Alignment Controlling Theory And Application Of Bridge Structure Formed In Stages Based On Unstressed State Control Method

The alignment control is important in the construction control for bridges formed in stages.In the process of construction,the elevation control of the structure is usually used to ensure that the alignment of the structure fits the target alignment.However,the elevation computation is closely related to the process of construction.Once the process of construction is changed,the elevation needs to be recalculated according to the new one.Meanwhile,for the reason that the elevation of structure is greatly influenced by the temperature and the temporary load in the process of construction,it is hard to achieve the alignment control of the structure.And that the viewpoint in the analysis theory of structure formed in stages based on the unstressed state amounts points out that the final state of the structure has no relationship to do with the process of construction provides the solving of the problems above with theoretical support.Based on the theory of unstressed state control method,a systematic study of bridge alignment control is carried out here.And the main work are as follows:(1)The formulation for the alignment control of structures formed in stages is established based on plane beam element.The fixed coordinates are chosen as the reference for the target alignment shape,and the external force potential is defined as the force potential to the coordinate origin,and the total strain energy of the structure is calculated based on the unstressed state amounts of the elements.The formulation for the alignment control of structure is established according to the principle of the stationary potential energy.The unstressed state amounts of elements in the structure can be determined exclusively from the formulation according to the target alignment.The alignment control equation is essentially a mechanical equilibrium equation expressed by unstressed state amounts.The equation amount of the alignment controlling formulation is the sum of the DOFS of nodes and the variable amount is the sum of the unstressed state amounts of structural elements.The amount of equations and the amount of variables are usually not equal to each other,so the formulation can not be solved directly.However,it can be solved after the linear control equation is dealt with according to the specific geometrical structure,i.e.the equations can be solved directly after the structural rigid body displacement is removed for internal static structure,and can be solved directly after the linear constraint condition of the internal redundant constraint is added for internal statically indeterminate structure.Numerical analyses show that the unstressed state amounts calculated from formulation of alignment control satisfy the requirement of the target alignment and internal force.(2)The unstressed state amount of the elements is stable for the elements in unstressed state.To establish the relationship between the unstressed state amount and the precast configuration of the plane beam elements,the mathematical relationship between the unstressed state amount and the precast configuration parameter of the plane beam elements is developed through analyzing the geometric configuration change in the horizontal rectangle beam elements based on the mathematical expression of the element curvature and length,and the correctness of the expression is verified by numerical examples.The analysis and the calculated result indicates that the precast configuration of elements is one-to-one in relation to the corresponding unstressed state amount and that the change in the precast configuration is essentially a change in the unstressed state amount of the elements.From the perspective of engineering applications,the beam elements can be prefabricated into different shapes as long as the element node positions meet the target alignment.(3)The research on the alignment control of steel truss girder in staged construction is carried out.The steel truss girder is simplified into the form of truss structure.The target alignment of steel truss girder is used as the calculation input,and the unstressed length of the truss girder is calculated by the alignment control formulation,so as to set the target camber of the truss girder.The results of the camber setting show that unstressed state control method require that the length of the chord and web member needs to be shortened,and there is no internal force in the process.That the unstressed length of the elements obtained from the camber setting is used for thealignment control of the intermediate construction process ensures that the finished bridge alignment fits the target state automatically,which indicates that the camber setting is reasonable.(4)In the case of disadvantageous wind or marine environment,it is difficult to do the linear observation and adjustment of the standard strand.So a method which uses the unstressed length of the cable to control the alignment of the standard strand is proposed including the accurate calculation and measurement control of the cable length.For the length measurement control,the traditional baseline length measurement method is used to study the cable length measurement,and the error of unstressed cable length obtained from this method is evaluated.As for the main factors influencing the unstressed length in the baseline length measurement method,the method of cable length measurement of the segmented suspension is proposed,and the accuracy of the method is evaluated.The analysis shows that the main factors resulting in the error of the unstressed cable length measured by the traditional baseline length measurement method are: the segment amounts of the cable;the influence of the elastic modulus of the steel wire;the wire diameter and the tension during the measurement.And for the suspension length measurement method,the advantages are as follows: it can increase the measuring length comparing to baseline length measurement method,thus the amount of segments is reduced;the influence of the elastic modulus of the strands can be eliminated by the corresponding cable;when the cable is in the suspended state,the deviation of the wire diameter has no effect on the unstressed length of the cable;the tension of the cable is automatically generated,which avoids the problem of tension applying and tension controlling;the suspension measurement method can greatly reduce the unstressed length measurement error of the cable,which greatly improve the accuracy of the standard strand alignment control.In this study,the unstressed state control method was adopted as the basis,and the unstressed state amount of the structure element is the principle line of the alignment control.The research results provide the theoretical support for the alignment control of the structure formed in stages,and the analysis theory of structure formed in stages is further improved.