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