Domes built in the 19th, 20th, and 21st centuries benefited from more efficient techniques for producing iron and steel as well as advances in structural analysis. Metal-framed domes of the 19th century often imitated earlier masonry dome designs in a variety of styles, especially in church architecture, but were also used to create glass domes over shopping arcades and hothouses, domes over locomotive sheds and exhibition halls, and domes larger than any others in the world. The variety of domed buildings, such as parliaments and capitol buildings, gasometers, observatories, libraries, and churches, were enabled by the use of reinforced concrete ribs, lightweight papier-mâché, and triangulated framing.