REVIEW OF PROVISION OF LOADS TO STRUCTURES SUPPORTING OVERHEAD TRAVELLING CRANES

摘要

Operational difficulties are experienced in South Africa with overhead travelling cranes and their support structures. With industry support, a programme was launched to research the basis of design of crane support structures systematically, in order to improve future designs. This paper reflects the insights developed from a combination of theoretical studies from the research programme, with considerations from practical experience with the design and maintenance of such facilities. The material was developed as input to the review of the South African Loading Code SABS 0160 (1989), which is presently in progress. An initial evaluation of SABS 0160 (1989) shows that crane loading provisions are considerably simplified in relation to the provisions of BS 2573 (1983), from which it was derived. Further comparison with other design codes such as Eurocode prENV 1991-5 (1997) and DIN 15018 (1984) shows that SABS 0160 (1989) does not possess the necessary conservatism that should be expected relative to the simplistic nature of the current load specifications. There is no evidence of deficiencies with regard to the safety of structures designed according to SABS 0160 (1989). Failures regarding serviceability limit state criteria do however occur. The most notable of these are fatigue failure of the support structure, crane wheel and rail wear, crane performance failure due to structures that are too stiff or too flexible. These failure occurrences suggest that provisions are adequate for a limited range of cranes, depending on the operational frequency of the crane and the loading state relative to the maximum capacity of the crane. These observations led to a more extensive comparison between the South African loading code and a range of codes and standards applied elsewhere, notably, ISO 8686-1 (1989), DIN 15018 (1984), NEN 2018 (1983), AISE TR 13 (1979) and BS 2573 (1983). The comparison shows marked differences in loads considered in the various design documents, and their respective magnitudes. The necessary adjustments to the present code are considered. An important component of the codified design process, is the crane classification. A classification system specifically for the support structure, reflecting the relevant design considerations, is proposed.