The elastic buckling of planar beams in the presence of frictionless unilateral contact
against rigid surfaces is reconsidered, taking also into account a possible elastic
translation of the rigid surfaces with respect to each other. Exclusive reference is
made to the case of small amplitude deflections, such as it is expected to occur in the
engineering application of buckling-restrained braces, where the gap between the
brace itself and the external containment structure is normally extremely small. Even
though this case precludes the occurrence of several deformed shapes possible for the
general case of large displacement (to be treated like Euler’s elastica), already
described in the literature, a significant variety of behaviors is still possible. Only
monotonic loading is considered. The main variables under investigation
are (i) the wavelength of the buckled beam for a given value of the axial
shortening and (ii) the total thrust exerted by the buckled beam against the
rigid constraints. It is found that both variables can assume several possible
values under the same load; in some cases, their values can be bounded
analytically. It appears that, even in the extremely simplified case considered
here, the actual behavior is dominated by the existing imperfections, both
mechanical and geometrical, thus being quite difficult to be predicted with
accuracy.