Degradation Analysis Of Bridge Pier Bearing Capacity Under Abrasion Of High-speed Sediment-laden Flow

As the most widely used structural form in bridge construction,it is very important to predict the bearing capacity change of concrete structure in high-speed sediment-laden flow.As an important part of bridge structure,pier is directly eroded by sediment-laden flow,which has a very serious impact on the load-bearing,safety and durability of the whole structure.Therefore,it is very important to study the erosion and bearing capacity of piers under high-speed sediment-laden flow.Based on COMSOL and ANSYS finite element software,the numerical simulation method is used to study the erosion of single pier and multi-pier and the stress change of damaged pier under axial compression.The specific contents include:1.Establish the water-sediment two-phase flow model.Based on Finnie’s abrasion theory,the erosion models of single pier and multi-pier under sediment-laden flow are established by particle tracking module,and the model coefficients are adjusted according to the actual engineering parameters.The effects of flow velocity,gravel particle size,sand content,pier diameter and compressive strength on average erosion rate and erosion width were analyzed.By comparing single pier erosion with multi-pier erosion,the influence of pier spacing and pier location on average erosion rate under multi-pier condition is analyzed.2.Choose reasonable proportion of gravel composition with different particle sizes according to actual working conditions,and get the total average erosion rate and annual average erosion thickness which are more in line with the actual engineering.According to the thickness of protective layer and flow velocity,the exposure time of reinforced bar in full erosion of pier can be predicted.The prediction of pier erosion has certain engineering significance.3.Establish the axially compressed model of bridge pier under the damage of protective layer,and study the change of axially compressed concrete and steel bars of bridge pier under different erosion angles and different corrosion rates of steel bars,which has a certain guiding role for the later maintenance of bridge pier.The results show that the abrasion of single pier is similar to that of any pier in multi-piers,in which the diameter of gravel has obvious influence on the average erosion rate and width of pier,while the velocity of flow,sand content and compressive strength only have influence on the average erosion rate,but have little influence on the erosion width,and the diameter of pier has no obvious influence on both.The larger the spacing is,the more uniform the average erosion rate of the three piers is.The maximum stress of the vertical steel bar,stirrups and the damaged section concrete increases with the increase of the erosion angle,but it is less affected by the corrosion rate of the steel bar.It only affects the lower part of the pier which is eroded and hardly affects the upper part of the pier which is not eroded.When the eccentricity is greater than the critical value,the eccentric compression bearing capacity of the pier after erosion is smaller than that under axial compression,and the larger the erosion area,the smaller the critical value.