Sensitivity Study On Mode Shape Translations And Rotations To Damage Of Frame Structures

In recent years, structural damage identification has become an important field of civil engineering research and development, and we can effectively prevent structural failure occurs by using the structural damage identification technology. In practical engineering, frame structure is widely used because of its wide scope, simple form and many other advantages. Through the damage sensitivity analysis of modal parameters of the frame structure, thus doing the damage identification research, and to obtain the damage identification method that suitable for general structures. In this thesis, the theoretical, numerical and experimental research are carried out in the sensitivity analysis of frame structure modal parameter, and some research results have been obtained.Aiming at the general frame, starting from the vibration equation of the structure, and using the structural stiffness matrix characteristics and the relationship between the freedom with zero quality and the freedom that has quality, then the sensitivity coefficients of mode shape translation, mode shape rotation, mode shape slope are derived. The expression of sensitivity coefficient is further analyzed and deduced, and the change rule of the mode shape slope is obtained: when the column is damaged, the mode shape slope of storey which has the damaged column is always increased.The two-story and two-span numerical frame model and the six-story and three-span numerical frame model are established respectively. The sensitivity coefficients of the mode shape translation, mode shape rotation, mode shape slope of two frames are obtained in the three damage conditions:damage of the bottom column, damage of the middle or the top column, and damage of the beam. Then using sensitivity coefficient expressions to calculate mode shape translation, mode shape rotation, mode shape slope sensitivity coefficients, and compared with the numerical results, then verifying the correctness of the derived expressions.The sensitivity analysis of the two frame numerical model shows that the change of the number of storeys and spans does not affect the change rule of the mode shape rotation and the mode shape slope. And the relationshipbetween the mode shape translation, mode shape rotation, mode shape slope and the stiffness of the damaged member is linear. As for the mode shape slope, when the column is damaged, the mode shape slope of storey which has the damaged column is increased.And as for the mode shape rotation, when the column is damaged, the mode shape rotations of joints which are connected to the damaged column are decreased and very sensitive to the damage; when the beam is damaged, the mode shape rotations of joints which are connected to the damaged beam are increased and very sensitive to the damage.The experimental study of three two-story and two-span steel frames is carried out.Getting joints mode shape translations by using the acceleration sensors, and calculating the mode shape rotation of each joint by using the displacement mode of beam element model in finite element. Three kinds of damage cases are manufactured for three models respectively, and the mode parameters of the three models are obtained, and the sensitivity analysis is carried out. And the modal parameters of undamaged frames are substituted into the mode shape sensitivity coefficient expressions to calculate the sensitivity coefficients of mode shape translation, mode shape rotation, mode shape slope of three steel frames, which are compared with the experimental results, and the correctness of the expression is verified, and the change rule of the mode shape slope is verified too.