04.15: New design rules for tubes in combined walls in EN1993‐5

Abstract

Steel tubes can be applied for many applications, structural as well as in pipelines. They may be loaded by combinations of internal or external pressure, soil load, bending moment and normal force. Important failure modes are local buckling, severe ovalisation (flattening of the cross section) and rupture of the pipe wall at local buckles or welds. Within the framework of a European research project called Combitube sponsored by RFCS (Research Fund for Coals and Steel), the structural behaviour of spiral-welded tubes for application in combined walls has been investigated. The main loads are bending moment, normal force, soil loads and loads from the infill sheeting. Analytical models were developed to predict the elastic-plastic behaviour under these loads, i.e. the bending moment curvature diagram, the curvature ovalisation diagram and curvature strain diagrams. The analytical models as presented in this paper are an extension of previous analytical models developed for pipelines, now including more parameters that influence the load deformation behaviour, in particular local buckling. The new rules are intended for the new version of EN1993-5 on Piling. They are validated with the results of full scale tests and extensive parameter studies.