AISC cheng200Q4.pdf
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1、ABSTRACT A n experimental program and associated numerical analysis were undertaken to study the shear lag effect in round hollow structural section (HSS) tension members that are welded to gusset plates. The connection is made by slot- ting the tube longitudinally, inserting the gusset plate, and t
2、hen placing longitudinal fillet welds at the tube-to-gusset interface. Transverse welds at the junction of the slot and the gusset plate may or may not be present. A total of nine specimens with three different tube sizes and various weld lengths were tested in the program. The majority of the speci
3、mens failed by fracture of the tube somewhere between the two gusset plates, and there was considerable ductility prior to fracture. Numerical analyses of the con- nections were carried out using an elasto-plastic model and measured material properties. Based on the tests and the numerical analyses,
4、 it is concluded that shear lag does not significantly affect the ultimate strength of the slotted tube connection, even with a weld length as little as 80 percent of the distance between the welds. The studies showed that the restraint provided by the gusset plate at the slotted end effectively inc
5、reases the load-carrying capacity of the tube as compared to the unrestrained portion of the member. In the numerical analysis, fracture is assumed to have occurred when the equivalent plastic strain reaches a critical value. The test results are discussed in light of the requirements in the America
6、n Institute of Steel Construction (AISC) Specification for Design of Steel Hollow Structural Sections (AISC, 1997). INTRODUCTION Tubular sections are used frequently in fabricated steel construction as tension members, for example, as bracing members. An inexpensive and easy way of making the end co
7、nnections is to slot the tube longitudinally and insert a gusset plate, which is then welded to the tube using fillet welds. This arrangement is shown pictorially in Figure 1. Part (a) of the figure shows the slotted tube and a represen- tation of the gusset plate. The connected tube and gusset plat
8、e are shown in Part (b). In addition to the four longitu- dinal fillet welds that will be present, there also may be fil- let welds across the thickness of the gusset plate at the top of the slot. An alternative to this arrangement is to slot the gusset plate rather than the tube. Fabricators prefer
9、 slotting the tube, however, since alignment of the elements and sub- sequent welding are more convenient with this arrangement. Only the slotted tube option is discussed in this paper and only circular tubes are treated. The work has implications when square or rectangular tubes are used, but those
10、 cases are not treated specifically. Gusset Plate Connection to Round HSS Tension Members ENGINEERING JOURNAL / FOURTH QUARTER / 2000133 J. J. ROGER CHENG and GEOFFREY L. KULAK J. J. Roger Cheng, Ph.D., P.Eng. is C. W. Carry professor of steel structures, Department of Civil this will be discussed l
11、ater). According to Figure 6, the strain in the region of the tube that is in con- tact with the gusset plate is about double the lowest strain. This reflects the fact that there is shear lag in the system-not all of the cross-section is at the same strain as the member enters the gusset plate. Thus
12、, when the weld length is short relative to the member size the large stresses at this location (i.e., shear lag) may result in fracture at the leading end of the slot-tube junction rather than at the mid-length of the tube. This is what was observed in Specimen S 5-1. The stress concentration at th
13、is location is also elevated when there is no transverse weld: S 1-1 fractured at the slotted end and at a reduced ductility as compared to the specimens with the weld end return. However, even with the stress concentration, the majority of the test specimens fractured at a location other than the s
14、lot-tube junction. This can be attributed to the stiffening effect provided by the gusset plate. The tube is restrained from contracting circumferen- tially by the gusset plate, whereas at mid-length the tube is free to contract. This effect is explored further in the numer- ical analysis. NUMERICAL
15、ANALYSIS In order to study the behavior of the connections, elasto- plastic numerical analyses were carried out using the finite element program ABAQUS (Hibbitt, Karlsson, and Sorensen, 1994). In the analyses, the materials are assumed to behave according to the incremental, isotropic-hardening plas
16、ticity model and connection failure is assumed to occur when the equivalent plastic strain in any part of the connec- tion reaches a critical value. This critical value was deter- mined from the tensile coupon tests, but in order to model and predict the connection failure adequately the material pr
17、operties beyond the initiation of necking had to be estab- lished. The details of how this was done are available else- where (Cheng et al., 1998). In all of the analyses, failure was assumed to occur in either the gusset plate or in the tube, but not in the weld. The numerical analyses provided a g
18、ood prediction of the behavior of the connection. The results are shown in Column 11 of Table 1, and the predictions are always with- in 2 percent of the physical test values. In each case, the numerical analyses also correctly predicted the location of fracture, and it also predicted the reduced du
19、ctility for both S 1-1 and S 5-1 that was observed in the tests. Although the analysis was not able to predict the deformation at fracture as accurately, it was still able to provide a reasonable pre- diction of the connection ductility. Figures 5 and 7 illustrate the good agreement between the actu
20、al load vs. deformation response and the numerical solution for Specimens S 4-1 and S5-1, respectively, except for the deformation at fracture. The strain distribution shown in Figure 6 and the normal (longitudinal) stress distribution shown in Figure 8 confirm the expectation that there is a signif
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