Torsion at Pile to Pile Sleeve Grout Connection and Proposed Design Procedure of Shear Keys-Paper

Paper

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The paper examines torsional loading in grouted pile-to-sleeve connections used in offshore steel jackets and proposes a procedure for sizing vertical shear keys.<br /><br />Integrated jacket, pile, and soil analyses were conducted for an eight-pile foundation using pile diameters of 84, 96, and 108 inches. As diameter increased, axial forces, lateral shear forces, and bending moments changed only marginally. Torsional moments, however, increased consistently across all piles—by as much as about 18% for the largest diameter compared with the smallest. This increase can make torsional resistance a critical design consideration.<br /><br />Existing design standards provide methods for checking grout-connection capacity and recognize that shear keys can improve load transfer, but do not give a specific procedure for designing keys against large torsional moments. The paper proposes adapting the NORSOK approach to account for vertical weld-bead shear keys. The method calculates the torsional capacity of connection segments with and without vertical keys, then combines their contributions to assess utilization and determine the required length of connection to be fitted with keys.<br /><br />Using vertical shear keys may offer a more economical way to increase torsional capacity than lengthening the grout connection, which can require longer sleeves and piles. The authors recommend further testing and verification before the proposed procedure is adopted more broadly.

Keywords

torsional loading

grouted pile-to-sleeve connections

offshore steel jackets

vertical shear keys

NORSOK approach

torsional resistance

grout connection capacity

pile foundation

weld-bead shear keys

design procedure