An assemblage of members of wood or metal, supported at two
   points, and arranged to transmit pressure vertically to those points,
   with the least possible strain across the length of any member.
   Architectural trusses when left visible, as in open timber roofs, often
   contain members not needed for construction, or are built with greater
   massiveness than is requisite, or are composed in unscientific ways in
   accordance with the exigencies of style.