LOCALIZATION AND PROPAGATION OF INSTABILITIES IN LONG SHALLOW PANELS UNDER EXTERNAL-PRESSURE

This paper discusses the response of long, shallow, elastic panels to uniform pressure loading. Under quasi-static conditions, the deformati on of such panels is initially uniform along their length, and their r esponse has the nonlinearity and instabilities characteristic of shall ow arches. Shallower panels deform symmetrically about the midspan and exhibit a limit load instability. For less shallow panels, the respon se bifurcates into an unsymmetric mode before the limit load is achiev ed. A formulation and a solution procedure are developed and used to a nalyze the response of such panels beyond first instability. It is dem onstrated in both cases that following the first instability the defor mation ceases to be axially uniform and localizes to a region a few ar ch spans in length. A drop in pressure accompanies this localized coll apse and causes unloading in the remainder of the panel. Subsequent de formation is confined to this region until membrane tension arrests th e local collapse. Further deformation can occur at a constant pressure and takes the form of spreading of the collapsed region along the len gth of the panel. The lowest pressure at which this can take place (pr opagation pressure) can be significantly lower than the pressure assoc iated with first instability.