Research On The Continuous Rigid Frame Bridge’s Model Updating Of Closure Jacking And The Solution Of Jacking Force Linear Programming

Closing roof pushing stage is the key stage in the construction of continuous rigid frame bridge,which determines the mechanical properties and safety of the structure in the construction stage and completed bridge state.The finite element model plays an important role in guiding the construction of this stage.It is necessary to simulate the construction in the finite element and check the calculation before the actual construction on site can be carried out.However,there is a big difference between the initial finite element model built according to the design data and the actual structure,so the derivation of finite element can not achieve the same effect when applied to the actual structure.Moreover,the multi-span continuous rigid frame bridge needs to apply multiple jacking thrusts successively,and the influence of jacking thrusts on the structure is different in different spans,and there is mutual coupling phenomenon,so it is difficult to derive the optimal jacking thrust combination.Based on this,this paper takes a six-span continuous rigid frame bridge as the support project,and studies the key issues in the closing roof pushing stage.Firstly,according to the design data,the initial finite element model of the six-span continuous rigid frame bridge is established to obtain the calculated values of the piers’ jacking displacement under the action of jacking forces at all levels,and then the measured values of the piers’ jacking displacement under the action of jacking forces at all levels are recorded in the actual construction.The results show that the variation law of the two displacement values is similar,but the former is generally 29%～36% higher than the latter,because there is a big difference between the initial finite element model and the actual structure,so the finite element model must be modified.Secondly,based on response surface methodology(RSM),the model of bridge structure is modified in the closing stage.Four parameters with strong sensitivity and large deviation were selected as parameters to be corrected.The experimental Design software Desk-Expert was used to generate test samples,and then the parameters with significant influence were screened out through the F-test method.Then,the response surface function of the pier top displacement of each bridge pier was fitted,and the modified values of parameters were solved by repeated iteration based on the measured response values.The modified finite element model is obtained by substituting it into the original model.The results show that the modified finite element model can effectively reflect the characteristics of the roof thrust stage of bridge structure.Finally,in order to solve the optimal jacking force combination of multi-span continuous rigid frame bridge,a linear programming method of "linear programming + finite element" is proposed.A linear programming model with single objective and multiple constraints was established based on the objective function of controlling the maximum cumulative displacement of each pier after 10 years of construction,and the constraint condition of the section stress of each pier in the jacking construction stage.In order to ensure that the same pushing effect can be obtained in the real bridge,the elements in the influence matrix are taken from the data of the modified finite element model.Finally,the optimal jacking thrust combination is obtained by using MATLAB software.The results show that the optimal jacking force obtained by applying this method can effectively improve the linear shape and internal forces of the bridge structure,and this method has universal applicability and can be effectively applied to solve the jacking force of multi-span continuous rigid frame bridge under different closing sequence.