Development of Algorithm for Automatic Defect Identification of Plate Structure in Impact Echo Assessment SAGAR DAS, A. K. RASHID, R. HAMID Department of Civil and Structural Engineering Faculty of Engineering and Built Environment Universiti Kebangsaan Malaysia 43600 UKM Bangi, Selangor MALAYSIA roszilah@eng.ukm.my Abstract: - Impact echo method is an effective way to assess flaw in concrete. The commercially available impact echo analysis is interpreted manually, thus, to evaluate large area by the method is neither practical nor cost effective. In order to enhance the method in application to plate structure such as bridge decks, where duration of investigation plays substantial influence on traffic activity, data analysis and interpretation should not only be rapid and objective but also provide automatic mapping of deck quality at the end of investigation. This paper represents the development of algorithm for automatic impact echo data analysis in frequency domain and verification on the validity of the proposed method. The algorithm is developed to compensate the in field variation of thickness frequency (f T ) of the investigated no defect portion of deck where a range of frequency at which f T would migrate is allowed. As a result, a software program can be developed based on this algorithm to eliminate the presence of skilled attendance during field investigation of slabs. Key-Words: - Algorithm, impact echo, plate structure, thickness frequency 1 Introduction Impact echo evaluation method has become a recognized option compare to other available acoustic methods since its assessment provides quantitative information of defects beneath the surface structure. Deck evaluation demands rapid screening of defects with least possible time. Even though other non-destructive methods like ground penetration radar (GPR) and infrared thermograph are more applicable in deck evaluation as those methods provide rapid evaluation with minimum traffic interruption, they have their own set backs. For GPR, the 2-D and 3-D visual data interpretation has made the GPR evaluation more user friendly for damage assessment of deck, but unfortunately, the GPR technique is not yet completely accepted by transportation engineers because its reliability is not satisfactory [1]. On the other hand, chain drag and infrared thermography are more suitable for assessment of near surface damage. These assessment methods are adversely susceptible to environmental condition where impact echo is not. For impact echo, previous research has shown that even moisture in concrete provide insignificant variation in P- wave velocity measurements [2]. Also, in comparison to electromagnetic waves, impact echo, which provides acoustic wave, can penetrate through metal ducts [3], thus offering information of cover below reinforcement. Thus practical application of impact echo method has become essential for condition assessment of deck. Impact echo method, although more practical, is not as popular as other conventional deck evaluation methods for following reasons; time consuming, require expert engineer for data interpretation and prolonged closure of lane during investigation. The time constraints are due to requirement of direct contact with the investigating surface. The assessment time can be cut short when data analysis is done automatically by means of any software, which considers all aspects of defect characterizing in frequency domain analysis. This paper looked into the development of algorithm to compensate the in field variation of thickness frequency (f T ) of the investigated no defect portion of deck where a range of frequency at which f T would migrate is allowed. As a result, a software program can be developed based on this algorithm to eliminate the presence of skilled attendance during field investigation of slabs. The automatic defect identification is applicable in bare (uncoated with asphalt) reinforced concrete deck and defects that are identified are delamination and void. 2 Background Proceedings of the 2nd WSEAS International Conference on ENGINEERING MECHANICS, STRUCTURES and ENGINEERING GEOLOGY ISSN: 1790-2769 186 ISBN: 978-960-474-101-4