Publication Date

2013-07-30

Availability

Open access

Embargo Period

2013-07-30

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Civil, Architectural and Environmental Engineering (Engineering)

Date of Defense

2013-07-15

First Committee Member

Antonio Nanni

Second Committee Member

Ronald Zollo

Third Committee Member

Carol Hays

Fourth Committee Member

Paul Ziehl

Abstract

The process of implementing a damage identification strategy for infrastructure is referred to as Structural Health Monitoring (SHM). This term has been used in the last decades to describe a range of systems implemented on constructed facilities, including Reinforced Concrete (RC), for the purpose of informing owners/operators on the condition of structures that experience gradual or sudden changes to their state of serviceability. The increased interest in SHM and its associated potential is due to its significant life-safety and economic benefits. Within the family of non-destructive test methods, Acoustic Emission (AE) is classified as a passive technology capable of providing information useful in locating active cracks in structural members. AE crack locating methods are affected by signal attenuation and dispersion of elastic waves due to macro inhomogeneity and the geometry of RC structural members. AE methods of crack location are already well established in steel structures but due to the heterogeneous nature of concrete accuracy, identification, and the attenuation of acoustic waves are still areas where development is needed. The goal of this dissertation is to advance AE technology applied to RC structures in order to locate cracks and to study wave propagation in relation to variables common to concrete mixture design and structural element geometry. The investigation is divided into three studies. The first study, considers the sources of uncertainty in the AE crack location process. A methodology is proposed to capture and locate events that are associated with cracks in RC members during loading and unloading regimes. In particular, the relationship between crack events and load is analyzed to assess the feasibility of using AE information to evaluate the cracking behavior of two RC slab strips as load is applied. A second study experimentally and analytically investigates the relationship between AE wave attenuation and velocity and the variables of RC constituent materials and structural geometry. To this end, ten slabs with variable parameters including strength, unit weight, aggregate size, aggregate type, geometry and presence of steel reinforcement were cast. AE signals were generated at known locations on the slab surface using Pencil Lead Breaks (PLBs), an ASTM standard method, and recorded by four AE sensors. Results confirm the effects of the above-named parameters on attenuation and velocity of acoustic waves. The outcomes of this study can be used to develop a reference database for AE wave attenuation and velocity applicable in the field for SHM of concrete members. The last study experimentally investigates the effects of cracks on AE wave propagation (attenuation and velocity). Two similar RC slabs are manufactured and load tested. In parallel with the well-established measurements of load and strain, an active AE monitoring is carried out throughout the load test. Variable AE wave velocity is introduced, tabulated and correlated to crack depth ratio as parameter describing the severity of crack in the RC member. The results show that cracks can prominently affect the attenuation and velocity of AE waves.

Keywords

Reinforced Concrete; Crack; Location; Acoustic Emission; Health Monitoring

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