Web Shear Capacity

A series of ten tests were performed to assess the affect of shear on the performance of the open – web I-joist. Two material thicknesses, 0.047 in and 0.060 in, were considered in the test program (Table 4). Clinches were of type “R” spaced three inches on center.

The load application was a simulated uniform loading condition (Figures 3 and 4) and for each test specimen the maximum applied uniform load, wtest, is listed in Table 4. The failure for each test

specimen occurred in the flat portion of the web between the junction of the chord and web and the edge of the stiffened hole (Figure 7). This web depth for the section was taken as 0.75 in for all test specimens, as indicated on Figure 2. The failure occurred at the location of the first compression web diagonal. The shear was assumed to be linearly varying along the length of the span, thus the computed shear force at the first compression diagonal, V2, is listed in Table 4.

The nominal shear strength of the web, Vn, was evaluated by using the AISI specification (North,

2001) . The controlling shear limit state for all test specimens was web yielding because the web flat width was defined as 0.75 in for test specimens. This flat width defined the corresponding h/t ratios. Web yielding is defined by the following equation:

Vn = 0.6Fyht,

Fig. 7. Typical shear failure.

where Fy = 50.2 ksi and t = 0.047 in or Fy = 52.9 ksi and t = 0.060 and h = 0.75 in. The accuracy of Equation (1) to estimate the shear capacity of the web is shown by the ratio of V2/Vn in Table 4. For the test specimens in this study, the V2/Vn ratio ranged from 0.99 to 1.21 with an average value of 1.08.