Mechanical Analysis And Construction Monitoring Of Steel Truss Bridge And Super High Temporary Pier Structure

In recent years,with the continuous advancement of "The Belt and Road" construction,the railway transportation system in China has developed rapidly.The continuous steel truss bridges are widely used in the construction of railway bridges in China as a mature structural form.The characteristics of the steel truss bridges are that the vertical and horizontal rigidity is large,and there is strong spanning ability.The constructions of longspan continuous steel truss bridges are usually to use cantilever assembly method.During the construction process,the key technical issues are structural system conversion and bridge closure.As soon as the bridge span is large,the temporary piers as the auxiliary structures can be set between the permanent piers to reduce the length of maximum cantilever erection of the bridge in the construction process,which can reduce the installation stresses of the steel truss structures and improve its anti overturning stability.Under complex terrain such as deep ditch canyons,the temporary piers may be very high.During the cantilever erection of the bridge,the structural stability and bearing performance of the ultra-high temporary piers directly affect the construction safety of the upper bridge.This thesis is based on the research background of the Yuanjiang Double-track Bridge Project of Yumo Railway,the finite element method is used to conduct mechanical analysis on the construction process of the steel truss girder structure and the super-high temporary pier.Then,based on the calculation results,the construction monitoring scheme about the construction is designed.The real-time monitoring of stress and displacement status of the super-high temporary pier during the construction is implemented.The main work and research results are as follows:1)According to the construction plan of the steel truss girder bridge,the mechanical model of the cantilever assembly of the steel truss girder bridge is established.The finite element method is used to calculate the stress and displacement status of the steel truss girder under the several cantilever working conditions before the structural system conversion.And the safety assessment of the structure under various construction conditions was carried out.It is confirmed that the safety factors of overturning of the steel truss beam meet the relevant specifications.In view of the closing conditions of the steel truss girder,a sensitivity analysis on the closure of the bridge was done.According to the analysis results,technical guidance is provided for the construction of the bridge closure,and the closure scheme of the steel truss girder bridge is formulated.2)Aiming at the contact relation between the large steel truss beam and the ultra-high temporary pier,based on the linear elastic structure of the steel truss beam,a mechanical analysis model is proposed to solve the pier-beam contact problem during the cantilever construction of the steel truss beam.Thus,a quantitative relationship of force transmission between steel truss beams and super high pier is established.And the stress and deformation states of the ultra-high pier structure subjected to the cantilever erection load of the steel truss beam are calculated by the finite element method.3)The ultra-high pier is a large steel structure lattice bracket,which is the main loadbearing structure during the construction of the steel truss bridge.According to the calculation results of the finite element method before construction,a stress and displacement monitoring scheme is formulated for the ultra-high pier structure.Consequently,the stress states of the ultra-high pier are monitored in real time during its assembly,installation and work.By comparing the construction monitoring data and the calculation results of the stress states,it is found that the results obtained by two ways are consistent.It is shown that the connection relationship between the pier and beam given in the present thesis is correct.During the construction,the measured stresses from the high buttress pier structure are all in the safe range,which effectively guarantees the safety of the cantilever erection of the large bridge.The research results obtained in the thesis by the mechanical analysis and monitoring technique for the large-scale steel truss bridge and ultra-high pier structure can provide beneficial references for construction techniques of similar ultra-large engineering structures.