Abstract
Electric overhead & gantry multiple girder cranes with top running bridge & trolley used at nuclear facilities are typically designed in the US per the American Society of Mechanical Engineers Nuclear Operating Guide-1 [1] (NOG-1) Standard which is approved by the US Nuclear Regulatory Commission (NRC). Per NOG-1, seismic qualification of the material handling equipment is a major design consideration based on the equipment’s safety classification. Nuclear material handling devices typically use steel wire ropes to hoist the critical load. Seismic events can cause excessive vibrations in the crane and the critical load that is hoisted by the crane hook leading to a potential slack rope condition, which is an important safety consideration per NOG-1.
The work presented in this paper compares two analyses methodologies — the linear response spectrum analysis and the non-linear time-history analysis — as it pertains to slack ropes. A simplified crane finite element model with linear springs representing the ropes is employed for the linear response spectrum analysis. A similar crane finite element model with tension only springs representing the ropes is employed for the non-linear time-history analysis. Equivalent sets of response spectra and five time-history input data are utilized. The aim of this paper is to investigate if the linear response spectrum analysis always yields conservative results for the slack rope condition as compared to the non-linear time-history analysis, and if so, the expensive non-linear time-history analysis required per NOG-1 for the slack rope condition can be avoided without compromising safety.
