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Welded steel wye branches are a key component of most water projects where flows must be divided. They are also a specialty item that requires many engineering considerations. Historically, the design of wye branches has been studied by many agencies over the years and design guidance can be obtained from several sources.
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... The surface stress at the point of discontinuities such as wye joints is limited to 3 times the yield stress. Call and Sundberg [9] showed that the AWWA M11 [1] monograph approach for crotch plate design in True wyes results in unrealistic dimensions. They further showed using the principle of virtual work how to obtain efficient dimensions of the crotch plate in true wyes and provided relevant recommendations. ...
This paper presents a failure case study of a field hydrostatic test that was performed on a buried 2700 mm (108 in.) in-diameter, 30-degree steel wye fitting under a pressure of 1.34 MPa (195 psi). The wye design had been modified from its original design by removing the joint reinforcement and increasing its thickness and yield stress due to fabrication and installation complications, a process commonly used in practice. During the hydrostatic testing, failure was observed both in the steel pipe and the inner lining. Rigorous three-dimensional linear and nonlinear finite element analyses (FEA) of the modified and original design were performed and results were compared. The FEA results are validated with data from field measurements and observations from the hydrostatic testing. Results show excessive yielding and plastic deformation in the modified design; while the original design presents acceptable results. The results of current study emphasize the importance of nonlinear FEA in design and analysis of complicated joints, such as large diameter wyes and tees, which is commonly avoided in practice.
