Experimental Study On The Bond-Anchorage Properties Between 630MPa High Strength Reinforcement With Increasing Transverse Rib Spacing And Concrete

With the continuous development of concrete structure form and volume,the use of high strength reinforcing bars has become an inevitable trend of future concrete structure.However,it is still difficult to popularize and apply high strength reinforcing bars at this stage,due to the lack of relevant codes for high strength reinforced concrete structure and the limited research on the mechanical properties of high strength reinforcing bars in concrete.The bond and anchorage between reinforcing bars and concrete is the basic condition of concrete structure under force and is also an important subject of concrete structure design and construction.So,in order to popularize the application of high strength reinforcing bar,it is necessary to study its bond performance with concrete.Crescent-shaped steel bar is a main kind of deformed bar used in concrete structure,and there are strict regulations on its shape condition in national standards.However,the researches on the influence of reinforcement shape on bond performance are mainly concentrated in the last century,and the researches on the crescent-shaped rib steel bar are very few.Therefore,it is necessary to study the bond performance of difference shapes of crescent-shaped rib steel bar with concrete.This paper mainly studied on the bond-anchorage properties between concrete and 630 MPa high strength reinforcement with increasing transverse rib spacing.51 pull-out specimens were made with T63 steel bars with standard shape or increasing transverse rib spacing.The effects of concrete strength,anchorage length,diameter of reinforcing bar and size of coarse aggregate on each kind of different reinforcing bars specimens are considered respectively.The influence of increasing transverse rib spacing on the bond-anchorage properties between concrete and T63 reinforcing bar was studied by comparing and analyzing the failure mode,bond strength and its influencing factors,bond-slip curve and its characteristic points of specimens.The results show that the failure modes of T63 reinforcing bars with standard shape and increasing transverse rib spacing are basically the same.The bond strength ratio of the same specimens of the two kinds of reinforcing bars is about equal to 1.The influence of various factors on the bond strength of the two kinds of reinforcing bars is basically the same.The shape and characteristics of bond-slip curves of the two kinds of reinforcing bars are basically the same,but there are only slight differences in the peak slip.Combining the comparison results,it can be thought that the bond properties of T63 reinforcing bar with increasing rib spacing in this paper are not significantly different from those of steel bar with standard shape.From the view of bond-anchorage,the T63 reinforcing bar with increasing rib spacing can be applied to practical engineering without differently treating.On the basis of experimental study,typical empirical formulas for calculating bond strength and bond-slip constitutive relations at home and abroad were collected and compared with the experimental results.The applicability of both empirical formulas and constitutive relations for T63 reinforcing bars is analyzed.The bond problem between deformed reinforcing bar and concrete is simplified to a plane problem and the thick-walled cylinder in mechanics of elasticity is used to analyze the problem.In the analysis,not only the influence of uncracked zone of concrete is considered,but also the influence of cracked zone of concrete is considered by described the stress in cracking with concrete softening theory in the fracture mechanics of concrete.The influence of different radial displacement distribution in the cracked zone on the calculating result was also considered in the analysis.The calculation method of bond strength considering both cracked and uncracked zone was obtained.The calculation results were in agreement with the test results,which proved the applicability of the calculation method in this paper.The relevant test and analysis results in this paper can provide basis for the application of T63 high strength reinforcing bar and the formulation of relevant regulations,and also provide reference for the optimization of the shape of crescent-shaped ribbed reinforcing bar and its production and manufacture.The processes and results of theoretical analysis can provide ideas for further analysis of bond and anchorage between reinforcing bar and concrete from the perspective of mechanical theory.