| In the mountain areas of Southwest in China, the bridge is vulnerable to flood. Simple bridge widely used in highway bridges in mountain area is severely damaged, but the reliability research of the action of the flood on the bridge structure is insufficient. The velocities of the channel along the bridge span direction have some certain spatial correlation, but the existing reliability researches of the bridge under the action of flood have not yet considered the characteristics of flow velocity. In fact, if the characteristics of the flow ignored, the analysis results may have great error, which does not match with the actual value. Therefore, the reliability analysis of bridge under the action of flood is conducted, and the spatial correlation of velocity is considered, which has an important engineering value.In this paper, the spatial correlation of flow velocity of open channel is analyzed by flume experiment data. The action of flood to the bridge is considered by force coefficient which calculated through the velocity distribution characteristics of the channel. According to the data of the damaged bridge, three typical failure modes of simply supported bridge are presented, the correspond performance function of each failure mode are established. Taking a two span concrete simply supported bridge as an example, the one-dimensional random field of flow velocity along the span direction of the bridge is simulated by the Midpoint method, analyzing the reliability index at different relative submergence depths and correlation distances of velocity. The influence of spatial correlation of velocity on the reliability of bridge is studied.The main conclusions of this paper are as follows:(1) The velocity has the spatial correlation, with the increasing of the distance, the velocity correlation coefficient decreased. The velocity correlation function can be fitted by exponential cosine type.(2) With the increasing of the velocity, the reliability index of the three typical failure modes of simply supported bridges are decreased. The reliability index of the abutment bearing is greater than the pier bearing. The reliability index decreases with increasing the relative depth of submergence, but the decreasing rate is different: when the relative depth of submergence *h between 1 to 2.5, the reliability index decreases rapidly,However,when the *h is greater than 2.5, the reliability index tends to be constant. At this condition, among the three kinds of failure modes, the reliability index of the upper structure overturning failure is the largest, and the reliability index of sliding failure is minimum. That is to say, the sliding failure of the bridge piers is most likely to occur.(3) When considering the spatial correlation of the velocity, the reliability index decreases with the increasing of the velocity, which is consistent with not considering the spatial correlation of the velocity. The spatial correlation of velocity has significant influence on the reliability index, without considering the spatial correlation of reliability index is conservative. As the velocity correlation distance increasing, the reliability index decreases, but the decreasing rate is more and more small, when the relative scale of correlation(correlation distance and bridge span ratio) is 2/35, the influence to the reliability index tends to be constant.This paper has done the following innovative work:(1) Based on the experimental data, the spatial correlation of velocity along the span direction of the bridge is analyzed,and the type of velocity correlation function are studied.(2) The one-dimensional random field of velocity along the span direction of the bridge is simulated by the midpoint method, analyzing the reliability index at such situations as different relative submergence depth and different velocity of correlation distance, studying the effect of velocity spatial correlation on the reliability of bridge under the action of flood. |
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