Experimental Study Of Damage Location Identification For Bolt Looseness At Flange Joints Of Leg Members In High-rise Steel 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 at flange joints of steel tubular tower may loosen and the bolt looseness often occurs at the joints of the tower legs, which may reduce the wind-resistant capability of the tower, increase the wind-induced displacement responses and affect the serviceability of the tower. When the number of loosened bolts is sufficiently large, it may endanger the safety of the tower-structure and even lead to its collapse if the bolt looseness and the corresponding locations cannot be detected and repaired timely. Therefore, it is essential to detect the locations of loosened bolts timely and accurately, the repair can be carried out to ensure the safety of the tower. However, detection of the accurate locations of loosened bolts during the structure’s service life is quite difficult.The purpose of this paper is to develop a new method for identifying the damage locations of bolt looseness at flange joints of tower legs of steel latticed tower. In the paper, the bolt looseness is reflected by the reduction of the bending rigidity of the equivalent beam element, whose stiffness matrix is obtained by comparing with a fined solid finite element (FE) model of the flange joint. A vector composed of the standardized mean square deviation of the wind-induced longitudinal strain responses at flange joints of the latticed tower in the tower leg directions under the damaged state of the tower compared to its undamaged state is proposed as a damage index. The damage index is to be shown to be sensitive to the damage locations and independent of wind load. Hence, the damage index vector can be used for Damage location identification for bolt looseness at flange joints by detecting its abrupt change information. The influence of measurement noise on the damage locations is also discussed in the paper. Finally, the proposed method is applied to a realistic transmission tower and verified with a steel tube tower, which shows that the proposed method can accurately identify the damage locations of bolt looseness.