Experimental Research On The Compressive Properties Of H-shaped UHPC Columns Piles In Integral Abutment Bridge

Ultra-High Performance Concrete(UHPC)is a novel construction material of ultra-high compressive strength,excellent durability and high ductility.Integral abutment bridges provide a sustainable alternative for bridge engineering with favorable performance and low maintenance costs.This thesis presents innovative H-shaped UHPC piles for integral abutment bridges to overcome the disadvantages of high horizontal stiffness in normal concrete piles and high costs and low durability in steel piles used for this bridge type,and hence,promotes the application and development of UHPC and integral abutment bridges in China.The vertical load carrying capacity should be considered highest priority for the design of H-shaped UHPC piles in integral abutment bridges,and then on the flexural capacity under the reciprocating temperature changes.The vertical compressive bearing capacity of H-shaped UHPC pile will decrease after weakening its lateral stiffness.Moreover,the compressive properties of H-shaped UHPC column pile is different from the normal concrete column pile because the difference of concete tensile strength and elasticity modulus.Therefore,the mechanical properties,cracking mechanism,failure mode and ultimate load-carrying capacity of H-shaped UHPC columns under the vertical load need to be revealed.The main contents and conclusions in the thesis are as follows:(1)The trial design result shows that the H-shaped UHPC pile replacing the rectangular reinforced concrete pile can meet the design requirement.The bending moment of main girder in the trial-design bridge is lower than that of the original bridge by 23.4%and 18.2%under the dead load and live load,respectively.That bending moment also reduced by 30.9%and 42.1%under uniform temperature rise and drop,respectively,and 34.6%and 48%,respectively,for axial force of the main beam.(2)The experimental result shows that,For axial compression specimens,the short columns with slenderness ratio of 13.5 is failed by compression,and the medium-lenth columns with slenderness ratio of 25 and 35 is damaged by combination of compression and bending,for axial compression specimens.The bearing capacity of plain H-shaped UHPC column decreases with the increase of slenderness ratio.For eccentric compression specimens,the failure modes can be divided into three types:local compression failure,full section compression failure and tensile failure.(3)The ABAQUS finite element analysis result is in good agreement with the experimental results.Parameter analysis shows that the bearing capacity of plain H-shaped UHPC columns decrease with the increase of slenderness ratio.Moreover,the relationship between bearing capacity and slenderness ratio is nonlinear under different eccentricity load.It means that the slenderness ratio and eccentricity have a coupling effect on the ultimate load carrying capacity.(4)The calculated method of eccentric compression capacity for the ordinary concrete or UHPC short columns can not be applicable for H-shaped UHPC short columns,because the proposed eccentric reduction factor will decrease linearly with the eccentricity increased.The current algorithms can not be utilized for bearing capacity of H-shaped UHPC medium-length columns.At last,the calculation method of bearing capacity for H-shaped UHPC column is proposed based on the numerical data,taking into consideration of the coupling effect between the eccentricity and slenderness ratio.