PSI - Issue 37

Mihaela Iordachescu et al. / Procedia Structural Integrity 37 (2022) 203–208 Iordachescu M. et al./ StructuralIntegrity Procedia 00 (2019) 000 – 000

204

2

the passing trucks (Zuo, and Letchford, 2010). Indeed, some cases of signaling supports collapsing on the roadways have occurred, with resulting damage and disruption to traffic. In particular, fatigue failures of cantilever traffic supports were reported in past decades by Dexter and Ricker (2002) and Weston McLean et al. (2004). A common feature of these fatigue failures was their location in specific zones like mast-arm to column connection, column to base-plate connection and anchor bolts. The present paper describes the research undertaken to analyze the failure preventively detected during a routine service inspection in an overhead porticoed structure for traffic signaling installed across the major north-south Spanish highway. The failure occurred after 25 years of service and was located at the middle-span bolted joint of the porticoed structure, when some loose bolts were found because they were partially or fully broken. The present failure analysis is based on the structural design data provided by the Spanish supervising authority for road and transportation and on the examination of the two groups of bolts (entire and broken) supplied from the dismantled joint by the maintenance company in charge of tunnels and traffic signaling on the highway. The research involves the elucidation in Fracture Mechanics terms of the structural behavior concerning the bolted connection where failure took place, the optical and scanning electron microscopy (SEM) fractographic study and microstructural analysis of the Zn-coated bolts with an in-service fracture that warned of the upcoming collapse, as well as on the tensile and fatigue tests of the bolt steel performed to assess its strength to static and cyclic loads.

Fig. 1. (a) Sketch of the supporting structure for traffic signaling; (b) Bolts removed from the middle span joint; (c, d) in-service inspection.

1.1. Structure features and failure description The damaged structure for signaling support regulated the traffic of a 3-lane carriageway close to the entrance to a long tunnel. The maximum speed allowed in the tunnel required most of the vehicles to decelerate, which induces vibrations of the signaling support typified in the Eurocode 3 (2005) and due to phenomena such as galloping, vortex shedding or truck- induced gusts. The risk of fatigue failure that this loading type involves for the connection joints of the signal support was not considered in design, since the highway construction dates from the late 1980s. A factor that aggravates such a risk is the environment aggressiveness because the support was located at an altitude exceeding 1200 m, and often the carriage-way was deiced with salt during winter in order to maintain good traffic conditions. The use of galvanized steel products for the signaling support structures protects them from the environment concerning local damage in the protective Zn-layer by localized corrosion phenomena such as pitting corrosion, stress corrosion cracking or, if combined, fatigue-corrosion (M. de Abreu et. al., 2018 and M. Iordachescu et. al., 2021). Fig. 1 shows a sketch of the porticoed supporting structure and Fig. 1c and Fig. 1d provide images of the undertaken service inspection of the damaged bolted joint. Fig. 1b shows one of the fractured bolts and two of the seven adjacent surviving bolts, together with the corresponding nuts and washers. They were supplied for the failure analysis after dismantling the bolted joint. All of them presented partial damage in the Zn-coating layer and scarce, dispersed corrosion pits when visually examined, even though the fracture surface of the broken bolt (Fig. 1b) also presented signs of progressive cracking despite the corrosion products deposited on it (an unequivocal sign that breaking had