2010 Project Progress Report
Program Name: Rapid FRP Repair of Damaged Reinforced
Concrete Columns
Program Manager / PI: Dr. Rudi Seracino
Company / Sponsor: FYFE Co., LLC
Project Number: NCSU-1
Overview: Develop a rapid FRP repair technique to restore strength and ductility to earthquake
damaged reinforced concrete columns with buckled and/or ruptured longitudinal steel reinforcement.
Experimental Plan: This research project is composed of two phases: (I) confined cylinder tests and (II)
full-scale column repair. For the first phase 6”x12” cylinders composed of various cementitious
materials, will be wrapped with different FRP-matrix alternatives. The cylinders will be tested in pure
compression, and stress-strain curves will be obtained. The strain will be measured using Particle Image
Velocimetry (PIV), which utilizes high resolution cameras and a Matlab-based program. The strain data
collected from the new PIV data acquisition system will be validated with the use strain gages in the
hoop and axial directions. Once the stress-strain curves have been collected for each wrap alternative,
the data will be compared to the predictions of current confinement models. If deemed necessary, new
constitutive models will be proposed. The observations and outcomes of phase I, will direct the repair
strategy adopted for phase II. The constitutive model(s) of phase I is will also enable the prediction of
the response of the repaired columns of phase II.
For phase II, up to 3 reinforced concrete columns (7ft high x 2ft diameter) will be available for
repair and testing under reversed-cyclic loading. Prior to repair, the columns will have been tested as
part of another (unrelated) research program to investigate the strain accumulation effect on the cyclic
response of reinforced concrete columns. The damaged columns will be classified as “moderately”
damaged where some of the longitudinal steel reinforcing bars are buckled, or “severely” damaged as
some of the longitudinal steel reinforcing bars will have ruptured. In both cases, all damaged concrete
will be removed, the intact concrete cleaned and the original circular concrete section restored. For the
moderately damaged columns, the section within the plastic hinge region of the column will be wrapped
with the optimal alternative from phase I. For the case of the severely damaged columns, it will likely be
necessary to replace ruptured reinforcing bars. The ruptured bars will be left in place and within the
concrete cover region of the section, additional longitudinal reinforcement will be anchored into the
concrete footing and extend beyond the plastic hinge region as necessary to develop sufficient strength
and/or strain capacity.
Goals and Motivation: The goals of the phase I cylinder tests are to compare the experimental data
with existing confinement models to determine their suitability for the new wrapping alternatives being
considered. If necessary, new models will be developed. An extensive test matrix which involves
innovative combinations of core materials, adhesives and matrices, and fiber sheets and grids has been
developed to determine the optimum rapid repair alternative. The results of phase I will be used directly
in phase II. The goals and motivation for Phase II are two-fold. First, current recommendations prevent
the use of FRP based repair systems for damaged reinforced concrete columns where the longitudinal
steel reinforcement is not straight. This research program presents a unique opportunity to quantify the
extent of ductility and strength that can be restored and ultimately, define true “damage control” limit
states for repair. Secondly, there is a need for rapid repair strategies that can restore sufficient ductility
and strength such that critical life-line infrastructure can resume emergency service within hours of a
seismic event. Hence, this proposed research program will focus on simple to install rapid curing
systems with a minimum service life of 3-5 years to provide sufficient time for replacement of members,
or structures, if necessary.
Previously Reported Findings: This is the first progress report since the proposed project was
approved.
Budget Update: $25,000
Findings Since Last Report: A literature review of existing FRP and FRP/steel spiral confined concrete
constitutive models is in progress. The test matrix for phase 1 has been finalized and approved.
Approximately 75% of the cylinder specimens for phase I are ready for testing. This involved several
trials to establish and document best practice for mixing materials and wrapping. The PIV strain field
measurement system has been acquired is in the testing and validation stage. Testing of the cylinders
will commence as soon as reliable data is consistently obtained with the PIV system.
Potential Member Company Benefits: The outcomes of this project can introduce a new market for
FRP repair of damaged concrete infrastructure and provide the framework for the development of new
FRP strengthening/repair systems including fiber grids and non-organic matrices.
Next Steps: The next major step is to test thirty confined concrete cylinders as part of phase I.
The stress-strain data will then be analyzed and critically compared against published FRP confined
constitutive models. Depending on the outcomes of the comparison, it may be necessary to develop a
new model appropriate for new repair alternatives being considered. As soon as possible the outcomes
of phase I will be used to finalize the best repair alternative(s) for the wrapping of the three large-scale
damaged reinforced concrete columns of phase II. In addition to testing the columns, phase II will
include the numerical modeling of the sectional response using the confined concrete models of phase I
to predict the behavior of the repaired columns.