Research On Damage Identification And Structure Rationality Of Multi-box Steel-Concrete Composite Bridge

Nowadays steel-concrete multi-box composite bridge is a new type in City Bridge. It has several advantages compared with the traditional R.C. Bridge or Steel Bridge. E.g. well mechanical performance and earthquake resistant behaviour, light weight, construction convenient and fast, saving scaffold and formwork, environment friendly and no disturbing to underneath transportation etc. Meanwhile this structure type is apt to seeking a better balance between mechanical performance and economic cost. Therefor, composite bridge is provided with wide application prospects in future. This paper bases on the background of a40-metre-span multi-box steel-concrete composite bridge, starting from model updating, damage identification and overall performance improvement of composite structure, by means of combination of theoretical analysis and experimental study, to get some results as follows:1) To make sure the rationality and accuracy of bridge condition assessment, it is necessary to update the initial model of a new built bridge by any accessible test data. This paper bases on the data from dynamic test of a40-metre-span multi-box steel-concrete composite bridge, determining updating parameters according to the sensitivity analysis, to correct the physical parameters of the initial FE model through a model tuning procedure (OLS) and further to reproduce the dynamic performances of a structure with greatest accuracy compared with the experimental results. A finite-element model updating method based on parameters of vibration modal and frequency is given for this bridge category.2) Based on the updated FEM mentioned above, which took concrete density and elastic modulus as updating parameters and modal frequency+MAC as reference data, this paper built some damage conditions in different positions of the composite bridge of the model to search methods of damage identification for steel-concrete composite bridge. It focused on the method of modal curvature difference.We detect the damage locations in steel-concrete composite bridge by modal curvature difference method (MCDM). The results indicate that the modal curvature difference method can well locate the damages in steel-concrete composite bridge, especially the damage in concrete. But the change rate of frequency as damage index is insensitive to the bridge damage and the method can’t be applied solely for practical.3) A beam test was carried out in the laboratory of Civil Engineering, Zhejiang University. Taking a5meters long steel-concrete composite box girder bridge as the research object and the finite element model is established. Based on the results of experiment, this paper discusses about the updating and validation of accurate finite element model for damage identification of the steel-concrete composite box girder bridge. By means of scale model test the updating of the accurate finite element model has been completed and validation is confirmed. In practical engineering, we can only obtain related parameters under current state by test to evaluate and identify the state of bridges in service, but lack test data when bridges are in good condition. In this case, the updated FEM provides a more reasonable standard for damage identification and condition assessment of bridges in service.4) Meanwhile, a method to improve horizontal integration of deck structure in multi-box steel-concrete composite bridge is proposed in the understanding of composite structure. In this paper we bring in a transverse prestress system to multi-box steel-concrete composite bridge to improve the integrity and additional deformation of bridges under the effect of external loads. Besides, with this method we can minish size and number of diaphragm appropriately. It’s demonstrated by theoretical deduce and numerical analysis furtherly.