Damage location identification for bolt looseness at flange joints of leg members in high-rise steel tubular tower structures

A number of high-rise latticed tower structures are made of steel tubular members. To facilitate the construction, the tower legs are constructed by connecting the steel tubular members with bolted flange joints. Under the wind load, the bolts of the flange joints may loosen; and this may endanger the safety of the tower if the bolt looseness and its locations cannot be detected and repaired timely. This paper proposes a new method for identifying the damage locations of bolt looseness of bolted flange joints at tower legs based on the abrupt changes of the structural responses of the towers to the wind load. The bolt looseness is reflected by the reduction of the bending rigidity of elements in the stiffness matrix of the beam element model which is equivalent to the refined solid finite element model of the flange joints. A vector composed of the standardized mean square deviations of the wind-induced longitudinal strain responses at flange joints in a damaged state of the tower related to those in its undamaged state is used as a damage index. It has been shown that the damage index is sensitive to the damage locations but independent of the wind load. Hence. the damage index can be used to identify the damage locations of the bolt looseness at the flange joints. Finally, the proposed method is applied to a latticed steel tubular tower, which shows that the proposed method can accurately identify the damage locations of bolt looseness.