TinT-BCB specimens were shop fabricated using round and square hollow sections with gusset assemblies at their ends. The total lengths of the specimens were determined based on the dimensions of the test setup. Side and section views of the first specimen (TinT#1) are shown in Fig. 2.2(a). The first test specimen consisted of a round
HSS1.900x0.125, eight 6”x1/2”x3/16” net section reinforcing plates, a square HSS2 ½ x 2 ½ x 1/8 section and two 3/8” thick gusset plates. The total length of the main brace, the outer tube and the entire assembly were 42”, 37.25” and 50”, respectively. The locations of the reinforcing plates were determined based on the geometry of the cross section. The nominal gap between the two tubes was 0.175” (Fig. 2.2a).
Design of TinT#2 and TinT#3 were identical to each other except for their outer tube sizes. Specimen TinT#2 was composed of a circular HSS1.900x0.125, eight 4½”x1/2”x1/8” net section reinforcing plates, a square HSS 2 ½ x2 ½ x 1/8 and two gusset assemblies. The main brace was encased with a square HSS 2 ½ x2 ½ x ¼ outer tube in Specimen TinT#3 while the design of the gusset assemblies and the main brace size of the specimen were identical to those of TinT#2. The total length of the main brace, the outer tube and the entire assembly were 42”, 37.25” and 51.50”, respectively, for both TinT#2 and TinT#3. Shop drawings of TinT#2 and TinT#3 are given in Fig. 2.2(b) and (c).
(a) TinT#1
(b) TinT#2
(c) TinT#3
Figure 2.2. Shop drawings of TinT-BCB specimens
Both ends of the main brace is slotted for welded gusset plate connections and two holes with a radius of 3/16” were drilled at the end of each slotted length. The slotted portion of the main brace (Fig. 2.2a and 2.2b) was fillet welded to the 3/8” thick gusset plates with 3/16” thick, 5” long welds. There was a 0.5” distance between the brace end and the vertical supporting plate. The 4.5” long net section reinforcing plates are connected to the main brace
with two 1/8” thick, 4.5” long fillet welds. Each gusset assembly consisted of a 3/8” thick gusset plate, four ¼” thick stiffeners, two horizontal supporting plates and two vertical supporting plates. Fig. 2.3(a) illustrates the details of the gusset assemblies. All the connections between the plates were either fillet or plug welded connections. Each gusset plate was connected to two horizontal supporting plates with three plug welds. Three holes with a radius of 1/4” were drilled from the 3/8” thick gusset plates, as well as the horizontal supporting plates (Fig. 2.3a). The three plug welds were 0.5” in diameter. 0.5” thick vertical supporting plates are fillet welded to the horizontal supporting plate from one side and fillet welded to the gusset plate on the other side. The welding details of the stiffeners are given in Fig. 2.3(a). Each stiffener is fillet welded to the vertical supporting plate, as well as the gusset plate. A right triangle with 3/8” side length are cut from the sharp edge of the ¼” thick stiffeners to allow continuous welding between the gusset plates and the vertical supporting plates. As shown in Fig. 2.3(a), a ¼” (i.e. the thickness of the fillet weld) distance between the end of the fillet welds and the edge of the triangle was left so as not to damage the edge of the stiffener plates (AISC, 2011).
Fig. 2.3(b) demonstrates the scheme of a typical chevron type TinT-BCB frame with stiffeners. In order to provide near-fixed end conditions, stiffeners are welded to the gusset plates and beam/column flanges. Stiffener sizes can be selected to provide the same
rotational constraint against in-plane and out-of-plane end rotations. It is noteworthy that dimensions of gusset plates in BCBFs are reduced substantially due to absence of the clearance between the assumed fold line and brace end, since end rotations are virtually fixed. Therefore, the reduction in gusset plate cost would compensate for the additional cost
of employing stiffeners. Still, BCBF arrangements without gusset plate reinforcement might be an effective option in some cases, which is discussed in the latter sections of this chapter.
Gusset assemblies of TinT#2 and TinT#3 were designed and detailed to represent the actual boundary conditions of beam-column-gusset connection in a TinT-BCBF. Thus, vertical and horizontal supporting plates shown in Fig. 2.3(a), were incorporated to represent beam/column flanges in an actual BCBF. Furthermore, the horizontal supporting plates were utilized to increase the thickness of the gusset assembly that is attached to the grips of the test equipment with the purpose of minimizing the possibility of uneven stress distribution, as well as the relative movement around the gripped area.
(a) Gusset assembly
(b) Configuration of a TinT-BCB frame with stiffeners
Figure 2.3. Illustration of a TinT Frame and details of gusset assembly
Stiffener
TinT- BCB Horizontal supporting plates (Column/Beam Web)
Vertical supporting plate (Column/Beam Flange)
Stiffener The area gripped by
The specified material properties for all specimens are given in Table 2.2. The main brace and the outer tube (BC) were made of ASTM A500 Gr.B type of steel with nominal yield stresses of 42 ksi and 46 ksi, respectively. Gusset plates, net section reinforcing plates and stiffeners to reinforce the gusset plates were cut from ASTM A36 type of steel plates.
Table 2.2. Specified Material Properties
Member Type of Steel Fy (ksi) Fu (ksi)
Square HSS ASTM A500 Gr. B 46 58
Round HSS ASTM A500 Gr. B 42 58
Gusset Plate ASTM A36 36 58
Stiffener ASTM A36 36 58
Net Section Reinforcing Plate ASTM A36 36 58
Coupon tests were carried out to determine the actual material properties of the main braces, which were expected experience plastic deformations. The dimensions of the coupon specimens and the loading rate adopted for testing were determined according to ASTM E8 (2015). The measured yield (Fy,meas), ultimate (Fu,meas) stresses and the strain value at the fracture obtained from the coupon test were around 55 ksi, 83 ksi and 29%, respectively, for the main brace of TinT#1 specimen. The main braces of TinT#2 of TinT#3 specimens were cut from the same piece. Therefore, the coupon test results were applicable to both TinT#2 and TinT#3 specimens. Two identical coupon specimens were cut from the main brace and tested. Based on 0.2% offset assumption, the measured yield (Fy,meas) stresses were found to be 56 ksi and 55 ksi for the first and second coupon specimens, respectively. The measured ultimate (Fu,meas) stresses were around 64.5 ksi and 63.5 ksi for the first and second coupon specimens, respectively. The average of the expected material strength factors, Ry and Rt
were 1.32 and 1.10, respectively. The strain values at the fracture were about 30% and 25.6%. The details of the coupon test results are given in Appendix.