Study On Mechanical Performance And Construction Monitoring Of Prefabricated Box Girder Bridge Using Reactive Powder Concrete

A new kind of ultra-high performance cement-based material,RPC(Reactive Powder Concrete),can significantly reduce the weight of structure and decrease the inertia load,when applying to build the prefabricated beam of bridge.It has lower shrinkage and high durability after hot water curing.Because of the requirements of stress and structure,the deck thickness of common concrete box girder is 28cm-30 cm usually;the punching shear is not a significant issue.However,the deck of reactive powder concrete box girder is very thin and span-depth ratio is larger.Therefore,how to control the extent of being damaged of box girder by using punching capacity becomes the key problem of designing this structure.Simultaneously,the punching failure is a typical three-dimensional stress state,it has numerous influence factors and complex mechanical properties.These technical problem have not being solved by establishing an unified and perfect punching mechanism and analysis standard in the world.This thesis is using the first Reactive Powder Concrete footbridge,Beichen delta bridge project which is located at the Hengsi Road in Changsha,Hunnan,as an example to analyze several key functions of the precast segment Reactive Powder Concrete box girder bridge,and key techniques of monitoring constructions.Main points are listed as follows:(1) Doing research on mechanisms characteristics of the bridge by establishing and analyzing the MIDAS F.E.M model.(2) Doing research on the key parameters and the solution of monitoring constructions of the full space support-construction of the box girder.(3) Doing research on stress mechanisms of the RPC bridge deck by establishing and analyzing the ANSYS F.E.M model.Our conclusions are:(1) The main girder plate section becomes thinner by decreasing about 25%-64% and the ratio of depth of beam to main span decreases from 1/14 to 1/27 after using the RPC.Obviously,it significantly reduces the weight of structure and effectively improves the bridge span.Meanwhile, the risk of the pier column being hit by a car is deducted.(2) Both the overall and the local mechanical properties of the RPC bridge met the specification requirements, and its stress level or deformation during service even had more safety margin.(3) Both the natural frequency and the maximum structure response of acceleration under pedestrian loading or vehicle loading of the RPC bridge can met the specification requirements.The driver shoud limit its top speed to 20 kilometers per hour when the 300 k N vehicle pass the bridge.(4) The construction should be strictly processed by following the calculation of the assembled geometry and unstrained geometry of the girder.(5) For RPC slab under the local loading of square area,the boundary between the flexural failure and the punching shear failure is the area length of 3cm-4cm.With the increasing of the thickess of the RPC slab,the ultimate capacity of the structure is significantly improved,and the impact on the structure which happened flexural failure is more obvious than the structure which happened punching shear failure.(6) Based on the mechanical performance and construction requirements,the minimum width of the RPC deck system is 6 cm.