Study On Seismic Response Of Temporary Consolidation And Ball Joint Support For Swivel Girder Bridge

With the continuous improvement of infrastructure construction,lots of bridges which cross rivers and tunnels cross the mountains were built.More and more bridges need to cross complex terrain such as mountains,rivers,and canyons.The idea of building roads and bridges to achieve regional connectivity has been widely accepted At the same time,the method of building roads and bridges is becoming mature,while long-span bridges still have challenges in construction.The rotating bridge technology has obvious advantages in crossing obstacles,but the construction process is more complicated,the equipment installation and turning requirements are high precision,and the general bridge construction time is 1-3 years.For the difficult terrain,the construction period of the rotating bridge project may be more longer These factors increase the risk of earthquakes during constructionDuring the cantilever construction of the swivel bridge,temporary consolidation support will be set between the pier and the upper main beam（A sand box and a steel pipe are arranged under the upper turntable as a support for the cantilever stage,and the beam can be easily lowered to achieve the contact of the ball joint after being removed.）.In the preparation stage of the swivel,the temporary support is removed At this time,only the ball joint structure plays a supporting role between the pier and the upper main beam,so as to facilitate the traction of the prestressed cable to complete the swivel.According to the construction situation of the bridge site,combined with relevant data,The seismic dynamic response of a s single-pier single-box single-chamber beam girder bridge with temporary consolidation support during the construction period of the cantilever hanging basket and connected by ball joint during the preparation phase of the swivel preparation are studied.The results are as follows:（1）By referring to the relevant literature,the characteristics of the bridge turning process and the motion law of the point under the ball joint support are summarized and calculated.It is proposed that in the plane of the foot,when the ball joint is in contact with the positioning pin,θ₁=0.37° is used as the criterion for judging the vertical plane safety and danger,and θ₂=0.57° is used as the criterion for judging the vertical plane foot-sliding surface contact criterion.Taking θ₃=0.72°、θ₄=0.95° as the vertical plane and horizontal plane collapse risk indicators（2）Through the structural mechanics and kinematics of the analog friction pendulum,the kinematics model of two mass points,three mass points and multi-mass points of the swivel bridge structure are constructed.The two-mass point model under the action of frequent earthquakes,design earthquakes and rare earthquakes are calculated which modulated EL-Centro ground motion to 0.05g,0.15g and 0.32g.The acceleration peaks of the upper ball joint are:1.2889 m/s²,3.8530 m/s² and 10.4030 m/s²,respectively.The acceleration peaks of the turntable are 0.2696 m/s²,0.8097 m/s²,and 1.7441 m/s².The upper ball joint has a peak displacement of 5.7 mm,16.2 mm,and 37.4 mm with respect to the lower ball joint.It can be seen that the acceleration of the main beam structure of the swivel bridge is reduced,and the spherical hinge surface serves as a vibration isolation effect.In the case of frequent earthquakes and design earthquakes,the bridge structure is safer,but in the rare earthquake,the upper ball joint and the concrete and the positioning axis collided（3）Carry out the numerical simulation of the bridge in the temporary consolidation state and the ball joint support state during the construction process The first 10 modes in two states are compared.From the data comparison,the first-order frequency of the temporary consolidation state is 1.537 Hz,the ball joint support is 0.496 Hz,and the vibration modes are horizontal rotation.The second and third modes are all rotating along the bridge surface and the transverse bridge surface,and the high-order vibration mode is characterized by spatial torsion.This shows that the structure of the swivel bridge is ’soft’ under the support of the ball joint,and the motion form of the space is more complicated.EL-Centro ground motion（suitable for Class Ⅱ sites）and Tianjin wave（north-south direction,applicable for Ⅲ-Ⅳ sites）are applied separately in the forward and transverse bridge directions to carry out temporary consolidation and ball hinge support Time-history analysis of bridges with 7-degree occurrence,design,and rare earthquakes,a total of 24 operating conditions It can be obtained that the acceleration of the pier top and the main beam structure of the bridge pier is significantly smaller than that of the temporary consolidation.The dynamic response of the structure and the torsion angle of the main beam when the ball hinge is supported are calculated in each case.By way of example,the forward acceleration and displacement time-history curves of the forward and horizontal bridges under the 7-degree design earthquake are compared and analyzed（4）Carrying out the 1/40 scale model shaking table test of the ball joint support in the swivel stage,and dividing 12 working conditions to study the test model in different ground motions,different acceleration peaks,and different angle between the bridge direction and the ground motion during construction.For these parameters,the model’s response under unidirectional ground motion is studied.In all working conditions,the bridge acceleration at the end of the beam in the condition 1（the EL-Centro ground motion with an acceleration peak of 0.15 g,along the direction of the main beam）is 0.5 m/s².The vertical acceleration is basically stable at 0.8 m/s²,and the vertical acceleration of the beam midpoint is basically stable at 0.2 m/s²,which is consistent with the numerical simulation results.Compared with the same acceleration amplitude of the same ground vibration,the acceleration of the main beam top along the bridge and the vertical bridge is found at different angles:the amplitude of the acceleration along the bridge decreases with the increase of the angle between the ground motion and the main beam;the vertical bridge acceleration The amplitude increases with the increase of the angle between the ground motion and the main beam,and it has this law under different ground motions.By calculating the in-plane rotation angle of the main beam of all working conditions,whether it is EL-Centro or Northridge ground motion,the angle of the main beam in each plane hits the maximum value under rare earthquakes.The maximum horizontal,vertical and horizontal plane rotation angles of EL-Centro are 0.84°,0.5280° and 1.2283°,respectively.The Northridge ground motion is 0.7470°,1.1920°,and 1.1910°.By comparing various contact-collision-collapse criteria,it is found that when the input ground motion direction is perpendicular to the main beam direction（cross-bridge input）,the bridge main beam is most easily overturned,and the risk is the highest.