Failure mode and phenomenon of T-shaped steel connection joints T-shaped steel high-strength bolt connection failure modes include: joint shear slip failure, mainly the friction between T-shaped steel and column flange is less than the shear force caused by load; local yield failure of column flange Local buckling failure of the web of the compression zone; compression of the T-shaped steel web; deformation of the T-shaped steel flange; bending or tensile failure of the high-strength bolt.
During the test, when the beam end load reached 45kN, the bolts at the T-shaped steel joints slipped, the joints were stressed, and the brittle ring appeared near the node domain. The bearing capacity in the P2Δ curve was instantly reduced, and the beam end displacement was reached. 18mm, the left flange of the column is convex, and the T-shaped key of the beam end and the flange of the column have obvious cracks. When the beam end load is added to 50kN and 62kN, the above-mentioned slip phenomenon occurs, and the bearing capacity is instantaneously reduced. The edge deformation is obvious. When the ultimate load reaches 8214kN, the column node domain has oblique crack, the beam end displacement is 13417mm, and the crack between the T-shaped key and the column flange is 1311mm. When the beam end load of TA2 is 58kN, the left flange of the column is convex and the surface is wrinkled and peeled. When the load reaches 72kN, the flange of the column flange is very convex, and the upper T-shaped key and the flange of the column show obvious cracks. The type key is deformed together with the column flange. When the ultimate load reaches 8619kN, the beam end displacement is 12619mm, and the T-shaped key and the column flange are cracked up to 1217mm. The test pieces TA21 and TA2 test damage photographs are shown in Fig. 2, and the load 2 displacement curves of the two test pieces are shown in Fig. 3.
The beam end bending moment is simplified into a pair of force couples, which respectively act on the upper and lower flanges of the beam. The ultimate ultimate bearing capacity of the connection is determined by the minimum value of the ultimate bearing capacity Ft of each component. Thus, the beam end bending moment can be expressed by the following formula. In the formula M=Fth0(1), h0=h-tbf, h is the total height of the beam, and tbf is the thickness of the beam flange.
T-shaped steel joint joint bearing capacity calculation joint friction surface shear bearing capacity joint friction bearing capacity design value <1> V ≤ 019nfμPm (2) where: nf is the number of force-transmitting friction surface; μ is the friction surface resistance The slip coefficient shall be adopted according to the text <1> table 712121; P is the pre-tension of a high-strength bolt, which shall be adopted according to the text <1> Table 71212; m is the number of friction-type high-strength bolts at the connected parts.
The tensile strength and shear strength of high-strength bolts are calculated in the axial direction of the bolt rod. The design value of the bearing capacity of each high-strength bolt is Nbt=018P. When the high-strength bolt friction type connection is subjected to the shear force between the friction surfaces and the external tension force in the bolt shaft direction, the bearing capacity should satisfy: NvNbv+NtNbt≤1(3) where: Nv, Nt are single row high-strength bolts respectively Shear and tensile force; Nbv, Nbt are the design values ​​of shear strength and tensile bearing capacity of a high-strength bolt, respectively.
T-shaped steel bearing capacity calculation Packer's test on the tensile properties of T-shaped steel joints shows that when the T-shaped steel flange is "thick plate", there is no lever force Q at the end of the T-shaped steel flange, the strength is controlled by the bolt tension, and its failure mode As shown in Fig. 4(a), this is generally not the case; when the T-shaped steel flange is “thin plateâ€, the T-shaped steel flange plate yields failure, and its failure mode is shown in Fig. 4(b); In this case, the T-shaped steel flange plate and the bolt fail at the same time, and the plastic hinge line is formed in the flange plate, the bolt will also reach the limit state, and their bearing capacity is fully utilized, as shown in Fig. 4(c). >.
The basic assumptions for the calculation of T-shaped steel flange plates are as follows: 1) neglecting the influence of the tensile force of the flange plate caused by the shear force at the bearing section; 2) ignoring the influence of the deformation of the flange in the plane on the load effect; 3) ignoring the T-shaped steel The influence of the friction between the flange plate and the column flange on the internal force of the section. According to the assumption, the flange plate is approximately calculated as a plane bend.
The bearing capacity of the T-shaped steel web is calculated at the tension flange of the upper part of the T-jointed beam-column joint. The T-shaped steel web mainly bears the tensile force generated by the bending moment, and also bears part of the vertical direction caused by the vertical load. Shear force, but this part of the shear force is small compared to the lower T-section steel. The frictional high-strength bolt connection between the T-shaped steel web and the flange flange is calculated by the same equation (2), and the bearing capacity of the flange itself is calculated as follows.
The basic assumptions are: 1) the T-shaped steel has uniform force on the web; 2) ignores the influence of the beam end angle on the force of the T-shaped steel web; 3) ignores the influence of the vertical shear force on the tensile capacity of the T-shaped steel web. According to the above assumptions, considering the weakening of the cross section of the bolt, the tensile load capacity of the T-shaped steel web is calculated as follows: Ft ≤ (btw-mtd0) ttwfy (6) where btw is the width of the T-shaped steel web, and mt is the high strength at the cross section. The number of bolts; ttw is the thickness of the T-shaped steel web.
Column bearing capacity calculation Column flange tensile strength calculation In the T-shaped steel connection beam-column joint, the column flange is bent and deformed due to the tensile force of the bolt. For the joints without stiffeners, the tensile forces are all borne by the column flanges. When the tensile force exceeds a certain limit, the column flanges will be destroyed by excessive deformation. There are two modes of failure, as shown in Fig. 5 and Fig. 6, and for the failure mode 1, the yield line is in accordance with the single figure 5, the failure mode 1 yield line distribution, the failure mode 2, the yield line distribution curvature distribution, and the column flange The maximum bearing capacity design value is: Ft=fyt2cf3.14+0.5s1a+b+4aNbta+b(7) where tcf is the thickness of the column flange, and other symbolic meanings are shown in Fig. 5.
For failure mode 2, the yield line is distributed according to the double curvature, and the maximum bearing capacity of the column flange is designed as: Ft=fyt2cf3.14+2a+s1-d0b (8) where the symbol is shown in Figure 6, and d0 is the bolt diameter. The bearing capacity of the column web is calculated according to the force characteristics of the T-shaped steel connection. The column web can be divided into the tension zone and the compression zone.
The web of the web of the compression zone is subjected to the pressure generated by the bending moment. For the column without the transverse stiffener, the calculated height edge of the web may yield due to insufficient strength of the local compression column, thus causing the node to lose bearing. Force, the length of the column web stress distribution is shown in Figure 7. The local compressive strength of the column web is <5>: σc=Dtcwlcc≤f(9) where: Dt is the pressure caused by the bending moment of the beam end, tcw is the thickness of the column web, and lcc is the length of the assumed local compressive stress distribution. , lcc=btf+2(tcf+ttf+r), tcf is the thickness of the column flange, and r is the radius of the arc connecting the flange and the web.
Web local stability condition <6>: hcwtcw ≤ 156t2cwDtfy235 (10) where hcw is the height of the column web. If the formula (9), (10) is not satisfied, transverse stiffeners should be placed on both sides of the column web facing the compression flange. The total cross-sectional area As required for the two stiffeners is: Asfy+tcwlccfy≥Dt(11 The weld between the transverse stiffener and the column web should ensure the transfer pressure Dt.
The calculated length of the tensile stress distribution of the web of the web in the tension zone is shown in Fig. 7. The strength condition of the web in the tension zone is: llcctwf≥m2Nt (12) where: lcl is the height of the column web The assumed distribution length of the edge stress, lcl=d0+2r; m2 is the number of bolts with the same height as the calculated point; d0 is the bolt aperture; r is the same as before.
Test Verification and Conclusion According to the above formula, two test pieces were calculated and compared with the test results, as shown in Table 1. The results show that the bearing capacity analyzed and calculated by this theory agrees well with the experimental values, but the test and research of the beam-column T-shaped steel joints need to be further developed for different steel strength grades.
Flanged Stainless Steel Ball Valve
Flanged Stainless Steel Ball Valve,Ss Ball Valve,Stainless Ball Valve,316 Stainless Steel Ball Valve
Zhejiang Chenxiang import and export trade Co., Ltd , https://www.chenxiang-valve.com