SLACK ROPE ANALYSIS FOR MOVING CRANE SYSTEM

摘要

The reliability and security of rope design for moving crane are very important especially for the nuclearplant in high seismic zones. The conventional linear analysis indicates that a slack rope occurs very likelyfor severe earthquake load excitation. In other words, the rope will overcome its lifted weight and will gointo compression. The nonlinear time history method according to NOG-4154 shall be applied for slackrope design. In order to perform nonlinear time history analysis subject to earthquake excitation, thetension-only nonlinear properties of element shall be taken into account. The designated program –GTStrudl or other nonlinear – program may have such a capability for solving nonlinear dynamic systems.However, the result shows that the current tension-only nonlinear finite element in GTStrudl has thereasonable accurate results with comparing theoretical results for damped single degree-of-freedom(SDOF), but it fails to converge for a large-scale DOF of computer model for trolley-bridge system due tosevere nonlinearity of rope. Simplified analysis shall be employed in rope slack nonlinear study. Becauseonly vertical mass of lifted weight is included, the rope forces caused by horizontal earthquake load inhigh modes are very small and can be neglected. According to this dynamic characteristic, we simplifyand use two-degree-of-freedom (2DOF) structural systems to represent a multi-DOF of bridge-trolley withlifted load system in vertical direction. The results show that this simplification proved to be very accurateand successful. This paper presents a very simple 2DOF nonlinear dynamic model and compares ropeforces between linear dynamic analysis and nonlinear slack rope analysis. The results also show that ropeforce could be much larger than those from conventional linear dynamical analysis varied with ropelength. The proposed slip-slack model shows that the brake slip device can limit rope force, predicts thedisplacement for prescribed design level, and prevents rope failure due to slack rope impact.