Pseudo-Static Experimental Research On Behavior Of Skewed Integral Abutment-Pile-Soil System

The integral abutment bridge(IAB)is a bridge system using an integral abutment,in which the main girder and abutment can be cast as a whole,avoiding the installation of bridge deck expansion joints and bearings at the bridge head,which significantly reduces the construction,especially the operation and maintenance costs.Therefore,IAB is widely promoted and applied around the world.Introducing the integral abutment into the skewed bridge to form a skewed integral abutment bridge(SIAB).It can effectively avoid the torsion drop phenomenon of the skew bridge deck and main girder under the action of earthquake.While due to the integration of girder and abutment,complicated abutment-pile-soil interaction occurs,further study of the complicated interaction is urgently needed.Therefore,a normal abutment-H steel pile specimen and a skewed abutment-H steel pile specimen were designed and manufactured based on an existing IAB.Pseudo-static tests were carried out on the behavior of normal and skewed integral abutment-H steel pile-soil system.The experimental finite element model is established by ABAQUS and compared with the experimental results to verify the correctness of the finite element model.A series of finite element models with different parameters are established and a series of parameter analysis were conducted.Main conclusions about experiment are as follows:(1)The hysteresis curves of the skewed abutment and the normal abutment-Hshaped steel pile specimens are all shuttle-shaped,and the equivalent viscous damping ratios are 0.248 and 0.246,respectively,indicating that the system has high energy dissipation and seismic performance.The peak bearing capacity of the skewed abutment specimen is 1.58 times that of the normal abutment specimen.The earth pressure behind the abutment of the skewed abutment is unevenly distributed,the reaction force of the specimen is eccentric to the loading direction,and the side of the abutment will suffer to friction,which may affect the bearing capacity of the system to a certain extent.(2)When loading in the positive direction,the earth pressure behind the skewed abutment increases first and then decreases with the increase of the loading displacement of the abutment,and reaches the maximum when the loading displaceme--nt is 0.017H(H refers to the height of abutment).As the loading displacement increases,the earth pressure behind the abutment changes from a triangular distribution to a double-fold line distribution along the depth of the abutment,and from a parabolic distribution to a three-fold line distribution along the width of the abutment.Since the existing passive abutment earth pressure theory does not consider the effect of reciprocating load or the influence of the skewed angle,the existing theoretical calculation values are quite different from the experimental value.In this paper,HuangLin method is used as a reference,and the Huang-Lin method earth pressure coefficient calculation formula is revised on the basis of experimental data.When the loading is negative,the earth pressure behind the abutment is always slightly smaller than the static earth pressure,which can be calculated according to the static earth pressure.(3)Under the action of reciprocating load,the soil behind the integral abutment has obvious flow phenomenon,and the sand behind the abutment continues to flow around the pile top,which causes the pile body to deform in a "snake shape".The assumed parabolic piles have different deformations,so the existing calculation theory is not suitable for the pile foundations of integral abutment.(4)In the specimen of the skewed bridge abutment-H-shaped steel pile,the loading direction and the strength and weakness axis of the H-shaped steel pile are at an angle of 45°,so the flange and web are both subjected to earth pressure.In the area of about 0.6m(5.8B)along the buried depth,the earth pressures on the flange and the web both increase first and then decrease.In the elastic state of the pile,when the pile is loaded in the positive direction,with the increase of the loading displacement,the earth pressure of the web first increases and then decreases,and the earth pressure of the flange increases with the increase of the loading displacement.When loading in the negative direction,both the web and flange soil pressures increase with the increase of the loading displacement.(5)In the normal abutment-H-shaped steel pile specimen,the H-shaped steel pile is only subjected to the bending moment along the weak axis.In the specimen of skewed abutment-H-shaped steel pile,the H-shaped steel pile is subjected to bending moments along the strong axis and the weak axis at the same time,and the angle between the resultant moment and the bending moment of the strong axis is 17°～34°.(6)The finite element analysis results show that the skew angle has a significant effect on the soil reaction force behind the abutment and the maximum horizontal deformation of the H-shaped steel pile,but has no effect on the maximum total moment.Sand compactness has a significant effect on the soil reaction force behind the abutment and the maximum resultant H-shaped steel pile moment,but it has no influence on the maximum horizontal deformation of the steel pile.The orientation of the H-shaped steel pile has no influence on its maximum horizontal deformation,and has a significant influence on the value and position of the maximum resultant moment and the maximum normal stress.