1 Copyright © 2013 by ASME Draft Proceedings of the 2013 Joint Rail Conference JRC2013 April 15-18, 2013, Knoxville, TN, USA JRC2013-2468 DEVELOPMENT OF A 5-CAMERA TRANSFER LENGTH MEASUREMENT SYSTEM FOR REAL-TIME MONITORING OF RAILROAD CROSSTIE PRODUCTION Weixin Zhao MNE Department, Kansas State University Manhattan, KS,USA B. Terry Beck MNE Department, Kansas State University Manhattan, KS,USA Robert J. Peterman CE Department, Kansas State University Manhattan, KS,USA Chih-Hang John Wu IMSE Department, Kansas State University Manhattan, KS,USA ABSTRACT Knowledge of transfer length during production is critical for maintaining continuous production quality in the modern manufacture of prestressed concrete railroad crossties. Traditional laboratory methods for measuring transfer length, using manual instruments such as a Whittemore mechanical gauge or surface mounted resistance-type strain gauge, are simply not suitable for production operation. They are too time-consuming to implement, require extensive surface preparation, and can also require special operator training to provide accurate and reliable surface strain profiles from which the transfer length can be determined in a post-processing manner. In contrast with earlier manual methods, the newly developed non-contact Laser Speckle Imaging (LSI) technique has been shown to be capable of providing rapid and accurate surface strain measurement and consequently also rapid transfer length assessment. This system has recently been automated and combined with the new Zhao-Lee (ZL) least-squares strain profile fitting technique for quickly and reliably processing surface strain data. The automated system and processing procedure have been shown to provide an improved assessment of transfer length, unhampered by human intervention and subsequent potential human judgment bias. This paper presents recent progress toward the development of a 5-camera non-contact transfer length measurement system that is capable of continuous monitoring of railroad crossties in a production plant. This is made possible using an optimized version of the previously successful LSI system, which minimizes the number of surface strain measurements required to achieve reliable transfer length assessment. Experimental results and analysis will be presented for the latest multi-camera prototype concept for this new system design, demonstrating that only a few discrete surface strain measurements are required to achieve accurate and reliable transfer length assessment. Thus, for the first time it is now possible to envision practical real-time quality control monitoring of railroad crossties during an in-plant production operation. INTRODUCTION Concrete railroad crossties have shown many desirable features over wood crossties, including long life expectancy, environmental friendliness, and better fuel economy of the trains, etc. [1]. Concrete railroad crossties are fabricated by casting concrete around already tensioned steel wires or strands. After the casting process is complete and the concrete has hardened, a detensioning procedure is undertaken by cutting the reinforcing wires or strands at both ends of the concrete crosstie to release the tension. The stress then transfers from the embedded wires or strands directly to the concrete. The prestressing force is developed gradually from each end of the concrete crosstie, where the stress is zero, to locations far away from the ends, where the stress level reaches its maximum. The