Study On Beam Falling Preventing Measures Of Simply Supported Beam Bridge Considering Traveling Waves Effect

In recent years,the frequency of earthquake disasters has increased rapidly,which is very harmful to the bridge structure.When it is serious,the beam will fall.There are four main reasons for bridge damage:(1)the seismic fortification standard is lower than the earthquake intensity;(2)the earthquake causes the foundation to cause damage and the bearing capacity to be greatly reduced;(3)there are some unreasonable aspects in the design and construction of bridge structures;(4)bridge structure itself is weak in seismic capacity.The damage of bridges can be divided into the following categories:(1)failure of superstructure;(2)failure of connecting members;(3)failure of pier part;(4)foundation failure.The research content of this paper:According to the latest design specifications of falling-proof beams at home and abroad,appropriate falling-proof devices are selected and the seismic responses of bridges with falling-proof devices are analyzed.Taking 5×30m simply supported beam bridge as the engineering background,The effect of abutment and foundation soil is taken into account by considering the nonlinear characteristics of limit devices and piers.Building MIDAS analysis model by simulating traveling wave effect with large mass method.The main conclusions are summarized below:(1)By changing the velocity of seismic wave,the influence of seismic wave velocity on seismic response of bridge is verified,and the results of uniform excitation and considering traveling wave effect are compared.The results show that the influence of traveling wave effect on the axial force of pier bottom is very complex,some piers increase by 8.5%,some piers decrease by 5.3%.After considering the traveling wave effect,the shear force of each pier decreases relatively,and the shear force under uniform excitation is relatively high.Approximate the uniform excitation has greater influence on pier bottom bending moment than the multi-point excitation,and the calculation results are safer.(2)The analysis results under different pier heights show that the bending moment and curvature of the pier bottom increase in varying degrees when the falling beam device is used and the traveling wave effect is taken into account,regardless of whether the collision effect is considered or not,the pier height is the same and the pier height changes as a whole.The bending moment and curvature of pier bottom tend to decrease with different integrallifting pier heights of adjacent piers.The relative displacement between piers and beams increases with the increase of pier height.The relative displacement increases by 1.746 cm when the height of two piers near the abutment is changed without considering the collision.The relative displacement increases by 2.752 cm when the height of two piers far from the abutment is changed.When the height of two piers near the abutment is changed,the relative displacement increases by 1.626 cm,compared with 2 and 3.When the height of two piers far from the abutment is changed,the relative displacement increases by 0.456 cm.(3)Through the comprehensive comparison and analysis of the model results considering impact and not considering collision,it is found that the curvature of most pier bottom after considering collision is smaller than that without considering collision,which decreases by about 5%;after considering collision,the bending moment of pier bottom tends to decrease by about 1%,and the decrease is smaller,so it can be judged that the collision between abutment and beam affects the bending of pier bottom.The relative displacement in the direction opposite to the collision direction after collision tends to increase by about 5%,and the change of displacement is not large enough to cause beam falling.(4)This paper analyzes the factors that cause the seismic falling beam,and puts forward that the bearing failure is an important reason for the falling beam.The MIDAS model is established to verify the results.The results show that the relative displacement between the piers and beams will increase by about 13% when the bearing is damaged,and the damage of the bearing will reduce the internal force of the pier appropriately.The research results of this paper have a certain reference value for the design and engineering application of the falling beam device and support.At the same time,it has certain significance for the same type of practical engineering application.