BUCKLING STRENGTH OF FLEXIBLE CYLINDERS WITH NONUNIFORM ELASTIC SUPPORT

The critical hoop thrust which destabilizes buried flexible pipes and culverts can be an important consideration when designing structures of this type. Often, the structure is placed in a small zone of good quality backfill which is in turn surrounded by another poorer quality soil. Critical hoop thrust is studied for flexible cylinders with nonuniform solid support. A closed form linear buckling solution is described, in addition to finite element results. The solutions presented can be used to assess the elastic stability of circular structures in square, circular and rectangular zones of elastic solid. The effects of modulus and the size of the envelope of higher modulus solid, as well as burial depth are examined. The behaviour of cylinders is also considered for a ''Gibson'' material which has modulus variation with depth, and for elliptical cylinders.