Sheathing Connection Test Program

The experimental program included 216 connection specimens that were subjected to tension monotonic and reversed cyclic loading. The monotonic tests were run at a rate of 2 mm/min, and the corresponding cyclic tests were performed by using the same CUREE test protocol as incorporated into the full-scale wall test program. The tests were conducted in accordance with the ASTM Standard D1761 (1995). The test specimen matrix was selected in such a way to include the effect of the variation of wood sheathing type (DFP, CSP and OSB), thickness (9.5, 11, 12.5 & 15.5 mm) as well as orientation with respect to the grain and fastener edge distance (6, 9.5, 12.5, 16 & 25 mm). Moreover the effect of different steel stud thickness (0.84, 1.11, 1.37 & 1.73 mm) and strength (Grade 230 & 345) were included (Okasha & Rogers, 2004). The primary aim of this research project was to provide information on connection performance to facilitate the predictions of the behaviour of steel frame / wood panel shear walls. Tests

were carried out on individual screw sheathing to stud connections, as shown in Figure 3. The screw type, as well as sheathing and steel matched that used in the construction of the full-scale shear wall tests, the results of which were used to compare with the analytical predictions.

Figure 3. Sheathing connection test set-up.

Table 2. Parameters for prediction of monotonic tests (Okasha & Rogers, 2004).

Specimen

Max. Load

EEEP Yield Load

ke

(0.4 max load)

ks

(max load)

(kN)

(kN)

(kN/mm)

(kN/mm)

CSP12.5-PR M

1.376

1.192

2.383

0.210

CSP25-PR M

1.740

1.487

1.513

0.197

OSB12.5-PR M

1.754

1.487

2.683

0.376

OSB25-PR M

1.955

1.643

1.168

0.194

DFP25-PR M

2.860

2.367

1.513

0.242

Table 3. Measured parameters of cyclic tests (Okasha & Rogers, 2004).

Max. Load

EEEP Yield

ke

ks

Specimen

Load

(0.4 max load)

(max load)

(kN)

(kN)

(kN/mm)

(kN/mm)

CSP25-PR C

2.228

2.024

0.691

0.209

OSB25-PR C

2.152

1.956

0.927

0.242

DFP25-PR C

3.186

2.785

0.735

0.311

The parameters listed in Tables 2 were adopted for the prediction of lateral resistance and deflection of full-scale shear walls under monotonic loading. Two failure modes were observed during the connection tests; screw pulled through the sheathing, and bearing / plug shear failure of the sheathing. These failure modes were in accordance with what was observed in the full-scale tests. The monotonic load capacity in connections loaded perpendicular-to-grain was higher (average 15%) than that in connections loaded parallel-to-grain. The results of the lower capacity parallel-to-grain
specimens were therefore selected in order to establish the connection properties required for the monotonic wall analyses. The connection shear capacities listed in Table 3 for the cyclic tests were much higher than those obtained for the monotonic tests (Table 2). This was not in accordance with the full-scale test results, for which the shear strength of the cyclic tests was lower or close to that measured for the corresponding monotonic tests (Chen, 2004). There are two possible explanations for this phenomenon; the loading speed for the cyclic connection tests was much faster than that used for the monotonic tests which resulted in a strain rate effect, and the large variation in the material composition of the wood panels, which may have a more noticeable effect when only single connections are tested compared with full size walls. In order to obtain a reasonable prediction of the wall behaviour, the load capacities for the monotonic tests were utilized for the shear walls under cyclic loading (Table 4). For the cyclic tests, the stiffness was taken as the average of the absolute values of the positive and negative results parallel-to-grain connection specimens. This average value takes into account the possible change in connection stiffness as the load in the wall changes direction.

Table 4. Parameters for prediction of cyclic tests (Okasha & Rogers, 2004).

Max. Load

EEEP Yield

ke

ks

Specimen

Load

(0.4 max load)

(max load)

(kN)

(kN)

(kN/mm)

(kN/mm)

CSP25-PR C

1.740

1.487

0.702

0.197

OSB25-PR C

1.955

1.643

0.926

0.230

DFP25-PR C

2.860

2.367

0.793

0.301