New Zealand port characterisation and wharf seismic response

Abstract

New Zealand Ports perform the vital role of facilitating the transfer of goods to and from the world markets. This critical infrastructure has been identified as a lifeline that needs to remain operational immediately after a natural hazard. For this reason the aim of this research presented was to investigate the vulnerability of New Zealand ports to seismic hazards. The research was specifically focused on understanding the seismic response of wharves. Data regarding all of New Zealand’s 14 ports was collected from port companies and was used to characterise New Zealand wharves and determine the most common structural configurations. The Cashin Quay 3 wharf at Lyttelton Port was chosen as a case study because it experienced significant damage as a result of the Canterbury Sequence of Earthquakes. For the purpose of quantifying the impact of earthquakes on wharves, a numerical model of the Cashin Quay 3 wharf was developed using OpenSees. The model was validated against measured deck displacements after the September 4th and February 22nd Canterbury earthquakes. Time-history, sensitivity and fragility analyses were conducted on the model to quantify its seismic response. In the time-history analysis the model was subjected to the entire earthquake sequence and the resulting deck displacement and pile moment history was presented. The results confirmed the presence of ongoing displacements as a result of small aftershocks experienced at Lyttelton Port and showed the significance of modelling both the wharf and soil embankment in an integrated model that captured the interaction between both components. The sensitivity analysis confirmed the influence of geotechnical parameters on overall wharf response. Fragility analysis of the CQ3 model consisted of subjecting the model to a series of scaled ground motions and fitting the response data to lognormal probability distributions. The CQ3 fragility curves accurately captured the damage state reached by the wharf after the September 4th and February 22nd earthquakes. Five variations were made to the CQ3 model based on the wharf characterisation study. These variations represent typical combinations of lateral load resisting mechanisms. Fragility analysis of the variations indicated the superior performance of the combination of tie-back and moment resisting pile-deck connections over the use of a raked pile.