Study On Damage Detection Of RC Continuous Beam Based On Modal Analysis

Engineering structures often subjected to all kinds of damage under different various environmental and use conditions, to some extent, the damage affect the safety, durability and normal usage function of the structure, therefore, it is great significance to study structural damage identification .According to the shown state of the structure, the damage existence, location and extent are detected by the damage identification method. The fundamental principles of dynamic damage identification is the correspondence relationship existed between structural dynamic parameters (natural frequencies, mode shapes, damping ratio) and the structural physical parameters (stiffness, quality and characteristics of the material constitutive).When the structure occurs damage, the changes of the physical parameters will cause to dynamic parameters'changes.The dynamic parameters are aquired with the use of dynamic testing ,according to the gained result,which is to find the injury-sensitive factor used to detecte the structure damage.In this paper, five pieces of two-span reinforced concrete continuous beam was tesed by loading - unloading steo by step, under the each unloading,the dynamic test was done for experimental beams by large-scale intelligent signal analysis and processing system (DASP) ,then dynamic characteristics of the tested beams under different state. Based on the test research result, and then compared finite element simulation results, which come to the better injury-sensitive factor. In the paper, the main contents are following as:First, the decline rate of natural frequencies is defined as the injury mark to detecte damage of the reinforced concrete continuous beams. The identification result show that the change characteristics of the frequencies is significantly different between RC continuous beams and supported beams; besides, with the appliance of the indicators of physical and mechanical, four kinds of working conditions were designed, the frequencies change of the RC continuous beams under different damage condition was analysed by finite element, which is effective to interprete the test result.Second, the relative change rate of the shape and the first-order differential of the shape relative change rate were defined as the injury marks to identify the reinforced concrete beams'damage. Comparated the processed result of the test data and simulation date respectively,and the identification effect of the above two methods, which showed that the first-order differential of the mode shape relative change rate can be better to determine damage of reinforced concrete continuous beam.The end, flexibility matrix is obtained based on the displacement mode shape, and then flexibility curvature mode shape is auquired with central difference method. Through testing and simulation analysis, the flexibility curvature method does not require the initial state information of the structure; to a certain extent, multi-location injury of span, damage in support can be better detected and damage extent can also be estimated.