Steel Shark Fin Deck Anchors for Cable-Stayed Bridges: Form, Function, and Fabrication

Deck anchors for cable-stayed bridges provide the connection between steel girders and stay cables, and typically consist of a welded assembly of ring plates, an anchor pipe, fin plates, stiffeners, and a gusset plate. The design of steel deck anchors involves many integrated design problems, including complex geometry and esthetics, structural analysis and design, and fabrication and erection. These design topics are largely discussed within the context of the shark fin deck anchor design of the Lewis and Clark Bridge, but also from a broader perspective with comparisons to other deck anchor designs. For this bridge, overall deck anchor geometry was driven by cable alignment, clearances, and integration with girder webs. A method for calculating work points was developed to ensure compatibility of the plane of the gusset and orientation of the anchor pipe with the sag of the cable. Smooth transitions between connected plates were shaped to reduce stress concentrations, improve fatigue performance, and unify the appearance of the steel assembly. With the varying stay sizes and stay inclination angles of the 104 stay cables along the bridge, a parametric design approach was employed. This approach helped optimize plate sizes and dimensions and provided a gradual evolution of form from one anchor to the next. Structural validation of the anchors was done by a combination of hand/spreadsheet calculations and nonlinear finite element models. Many practical considerations such as weld details and inspection, shipping height limitations, and clearances for strand installation equipment had an appreciable effect on the anchor form.