Damage identification and assessment of civil infrastructure using local and global methods

[Truncated abstract] Structural health monitoring methods can be generally classified as either local or global. Global methods are based on relatively low-frequency vibration measurements of the structure. Their advantages are that only a small number of sensors are needed and the low structural vibration modal properties are relatively easy to be measured. However, a small number of low global vibration modes are often not sufficiently sensitive to minor damage in a structure. Local methods, on the other hand, could be very sensitive to small damage but their detection range is usually small. To overcome the limitations of the two approaches, an integrated health monitoring system that combines the global vibration measurement and local wave propagation and acoustic emission data is developed in this study. It takes the advantages of these approaches to compensate their limitations. An impulse hammer and accelerometers are used to generate impact forces and to record acceleration histories at several control points of the structure for global vibration measurement. PZT actuators and PVDF sensors are attached on surface of the structure to generate and record guided wave (GW) propagations along the structure. The PVDF sensors are also used to capture acoustic emissions (AE) due to crack initiation for passive structural health monitoring. Two reinforced concrete (RC) beams and a steel bar under different damage scenarios are tested to verify the performance of the system. ... For steel rebar, the reflection and transmission (RT) coefficients are adopted in numerical simulation to quantify the discontinuities such as crack depth in the steel bar. The fracture mechanics model is used to obtain the RT coefficients. Further, a pipe SE is also developed. Parametric studies are performed to evaluate the effect of additional masses on wave propagation in pipes. Moreover, imaginary SEs are proposed in this study, which are combined with the real structural elements to model wave reflections at structural boundaries. The imaginary SEs make modelling wave reflection at boundaries possible. Numerical simulations and experimental results show that SE method is effective in modelling GW propagations and GW propagation is sensitive to local structural damages. To identify structural damage from measured data and finite element model, in this research, a finite element (FE) model updating process using a newly developed optimization method, Clonal Selection Algorithm (CSA), is presented. A finite element model for prestressed and reinforced concrete beam is developed. The model updating method is used to identify damage or prestress force from measured data. Several objective functions are compared. A similar SE model updating procedure is also presented to identify structural damage. Two spectral elements with structural damage (DSE) are developed to model the local (cracks in reinforcement bar) and global (debonding between reinforcement bar and concrete) damage in one-dimensional homogeneous and composite waveguide, respectively. Transfer matrix method is adopted to assemble the stiffness matrix of multiple spectral elements. Two displacement-based functions and two frequency-based functions are used as objective functions in this study. The results demonstrate the capability of the proposed method in damage identification based on measured wave propagation data.