Study On Methodologies For Seismic Estimation Of Beam Bridges

Earthquakes usually cause catastrophes to the society. In order to reduce the amount of casualties and property losses, search and rescue should be in action efficiently after a destructive earthquake. And the availability of the traffic system is one of key factors for search and rescue to carry out immediately and smoothly. However, there are many seismically vulnerable elements in the traffic system, such as bridges. It is very useful for earthquake emergency department to estimate damages to bridges after the earthquake happened. Beam bridges have an important place in highway bridges. There are two reasons. One is beam bridges constructed widely for this kind of bridge is easy to be built with simple structure; the other is many overpasses are the joints of roads system and these bridges usually are beam bridges. So, it is necessary to study the methodologies for seismic estimation of beam bridges.The main content of thesis is as following.1. Three models with different requirement of input parameters were acquired by consulting existent method for seismic estimation of bridges, and the empirical regression model was the main study item of the three models. These models are stated as following. (â…°)Neural network model. More comprehensive influence factors of seismic damage were selected, and neural network model was built for beam bridge seismic damage estimation, which was based on BP algorithm and seismic damage material of typical bridges; Because of elaborate seismic influence factors were selected, estimation results of neural network model would be more close to the practical situation. (â…±)Statistics regression model. In order to apply the model of seismic estimation for beam bridges in emergency mission after earthquake, according to fields of bridges in the Chinese Emergency Database, influence factors of the seismic damage were selected. The least square method was used to analyze data of damage bridges in Tangshan Earthquake and Wenchuan Earthquake. And statistics regression model was established with regression equation, regression coefficients and damage degree indicators. (â…²) Inference model. Considering the chance that a bridge record was not complete in the database, inference model was built to estimate seismic damage of beam bridges roughly.2. Seismic estimation software to apply these three models was developed with VC++6.0 and Access2003. Main interfaces and operation problem solutions were introduced. The software was tested with seismic damage material of typical bridges.3. Based on gradation criterion of seismic damage for beam bridges and the exist gradation criterion of seimic damge for bridges, recommendation values of beam bridges'seismic loss rate was acquired by analyzing two project cost samples, and the set of loss rate values could be used for assessment of beam bridges'economic loss.