The Making of the Trees

The project to make and roll the steel that went into the World Trade Center began in 1967.The steel for the bases of Towers 1 and 2 had to be able to withstand incredible stress, Lukens was chosen due to their expertise in the production of small-batch specialty steels.

The process started with scrap entering the plant via truck and train. It was selected and sorted according to the particular “recipe” to produce steel with the necessary properties of strength and flexibility, as determined by Lukens/ Engineers.

The scrap was then melted in the electric arc furnace, and poured into molds forming ingots. These ingots were then sent to the rolling mill, where they were reheated and rolled to the proper thickness.

The steel plates were then sent to Plant 5, where they were flame cut into the distinctive “tree” shape. The finished trees were then shipped (using three rail flat cars each) for final assembly by Pittsburgh-Des Moines.
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The trees were made, rolled and welded in 1968 and 69, and shipped to New York via rail. The trees are massive, up to 70 tons in weigh, and spanned the first nine floors of the two World Trade Center towers. The buildings were completed in 1970, standing 1,350 feet or 110 stories tall, and stood until the tragic day in September 2001.

The photo above shows Pittsburgh-DesMoines Heavy Assembly Shop (HAS) on Neville Island. The building is still there today, but it is under different ownership. PDM's fabrication plant at Neville Island was established in 1907.