## 3 Methodology
### Structure Deterioration Identification
#### 3.2.4 Establishment of Bridge Model Update Process
Furthermore, this article integrates the classification according to the mechanical characteristics of the bridge, which can be obtained based on the classification method of structural damage force form. For bending cracks, as they are usually caused by the bending force acting on the bridge, the overload, uneven load distribution, structural design, or material fatigue should be considered; for shear cracks, as they are usually caused by the horizontal force (shear force) acting on the bridge, the rigidity of the structure and the support conditions should be considered; for torsional cracks, as they are usually caused by the torsional moment acting on the bridge, the support parts of the bridge or asymmetric load problems should be considered; for compressive cracks, as they are related to the vertical load (pressure) acting on the bridge, the specific aspects related to overload, foundation problems, or improper structural design should be considered; for fatigue cracks, as they develop gradually due to the repeated cyclic loading of the structure, they  
Figure 11: Flow chart for updating parameters of bridge finite element model. are usually found at welding points, connections, or materials; and for freeze-thaw cracks, as they are usually caused by seasonal temperature changes and the freeze-thaw cycle of structural materials, they should be considered related to environmental temperature, mostly occurring in cold climates. Classification of Structural Deformation  
Similarly, through the monitoring and analysis of different types of deformation, the structural behavior of the bridge under various conditions can be accurately assessed, thus providing a scientific basis for the design, maintenance, and reinforcement of bridges. Bridge deformation should first be classified based on its nature. When the overall bridge and its components move along a certain direction or rotate around a certain axis, the rigid body displacement of the bridge caused by translation and rotation should be considered. However, when bridge components (beams and pier columns) exhibit bending within a plane perpendicular to their axis, deformation caused by shear forces, tension or compression along their axis, or torsion around their axis, they should be categorized into deformation types such as bending deformation, shear deformation, axial deformation, and torsional deformation according to their deformation forms. Application of Bayesian Model Updating and Adaptive Nested Sampling Method  
Currently, research on bridge model updating methods based on dynamic response has become relatively mature. [PERSON] and others have proposed a Bayesian model updating method based on the adaptive nested sampling (ANS) algorithm [44]. This method constructs a probability objective function using modal parameters and approximates it using the ANS algorithm. ANS retains the characteristics of nested sampling (NS) by progressively narrowing the sampling range, allowing the samples to eventually approximate the optimal parameters. By approximating layer by layer, the high-dimensional integral problem is transformed into a simple one-dimensional integral problem, simplifying the calculation process of the evidence value and the posterior probability density value [45; 46]. The ANS algorithm reduces the number of finite element simulation calls by approximately 84% compared to the traditional NS algorithm, saves about 86% of the computational time, and obtains uncertainty correction results with equivalent accuracy. Therefore, for the analysis results of bridge point cloud data, the error between the design parameter data of the finite element model and the corresponding actual structure test data can be minimized by adjusting the model parameters to be updated. This leads to the deduction of a more accurate finite element model, obtaining model parameters closest to the current operational bridge, and completing the construction of a model updating method based on static response.