One of the most famous buildings of the structural expressionist style, the skyscraper's distinctive X-braced exterior shows that the structure's skin is part of its "tubular system". This is one of the engineering techniques which the designers used to achieve a record height; the tubular system is the structure that keeps the building upright during wind and earthquake loads. This X-bracing allows for both higher performance from tall structures and the ability to open up the inside floorplan. Such original features have allowed 875 North Michigan Avenue to become an architectural icon. It was pioneered by Bangladeshi-American structural civil engineer Fazlur Khan and chief architect Bruce Graham.