## 1 Introduction  
Ship-to-shore (STS) gantry container cranes are commonly used to transfer loaded containers to and from ships. The safety and efficiency of their movements are economic building blocks for many nations. The basic container crane transfer mechanism is shown in Figure 1. The container crane is located on rails which are laid on a quay wall/wharf. The rail gage/span is about 30.5 m to allow room between the legs for the hatch covers and maintenance vehicles [1]. The portal frame serves as the main structure supporting the whole crane. Thus, most of the failure mechanisms that appeared during past earthquakes were due to the portal legs. The height of the trolley and boom are approximately 48.7 m to suit the needs for vessels. However, the higher the trolley above the quay wall, the more difficult it is to control the load [2]. The 63-m outreach allows the crane to lift containers for vessels with 22 containers on deck. The whole structure is made of steel plate, except for the diagonal braces which use steel tubes. Aside from the crane's own weight, other external loads to which the crane is subjected include stairs, drive trucks, stowed pins, machinery house, \(\frac{1}{2}\) festoon, snag device, boom hoist rope, etc. The material properties and the kinds of loadings are described in detail in the following sections. Unlike the types of structures that are extensively studied all over the world such as buildings, bridges, nuclear power plants, etc., STS container cranes do not receive the attention they deserve, as ordinary people have limited exposure to them during everyday use; as a result, they do not receive the attention they deserve. For crane design, wind loads (i.e., operating condition loads and overload conditions) are the most important sources used to design the cranes, more so than seismic load because earthquakes rarely occur [3], especially in low-seismicity countries. However, once such a crane collapses due to earthquake, the economic and human influence will be hard to predict. Just as with the design of any commonly used structure, STS container cranes need to be designed in the presence of major sources of uncertainty. Some of the major design variables may be similar or the same to those of the other commonly used structures. However, the propagation of uncertainties from the parameter to the system level is expected to be very different because of the unique configurations  
Figure 1: Overall dimensions of a Korean container crane. of the STS systems, different performance requirements of the systems, and different consequences of failure. The overall design concept of an STS crane is critically evaluated in this paper while emphasizing the presence of uncertainty in the design variables. This study identifies several important design parameters and their effects or sensitivity in maintaining or satisfying the overall performance requirements subjected to similar risks and reliabilities of other structures. Since the major sources of uncertainty cannot be completely eliminated, managing these uncertainties in the most appropriate way is expected to produce the most economical and damage-tolerant STS that can benefit the world communities in the most efficient way. Alternatively, efforts must be made to reduce the implication of the presence of uncertainty in them as much as possible. In this study, time-history ground motions are applied to a three-dimensional (3D) finite element (FE) model with an assumption that the output is a deterministic function of a variety of input variables. The FE model of this study refers to an STS container crane located in South Korea. The analysis employs a tornado diagram approach in which all random variables are expressed as a set of horizontal bars, referred to as swings [4; 5; 6]. The wider the swing of an input variable, the larger the effect on the response of the structure. The rest of this article is structured as follows: Section 2 will introduce the methodology of the sensitivity analysis.