Theme Lecture – Mechanical Behavior of Steel Lap Welded Pipeline Joints Under Severe Seismic Loading Conditions
Welded lap joints are commonly used in large-diameter steel pipelines for water transmission. Their structural performance constitutes a key issue for safeguarding pipeline structural integrity with no loss of pressure containment, required even after a severe seismic event. Full-scale experiments are presented, which are part of an extensive project sponsored and coordinated by Northwest Pipe Co. on the structural performance of welded lap joints under severe ground-induced (seismic) actions.
In the first part of the work, a series of large-scale experiments is described on welded lap joints in 25.75 inch outside diameter steel pipes, with wall thickness of 0.135 in (3 specimens) or 0.250 in (3 specimens). The specimens were internally pressurized to 40% of yield pressure, and then subjected to four-point bending. Measurements of the bending load, characteristic displacements, and local strains at the joint area are reported. In all tests, the welded lap joints tested were capable of sustaining remarkable bending deformation, without any loss of pressure containment. This behavior supports the argument that welded lap joints, if appropriately constructed, can be used in seismic areas where severe and permanent ground-induced actions in the pipeline may occur.
Numerical calculations are also reported complementing the experimental work. Nonlinear finite element simulation tools are employed to investigate the bending capacity of internally-pressurized welded-lap 24-inch-diameter pipeline joints, considering two thicknesses (0.135 in and 0.250 in). The numerical work: (a) simulates numerically the seven large-scale experiments presented in the first part; (b) elucidates some interesting issues of welded lap joint behavior under severe bending deformation.
Based on the above experimental and numerical results, a discussion is offered on the design of welded lap joints in pipelines constructed in seismic areas.