Seismic Design of Bell-and-Spigot Joints for Large Diameter Steel Pipe

摘要

The circumferential joints that join sections of large-diameter welded steel pipe play a critical role in the long-term serviceability of tunnel linings and pipelines. The two types of field-welded circumferential joints typically used are butt joints and bell-and-spigot joints (more commonly called double or single lap-welded joints). Lap-welded joints are quicker, and therefore less costly, to install because fillet welds take less time than butt welds and the fit-up between pipe sections is easier. Single lap-welded joints are common in tunnels where double lap-welded joints cannot be used due to lack of access. They have been used successfully on many projects and tests have shown them to have good ultimate strength. However, lap-welded joints are geometrically eccentric, which introduces additional stresses within the joint. As a result of this eccentricity, several case studies have documented the poor performance of lap-welded joints in earthquakes, which raises concerns about their use in regions of high seismicity.rnThis paper presents a methodology for evaluating the performance of single lap-welded joints in large-diameter steel pipes that experience seismic longitudinal (or axial) loading. A simple two-dimensional analytical methodology that ignores the effect of hoop stresses is proposed. The methodology is used to calculate stress states and determine joint capacity as expressed by joint efficiency. The calculated joint efficiency can then be used to evaluate the performance of various joints under operating stresses and determine whether yielding would occur under seismic loading. Allowable joint efficiencies and joint details as proposed by various codes can be un-conservative in certain circumstances, since the codes do not address the impact of seismic demands. The methodology is applied to an example to demonstrate its practical application.