| Continuous rigid frame bridges generally adopt cantilever pouring construction method and support cast-in-place construction method.The disadvantage of these methods are the long period;besides,the two construction methods will affect the normal operation of the train when the bridge needs to cross the railway line.In recent years,the swivel construction method has been widely used,both at home and abroad,and continuous rigid frame swivel bridges often adopt spherical hinges with adjustable rotation posture.As the spherical hinge structure bears the weight of the rotating body from the bridge superstructure,the study of its mechanical behavior then is crucial to the improvement of the safety and stability of the bridge.In turn,the research on the ultimate compressive strength and failure mechanism of the spherical hinge material turns out to be very important.Besides,apart from its own weight,continuous rigid frame bridges can also be affected by the dynamic effects of rotation speed and rotation acceleration on the bridge structure,induced vibration effects during rotation,pulsating wind effects,and earthquakes.More importantly,the complex stress that the bridge bears when swiveling makes it necessary to study its mechanical behavior.All in all,the present research concerns the following issues:(1)The Ultra-High Performance Concrete(UHPC)material was applied to the spherical hinges,and the compressive strength test of the UHPC cube and the spherical hinge was carried out.By doing this,the influence of spherical hinge radius,steel fiber content,fiber length,water-cement ratio on the compressive strength of UHPC spherical hinges was studied,and the best mix ratio of UHPC spherical hinges was obtained.In order to improve the safety performance of UHPC spherical hinge,three types of UHPC spherical hinge reinforced specimens were designed by constraining the spherical hinge core concrete method.The results turn out that respectively the compressive strength is increased by 65.3%,90.3%,and 186.3%.(2)The ultimate compressive strength and failure mechanism of UHPC cubes and spherical hinges are studied via the theory of limit state analysis.And the theoretical formula of UHPC spherical hinge compressive strength is derived through the mechanical model under uniaxial compression.As a result,it is discovered that the radius of curvature of the UHPC spherical hinge will cause its maximum compressive stress to be about twice the average compressive stress of the cube.In other words,the strength of the UHPC spherical hinge in the test is lower than that of the UHPC cube.Using fiber anti-cracking theory,stirrup-constrained high-strength concrete and steel tube-constrained high-strength concrete mechanical models,the theoretical formulas for the compressive strength of three confined concrete spherical hinges under axial compression are deduced,and the failure mechanisms of the three are analyzed.All the experimental results turn out to be consistent with the theoretical research.(3)Through the UHPC spherical hinge model test of the continuous rigid frame bridge,the distribution of the compressive stress of the spherical hinge along the radial direction was tested.It is then attained that the influence of the rotation process on the compressive stress is limited.In addition,the present research tested the relationship between rotation speed,rotation acceleration and the tensile stress of the beam as well as the torsional stress of the bridge pier,and derived the theoretical formulas of the maximum rotation speed and acceleration for construction under different rotating tonnages and different spans.This research also tested the vibration of the beam during the horizontal rotation,and it is found that the peak value of the vertical vibration displacement is only related to the first three modes of the main beam longitudinal bending.In addition,this paper discusses the relationship between the vertical vibration speed,acceleration and vibration frequency of the beam.It then proposes that by controlling the speed to control the vibration frequency within the first-order frequency range of the beam,the vibration amplitude during the horizontal rotation can be reduced.(4)This paper takes a 10,000-ton continuous rigid frame rotating bridge as the test support project,and employs the finite element simulation analysis method to study the dynamic response of the seismic action to the bridge’s horizontal rotation system.By analyzing the time history of 18 real seismic waves in three directions that met the calculation requirements,and comparing with response spectrum method,it is obtained that the main seismic response is the lateral bending moment and vertical axial force at the bottom of the pier:the UHPC spherical hinge bears all the axial force and 20%of the bending moment,and the supporting foot structure bears the remaining 80%of the bending moment.Based on these data,this paper proposes an optimization algorithm for the earthquake response of the bridge translation system and evaluated the seismic performance of the continuous rigid frame bridges from 5000t to 15000t domestically.To be specific,when the compression stress of the spherical hinge increased by 11%-20%,the compression stress of the supporting feet should reach 200～331.9 MPa.In this case,the radius of the spherical hinge should be appropriately increased;besides,the anti-overturning moment of the supporting feet can be increased to improve the seismic performance of the swivel bridge during the horizontal rotation.(5)This paper also studies the dynamic response of the fluctuating wind effect to the bridge horizontal rotation system by applying time history analysis method and calculated the static three-component force coefficient of the main beam.Through the numerical analysis of the two-dimensional flow field,the influence of the aspect ratio of the main beam and the cantilever width on the three-component force coefficient was obtained.Based on the above data,and section optimization is suggested to be this:when the aspect ratio reaches 0.21 and the cantilever width is 2.5 m,the drag coefficient of the main girder is small and the torque effect is basically zero.At this time,the continuous rigid frame swivel bridge gains the best aerodynamic characteristics.Based on the power spectrum of the downwind and vertical fluctuating wind,the calculation formula of fluctuating wind speed time history was programmed.On the other hand,the use of the time domain analysis method shows that dynamic response of the bridge translation system under wind-induced vibration is based on the transverse bending moment of the pier bottom,the longitudinal direction of the beam,and the transverse bridge direction is the main bending moment.The lateral bending moment at the bottom of the pier reaches 54%of the seismic response and 131%of the static wind.Therefore,it can be concluded that the effect of pulsating wind is not negligible.(6)Finally,the construction monitoring was carried out on the rotation process of the experimental support project.Based on the study of the relationship between the main beam stress and the continuous rigid frame bridge speed,the construction speed was increased to 0.05 rad/min.While ensuring the safety of the system,the construction time was greatly shortened,and the impact of train vibration on the bridge’s horizontal rotation system was also avoided.At the same time,the compressive stress of the UHPC spherical hinge,the stress of the pier bottom and the vibration acceleration of each controlled section of the beam were tested,the results consistent with the theoretical ones.In the whole process,the entire bridge rotation was completed smoothly and safely. |
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