This paper reports results of tests of four model bridge piers. The principle objectives of this experimental program were to verify the axial load-moment curvature P-M-phi relationship for hollow columns and to examine the validity of the plane-section assumption for hollow-pier sections. This was necessary to validate completely the computer analysis programs for the design of slender, nonprismatic, and hollow concrete bridge piers. It is concluded that the plane-section assumption is valid for rectangular solid and cellular cross sections if the unsupported wall length to thickness ratio does not exceed six.