Study On Stiffness Mechanism And Design Method Of Large-span PC Continuous Rigid Frame Pier

In recent decades,with the rapid development of economy,there is tremendous achievement in our country bridge building,large-span bridges are widely used in bridge construction.Continuous rigid frame bridge has the advantages of less expansion joints,good overall performance,large structural rigidity and excellent seismic performance,so it is adopted widely.For continuous rigid frame bridge,the internal force distribution of pier and beam is determined by the stiffness ratio of pier beam.When the stiffness of pier body is too small,the bending moment of the pier top girder is small,which will aggravate the bending of the girder and increase the risk of cracking of the girder.When the stiffness of the pier is too large,and the pier cannot adapt to the longitudinal deformation of the main girder caused by temperature change,concrete shrinkage and creep,which will lead to greater structural sub-internal force.Pier stiffness is influenced by pier style,pier height,section size and concrete elastic modulus.By analyzing the effect of each factor on the bridge stiffness,and providing reference for pier stiffness adjustment of continuous rigid frame bridge,t the same time,it has great significance for optimizing the pier beam internal force distribution and controlling mid-span sag of main girder.In this paper,based on the construction of Rong Ba bridge,some important issues about pier stiffness are studied.1.Characteristics and development process of continuous rigid frame bridge are summarized and analyzed,the present situation of bridge pier rigidity rationality research is elaborated,and introduced the common pier style and characteristic,the bridge pier stiffness theory and formula are discussed and derived.2.Finite element software Midas/civil was used to analyze the influence of geometric parameters(pier height and section area)of pier on main mechanical indexes of continuous rigid frame bridge.The analysis results show that the change of pier stiffness has little influence on the internal force and deformation of the main beam,however it has significant influence on the internal force and deformation of the pier body.When the pier height less than 60 m,it is more suitable to adopt single limb solid pier,when the pier height between 60 m to 100 m,it is the more suitable to use double limb solid pier,for more than 100 m high piers,the single limb box pier which has large anti-pushing rigidity is a good choice.3.By studying the concrete strength grade,the effect of pier reinforcement ratio on elastic modulus of pier concrete,the influence rule of the different concrete strength and different pier reinforcement ratio on structure stress.The analysis results show that it is not economical to improve the stiffness of piers by increasing the concrete strength,the reasonable range of concrete strength is C35~C55.The reinforcement ratio of pier has a great influence on the elastic modulus of pier,when the reinforcement ratio of pier is more than 2.5%,the influence of reinforcement on the elastic modulus of pier should be considered.4.The effects of pier design parameters(pier height,longitudinal width,and distance between two legs)on mechanical behavior of solid pier with two legs under different span sizes were studied by orthogonal analysis.Based on the single factor sensitivity analysis,pier height has the most dramatic effect on the stress of pier bottom,the main span has the most influence on the transverse horizontal displacement,and the cross section area has the greatest impact in the maximum cantilever state stability safety factor.5.On the basis of grey correlation analysis method,multi-index comprehensive evaluation of the reliability index was conducted by 4 indexes which are bridge pier bottom stress,displacement of pier top,safety factor and concrete content,the optimal parameter combination was obtained which can use in the various index,when the main span is 120 m,pier height is in a reasonable range of 65 m to 75 m,pier width along the longitudinal direction and double limb spacing is appropriate for 3 m to 4 m.6.Take steel-concrete bridge as an example,the control effect of common concrete pier after configuration section on the pier top horizontal displacement was analyzed,the results show that when the steel ratio is 4.5%,the pier top horizontal displacement will decrease 50.7%.Therefore,it is feasible to control the displacement of the pier top with continuous rigid structure by distributing section steel in ordinary concrete piers.