Local Stress Analysis On Railway Pier-tower-girder Fixed Segment Of An Extradosed Cable-Stayed Bridge

Pier-tower-girder fixed segment of railway extradosed cable-stayed bridge has the advantage of high rigidity,which is often used in large-span railway bridges,but the stress of its fixed segment and cable anchorage area is complicated.This paper takes the new railway bridge A’pengjiang grand bridge(135m + 240 m + 135 m extradosed cable-stayed bridge)as the engineering background.The finite element software is applied to simulate and analyze the construction process of the whole bridge,and the solid finite element model is used to analyse the local stress of pier-tower-girder fixed segment,cable tower anchor zone and cable beam anchor zone,and comparing the finite element calculation results with the measured data.This paper focused on the analysis of reasonable rod system calculation model of pier-tower-girder fixed segment,transmission law of internal stress of the tower end and beam end at the pier-tower-girder fixed segment and the distribution of the stress of main stress,and the influence of the main tower and diaphragm on the stress distribution of the main beam is discussed.The main analysis contents are as follows:1.In order to improve the construction efficiency,the construction method of tower and beam synchronous construction is adopted for A’pengjiang grand bridge,which is different from the conventional construction method of first tower and second(then/rear)beam,and it requires the overall pouring construction in the pier-tower-girder fixed segment.The finite element software Midas / Civil is used to simulate the process of entire tower and beam synchronous construction.The analysis and summary of the main beam internal stress and stress distribution in the construction process at several important construction stages provide reliable analysis data for the solid model and theoretical basis for construction monitoring tasks at the same time.2.The spatial stress distribution at the part of the pier-tower-girder fixed segment of the extradosed cable-stayed bridge is extremely complicated,and it needs to be paid more attention in the bridge design calculation.If the rod system model is established for simulation calculation just according to the construction process,the stress distribution law of the pier-tower-girder fixed segment cannot be well understood.Therefore,based on the calculation results of the overall rod system model,this paper uses the finite element software Midas / Fea to establish a local entity analysis model for the pier-tower-girder to conduct a detail analysis of the local stress and distribution law of the pier-tower-girder fixed segment under the main construction stage of the main beam.3.Enbedding a strain gage at the pier-tower-girder fixed segment to monitor the stress change of the part during the whole construction process.Through the comparison and analysis of the calculation results of the overall rod system model,the calculation results of the local solid model,and the field measurement data,the difference of them can be verified.The accuracy of calculation results and test results verified mutually can provide experience for the same type of bridge construction monitoring,and ensure the safety of the bridge structure during the construction.4.The structure and stress distribution are very complex at the pier-tower-girder fixed segment.The load on the main beam will affect the stress of the tower,and the load on the tower will also affect the stress of the main beam.Removing the main tower and diaphragm of the pier-tower-girder fixed segment respectively,setting up 4 groups of comparative analysis models of local entities,and analysing the local stress of this part under the action of a single concentrated load at the end of the tower and the beam,the internal force transmission law and stress distribution of the pier-tower-girder fixed segment can be fully understood,and the effect of the main tower and the diaphragm on the stress and distribution of the No.0 block of the main beam can be analysed and studied.5.The conventional simulation method of the pier-tower-girder fixed segment of the extradosed cable-stayed bridge in the overall rod system model is to convert the diaphragm into a uniformly distributed external load and apply it to the corresponding unit of the main beam.Simply connecting the central node of block No.0 of the main beam with the node at the top of the pier and the node at the bottom of the tower,the accuracy of the calculation result obtained in this way requires a further verification.According to the actual structure of the pier-tower-girder fixed segment,this paper uses different types of rod model to simulate the pier-tower-girder fixed segment part.Compareing the calculation results of the main beam stress processed by different rod models and different units section with the calculation results of the local solid model,a reasonable rod model simulation method and unit section determination method for the pier-tower-girder can be obtained.6.The main tower of the A’pengjiang grand bridge is relatively short,and the stay cables on the left and right sides of the main tower are staggered and arranged tightly.The side and mid spans are relatively large,and the side cable forces on the side spans are greater than those on the mid-spans.All of them bring an unbalanced force along the bridge.In this paper,the stress and distribution law of the cable tower anchorage area under the cross-anchoring method are obtained through analysing the local stress of the cable tower anchorage area,which provides a reference for the design of the cable-stayed bridge with the same type of cable-stayed cross-anchor.7.The stay cable of A’pengjiang grand bridge is spatial cable plane.The cable is anchored on the roof of the main beam by wedge-shaped concrete anchor blocks,forming a certain vertical and horizontal inclination angle with the main beam,connecting the left and right anchor blocks by a beam.In this paper,the A11 cable stay with the largest cable force is selected to esrablish a solid finite elemeny model of the cable-beam anchorage zone,which analyses the local stress in this section and get the stress and distribution of the cable-beam anchorage zone.