Study On The Performance Of Steel Bracing Connection Of T-Girder Bridge And Design Method

T-girder bridge has been widely used in the short to medium span bridge in China.With the increasing of life cycling and vehicle load,the transverse connection of the bridge has been damaged seriously.So,strengthening the transverse connection of the T-girder bridge quickly and effectively is of great practical significance.In this paper,two methods have been proposed,i.e.,triangle brace steel diaphragm and K brace steel diaphragm.The influence of the two diaphragms on the mechanical properties of the T-girder bridge has been studied.Design methods for the two diaphragms strengthening T-girder bridge have been proposed.The main research content and conclusions of this work are as follows:(1)The influence of strengthening methods and installation height of the triangle brace steel diaphragm on the integrity,load distribution and transverse stiffness of the T-girder bridge is studied based on a bridge model by experiments and simulations.The natural frequency and modal shape of T-girder bridge strengthened with different numbers of triangle brace steel diaphragm have been discussed as well.The results show that the load distribution and integrity of the strengthened T-girder bridge can be improved significantly.When the load is applied on the midspan of the bridge,strengthening at quarter span of the bridge has the best effectiveness.The maximum deflection decreases 27.6% and the maximum strain decreases 62.4%.(2)The influence of the location and number of the K brace steel diaphragm on the integrity and transverse stiffness of the T-girder bridge is studied based on a bridge model by experiments and simulations.The dynamic properties of the T-girder bridge strengthened with K brace steel diaphragms are studied as well.The results show that the K brace steel diaphragm can strengthen the transverse connection and decrease the maximum deflection and longitudinal strain of the T-girder bridge significantly.When the load is applied at the midspan of the exterior girder,the maximum deflection reduces 30.0% with the K brace steel diaphragms installed at thirds span.(3)The mechanical properties of the concrete T-girder strengthened with two K brace steel diaphragms at midspan are studied by experiments.The load distribution,deflection,strain,crack load,ultimate bearing capacity,support displacement and failure mode of the concrete Tgirder bridge with or without K brace steel diaphragms are analyzed in detail under different load cases.The finite element models of the concrete T-girder bridge strengthened with two K brace steel diaphragms are established and compared with the experiments.The results show that K brace steel diaphragms can improve the integrity and load distribution of the T-girder bridge,and decrease the deflection of the T-girder bridge.Moreover,the crack load and the ultimate bearing capacity of the T-girder bridge are increased and the development of cracks is prevented efficiently.The ultimate bearing capacity increases 11.0% at most.(4)The stiffness calculation methods of bracing steel diaphragms are summarized and the stiffness calculation methods for triangle brace steel diaphragm and K brace steel diaphragm have been proposed respectively.The internal forces influence line of each girder has been obtained by rigid-jointed girder method based on the proposed stiffness calculation methods.The results are compared with those obtained based on the deflection and strain respectively.The mechanical property of K brace steel diaphragm in strengthening the T-girder bridge is analyzed and the stiffness of the brace is calculated.The results show that the internal forces influence lines obtained based on the proposed stiffness calculation methods agree well with the experiment and simulation.The stiffness of the brace is influenced by the width of the top flange,the angle between the diagonal brace and the web,and the torsional rigidity of the Tgirder.(5)The impact of triangle brace steel diaphragm and K brace steel diaphragm on deflection and stress of the prestressed concrete T-girder bridge is studied.The influence of the diaphragm number,cross section size of the brace and installation location on the strengthening effect is studied.The design methods for strengthening T-girder bridge with triangle brace steel diaphragm or K brace steel diaphragm are proposed.Additionally,a 30 m prestressed T-girder bridge strengthened with triangle brace steel diaphragm or K brace steel diaphragm is presented.The results show that the maximum deflection of the T-girder bridge reduces more than 12.5%with triangle brace steel diaphragm or K brace steel diaphragm.Based on the study in this work,K brace steel diaphragm is more recommended.