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Study of Hidden Corrosion on Prestressing Strands

Parajuli, Bishal
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1452257376

Abstract Details

2016, Master of Science, University of Toledo, Civil Engineering.
A parking garage near the north entrance of the University of Toledo built in 1976 had a prestressed spandrel beam fail. The L shaped prestressed spandrel beam exhibited a large dominant crack at the mid-span of the beam. The crack had nearly traveled to the entire depth of the beam and was few inches below the top of the beam. So it was hypothesized that this beam suffered brittle failure since there would have been micro-cracks if the failure was of ductile nature. On visual inspection of this beam and some other beams in the garage, there were signs of corrosion of prestressing strands. Rust in the steel reinforcement was visible along with some color changes in the neighboring concrete. As these indications of corrosion were not easily visible until the concrete covering these strands fell off due to deterioration; the late diagnosis caused much damage to the prestressing strands. When the steel suffered corrosion, the steel was substituted by the rust which increased the volume of the reinforcement. This research was aimed at understanding the cause of the brittle failure of the beam. The beam failed with two broken strands so cross sectional analysis becomes significant to know the behavior of concrete with progressive corrosion of its strands. The number of corroded strands for the beam to suffer brittle failure was determined by varying the strand number and is checked against the experimental values in Response 2000. Response2000 provided all the necessary results for the ultimate moment strength and the cracking moment. In order visualize the corrosion induced crack propagation, analysis of the beam was done in finite element software ABAQUS. It provided insight on the crack growth and the failure of the beam. Hand calculation was done to verify the results of Response2000 taking into account the load specifications of American Society of Civil Engineers/Structural Engineers Institute (ASCE/SEI) 7-10 and Precast/Prestressed Concrete Institute (PCI). The results from Response2000 and Mathcad indicated the beam was initially designed to provide enough capacity to perform well under the service load. But over the period of time, the beam suffered corrosion due to environmental effects and loading. The flaws in the concrete made the steel strands vulnerable to corrosion attack and the degraded strands did not perform to their full capacity. According to ACI 318-11, a structure is ductile if this ratio is greater or equal to 1.2. If this ratio falls below 1.2, the beam loses its ductility and becomes brittle in nature. When the analysis was run for two broken strands as that in the parking garage beam at failure, there was shift in the failure mode from ductile to brittle suggesting the corrosion of strands has affected its ductility and strength. The progressive corrosion of strands eroded them which in reduced the strength of the concrete and eventually led to the failure of beam. The moment capacity results from the analysis and hand calculation were in good agreement. The moment due to the estimated loading on the beam at failure was significantly less than the calculated capacity. Two hypotheses on the reason the failure load was less than the calculated capacity were examined. Magnetic flux leakage method for corrosion inspection was carried out, in collaboration with a team led by Prof Ghorbanpoor from University of Wisconsin, Milwaukee, on the suspected beams to further support the analytical and the scan results suggested irregularity in the strands. The result obtained from the magnetic inspection was consistent with the actual strand condition in most of the beams but on the beam 8-9-4CW between column 8 and 9, the scan results did not give the real picture of the strand condition inside the beam. The magnetic inspection suggested that the strands had some general corrosion which was not the case when the beam was excavated and strands were visually inspected.
Douglas Nims (Committee Chair)
Mark A. Pickett (Committee Member)
Liangbo Hu (Committee Member)
137 p.
Civil Engineering
corrosion of prestressing strands; finite element analysis; magnetic inspection of corrosion

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Citations

  • Parajuli, B. (2016). Study of Hidden Corrosion on Prestressing Strands [Master's thesis, University of Toledo]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1452257376

    APA Style (7th edition)

  • Parajuli, Bishal. Study of Hidden Corrosion on Prestressing Strands. 2016. University of Toledo, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=toledo1452257376.

    MLA Style (8th edition)

  • Parajuli, Bishal. "Study of Hidden Corrosion on Prestressing Strands." Master's thesis, University of Toledo, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1452257376

    Chicago Manual of Style (17th edition)

toledo1452257376
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This open access ETD is published by University of Toledo and OhioLINK.