Rope failures on tower cranes

This paper discusses two actual cases of wire rope failures which occurred in Toronto, Canada. Luckily, no one was injured. Subsequent investigations by the Canadian Safety Authorities and inquests by the Ministry of Labour raised much concern over the use of improper rope types on tower cranes. The political problem is that tower cranes tend to operate on public land and in many cases over public accessible streets and pathways. Although loads are not lifted over 'traffic' or 'people', a sudden rope failure can have a much wider damaging effect as the 'concrete bucket' tend to drops. Another important fact to mention is that tower cranes in Canada are much more heavily used than in other countries. This has something to do with our building technique which involves so called 'slip forms'. Such 'slip forms' are used to continuously pour concrete into a form which is being 'raised' as the concrete solidifies. This technique requires a constant supply of concrete which is hoisted up by tower cranes; in most cases hundreds of lifts per day. This is in sharp contrast to Europe where concrete is mainly 'pumped' not 'hoisted' and consequently, tower cranes are used to lift 'building materials' only and not concrete buckets. The effect is that tower cranes in Canada are employed to a much higher 'utilization' than in Europe. This realization and the acknowledgement that rotation resistant ropes (e.g. 8x25, 19x7, 19x19) are much more prone to undetected internal failures led the CSA 2248 Standard Committee to suggest to ban such rope constructions to be used on tower cranes in Canada. The following is the inspection report (adapted for this paper) on a tower crane rope failure as it actually happened in the City of Toronto in 2002, and a report on the testing of another 19x7 wire rope which had failed on a luffing jib tower crane some months after. lt should be noted that his paper is not intended to meet strict 'scientific' standards as its purpose is to reach out to 'users' and groups who are actually confronted with these problems on a day-to-day routine.

 Author(s): Buschmann, K.