Research On Punching Shear Performance And Bearing Capacity Calculation Method Of UHPC Bridge Deck

Ultra-high performance concrete(UHPC)has a good propect in bridge engineering not only because it has the characteristics such as ultra-high strength,high durability,and high toughness,but also because its mechanical performance is significantly better than the normal concrete.At present,the traditional concrete bridge deck have the disadvantages of large weight,easy cracking and poor durability.So if the normal concrete is replaced by UHPC to produce bridge deck,it will effectively reduce the thickness,save the materials and decrease the structural weight.However,there is a key issue urgent to be solved of UHPC in its application to the bridge deck.That is whether it will bring the problem of punching shear failure after thinning the bridge decks.At the same time,taking the high price of UHPC raw materials and the research results from our research group into account,the use of the granite stone powder to replace some part of the silica fume can not only reduce the costs,but also have a significant environmental effect.Therefore,the punching shear performance of UHPC bridge deck which mixed granite stone powder is researched in this paper.Based on the research of the critical thickness of the UHPC bridge deck at bending and punching shear failure,different parameters will be investigated to explore their influence on the punching shear performance of UHPC bridge deck.Finally,a calculation formula of ultimate bearing capacity will be put forward.The main contents and conclusions in this paper are as follows:(1)Researching the critical thickness between bending and punching shear failure.Regarding the deck thickness as the main parameter,we manufactured five tested decks of UHPC mixed with granite stone powder and one piece of normal concrete deck to research the critical deck thickness between bending and punching shear.The experimental results show that,all tested decks failed in punching shear,the bottom deck shapes like a "pot bottom",and the top deck punches out a clear cone.Before the slabs reach the ultimate bearing capacity,the bottom deck deflection deformations are increase with the thickness increasing.On the condition of the same thickness,the problem of brittle failure was improved when using the UHPC deck compared with the normal concrete because the UHPC deck is significantly better than the normal deck.Because its steel fiber has the function of crack resistance,energy dissipation and "bridging" effect.When the thickness of UHPC bridge deck was increased 30%～100%,the ultimate bearing capacity increased 32.5%～65.8%,besides the deformation and damage range of the tested plate were gradually increased According to the experimental results and the theoretical analysis,it should be recommended that the critical thickness of UHPC bridge deck mixed with granite stone powder be no less than 100mm in order to avoid punching failure.(2)Investigated the punching shear performance of UHPC bridge deck in different influence factors.Six equal thickness of UHPC bridge decks were fabricated to study the punching shear performance based on the parameters of the volume fraction of steel fiber,the reinforcement ratio and the replacement rate of granite stone powder.The results show that the ultimate bearing capacity increased from 250kN to 355kN when the volume fraction of steel fiber changed from 0%to 3%.When the reinforcement ratio increased from 0%to 3.50%,the ultimate bearing capacity increased from 180kN to 355kN.The granite stone powder mixed with 10%silica fume has little influence to the punching shear ultimate bearing capacity and the reduction scope was only 3.17%.(3)Put forward the calculation method of UHPC bridge deck punching shear bearing capacity.After summarizing and comparing the calculation methods of punching shear ultimate bearing capacity,the reasons of deviation under each calculation resultsare discussed based on the experimental results.Finally,according to the punching shear stress mechanism of UHPC bridge deck mixed with granite stone powder,a simplified punching shear ultimate bearing capacity formula is put forward.