Gusset plate connections under monotonic and cyclic loading

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990 Can. J. Civ. Eng. Vol. 32, 2005 Fig. 14. Summary of load sequences: (a) LS1 – tension first, (b) LS2 – compression first, and (c) LS3 – tension first with three cycles at each increment. Technology Council (Applied Technology Council 1992) ATC-24 guideline). A preliminary analysis showed that the yield displacement, δy, was not significantly affected by gusset plate thickness (Walbridge et al. 1998). Therefore, the same yield displacement of 2.5 mm was used for every model. Increments of displacement were added until the total deflection on the gusset plate was about six times the yield displacement, that is, 15 mm. This load sequence is illustrated in Fig. 14a. The second load sequence, LS2, was similar to LS1 except that it started with a compression cycle rather than a tension cycle. This load sequence is illustrated in Fig. 14b. The third load sequence strictly follows the additional ATC-24 guideline recommendation that three load cycles be imposed for each load block. This load sequence is illustrated in Fig. 14c. Following the load sequence study, gusset plate – brace member subassemblies were conceived to investigate the following four types of behaviour: Brace member yielding in tension before yielding of the gusset plate (YBT). Gusset plate yielding in tension before yielding of the brace member (YGT). Buckling of the brace member before buckling of the gusset plate (BBC). Buckling of the gusset plate before buckling of the brace member (BGC). The investigated models covered the above four cases for three different gusset plate thicknesses: 6, 9, and 12 mm (corresponding to models GP1, GP2, and GP3, respectively). For each thickness, two brace sections were selected, namely, one that would result in failure due to yielding of the gusset plate in tension (YGT) and one that would result in failure due to yielding of the brace member (YBT). The block shear and net section equations in CAN/CSA S16-01 (CSA 2001) were used for predicting the gusset plate and brace member yield strengths for this step. For each brace member section, two brace lengths were modeled, namely, one corresponding to a slenderness, kL/r, of 50 and one corresponding to a slenderness of 100. These kL/r values were computed assuming an effective length factor, k, of 1.0 (i.e., pin-pin). For most of the gusset plate – brace member combinations studied, the shorter brace member had a predicted capacity in compression higher than that of the gusset plate, whereas the longer brace member had a predicted capacity lower than that of the gusset plate. The method proposed by Thornton (1984) and the CAN/CSA S16-01 (CSA 2001) column curves were used to predict the gusset plate and brace member buckling loads in this step. The parametric study was conducted with 450 mm × 550 mm gusset plates, similar in geometry to the specimens tested by Rabinovitch and Cheng (1993). Table 4 summarizes the brace member – gusset plate combinations investigated. Results of the parametric study Under cyclic loading, the capacity in the tension cycle was limited either by yielding of the brace member or the gusset plate, depending on the brace member – gusset plate combination under investigation. Yielding of the gusset plate was determined from a comparison of two plots: applied force versus gusset plate displacement and applied force versus total displacement, which includes the gusset plate and brace member displacements. If yielding of the gusset plate was taking place, both plots would show nonlinear behaviour. If only the brace member was yielding, the gusset plate displacement plot would not show any plastic displacement. In the compression cycle, the load carrying capacity was limited by either buckling of the gusset plate, as shown in Fig. 15, or buckling of the brace member about its weak axis, i.e., out of the plane of the gusset plate, as shown in Fig. 16. The last two columns of Table 4 summarize the modes of failure, that is, the load limiting mechanisms in tension and compression for each brace member – gusset plate combination. As detailed in Walbridge et al. (1998), the predicted and analytically determined failure modes were identical for all the brace member – gusset plate combinations investigated. Effect of load sequence Results of the load sequence investigation are presented in Fig. 17 for model GP2B5, which consists of gusset plate GP2 and brace member B5 as per Table 4. The displacement © 2005 NRC Canada
Walbridge et al. 991 Table 4. Gusset plate – brace member subassembly models. Brace type Gusset plate type Fig. 15. Buckling of gusset plate (BGC). Brace section plotted in Fig. 17 is the total axial displacement measured at the location indicated in Fig. 13. Specimen GP2B5 was designed to have the brace yield in tension before the gusset plate and the gusset plate buckle in compression before buckling of the brace member. A comparison of Fig. 17a and 17b indicates that there is little difference in behaviour between load sequence LS1 and load sequence LS2. The gusset plate – brace member assembly behaviour under load sequence LS3 is similar to that observed under load sequence LS1 except for the fact that the initial stiffness of the assembly in tension tends to be smaller for load sequence LS3. The hysteresis curves for load sequence LS3 indicate that the capacity of the assembly deteriorates slightly with Failure mode Brace slenderness, kL/r Tension Compression B1 GP1 W200 × 21 50 YBT BGC B2 GP1 W200 × 21 100 YBT BBC B3 GP1 W200 × 27 50 YGT BGC B4 GP1 W200 × 27 100 YGT BBC B5 GP2 W200 × 27 50 YBT BBC B6 GP2 W200 × 27 100 YBT BBC B7 GP2 W200 × 42 50 YGT BGC B8 GP2 W200 × 42 100 YGT BBC B9 GP3 W200 × 31 50 YBT BBC B10 GP3 W200 × 31 100 YBT BBC B11 GP3 W200 × 59 50 YGT BGC B12 GP3 W200 × 59 100 YGT BBC Note: YGT, yielding of gusset in tension; YBT, yielding of brace in tension; BGC, buckling of gusset in compression; BBC, buckling of brace in compression. increasing number of cycles at each loading block. The differences between load sequence LS3 and load sequence LS1 are believed to be very small. For this reason, the less time consuming load sequence LS1 was adopted for the remainder of the study. Effect of load limiting mechanism The load limiting mechanism in the tension cycle was either yielding of the brace member (YBT) or yielding of the gusset plate (YGT). In the compression cycle, the load limiting mechanism was either buckling of the brace member (BBC) or buckling of the gusset plate (BGC). Figure 18 shows the difference in behaviour of the gusset plate – brace © 2005 NRC Canada
Page 1 and 2: Introduction Gusset plate connectio
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Gusset plate connections under monotonic and cyclic loading

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