Graduation Year

2019

Document Type

Thesis

Degree

M.S.M.E.

Degree Name

MS in Mechanical Engineering (M.S.M.E.)

Degree Granting Department

Engineering

Major Professor

Alberto A. Sagues, Ph.D.

Co-Major Professor

Christopher L. Alexander, Ph.D.

Committee Member

Rasim Guldiken, Ph.D.

Keywords

Cost Effective, Highway Bridges, Impedance, Magnetic, Non-Destructive

Abstract

With increasing use of grouted post-tensioned tendons in structures, there is a critical need for equipment to determine deficient grouting. Inadequate grouting can cause dangerous corrosion of the high-strength post-tensioning steel in the tendons. Evaluation should be non-destructive, and early detection is needed to take timely remedial actions to repair or replace any tendons that are affected before catastrophic failure occurs. In particular, there is need for an imaging method that shows the cross-section of the tendon being tested and flag any deficiencies present relative to the location of the strands in the cross section. The method should be rapid, economical, and not require specialized training, so as to allow for wide implementation.

A combination of both impedance and magnetic non-destructive sensors meeting those requirements has been pioneered by previous work performed at the University of South Florida. However, in that work, the measurement devices were suitable for laboratory use, but not optimized for field use. Specifically, only one sensor could acquire data at a time, and the system was not integrated into a single portable unit. It was important to investigate how the two sensors could be efficiently combined and optimized for extended field use while still maintaining adequate performance. This work implemented the integration of the two non-destructive sensors and was demonstrated in field structures.

The MARK III Field Tendon Imaging Unit (FTIU) created here combines both sets of sensors in a compact 3D-printed shell. The unit contains a high frequency signal generator, an impedance measuring circuit, a capacitive coupler to the tendon that identifies through impedance changes the presence of grout deficiencies, and a magnetic force measuring system that identifies and images the position of the steel strand bundle. The unit is capable of operation in commonly used 4.5-inch and 3.5-inch diameter bridge tendons, tolerant of irregular tendon shape, and designed for fast and economic replication. Operation does not require highly specialized personnel and images are obtained and displayed in a few seconds. Testing was conducted with in-house cast tendons with specific purpose built grouting deficiencies and field tendons that are currently in use in Florida Department of Transportation bridges. As field tests were performed, the unit was updated to reflect any areas that needed improvement. The real time cross-sectional tendon images that were generated with this unit successfully identified areas of deficient grout. The designed FTIU successfully met the target need for a compact, lightweight, rapid, non-destructive, economical device to determine in the field grouting deficiencies in bridge tendons.

Download

Share

COinS