Stress analysis and design recommendations for the inner anchor structure of a sleeve-type pressure anchor

Abstract

Pressure-type anchors transfer uplift loads to the grout and bedrock through the inner anchor head at the bottom of the anchor borehole. To satisfy the requirements for strength, stiffness, and uniform compressive stress distribution under large uplift loads (e.g., ultra-high-voltage (UHV) transmission tower foundations), a sleeve-type pressure anchor comprising a regular octagonal sleeve and eight radial stiffeners is proposed. First, based on engineering experience and code-based calculations, recommended ranges of key dimensions and bearing capacity for high-load pressure-type anchors are provided. Subsequently, a three-dimensional finite element model is established to investigate the stress distribution and deformation characteristics of the inner anchor head under the ultimate uplift load. Finally, a parametric sensitivity analysis is conducted by varying the thicknesses of the anchor plate and stiffeners, and recommended dimensions are proposed for four conventional specifications. The results indicate pronounced stress concentration in the connection zone between the anchor bar and the anchor plate; therefore, stresses at representative locations such as the outer edge of the anchor plate are suggested as strength-controlling indicators. The inner anchor head, designed using the recommended parameters, meets engineering requirements for stress level and vertical displacement. This study provides a basis for quantitative design and engineering application of inner anchor heads for pressure-type anchors.