Study On Mid-span Deflection And Crack Control Of Long-span Continuous Rigid Frame Bridge

Many long-span continuous rigid frame bridges have different degrees of deflection and cracking problems due to various reasons.Excessive deflection and cracking affect the durability and safety of bridges.Scholars at home and abroad have done a lot of research on the downwarping and cracking of rigid frame Bridges,but no control scheme has been put forward from the source of bridge design and construction control to prevent the downwarping and cracking of beam body.In this paper,the factors affecting the downwarping of rigid frame Bridges and the cracking of beams are investigated by combining theoretical research with finite element analysis.The main contents include:(1)To explore the influence of concrete shrinkage and creep on the deflection of rigid frame bridge;Using Midas Civil and Midas Fea to establish a finite element model of a(127+240+127)m three-span prestressed concrete continuous rigid frame bridge,comparing the similarities and differences between the calculation results of solid and beam elements considering concrete shrinkage and creep;By providing a support between the two thin-walled piers,the difference of the force and deflection of the continuous beam bridge and the continuous rigid frame bridge under the contraction and creep is compared.(2)Taking the(127+240+127)m continuous rigid frame bridge as an example,the finite element software Midas Civil was used to establish a full bridge model to study the trend of prestress loss of each part in the bridge construction and later operation;The tension control stress is reduced,and the influence of prestress loss on the deflection of the bridge is explored;Based on the(45+80+45)m continuous rigid frame bridge,the feasibility of the "constant zero moment method" beam is explored,and the principle of "small cantilever with small beam,large cantilever with large beam" is adopted.,optimized matching of the(72+128+72)m continuous rigid frame bridge deck bundle,The results show that this beaming idea can effectively control the deflection of the bridge.(3)The effects of construction factors such as concrete overrun steel beam tensioning sequence and side span weight on the deflection of(127+240+127)m continuous rigid frame bridges are studied.The results show that the concrete super-square will increase the full-bridge deflection;the tension sequence of the steel bundle in the closed section has no effect on the deflection;the mid-span deflection will decrease with the application of the side span weight,and the side-span deflection will increase.(4)The influence of beam stiffness on the deflection and force of(127+240+127)m continuous rigid frame bridge was investigated by changing the thickness of the web and the height of the beam.Under the condition of constant prestress,the deflection of the bridge increases with the increase of the thickness of the web,decreases with the increase of the height of the root section of the beam,and increases with the height of the mid-section.(5)Based on the(127+240+127)m continuous rigid frame bridge,the influence of concrete super-section and prestress loss on the main tensile stress of the whole bridge is studied.The whole bridge model was established through Midas Civil and Midas Fea,and the stress of the zero block in the ten years of the bridge was compared.The results showed that the Midas Fea calculation result was more specific and intuitive,and the Midas Fea calculation result was larger than the Midas Civil calculation result.