Study On The Control Of Mid-span Deflection And Crack Of Long-span Prestressed Concrete Beam Bridges

Due to various reasons, a lot of big span prestressed concrete bridges appeare problems:different nature large mid-span deflection and too much cracks. With the increase of bridge span,cracks and excessive deflection problem appear more serious phenomenon. Large mid-spandeflection and too much cracks development affect the durability and safety of long-span PCbeam bridges. Study the large deflection of the bridge middle and the crack control method hasimportant engineering value and social significance. Based on the numerical simulation,experimental analysis and the engineering case, the thorough system research of the deflectionand crack control of the long-span PC beam bridge is carried on, and main work is shown asfollow.1. To study the steel beam configuration method, it can well control the deflection. Thepresented dead load zero moment method is a method to control the deflection, through the zerobending moment method of superposition process found that the presented moment is generallythe last segment configuration with less steel cable. It often causes large deflection of structure,and then put forward the improvement of the "big cantilever with large steel cable and smallcantilever beam with small" of the dead load zero moment method. Based on the deflectioncontrol principle, the optimization design procedures of the cantilever construction stage ofprestressed steel beam configuration are written using the APDL program language of ANSYSsoftware. Through the professional software read, the basic calculation results can be obtainedafter data input. Through optimization design program, the optimal configuration of steel beamand the minimum deflection can be obtained under a certain number of materials.2. The construction control of middle span pusher and side span heavy is studied. Before themiddle span folded, the pusher can effectively reduce the perpetuation bending moment of mainpier of long-span rigid frame bridge, and it is advantage to the durability and safety of the mainpiers, so the pusher can be as the basic method that put to offset bending moment of main piersof large-span rigid-frame. The construction control of side span weight can balance two piersaxial force and reduce the mid-span deflection of the main pier of the double limb thin-walledpier rigid frame bridge. The construction control of side span pressure heavy can improve themid-span deflection of main piers. The construction control of side span pressure weight increase bending moment of both limbs and single limb thin-walled pier bridge main pier, at the sametime in the side span pressure weight reducing the deflection, combined with middle span pushercase to reduce bending moment of the main piers, and the stress of the pier is in good condition.3. The edge support active settlement method is put forward and studied. The research showsthat the method can effectively reduce the mid-span deflection of PC beam bridges, such as rigidframe bridge and continuous girder bridge. For example, a rigid frame bridge with200m span,edge support sinks200mm, and mid-span deflection can be reduced40.3%.4. The box girder web plate and the influence of the beam high to structure stress anddeflection are thorough studied, and clear the stiffness index. The increase of web thickness has abig improvement to structural shear strength and the main tensile stress, so in the design it shouldbe appropriate increase the web thickness. The increase of the mid-span and root height of boxgirder is of great help to minimize mid-span deflection. The bridge stiffness index is carried outin-depth analysis and discussion, and the bridge rigidity test indexes are determined.5. The test of steel fiber reinforced concrete beams is carried out, the basic features of the steelfiber reinforced concrete beams is obtained by experiment. Aiming at the problem existing in themain shear formula, such as the contribution of longitudinal tensile reinforcement to the shear,the using range of steel fiber volume content and the parameter selection of shear contribution ofsteel fiber, ANSYS optimization design function is used fitting the experimental data, and theultimate shearing resistance formula of steel fiber reinforced concrete beam is obtained.