WASHINGTON — U.S. President Donald Trump's administration said Wednesday it will impose 50 percent tariffs on steel, aluminum and copper imports based on their "full value" paid by U.S. customers in America rather than "artificially low" foreign prices. It also plans to adjust tariffs on derivative metal products, under which no additional sectoral duties will be imposed on products containing less than 15 percent steel, aluminum or copper by weight, while a 25 percent tariff will apply to those exceeding that threshold, a senior U.S. official said in an online briefing. Trump signed a proclamation on the adjustments that are set to take effect at 12:01 a.m. on Monday (Washington time). The White House said that the changes are intended to strengthen the metal tariffs to "more effectively address the national security threat posed by such imports." "The proclamation defines the way that tariffs are assessed, ensuring that they reflect the full value of imported steel, aluminum, and copper products -- not an artificially low foreign price," the White House said in a fact sheet. It appea