This paper describes a kind of innovative posttensioned and shaped hyp
ar space truss characterized by an economical fabrication and construc
tion process. The hypar truss, assembled initially in a planar square
layout on the ground, is posttensioned at the short bottom chords at o
ne diagonal. As a result, the top chords become curved and thereby a n
onzero Gaussian curvature surface of a hypar space truss is shaped. A
distinguishing feature of posttensioned and shaped hypar trusses, comp
ared with conventional metal trusses, is that the shape formation and
erection is completed by a simple posttensioning process, rather than
by the traditional techniques involving the use of cranes and scaffold
ing. The essential aspects of shape formation are discussed and a smal
l-scale posttensioned and shaped hypar is formed in this paper. Result
s of experiment and nonlinear finite-element analysis indicate that, e
ven within the yield limit of the members, a planar square layout can
be deformed to a significant hypar shape by the proposed shape formati
on method. Potentially, this procedure can offer economies over tradit
ional construction methods.