Research On Wind-resistant Performance Of Continuous Steel Truss Bridge Under Launching Construction

With the rapid development of long-span bridges,steel truss girder has gradually becoming an important form of the main girder structure of long-span bridges.The incremental launching method construction is a commonly used construction method for long-span steel truss bridges.In the large cantilever state during the launching construction stage,the main girder structure has low frequency and weak wind resistance.It is easy to cause large vibration or even destabilization under wind load.In addition,the transient impact dynamic effect caused by the change of launching force(especially the static and dynamic friction force at the moment of launching startup)of large cantilever box girder has adverse effects on the stress of steel truss beam and substructure.There are no provisions in the current code to guide the design.Therefore,it is of certain engineering application value to develop the wind resistance and launching transient dynamic effect of steel truss bridge during construction period,and provides reference for similar bridge construction in the future.Aiming at the problem of wind-induced vibration of large cantilever in launching construction of steel truss bridge,this paper takes the 11-span continuous steel truss bridge with span 84+9×108+84m under construction as the engineering background,carries out experimental and Numerical Simulation Research on wind resistance and start-up transient impact effect under the most disadvantageous conditions of launching construction.The main works are as follows:(1)The wind tunnel force test were carried out for section model of launching nose and main beam,and obtained the three-component force coefficients at different wind attack angles.Next studied the calculation methods of wind loads on truss beams under different national codes,and compared the calculation values of wind loads on truss beams with the experimental values,finally summarized the applicability of national codes to the calculation of wind loads on truss beams is summarized.of wind loads on Truss Girders in different national codes.The calculation methods of wind loads on railway steel truss bridges are discussed.(2)The three-component force coefficients are obtained by wind tunnel force test,and calculated the wind-resistant stability coefficients of transverse and longitudinal bridges during the launching construction of guide girders and main girders.The results show that under the condition of large cantilever,the design reference wind speed is 38.5 m/s,and the main girder does not satisfy the requirements of transverse and longitudinal wind stability;the construction safety may be affected when the instantaneous wind speed exceeds 20 m/s(level 8 gale).(3)Based on Davenport random buffeting theory,the finite element model of steel truss bridge umder construction state is established by Ansys,and the buffeting response is analyzed.The analysis shows that when the wind speed is 30.8m/s,the maximum buffeting amplitude of the launching nose is about 4.2cm under large cantilever state,accounting for 14% of the dead load,and the vertical support reaction at the bearings accounts for 13% of the dead load.The buffeting effect may cause structural fatigue effect and affect the safety of construction personnel.Therefore,it is necessary to take appropriate consideration of its role and take appropriate emergency measures when necessary.The coupling effect of pier-beam causes the error of buffeting displacement at the launching nose and vertical support reaction to be less than 2%,and the influence on wind-induced buffeting can be neglected.(4)Transient dynamic analysis is carried out of steel truss beam under launching construction,and proposed a numerical analysis method of transient dynamic effect of launching start-up,finally studied the impact coefficient of support reaction under different damping ratios with wind load.The research shows that the transient impact effect under launching construction of long-span bridges can not be neglected.In practical engineering applications,it is necessary to select appropriate impact coefficients for different spans.For the commonly used 110 m span bridges,the impact coefficient can be chosen as1.02,and the area with large wind load can be enlarged to 1.05.