Ship Loader Platforms Using a Pile/Micropile System

In 2008, a condition survey indicated that major structural improvements were necessary to extend the service life of the 50-year-old United Harvest grain import/export dock located on the Columbia River at the Port of Kalama in Kalama, Washington. Rather than repair the dock, the owner elected to replace it, modernize the dockside grain-handling equipment, and install two 150-foot [45.7 m] boom fixed-tower ship loaders to increase the ship loading rate from 1,200 metric tons per hour (mtph) [1,323 short tons per hour (stph)] to 3,200 mtph [3,527 stph]. To support the towers and resist the ship berthing and mooring loads, two new batter pile-supported concrete platforms were constructed. Because the riverbed at the site consisted of approximately 65 feet [20 m] of highly liquefiable sand over solid basalt, a micropile was installed inside each batter pile and pretensioned into the basalt to resist the high-tension loads on the piles. By setting the lock-off load equal to just greater than the maximum non-seismic tensile demand of each pile, the micropile force/displacement response exhibited a bilinear behavior under tensile loads. The tensile strain of the pile/micropile system increases when the non-seismic forces are overcome, and this behavior is used to reduce seismic forces on the platform. This paper focuses on the selection of the fixed-tower ship loaders, the design of the ship loader platforms, and the pile/micropile bilinear response and its incorporation into the design per the International Building Code (IBC).