Numerical (FEA) evaluation of crane end buffer impact forces
The current codes of practice for the design of structures which were studied during this investigation do not explicitly account for the flexibilities and interactions of the Electric Overhead Travelling Crane (EOHTC) and the crane support structure. This leads to analysing the EOHTC and the gantry structure as a decoupled system for ease of computation. Thus, the interaction of the various components of the EOHTC and gantry structure is ignored, which may result in an incorrect assessment of the forces computed in the gantry structure’s members. This led to a study to determine the effects of a EOHTC on the gantry structure. The research was conducted through a series of limited experimental tests and extensive advanced Finite Element Analysis (FEA) simulations. This resulted in developing a computationally efficient FEA model of the full scale experimental EOHTC testing facility in the structural engineering laboratory at Stellenbosch University. The FEA model was developed to conduct simulations for the various load models, namely, vertical wheel load, horizontal longitudinal load and the horizontal lateral load models, as prescribed by the various codes. The research was then focussed at determining the maximum end buffer impact force responses when the crane runs into the end stops. The other load models were investigated by another researcher using the same FEA model. The results from the experimental tests were used to calibrate the FEA simulations. This proved exceptionally challenging due to the various structural response phenomena which occur during the impact of the crane against the end stops. A good correlation between the experimental values and the values predicted by the FEA simulations was achieved for the first impact. Modal analysis and modal superposition methods of analysis were used to determine the effect of the modes of vibration on the structural response to the end buffer impact. A FEA sensitivity analysis was conducted on a set of identified parameters which have a significant effect on the structural response to the end buffer impact. The maximum end buffer impact force was determined for a chosen level of reliability based on the responses from the sensitivity analysis using the Lagrange Multiplier method. These maximum end buffer impact forces are then compared with the forces prescribed by the codes. SABS 0160 slightly underestimates, while SANS 10160 severely overestimates the end buffer impact force obtained from the constraint optimization technique for a target level of reliability of β =3.