Liftech received an Award of Merit for Excellence in Structural Engineering from the Structural Engineers Association of Northern California (SEAONC) in recognition of our engineering work on the seismic friction damper.
Liftech developed a seismic friction damper for four new container cranes for APL Limited at the Port of Los Angeles. The four cranes and their dampers were manufactured by ZPMC for approximately $46 million.
The new dampers are designed to help protect the cranes and the wharf from damage. They are more economical, lower maintenance, and easily resettable as compared with any other existing crane seismic isolation and damping systems.
The damper is located at the bottom of each lower diagonal brace and includes a center gusset plate with long slotted holes, lap plates, Belleville (disc) washers, and tensioned bolts. The sliding surfaces are bronze bearings and stainless steel liners. Restraint rods provide added safety, hold the diagonal brace during erection, and can be used to restore the joint to its original geometry after sliding occurs.
Friction developed from the bolt-clamping forces restrains the joint until a predetermined threshold force occurs during a significant earthquake. Once the threshold is exceeded, the joint slides, increasing the crane’s flexibility and dissipating seismic energy as heat. Both phenomena reduce the seismic response and reduce seismic forces. Belleville washers provide a well-known, nearly constant clamping force as the plates and bearings wear and thermally deform through multiple cycles of relative plate movement.