Base connection details for high masts

High masts, typically used for lighting or communications purposes, are essentially simple structures, but problems have arisen at the base weld detail. Known failures of masts with stiffened bases have been attributed to the concentration of stress at the uppermost tip of the stiffeners, so it has been recommended that the stiffeners be omitted in favour of thicker base plates. There have, however, recently been some fatigue failures of masts with this new detail, leading to renewed concern. The paper describes an analytical study which has been done to assess the influences of different base details. The reason for failures is identified primarily as increased local bending stresses in the mast plate where unstiffened bases are used. It is shown that stiffeners significantly reduce the maximum surface stresses in most cases, and that good grouting is important. For large masts the use of holding down bolts both inside and outside of the mast is recommended.