Increasing Hurricane Winds? Dockside Crane Retrofit Recommendations

Abstract

Recent hurricanes have struck the US East and Gulf Coasts with historic fury. Studies indicate that the intensity, size, and duration of tropical cyclones (hurricanes and typhoons) are increasing dramatically and may be correlated, at least in part, to increasing ocean surface temperatures (Emanuel 2005 and 2006, Hoyos 2006). This appears to be a global phenomenon and many scientists predict the trend is not likely to abate any time soon. Dockside cranes are typically designed to resist hurricane wind pressure based on 50-year mean recurrence interval (MRI), 3-second gust wind speeds, at 10 m above ground. Refer to the ASCE–7 standard (Minimum Design Loads for Buildings and Other Structures). These design wind speeds are statistical, based on historic wind speed data. Does this historic data reflect current trends? Dockside container cranes, unlike buildings, have very little redundancy in their structural design for resisting wind loads. In hurricane-prone regions, the cranes are held by one or more tie-downs at each corner. Slight increases in wind speed have amplified effects on corner tie-down uplift forces (McCarthy, Vazifdar 2004). If a single tie-down fails, the crane will likely collapse. This paper presents recent trends in hurricane wind loads, a novel new design “ductile link” tie-down system, and an acceptable risk method for guiding the selection of an appropriate level of retrofit for an existing crane structure.