Beam-type Experimental Study On Bond-slip Properties Between Concrete And 600MPa High-strength Rebars

In the context of the state’s encouragement of green energy conservation,the use of economic energy-saving resources is an important measure for the sustainable development of the engineering construction industry.Compared with ordinary steel bars that are now widely used in China’s concrete structures,high-strength steel bars have high strength,reduce the use of steel,and have low comprehensive costs.At present,there are a lot of researches on the experimental and theoretical aspects of anchoring problems of ordinary steel bars in China,but there are few corresponding researches and specifications for high-strength steel bars.In this paper,the research on the bonding and anchoring performance of 630MPa-level high-strength steel bars and concrete is carried out.400 MPa,630MPa-level steel bars and concrete-bonded beam specimens are made for comparative tests.By changing the anchor length,steel bar diameter,and concrete strength,combined with the test piece failure Morphological comparison and analysis of the influence of various factors on the bond-slip curves of the two types of steel bars.The results show that the effect of anchoring conditions on the anchoring performance of ordinary and high-strength steel bars and concrete is consistent.The characteristics and trends of the bond-slip curves of 400 MPa and630MPa-grade steel bars and concrete are essentially the same,and they can be divided into five periods: elastic stage,sliding stage,internal crack stage,descending stage,and resisting stage.Using the method of strain gauge test inside the steel bar and calculating the difference in stress between adjacent measuring points through mechanical equilibrium conditions,the relationship model between the steel bar strain and the bonding stress was established,and the adhesion between the different strength grade steel bars and the concrete contact surface in the anchoring zone was obtained.Junction stress distribution.The results show that the bond stresses of 400 MPa and 630 MPa steel bars are the maximum near the loading end,and gradually decrease toward the free end.When the distance from the loading end is 0.1la to0.2la,the bonding stress reaches the maximum value.When the end is 0.4la ～ 0.6la,the bonding stress gradually enters a stable period.The test results provide a reference for the theoretical calculation of the bonding stress and the study of the constitutive relationship ofthe bond slip.Based on the statistical analysis of the beam test results,a calculation formula for the bond strength of 630 MPa high-strength steel bars and concrete was proposed,and a second-order moment method was used for reliability analysis.The calculation formula of the junction length indicates that the anchorage length of the 630 MPa high-strength steel bar obtained by reliability analysis is smaller than the design anchorage length calculated according to the current "Code for Design of Concrete Structures"(GB50010-2010),and the630 MPa steel bar is calculated according to the code The anchor length is feasible.The related analysis results in this paper provide the basis for the application of 630 MPa high-strength steel bars.The related results have been written into the "Technical Regulations for Heat-Treatment Ribbed High-Strength Concrete Structures" in Shaanxi Province.