Study On The Anchoring Performance Of Novel One-sided Bolt With Flip-top Washer

The bending modulus of the square steel tube section is the same in the direction of the main shaft and the weak axis,and has excellent force performance.It has been widely used in industrial and civil buildings in recent years.However,for the rectangular square steel tubular column with a closed section,due to the shielding of the pipe wall,an additional hand hole is required for the connection of the high-strength bolt.In order to solve this problem,one-sided bolt technology has been developed at domestic and foreign in recent years.The one-sided bolt has the advantages of one-sided installation and convenient construction,which can avoid the problems of ordinary high-strength bolt installation.Based on the development ideas of existing one-sided bolt fasteners at domestic and foreign,this paper proposes a novel one-sided bolt with flip-top washers.It adopts experimental research,finite element analysis and other methods to form its forming process,force transmission mechanism and single bolt anchoring performance and group anchoring performance.（1）We complete the design of the novel one-sided bolt.The novel bolt is made of ordinary10.9 high-strength bolt.The core components are four L-shaped washers and four torsion springs.When installed,the torsion springs drive the profiled washers to flip and rebound to realize one-sided operation.Simple and convenient,without additional aids.（2）We measure the pre-tightening force and time-varying effect of the bolt.Through test,the pre-tightening force of M16、M20 novel bolt and the 10.9 high-strength bolt are measured,with finite element model verified.At the same time,the loss of the pre-tightening force within60 hours of the bolt is measured.The results shows that L-shaped washer of the novel bolt has a suspended area,and the pre-tightening force reaches about 60%of the same type 10.9 high-strength bolt.However,the novel bolt pre-tightening loss can be solved by over-torque.After applying the pre-tightening force for 60h,the pre-tightening rate of the high-strength bolt and the novel bolt is more than 90%,and the pre-tightening relaxation value accounts for more than70%of the total slack value within the first 10h.（3）We also complete the anchoring performance test of 9 single novel bolts and the optimized design of L-shaped washer based on 52 sets of finite element parameter analysis.The test shows that there are two kinds of failure modes of the bolts:one is the shear failure of the profiled washer,and the other is bolt rod damaged.As the thickness of the washer increases,the bolt failure mode changes from the 1 to 2.When the thickness of the washer increases from0.1d₀ to 0.2d₀ and 0.3d₀（d₀ is the nominal diameter of the bolt）,the tensile load capacity of the M16 bolt is increased by 6.1%and 8.6%,and the initial stiffness is increased by 17.6%and20.6%;the tensile load capacity of the M20 bolt is increased by 134.0%and 136.5%,and the initial stiffness is increased by 87.9%and 100.3%;the tensile load capacity of the M24 bolts is increased by 80.2%and 144.9%,and the initial stiffness is increased by 61.8%and 60.7%.The parameter analysis shows that the main factors affecting the bearing performance of the washer are:washer thickness‘e’,washer sidewall height‘h₀’and washer contact surface size‘s₁’,when e=0.2d₀,h₀=0.25h₁,s₁=0.2d₀（h₁ is the height of the bolt head）,the anchoring performance of the novel bolt is equivalent to that of the same type of high-strength bolt.The influence degree of the novel bolt anchoring performance from strong to weak is:washer thickness‘e’>washer sidewall height‘h₀’>washer contact surface size‘s₁’>washer lower contact surface size‘s₂’>profile washer upper surface slope‘γ’>washer contact surface anti-slip coefficient‘μ’.（4）We complete the anchoring performance test of the novel bolt group in the square steel tube.The test consists of 9 bolted square steel tubular T-stub test pieces,and the influence of factors such as the number of bolts,the spacing,the thickness of the column flange and the thickness of the end plate are investigated.The results shows that the failure mode of the connected test piece is divided into three types according to the relative strength of the column flange,the T-stub end plate and the bolt:one is the T-stub end plate yielding;the second is the column flange yield;the third is the bolt bolt pull damage.When the strength of the bolt and the column flange is relatively large and the end plate of the T-stub is thin,the failure state of the test piece is the yield of the T-stub end plate,which generates the force.When the strength of the end plate of the bolt and the T-stub is relatively large and the wall of the pipe is relatively thin,the failure mode of the test piece is the yield of the column flange.At this time,the anchoring performance of the group bolt is greatly affected by the bolt distance g₂ of the column cross-section,and when g₂ is small,the bolt hole is far away from the web of the column,and the flange of the column is bent and damaged;when the g₂ is large,the bolt hole is closer to the web of the column,and the flange of the column is sheared and damaged.When the T-stub end plate and the pipe wall are relatively thick and the bolt strength is small,the failure state of the test piece is that the bolt is damaged by the tension.The anchoring performance of the novel one-sided bolt is similar to that of the ordinary high-strength bolt.The test load-displacement curve agrees well.The novel bolt has a reasonable opening,and the bolt hole has less weakening on the bearing capacity of the upper flange.The design value of the tensile bearing capacity of the novel bolt group connection test piece is in good agreement with the calculated bearing capacity of the one-sided bolt connection node given in the domestic and foreign codes or references.Finally,we summary the full-text research and discuss the topics that need to be further studied for the novel flip-top washer one-sided bolt.