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Case report Cantilever steel post damaged by wind Wei Sha a, *, Savko Malinov b a School of Planning, Architectu re and Civil Engineer ing, Queen’s University Belfa st, Belfast BT7 1NN, UK b School of Mecha nical and Aerospa ce Engin eering , Queen’ s Unive rsity Belfast, Belfast BT7 1NN, UK 1. Introduction Bushmills Primary School, in Northern Ireland, has two electronic patrol signs (towards 100 kg each) on cantilever posts whi ch were erecte d in Nov emb er 2010. Ove ra per iod of time, the pos ts had bee n und er a con tin uous swa yin g mov ement or vibration, caused by wind. Gusts and storms on 20 November 2013 caused one post to sheer in two places and fall with a consequence of blowing off the housing door. The post was situated in an exposed position. Fig. 1 shows the damage to the post. As can be seen in the phot os, it br oke at bo th the top and bott om of the aperture, at opposi teends. The post had anouter diameter of 142mm, and a wall thickness of 4 mm. Luckily, the post fell outwards but live cables were expos ed. The Depa rtment for Regi onal Deve lopment in North ern Irela nd ( DRDNI) was concerned abou t othe r simi lar cantilever posts and the appropriate Traffic Officers were made aware of this incident. This incident was reported through the procedures as set out in the health and safety manual used by DRDNI. Bushmills Primary School had not noticed any damage to the sign prior to the gusts. The School crossing patrol officer again had not noticed any damage and believed the sign was operational that morning. The sign was located next to Bushmills Out doo r Edu cat ionCentre . Sta ff fro m tha t building con firmed tha t the sig n wasblown down in the win d and the y had not noticed any previous damage. The sign was overlooked by a number of houses, and nobody witnessed any vandalism. The sign had a live cable running through it. If it was cut by vandals, the chances are that the culprit would be electroshocked or electrocuted. The post was then salvaged by cutting the remainder of the way through and removing the stump. The breaks are fairly straight and clean. The subsequent cuts show the marks of the angle grinder. The initial concern of the Roads Service is that this may be a fatigue failure due to cyclic loading within the design range rather than tensile failure due to the post being Case Studies in Engineering Failure Analysis 2 (2014) 162–168 A R T I C L E I N F O Article history: Recei ved 21 April 2014 Received in revised form 17 August 2014 Accepted 3 September 2014 Available online 16 September 2014 Keywords: Structural steel Cracks Fracture Metallurgical failure analysis Surface layers A B S T R A C T Ananal ysis for the caus e of fr acture fail ure of a cant il ever st eelsign post damaged by wi nd hasbeen carried out. An unu sual cause offai lur e hasbeen identi fied, whi ch is the sub jec t of this paper. Microscopy and microanalysis of the fracture surface showed that the failure was due to pre-existing cracks, from the fabrication of the post. This conclusion was reach ed after detecting and analysing a galv anised layer on the fracture surfaces. 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/ ). * Corres pondi ng author. Tel.: +44 28 9097401 7; fax: +44 28 9097427 8. E-mail address: [email protected] (W. Sha). Contents lists available at ScienceDirect Case Studies in Engineering Failure Analysis journal homepage: www.elsevier.com/locate/csefa http://dx.doi.org/10.1016/j.csefa.2014.09.001 2213-2902/ 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/ licenses/by-nc-nd/3.0/).
