Analysis of the bending strength of U-section steel sheet piles crimped in pairs

U-section steel sheet piles are one of the largest structural sections available and are a popular product for constructing large retaining walls throughout Europe and Asia. U-section piles have been widely used throughout the 20th Century. However, in recent years their bending strength has been an issue of uncertainty because they are connected together by interlocking joints located along the pile wall centreline. As the piles resist bending moments, inter-pile movement can significantly increase bending stresses. When this occurs, the wall is said to have exhibited reduced modulus action, also known as clutch slippage. U-shaped piles are normally driven in pairs and the common interlock may be crimped or welded to prevent this inter-pile movement. The resulting pair of piles is asymmetric in cross-section and may exhibit a reduced bending strength due to oblique (biaxial) bending. The recently introduced Eurocode 3 Part 5 has taken this into account and applies a reduction factor to the bending strength. The work presented herein has been carried out to determine suitable values for the reduction factor. The work has involved the experimental testing 1/6th scale U-piles and the research shows that freedom of lateral movement is essential to the development of oblique bending, and piles that are restrained against lateral movement will not exhibit significant oblique bending