1. Behavior of SFOBB Laced Members
Research Assistants: Timothy D. Vesco and Adrianne M. Dietrich
The SFOBB members are made of built-up shapes that are interconnected with lacing. The axial and tensile capacities of these members depend on the interaction between the main components and the lacing elements. Large scale experiments were conducted on laced members to establish their axial capacities and failure modes. The figure below shows the test set-up that was used for the investigation. The results of these experiments showed the AASHTO equations need to be modified to determine the axial capacity of laced members.
View of Laced Member with End Connections
2.Behavior of SFOBB Gusset Plate Connections
Research Assistant: Adrianne M. Dietrich
Large scale experiments were conducted double gusset plate connections that are common in the SFOBB to determine the behavior of the edge buckling of these plates. The figure below shows the test set-up that was used for this investigation. The results of these experiments showed that AASHTO edge buckling equation should be modified in order to capture the observed behavior.
View of Test set-up used for Double Gusset Plate Experiments
3. Behavior of SFOBB Perforated Members
Research Assistant: Adrianne M. Dietrich
The laced members of the SFOBB proved to have inadequate axial capacity under seismic loads. Based on this, the laced members are replaced by perforated plates in an effort to improve the ductility and the axial capacity. Large Scale experiments were conducted on perforated members to determine their axial capacity and failure modes. The figure below shows the test set-up that was used for this investigation. Based on these experiments, it was shown the AASHTO equations can be used to determine the axial capacity.
View of Perforated Member with its End Connection
4. Cyclic Behavior of Shear Links in Richmond San Rafael Bridge Towers
Research Assistant: Sherif El-Fass
The tower of the Richmond San Rafael bridges utilizes build-shear links as part of the eccentric braced towers. The dimensions of these links are beyond the existing data of rolled shape link. Full scale experiments were conducted on the built-up shear links to determine their ultimate capacity and failure mode. The figure below shows the test-up that was used for this investigation. The results of these experiments showed the over-strength factor for these links exceed 2.1 and their plastic rotation is 10% radians.
View of the test set-up used for Shear Link Experiments
5. Cyclic Behavior of Retrofitted Richmond San Rafael Bridge Tower Legs
Research Assistant: Jeremy Woodgate
The tower legs of the Richmond San Rafael legs are made of built-up shapes that have elements exceed the seismic compactness ratios. In an effort to reduce these ratios, the tower legs were propped to be filled with concrete that are placed in parts with expandable material in between. Large scale experiments were conducted on retrofitted sections of the tower legs to determine their behavior and ultimate capacity. The figure below shows the test set-up that was used for this investigation. The results of these experiments showed that this detail will prevent the local buckling however, it will shift the failure model to the net section fracture at bolt-hole locations.
View of End Loading on the Tower Leg
6. Built-up Shear Links As Energy Dissipators for Seismic Protection of Bridges
Research Assistant: Peter Dusicka
The tower of the new SFOBB is made up of four independent legs, each of which is composed of five vertical sections. Cross bracings and shear link beams will help connect the four legs. The shear link beams are designed to move independently of the tower to absorb seismic energy during an earthquake and to protect the tower from catastrophic damage. The damaged beams can be individually removed and replaced. Large Scale experiments were conducted on the shear links and their connections to the tower legs of the proposed eastern spans of the San Francisco-Oakland Bay Bridge. The objectives of these experiments were to determine the deformation capacity, maximum resistance and ultimate failure mode of built-up shear links by apply incrementally increasing cyclic plastic deformations. The figure below shows the test set-up that was used for these experiments. Variety of plate steels were used for the shear link in this investigation such as ASTM A709 Gr 50, ASTM A709 HPS Gr. 70, Japanese LYP Gr. 14.5 and 30 ksi. The results of these experiments illustrated the suitability of using these steel for seismic applications. However, the over-strength associated with the steel varied significantly. The typical failure mode for stiffened link is at the weld toe of the stiffener to the web while for the unstiffened web is the weld between the flange and the web.
View of Scaled SFOBB Towers and Shear Link Specimens