In order to estimate the ultimate strength of steel pipe bend for gas transportation use, full-scale tests of both closing and opening mode bending were carried out. The final objectives of this research work is to optimize the allowable design strain or deformation of steel pipe bend subjected to permanent ground displacement induced by liquefaction due to a great earthquake. In order to discuss the allowable value, ultimate strength of steel pipe bends is studied with respect to crack initiation. Especially, the effects of materials, dimensions and geometry shape on ultimate strength of steel pipe bend were discussed by both experiments and numerical analysis. It is confirmed that steel pipe bends largely deformed up to occurrence of a wrinkle before crack initiation. The ultimate strength of steel pipe bend was evaluated at least 30% as a local strain independent of materials. The dependency of ultimate bending angle on original center angle of pipe bend was clarified.
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