Shake table testing for the seismic response of a container crane with uplift and derailment

Abstract In the seismic analysis, the boundary condition of a container crane is a complex problem when dealing with the contact between the crane's toes and the ground surface or wharf deck. In operation, the wheels of container cranes move on rails freely but are usually anchored when at rest. Therefore, the wheels could be lifted up and derailed due to seismic excitation. The boundary condition of a container crane has not been fully addressed in past research. It has mostly been simplified as pin supports without considering the possibilities of uplift and derailment of the crane legs. Hence, there is a need to conduct a study focusing on the effects of derailment and uplift on a container crane's seismic response. This paper investigates the seismic response of a container crane via a shake table testing of a 1/20 scale crane constructed according to the similitude law, with a simulation of the boundary condition of the scale crane as a pin and a friction boundary. A white noise test was conducted to determine the natural frequencies of the scale crane, then the seismic response of the container crane was determined via three input ground motions. The three input ground motions were designed by matching real earthquakes to the Korean design elastic response spectrum and scaling down for the shake table testing. Under these seismic excitations, the responses of the container crane were considered in terms of uplift, derailment, portal movement, and bending moments. The shake table testing shows that the maximum difference in the natural frequencies of the crane for the portal sway mode, between the friction boundary and pin support, was 2.1%. Due to the effects of derailment and uplift of the landside legs, the bending moments in the crane's seaside legs with a friction boundary were 109% higher than those with a pinned boundary. In addition, a residual deformation was observed in the portal frame after the vibration had stopped when the scale crane was assigned a friction boundary.