A.1.1 Beam Coupons For the connection to behave properly, the A572 Grade 50 beams were designed to remain elastic throughout the connection tests. To confirm the mechanical properties of the beam, two coupons were taken from an extra beam section, one along the edge of the flange and the other at the center of the web. The coupons were subjected to a monotonic loading protocol at a rate of 0.127 mm (0.005 in.) per min. until 0.4% strain and then 1.27 mm (0.05 in.) per min. until failure. The results are shown in Figure (a-d). The coupons yielded at 376 MPa (54.5 ksi) and 386 MPa (56.0 ksi), which both exceeded the required strengths for A572 grade 50 materials. 600 600 80 E = 197 GPa y = 376 MPa 40 200 20 0 1000 2000 3000 4000 300 0 5000 20 0 0.0 Strain, (SG) (a) 40 200 100 Leff = 62.4 mm 0 60 400 0 0.1 0.2 0.3 Strain (SG & LVDT) (b) 600 Stress (ksi) 300 Stress (MPa) 60 400 100 80 500 Stress (ksi) 500 600 80 E = 197 GPa y = 386 MPa 40 200 20 Leff = 62.4 mm 0 0 (a) 1000 2000 3000 Strain, (SG) 4000 0 5000 60 400 300 40 200 20 100 0 0.0 (b) 0 0.1 0.2 Strain (SG & LVDT) Figure: Stress-strain relationship of the beam coupons. 0.3 Stress (ksi) 300 Stress (MPa) 60 400 100 80 500 Stress (ksi) 500 A.1.2 Steel Bars For beam-column Tests A and B, steel bars were used as the tendon elements. Monotonic and cyclic tests were conducted on dogbone specimens of these steel bars. The tests were run in displacement control at 2.5 mm (0.1 in.) per min. The bar dimensions for the tests are shown in Figure. Each bar was machined as per the ASTM E8-03 standard for tensile testing of round bars (ASTM, 2003). Steel bars were used in the connection instead of SMA bars in order to provide a less expensive first-run test on the connection and to provide a benchmark performance comparison of a recentering connection using superelastic SMAs. Two different types of steel bars were used. In Test A, plain steel threaded rod of unknown ASTM grade was purchased and machined. The stress-strain curves are shown in Figure for a) a monotonic test used to calculate the elastic modulus and the yield stress, b) the same monotonic test used to show gross strain based on the LVDT reading, and c) a cyclic test. The elastic modulus, yield stress, and ultimate stress were found to be 197 GPa (28,600 ksi), 325 MPa (47.1 ksi), and 490 MPa (71.1 ksi), respectively. During the monotonic loading, the bar fractured at approximately 32% strain. During the cyclic loading, the bar had a stable hysteretic response with the yield plateau beginning and ending at approximately 375 MPa (54.4 ksi) and 450 MPa (65.3 ksi), respectively. In Test B, standard A36 steel was used. The bars were already machined from previous work (Penar, 2005) on the beam-column connection. Only one mechanical test, a cyclic loading protocol, was run on this bar and is shown in Figure . The elastic modulus and yield stress were found to be 197 GPa (28,500 ksi) and 350 MPa (50.8 ksi), respectively. The bar was not stretched until failure, therefore neither the ultimate strength nor the ultimate strain was known. 7 Strain (%) 6 5 4 3 2 1 0 0 2 4 6 8 10 12 Steps Figure: Cyclic loading protocol for the mechanical testing. Figure: Dogbone mechanical test specimen dimensions ( units in mm). 600 600 80 60 400 50 300 40 30 200 = 12.7 mm Leff = 56.1 mm 0 500 70 400 60 50 300 (a) 30 20 20 100 10 0 1000 2000 3000 4000 5000 0 40 200 10 0 0.00 Strain, (Strain Gauge) 0.05 0.10 0.15 0.25 0.30 0 0.35 Strain (LVDT) (b) 600 80 60 400 Stress (MPa) 0.20 40 200 20 0 0 -20 -200 Stress (ksi) 100 Stress (MPa) 70 Stress (ksi) Stress (MPa) 500 80 Stress (ksi) E = 197 GPa y = 325 MPa -40 -400 -60 -600 0.00 -80 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Strain (LVDT) (c) Figure: Stress-strain of the steel threaded bar for Test A. 600 50 30 200 20 100 = 12.7 mm Leff = 73.7 mm 0 0 (a) 1000 2000 Strain (Strain Gauge) Stress (MPa) 40 60 40 200 20 0 0 -20 -200 -40 10 -400 0 -600 3000 80 400 300 Stress (ksi) Stress (MPa) E = 197 GPa y = 350 MPa -60 -80 0.00 (b) 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Strain (LVDT) Figure: Stress-strain of A36 steel bar for Test B (data from Penar, 2005). Stress (ksi) 400 A.1.3 NiTi Bars The loading protocol followed for the SMA mechanical testing was the same as that for the steel testing as shown in Figure. Again, this protocol was implemented using displacement control, with the strain calculated as the crosshead displacement divided by the effective length of the specimen (69.9 mm (2.75in.) in this case). It should be noted that this gross strain is smaller than that which is obtained from the more concentrated strain recorded from the extensometer. The NiTi bars had an elastic modulus and yield strength of approximately 23 GPa (3300 ksi) and 325 MPa (47.0 ksi), respectively. These values were both less then seen in previous research testing of similar bar specimens (McCormick 2006). 500 70 Stress (MPa) 50 300 40 30 200 Stress (ksi) 60 400 20 100 10 0 0.00 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 Strain (EXT) Figure: Stress-strain of the NiTi dogbone. A.1.4 Aluminum Bars In order to create a connection with a parallel resisting system as proposed in the SDOF study of CHAPTER 3, low strength aluminum (AL) bars were used. A low strength material was needed in order to prevent the connection beam from being overloaded. Readily available 6061-T6511 AL was purchased and tested; it displayed a yield strength of approximately 414 MPa (60 ksi). Since lower strength material was desired, the AL was annealed. First the tendons were machined and threaded. Next, the tendons were heated to 425 °C for 4 hrs., then cooled 30 °C/hr. until the temperature fell below 260 °C, and then finally air-cooled (annealing procedure adopted from the Handbook of Aluminum) (Alcan, 1970). The loading protocol followed for the AL mechanical testing was the same as that for the steel and SMA testing as shown in Figure. The effective length of the test specimen was 71.9 mm (2.83 in.). The resulting stress-strain relationship is show in Figur. The elastic modulus and yield stress were 32.4 GPa (4700 ksi) and 117 MPa (17 ksi), respectively. The low strength was a direct result of the annealing process. 150 20 10 50 0 0 -50 -10 -100 -150 -0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 (a) Strain (Extensometer) -20 -0.01 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 (b) Strain (LVDT) Figure: Stress-strain for the annealed aluminum bar. Stress (ksi) Stress (MPa) 100