Structures are groups of elements united to support loads with stability. There are different types of structures including frame, shell, arch, mass, and suspension structures. Frame structures are composed of long elements joined together, leaving empty space to support loads. Shell structures surround a volume using a thin outer material. Arch structures use geometry to displace forces to the sides. Mass structures are simply made of clumped materials. Suspension structures hold elements with cables from a tall column, making them suitable for large bridges.