast-in-place composite floor system occurred, but nearly all perimeter columns and shear walls in the area remained standing. The authors were retained to investigate and evaluate the cause of the failure and study the progressive collapse. The investigation included site inspections of the garage collapse site and examination of garage structural components at an offsite location where debris was retained following demolition efforts. Visual inspection of the debris, review of eyewitness accounts, examination of construction documents, and structural analyses were used to evaluate the cause of the progressive collapse. Hand calculations and a three dimensional non-linear fracture mechanics model were also used to assess structural behavior of the composite reinforced concrete garage system. Strength of as-designed and influence of as-constructed connection conditions between the precast formwork floor system and cast-in-place columns and shear walls were evaluated. Results of the investigation were used to successfully assess the cause of the failure and make recommendations on how to avoid such accidents in the future. © ASCE 2013.
Lee S.Y.,CTLGroup |
Daugherty A.,CTLGroup |
35th International Conference on Cement Microscopy 2013 | Year: 2013
Radiation shielding concrete (RSC) is used in applications such as nuclear power plants, health care facilities, collegiate test reactors, national laboratories, and research facilities. The type and quantity of aggregates in RSC are important component for radiation protection properties of the concrete. Either natural heavyweight aggregates or synthetic aggregates are used in RSC. ASTM C638 Standard provides two classes of aggregates/materials used in RSC; (1) Class 1 - gamma ray shielding, and (2) Class 2 - neutron shielding. Iron ores are one of the most common Class 1 natural aggregates for gamma ray shielding. Colemanite is the most common Class 2 natural aggregate. Minerals with substantial boron content, such as colemanite, have been proven to be particularly effective in absorbing thermal neutrons without producing highly penetrating gamma rays. Iron ore and colemanite aggregate samples were petrographically examined in accordance with ASTM C295 to detect potentially harmful (deleterious and undesirable) materials in RSC. Each sieve fraction of an aggregate sample was examined, and its constituents identified, classified, and tabulated into the following three categories: (1) particles consisting almost entirely of iron-bearing metallic minerals (or boron minerals for the "colemanite" aggregate), (2) particles of mixed iron-bearing metallic minerals and impure materials, and (3) particles of impure materials. Particles in each category were examined using different test methods and techniques (combinations of transmitted and reflected light microscopy, X-ray diffraction, and X-ray fluorescence) to determine potentially harmful materials in RSC. Although ASTM C295 applies to aggregates for general use as well as for RSC, pétrographie examination of these specialized aggregates for RSC involves in more stringent QA requirements, different levels and extent of examination, and proper experience and training of the petrographer performing the examination.
Brewe J.E.,CTLGroup |
American Concrete Institute, ACI Special Publication | Year: 2011
The Oklahoma City Bombing is used as a case study to demonstrate how structural damage investigations can lead to code changes and improvements in design. This paper describes the use of seismic detailing to improve blast resistance. Such detailing has been incorporated into the soon to be published ASCE/SEI Standard on Blast Protection of Buildings.
Dodge E.C.,CTLGroup |
Lewis A.R.,Simpson Gumpertz and Heger
Construction and Building Materials | Year: 2013
Our practice in forensic engineering often includes investigating the causes of reported problems, documenting the extent and types of problems found, developing repair solutions, implementing a pilot (mockup) repair program, and monitoring the general implementation of the final repairs. This paper focuses on the somewhat unique problems associated with building a roadway above occupied spaces and the non-destructive testing we used to help solve those problems. This paper summarizes our efforts to identify, investigate, and repair the leakage problems. We outline relevant design details, describe the problem, review available resources, show representative results from a non-destructive GPR investigation program, and present the results of the repairs. © 2012 Elsevier Ltd. All rights reserved.
Journal - American Water Works Association | Year: 2013
Over the past 70 years, prestressed concrete cylinder pipe (PCCP) has been used to construct approximately 19,000 mi of our nation's water transmission mains. Numerous unanticipated performance shortfalls, caused largely by the actions of one manufacturer during the 1970s, have resulted in concerns among owners related to use of PCCP that continue to this day. An emerging PCCP risk management strategy is to use the combination of electromagnetic inspection, finite-element-based structural analysis, and acoustic monitoring to gauge extent, significance, and rate of deterioration. This article examines the state of the art as it relates to PCCP risk assessment and provides constructive input related to the limitations associated with the various technologies currently being used. Additionally, suggestions for getting the most out of a risk assessment are presented.