An Analytical Study on the Effects of End Conditions on the Behavior of 45- and 90-Degree Elbows Subjected to Bending

摘要

Regarding the high seismic vulnerability of elbows as important parts in all piping systems, in this paper two types ofrnelbows, 45 degrees and 90 degrees, with two common types of connections, namely simply welded, and flange connection,rnhave been considered to investigate analytically the effect of end conditions on the ultimate state behavior of elbows. Severalrngeometrical conditions have been considered in each case, and various lengths have been supposed for the straight part of thernpipe connected to the elbow, including D/2, D, 2D, and 3D (D is the diameter of the elbow). Loading cases include both inplanernand out-of-plane bending moments applied to one end of the connected pipe. The analyses have been performed byrnusing ANSYS computer program. In each case both yielding moment and failure moment have been obtained. Failurernmoment here is defined as the moment value in which the relative rotation of the two ending part of the elbow begins to varyrnrapidly with a little increase in the applied moment value. Results show that in the case of welded elbows by increasing thernlength of the straight part both yielding and failure moments increase, and ovalization occurs in higher moment values. Inrneach case there is a limit value for the length of the straight part, more than which the increase has no significant effect on thernultimate sustained values of loading moments. This length can be called as the effective length in each case. Generally, thernin-plane applied moments have greater effects on the elbow behavior, and the 45 degree elbows are less sensitive to the endrnconditions comparing with the 90 degree elbows. In the case of flange connections the effect of end conditions is much lessrnand it can be said that in this case the flange makes the pipe to behave almost as a built-in beam.