Min Koo Kim

Localization and Quantification of Concrete Spalling Defects Using Terrestrial Laser Scanning

AbstractDuring construction and maintenance of concrete structures, it is important to achieve and preserve good surface quality of their components. The current quality assessment for concrete surfaces, however, heavily relies on manual inspection, which is time demanding and costly. This study presents a new technique that can simultaneously localize and quantify spalling defects on concrete surfaces using a terrestrial laser scanner. Defect-sensitive features, which have complementary properties to each other, are developed and combined for improved localization and quantification of spalling defects. A defect classifier is developed to automatically diagnose whether the investigated surface region is damaged, where the defect is located, and how large it is. Numerical simulations and experiments are conducted to demonstrate the effectiveness of the proposed defect-detection technique. Furthermore, a parametric study with varying scan parameters is performed for optimal detection performance. The resul...

Investigating electro-mechanical signals from collocated piezoelectric wafers for the reference-free damage diagnosis of a plate

The electro-mechanical (EM) signals from piezoelectric (PZT) wafers are investigated for reference-free damage diagnosis so that a notch in a plate can be detected without requiring direct comparison with a baseline EM signal. Two identical PZT wafers collocated on both surfaces of a plate are utilized for extracting the mode-converted Lamb wave signals created by a notch. As harmonic input voltage signals are exerted on the collocated PZT wafers, the corresponding mode-converted Lamb wave signals become steady-state in the presence of damage. Applying fast Fourier transform to these mode-converted Lamb wave signals followed by a proper normalization, the EM signals associated with the mode conversion can be obtained. The theoretical finding of this paper is validated through spectral element simulations of a cantilever beam with a notch. The effects of the size and the location of the notch on the mode-converted EM signals are investigated as well. Finally, the applicability of the decomposed EM signals to reference-free damage diagnosis is discussed.

Piezoelectric transducers for assessing and monitoring civil infrastructures

Abstract: Piezoelectric transducers are being commonly used for sensing and actuation applications for smart structural systems. In particular, they are widely used for structural health monitoring (SHM) thanks to such attractive characteristics as multi-functionality, nonintrusivity, light weight, low cost, rapid response time, and high repeatability. This chapter first deals with the basic principles of piezoelectric transducers and the characteristics of piezoelectric materials. Subsequently, various piezoelectric transducer-based SHM methodologies including guided wave, impedance, and acoustic emission techniques are summarized. Then, their state-of-the-art applications to SHM fields are presented. Future trends are also discussed in this chapter.

Active dimensional quality assessment of precast concrete using 3D laser scanning

Quality assessment of precast concrete panels is an important factor that affects overall quality of construction. As prefabrication becomes popular at construction sites, demands for automatic and accurate inspections of the dimensions of the precast concrete panels have increased. Current techniques for measuring the dimensions of precast concrete panels, however, heavily rely on qualified inspectors, and are time and labor demanding. To overcome these limitations, a dimensional measurement technique for precast concrete panels is proposed using a 3D laser scanner. For autonomous implementation of the dimensional measurement, a new feature extraction algorithm of extracting only boundary points of the precast concrete panels is developed. To increase the measurement accuracy, a compensation model is employed to account for the dimension losses caused by an intrinsic limitation of laser scanners. This study focuses on measurements of length, width and squareness of precast concrete panels in a noncontact and speedy manner. Experimental validations on actual precast slabs are conducted to verify the applicability of the proposed dimensional measurement technique for precast concrete panels.

Formulation of a framework for quality assessment of precast concrete based on 3D laser scanning

This study presents a framework for quality inspect ion of precast concrete components using the 3D laser scanning technique. As precast concrete-ba s d rapid bridge construction is getting standardiz ed, quality assessment of the precast concrete becomes critical for preventing any failures during the construction process. Moreover, as Building Informa tion Modeling (BIM) gains popularity in the construction industry, autonomous and intelligent i nspection systems are needed. Current method for quality control of precast concrete components, how ever, heavily relies on visual inspection and conta cttype measurements, which are time and labor demandi ng. Also, storage and delivery systems of inspectio n information such as the procedures and results of q uality inspection are lacking. To overcome these limitations of the current quality assessment techn ique for precast concrete, this study aims to devel op a BIM-based framework for efficient quality inspectio n of precast concrete with the use of a 3D laser scanner. First, we formulate practical guidelines i ncluding detailed inspection procedure, selection o f optimized scanner and scan location, inspection cri teria, and data storage and delivery system. Second , t investigate the applicability of 3D laser scanning to precast concrete quality inspection based on the proposed framework, a case study inspecting quality of a lab-scale object assumed as precast concrete component is presented for detecting defects.

Full-Scale Application of a Dimensional Quality Assessment Technique to Precast Concrete Panels using Terrestrial Laser Scanning

Nowadays, precast concrete panels are one of the most popular construction components. To safeguard the overall quality of construction projects, it is important to ensure that the dimensional quality of precast concretes conform to the design specifications. In order to achieve this, a terrestrial laser scanning (TLS)-based automated dimensional quality assessment technique has been developed by the author’s group. The scope of this paper is such that the developed dimensional quality assessment technique is further advanced so that this technique can also be applied to full-scale precast concrete panels with complex geometries. A full-scale precast slab with dimensions of 10,610 mmx1,980 mm in a precast manufacturing company is used as a test target to validate the effectiveness of the dimensional quality assessment technique. The challenges encountered during the data analysis of the full-scale test are investigated and resolved using optimized algorithms. Furthermore, comparison of the effectiveness between the conventional technique (deviation analysis) and the proposed technique is conducted. The average dimensional error for the proposed technique is 5.2 mm, while that of the conventional deviation analysis is 10.2 mm, demonstrating that the proposed technique can have high potentials in estimating and assessing the dimensional properties of the precast concrete panel.

Understanding a Reference-Free Impedance Method Using Collocated Piezoelectric Transducers

A new concept of a reference-free impedance method, which does not require direct comparison with a baseline impedance signal, is proposed for damage detection in a plate-like structure. A single pair of piezoelectric (PZT) wafers collocated on both surfaces of a plate are utilized for extracting electro-mechanical signatures (EMS) associated with mode conversion due to damage. A numerical simulation is conducted to investigate the EMS of collocated PZT wafers in the frequency domain at the presence of damage through spectral element analysis. Then, the EMS due to mode conversion induced by damage are extracted using the signal decomposition technique based on the polarization characteristics of the collocated PZT wafers. The effects of the size and the location of damage on the decomposed EMS are investigated as well. Finally, the applicability of the decomposed EMS to the reference-free damage diagnosis is discussed.