On the Use of L-shaped Granular Chains for the Assessment of Thermal Stress in Slender Structures A. Bagheri & E. La Malfa Ribolla & P. Rizzo & L. Al-Nazer & G. Giambanco Received: 20 September 2014 /Accepted: 20 October 2014 # Society for Experimental Mechanics 2014 Abstract Slender beams subjected to compressive load are common in civil engineering. The rapid in-situ measurement of this stress may help preventing structural anomalies. In this article, we describe the coupling mechanism between highly nonlinear solitary waves (HNSWs) propagating along an L- shaped granular system and a beam in contact with the gran- ular medium. We evaluate the use of these waves to measure stress in thermally loaded structures and to estimate the neutral temperature, i.e. the temperature at which the stress is null. We investigate numerically and experimentally one and two L- shaped chains of spherical particles in contact with a prismatic beam subjected to heat. We find that certain features of the solitary waves are affected by the beam’ s stress. In the future these findings may be used to develop a novel sensing system for the nondestructive prediction of neutral temperature and thermal buckling. Keywords Highly nonlinear solitary waves . Curved chain . Discrete particle model . Nondestructive testing, Thermal buckling . Neutral temperature Introduction Columns, beam-like structures, and continuous welded rails (CWR) all subjected to axial stress are common in civil engineering. For example, a section of CWR that is several hundred meters long is prone to buckling in hot weather and breakage or pulling apart in cold weather. To prevent these accidents a reliable nondestructive methodology able to deter- mine thermal stress or the rail neutral temperature (RNT), defined as the temperature at which the net longitudinal force in the rail is zero, is needed. For example, the knowledge of the neutral temperature T N would allow for the estimation of the critical temperature T cr that a structure may withstand before buckling by using the following relationship: T cr ¼ T N - σ cr Eα ð1aÞ where σ cr is the Euler stress, E is the Young’ s modulus, and α is the thermal expansion coefficient of the material. The measurement of the in situ stress or alternatively of the RNT has been a long-standing goal [1], as the in-situ measurement of the current temperature T c and the current stress σ c can be utilized to estimate the neutral temperature by: T N ¼ T c þ σ c Eα ð1bÞ A. Bagheri : P. Rizzo (*) Laboratory for Nondestructive Evaluation and Structural Health Monitoring Studies, Department of Civil and Environmental Engineering, University of Pittsburgh, 3700 O’Hara Street, Pittsburgh, PA 15261, USA e-mail: pir3@pitt.edu A. Bagheri e-mail: abb46@pitt.edu E. La Malfa Ribolla : G. Giambanco Department of Civil, Environmental, Aerospace, and Materials Engineering, University of Palermo, Viale delle Scienze, Ed. 8, Palermo 90128, Italy E. La Malfa Ribolla e-mail: emma.lamalfaribolla@unipa.it G. Giambanco e-mail: giuseppe.giambanco@unipa.it L. Al-Nazer Office of Research and Development, Federal Railroad Administration, 1200 New Jersey Avenue, SE, Washington, DC 20590, USA e-mail: leith.al-nazer@dot.gov Experimental Mechanics DOI 10.1007/s11340-014-9964-1