ABSTRACT
The orthotropic steel deck is a welded structure consisting of a flat and thin steel plate stiffened by a series of longitudinal ribs with support by orthogonal crossbeams. Since its development in 1950’s, the orthotropic steel deck system has been utilised all over the world. Over the last few decades, many reports have been published concerning fatigue cracking in orthotropic steel decks resulting from the complicated welded details and minimised plate thickness to reduce weight. In Japan, more than 2,300 orthotropic steel deck bridges have been constructed so far and fatigue cracking in orthotropic steel decks has been observed mainly in heavily trafficked urban expressways. In 1980’s and 1990’s, fatigue cracking at the rib-to-crossbeam connection and the welded rib splice was a major issue, while during the last 15 years, fatigue cracking at the rib-to-deck welded joint has been increasingly observed where trapezoidal ribs are used.
The objective of this paper is to present a novel inspection method using phased array ultrasonic testing for rib-to-deck welded joints of orthotropic steel decks. Phased array ultrasonic testing has been used for medical diagnosis for more than forty years. Meanwhile, application of the phased array ultrasonic testing to industries wasn’t so popular until 1990’s, and then the rapid technology development encouraged the use of phased array ultrasonic testing in the industrial field. A phased array ultrasonic probe consists of multiple transducer elements each of which can act as a single ultrasonic transducer. The transducer elements are arranged in various patterns where individual and independent driving of an element must be attainable without inducing vibration in nearby elements and the performance of each element must be as close as possible for the formation of a homogeneous beam. Due to the ability to control the acoustic characteristic of ultrasonic beams, phased array ultrasonic systems can achieve the electronic scanning techniques that are not made possible by using conventional ultrasonic systems. Three main advantages of phased array ultrasonic testing over conventional ultrasonic testing are increased inspection sensitivity, increased inspection coverage and decreased inspection time.
Fatigue cracks initiated at the rib-to-deck weld root can grow into either the deck plate or the weld bead. Therefore, in order to detect fatigue cracks at the rib-to-welded joint as internal part-through cracks at the early stage of development, both the deck plate and the weld bead are necessary to be examined. In view of this, an electrically driven scanner holding twin phased array ultrasonic probes is developed, allowing us to perform simultaneous examination of the deck plate and the weld bead (Fig. 1). The developed scanner is applied to the orthotropic steel deck of the Meiko-Chuo Bridge, a three-span steel cable-stayed bridge and the ability to detect internal part-through cracks in the weld bead is verified. Electrically driven scanner holding twin phased array ultrasonic probes (a) general view drawing and (b) schematic of twin probes fixed to the deck plate and the rib wall. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig29_1.tif"/>
