The Strong Frame special moment frame using the Yield-Link® structural fuse incorporates the capacity-based design approach, wherein energy dissipation is confined predominantly within the reduced region of the Yield-Link structural fuse. Member and connection design is based on the maximum probable tensile strength, Pr-link, of the reduced region of the Yield-Link (see Figure 1).
(a) Design Parameters
(b) Yield-Link Stretching and Shortening from Testing
Figure 1 — Yield-Link Design for Energy Dissipation
The following are steps for the Strong Frame connection design:
Model and analyze moment frame with Yield-Link® moment connections to get demand loads (moment, shear and axial) using code level forces.
Design Yield-Link yielding area to resist the maximum axial force from all the standard LRFD load combinations. This means our Yield-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 Yield-Link as:
Pr-link = Ay-link x Rt x Fu-link
Ay-link = area of reduced Yield-Link section, 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: