Experimental Study On Flexural Performance Of Ultra-high Strength Concrete PRC Pipe Pile

Prestressed high strength concrete pipe pile(PHC pipe pile)is widely used in foundation pit engineering due to its advantages of high bearing capacity,low cost and convenient construction.However,when it is used in foundation pit support,it has the defect of insufficient lateral resistance.As a product with relatively good ductility,prestressed concrete pipe pile with hybrid reinforcement(PRC pile pile)is widely used in prefabricated trestle,pile-slab soilless subgrade engineering,pile foundation engineering of power system and so on.Especially in recent years,with the rapid development of underground space,foundation pit engineering abound and the requirements for pile performance are getting higher and higher.However,C60 and C80 are the main concrete strengths of all kinds of pipe piles commonly used in engineering today,and for hard soil areas,increasing the resistance of the pile itself is also one of the requirements,so it is imperative to improve the working performance of PRC pipe pile by improving its concrete strength.In this paper,C105 grade concrete is used in the production of PRC pipe piles.Considering the parameters of concrete strength,non-prestressed reinforcement and its quantity,eight pipe pile specimens are designed and fabricated.The bending performance was studied experimentally and calculated theoretically.The main research contents and conclusions are as follows.(1)8 ultra-high strength concrete(C105)pipe piles,including 7 PRC pipe piles and 1 PHC contrast pile,were tested for flexural performance.The stress process,failure characteristics and development law of fracture distribution of PRC pipe piles and PHC pipe pile were analyzed.The results show that: the stress process and failure mode of C105 grade PRC pipe piles are basically the same as those of C60 and C80 grade PRC pipe piles;there is no obvious difference in crack distribution and crack width,but the improvement of concrete strength can significantly improve the cracking moment,ultimate bearing capacity and stiffness.(2)Based on the test results of load-deflection curve,component section strain curve,deformation curve and crack width,the influence laws of concrete strength,nonprestressed reinforcement and its quantity on the flexural performance of ultra-high strength concrete PRC pipe pile specimens were analyzed.The results show that:Compared with PRC pipe piles with concrete strength grades of C60 and C80,the cracking bending moment and ultimate bending moment of C105 concrete pile are improved,and the stiffness is significantly improved,which has little effect on the crack development.Compared with PHC pipe piles,the bearing capacity and ductility of PRC pipe piles are improved.With the amount of non-prestressed steel reinforcement increases,the cracking moment decreases slightly,the ultimate bending moment increases slightly,but the ductility improves greatly.The number of cracks increases and the crack width is smaller under the same level of load.(3)The results calculated by the cracking moment calculation formula in the current atlas DBJT19-34-2009 were agree well with the experiment result,and can be used for the anti-cracking calculation of the ultra-high-strength concrete PRC pipe piles.(4)Based on the analysis of the test results,considering the influence of concrete strength on the concrete area ratio α in the compression zone,the influence coefficientβ of α was introduced to amend the existing calculation formula for the flexural bearing capacity of PRC pipe piles.Compared with the experimental results,the modified formula is in good agreement with the experimental value.