Structural capacity of timber I-joist with flange notch: Experimental evaluation

• Notch location and size considerably affect the load carrying capacity of I-joist.
• Load capacity of notched I-joist reduces up to 80% compared to control I-joists.
• Stiffness of notched I-joists is reduced up to 46% compared to control I-joists.
• Crack initiates at the inner bottom corner of the notch of the I-joist.
• Crack propagates towards the bottom flange with an angle ranging from 63° to 77°.

Timber I-joist is a common building construction element in North America and Europe due to its availability and easiness of passing the service conduits and ducts through openings in the Oriented Strand Board (OSB) web of I-joists. However, in order to provide passageway for service conduits and ducts, cuts and notches in the flange of I-joist are frequently made during construction without considering the structural integrity of the system. Flange stiffness is very critical as it provides the flexural strength to the I-joist, hence it is prohibited to cut or notch the I-joist flanges. This study examined ten series of timber I-joists with single flange notch at different locations in two span lengths (12 and 20 ft) and compared with the uncut I-joists to understand the reduction in load capacity, stiffness and failure mechanism of the tested I-joists. A total of 100 I-joist specimens, which included uncut and flange notched I-joists, were tested in this experimental study. It was observed that with the increase in distance of the notch from the support, the load carrying capacity of notched I-joists can even decrease up to 80% in comparison with the uncut I-joists. Moreover, the effects of notch location and notch size were also investigated, and it was found that these notches significantly affect the load carrying capacity of an I-joist.