was the tallest structure of its type in the world. Trump Tower used of concrete and 3,800 tons of steelwork. The use of a concrete superstructure was in contrast to many other skyscrapers, which were built on steel frames. Scutt said a concrete frame was easier to build and was more rigid than a steel frame was. More specifically, it employed a concrete tube structure, which had been pioneered by Bangladeshi-American structural engineer Fazlur Rahman Khan in the 1960s. Trump Tower has been described as one of the city's least energy-efficient buildings per square foot. In 2017, Trump Tower's Energy Star score was 44 out of 100, below the city's overall median Energy Star score and lower than the 48 out of 100 score recorded in 2015. In May 2019 it was reported that eight of Trump's buildings in New York City, including Trump Tower, failed to meet the city's 2030 carbon emission standards, which were implemented as part of the city's "Green New Deal". The city threatened to fine Trump Organization for each year the infractions went unfixed. Interior Lower stories Originally, Trump only wanted to build an office building on the site, but the plot was in the Fifth Avenue special zoning district, which allowed more floor area for mixed-use towers with public space. In return for providing privately operated public space (POPS), Trump received floor area ratio (FAR) zoning bonuses that amounted to , allowing him to add several floors to the building. The public spaces in Trump Tower include the main lobby, the lower-level concourse and restrooms, and two outdoor terraces on the fourth and fifth floor. Under city law, POPS must be accessible from the street, provide a place to sit, and not require the public to purchase anything. The Trump Organization built a five-story, atrium, which serves as the tower's main lobby. The atrium is connected to the Fifth Avenue lobby to the west and 590 Madison Avenue's atrium to the east. Under the POPS agreement, the atrium is supposed to be open to the public from 8 a.m. to 10 p.m. seven days a week. When the tower opened, the Fifth Avenue Association awarded the first-prize "mixed use building" award to the atrium, the association's first such award in five years. Sometime prior to 2008, the Trump Organization removed the public bench and installed a counter selling Trump-branded merchandise in the public space