r - The Hong Kong Polytechnic University

The 5th Cross-strait Conference on Structural and Geotechnical Engineering (SGE-5)
Hong Kong, China, 13-15 July 2011
SMART AGGREGATE-BASED DAMAGE DETECTION OF
FRP-STRENGTHENED COLUMNS UNDER REVERSED CYCLIC
LOADING
Haichang Gu 1 , Rachel Howser 2 , Yashar Moslehy 2 , , Hemant Dhonde 2 , Gangbing Song 1 , Y.L. Mo 2 ,
and Ashraf Ayoub 2
2 Department of Mechanical Engineering
1 Department of Civil and Environmental Engineering
University of Houston
4800 Calhoun, Houston, TX, 77004
ABSTRACT
Structural health monitoring is an important aspect of maintenance of large civil infrastructures,
especially for bridge columns in areas of high seismic activity. In this project, recently developed
innovative multi-functional piezoceramic-based transducers, called smart aggregates, were utilized
to perform health monitoring of a shear-critical reinforced concrete (RC) bridge column before
and after reinforced polymer (FRP) sheets were wrapped around the column for more strength.
During the experiment, the concrete column without FRP was first subjected to reversed-cyclic
loading protocol until failure. After the column failed, it was wrapped with fiber reinforced
polymer sheets, commonly used to retrofit seismically damaged structures, and the FRP
strengthened column was retested under the same reversed cyclic loading pattern. During the
reversed loading tests, based on developed smart aggregates, an active-sensing and an impact
response-based approach were used to evaluate the health status of the RC column and the FRP
strengthened column. Wave transmission energy is attenuated by the existence of cracks during the
loading procedure, and this attenuation phenomenon alters the transfer function curve between the
actuator and sensor. To detect the damage occurrence and evaluate the damage severity, transfer
function curves were compared with those obtained during the healthy status. A transfer
function-based damage index matrix was developed to demonstrate the damage severity at
different locations. Furthermore, a weighted damage index is developed to quantitatively evaluate
the overall damage status. Experimental results verified the effectiveness of the smart aggregates
in health monitoring of the FRP-strengthened column as well as the un-strengthened column. The
experimental results show that the proposed smart aggregate-based approach can successfully
detect the damage occurrence and evaluate its severity.
KEY WORDS
FRP, RC columns, piezoceramic, smart aggregate, health monitoring, weighted damage index.
INTRODUCTION
Natural hazards, such as earthquakes, cause severe damage in RC structural systems. RC columns
are typically the primary elements of energy dissipation in bridges subject to seismic loads. Failure
of bridge columns can result in the collapse of bridge girders, which was the scenario for the
majority of the bridges damaged in past earthquakes. It is imperative to quickly assess the severity
of the damage and the health status of an RC structure in real time or near real time after a disaster
event to provide vital structural safety information for decision makers. This is especially true for
large-scale infrastructures where it is desirable to design an automated and distributed system to
perform structural health monitoring.
In this project, innovative piezoceramic-based devices, called smart aggregates, were used as
transducers for structural health monitoring of RC columns under a reversed-cyclic loading
procedure. The proposed smart aggregate is a multi-functional device. In additional to the
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