Experimental Study On Anchoring And Lap Performance Of Spiral Stirrup-corrugated Pipe Grout Anchor Connection

China put forward the "dual carbon" strategic goal in September 2020,and green building is an important means to achieve carbon emission reduction.As the main form of "green building",prefabricated structure is widely used in a variety of building structures.China is a big grain country,and the safety of grain reserves is an important guarantee for national food security.The large storage capacity of bungalows is the leading warehouse type of grain reserves in my country."Practice provides a new direction of development.The connection performance of the steel bars at the nodes is the basis for ensuring the structural safety of the prefabricated one-story warehouse.Aiming at the shortcomings of the existing grout anchor connections,this paper proposes a spiral stirrup-corrugated pipe grout anchor connection method.Since the wall of the grain bungalow is mainly subjected to the side pressure of the grain,the steel bars at the connecting parts of the wall are in a state of tension when fully loaded;when loading and unloading grain,the internal steel bars are in a state of repeated tension.At present,there is no complete theoretical system for the study of the mechanical properties of the spiral stirrup-bellows grout-anchor connection under uniaxial and repeated tensile loads.Therefore,it is of great practical engineering significance to study the anchorage and lap performance of the spiral stirrup-bellows grout-anchor connection.In this paper,the anchoring and lap performance tests of the spiral stirrup-corrugated pipe restrained grout anchor connection were carried out to clarify the failure form and crack development of the specimen,and to analyze the load-slip curve of the specimen,the strain of the steel bar and the variation law of the strain of the spiral stirrup.,to study the influence of different parameters such as steel bar diameter,anchorage length,corrugated pipe diameter,grouting material strength and loading method on the anchorage and lap joint performance.The main research contents and conclusions of this paper are as follows:(1)Aiming at the bonding and anchoring properties of steel bars and grouting materials under the constraint of spiral stirrups and corrugated pipes,48 anchoring specimens were designed for central pull-out tests,and the failure patterns,crack development,and steel strain variation laws of the specimens were analyzed;The effects of different influencing parameters on the anchorage performance under the constraint of spiral stirrup-bellows were studied.According to the test results,the calculation formula of the ultimate bond strength considering whether the bellows is formed or not is established,the critical and ultimate anchorage lengths under the constraint of spiral stirrups and bellows are proposed,and the applicability of the formula is verified,and the anchorage length is given.Recommended value: when the aperture ratio D/d=4.28 and the steel bar diameter is 14 mm,the anchorage length is not less than 5d;when 2.5≤D/d<4.28,and the grouting material strength is 60 MPa,the anchorage length is not less than 7d;D/d= 2.5,and when the strength of the grouting material is greater than80 MPa,the anchorage length shall not be less than 5d.(2)In order to study the lap performance of steel bar and grouting material under the constraint of spiral stirrup-corrugated pipe,63 lap joint specimens were subjected to uniaxial tensile and repeated tensile tests on the basis of the anchorage length of the central pull-out specimen.The failure mode,crack development and strain variation of spiral stirrups of the specimen were analyzed;The effects of different influencing parameters on the lap joint performance under the restraint of spiral stirrups and bellows were studied.Based on the bondslip theory and the core-confined concrete mechanics model,a formula for calculating the ultimate lap length is established.The recommended value of the lap length is given: when the aperture ratio D/d is 2.5～4.28,the lap length of the steel bar with a diameter of 14 mm should not be less than 10 d,and the lap length of the steel bar with a diameter of 16 mm should not be less than 15 d.When subjected to repeated tensile loads,the lap length of 14 mm steel bars shall not be less than 15 d.(3)Based on the characteristics of the bond-slip curve and the regression fitting of the test data,the calculation formula of the characteristic value of the bond strength is established,and the average bond stress-slip between the reinforced grouting materials under the constraint of the spiral stirrup-corrugated pipe is proposed.shift constitutive relation;The distribution of bond stress between reinforcement and grout material under the constraint of spiral stirrupbellows is studied by using strain gauge method.It is found that the bond stress is uneven along the anchorage length and reaches its peak at 0.3la from the loading section.The position function of bond stress distribution is established,and the bond-slip constitutive model considering bond stress distribution is given.