The Strong Frame special moment frame incorporates the capacity-based design approach, wherein energy dissipation is con ned predominantly within the reduced region of the Yield-Link® structural fuse. Member and connection design is based on the maximum rupture strength, Pr_link, of the reduced region of the link (see Figure 1).
(a) Design Parameters
(b) Yield-Link Failure Mode
Figure 1 — Link Tested to Failure at 6% Story Drift
The following are steps for the Strong Frame connection design:
Model and analyze moment frame to get demand loads (moment, shear and axial) using code level forces.
Design link yielding area to resist the maximum axial force from all the load combinations. This means our links are designed to remain elastic under code force load combinations including lateral plus gravity loads.
Once the yielding area is known, calculate the maximum rupture strength, Pr_link , of the link as:
Pr_link = Ay_link x Rt x Fu_link
Ay_link = specified area of the reduced link area, in.2
Rt = ratio of expected tensile rupture strength to minimum tensile stress of the link stem material, 1.2
Fu_link = specified minimum tensile strength of link stem material, 65 ksi
It is worthwhile to point out that we are using Rt and Fu for this calculation where other SMF connections typically use Ry, Fy and a Cpr factor that is less than or equal to 1.2. Using Ry of 1.1, Rt of 1.2, Fy of 50 ksi, Fu of 65 ksi and Cpr of 1.2. The difference in demand can be seen below: