Research On Macroscopic Feature At The Top Of The Damaged Tower Body Of Which The Same Layer Two Bolt Connections State Changes

Tower crane is widely used in building construction. One of the reasons for the tower crane fall down is due to the tower section connection high-strength bolts’preload does not meet the requirements of design value, in the process of its using, the high-strength bolts to loosen, caused the accident. If the bolts looseness can be detected, it’s important for the safety of the tower crane operation.The losseness of the connecting bolts which are at the tower section can be equivalent to the change of the joint stiffness. Hao Longlong has done a detailed study on connecting bolts looseness at the limb and concluded the trajectory at the top of the tower body when the single bolt loosens. After a bolt loosens on the limb, another bolt on the limb will loosen quickly. In this paper, on the basis of the Hao Longlong’works, the author studys the macroscopic feature at the top of the tower body when the changing of two bolts connection on the same layer section.Considering the influence of wind load, the author compares the results of the analysis with the type-examination, and concludes that the relative error is in between5.8%-22.0%. The damaged dynamic simulation model was established on the basis of the finite element model.The author studys the trajectory feature at the top of the tower crane when bolts loosen at the two limbs based on the damaged dynamic simulation model, and concludes respectively macroscopic feature when the adjacent limb bolts connection loosen and diagonal limb bolts connection loosen:1. In terms of adjacent limb bolt connection, the trajectory at the top of the tower body changes from point to approximate circle firstly, and then into a concave petals shape as the stiffness decreases.2. In terms of diagonal limb bolts connection, the trajectory at the top of the tower body changes from point to circle.3. The macroscopic feature at the top of the tower body---the minimum circumscribed circle diameter and the distance off the center are gradually increasing as the stiffness decreases.In orderto verify the correctness of the conclusion, the author does the physical simulation experiments, and designs the simulating device for tower body damage experiments. The author does the physical simulation experiments on adjacent limb bolts connection looseness, gets the trajectory graphics at the top of the tower crane under the different states, and verifies the correctness of the macroscopic feature.