Bay Bridge Demolition – Pier E2
By Mark Palmatier | November 16, 2022
Dominating the Bay Area landscape since 1933, the Oakland-San Francisco Bay Bridge has stood as a monument to depression-era construction and as an iconic gateway to the port of Oakland for over a quarter of a century. But even icons can need some refurbishment, and when a new Eastern Span was completed in 2013, it necessitated the demolition of the old.
Due to multiple factors, a spectacular and explosive sendoff was deemed inappropriate for the old Eastern Span. Therefore, a more methodical demolition approach was required. To facilitate this, tower cranes would be needed to remove the structural steel members in a strategic and methodical process to not upset the balance of the remaining structure. But a crane tall enough to reach the highest members of the bridge super structure would need a foundation much more stable than a barge moored to the bridge pier. To provide a stable platform for the 200’+ crane that would be required, it was determined that a steel frame would be anchored directly to the existing concrete foundation of Pier E2.
Design of the crane support frame was a continuous process of investigation and problem solving. Not only did the tower platform need the strength to support the weight of the tower crane and anything it picked up, but also had to resist the torque and overturning forces it would generate throughout the demolition operation. After building a computer model of the frame structure, and analyzing multiple crane loading conditions, a conceptual layout began to emerge.
While the crane loading and frame analysis was taking place, a parallel investigation into the structural adequacy of the existing pier was underway. Determining the structural adequacy of the pier was critical. This took the form of both an overall structural analysis of the pier as well as a more focused investigation into the strength and condition of the nearly 80-year-old concrete that had been exposed to harsh environmental conditions.
Special attention was paid to the concrete anchors that would be used to secure the frame to the existing pier. Ultimately, all loading, be it vertical, horizontal, or rotational, would focus on and collect at the anchors. Throughout the design process, the necessary strength the anchors needed to have to meet the loading requirements had to be in balance with a multitude of other factors such as:
- The anchors required sufficient embedment to meet strength, but couldn’t be so deep that labor costs became unsustainable
- The strength of the anchors had to be balanced with the strength of the existing 80-year-old concrete to ensure they were not pried or pulled out.
- Each anchored required a minimum spacing and edge distance, but with only so much real estate to work with on the pier face, the design had to be efficient
- With the potential of wave action and storm surge, the anchors must be designed for a submerged condition as well as take into account a highly corrosive environment
Ultimately, the solution for all the required factors took the shape of utilizing key anchorage groups for the frame, consisting of over 100 anchors total. To ensure neither the anchors themselves nor the existing structure was overloaded under the various loading conditions, some anchor groups were designed to resist loading in specific directions through the strategic use of slotted holes, oversized holes, washers, and bearing plates.
Throughout the design process was an over-arching and common theme: collaboration. From close coordination with the general contractor and crane operator during the initial crane loading analysis, to working closely with the bridge specialist performing the pier structural analysis, and CalTrans, the bridge owner; there were numerous points where the project could have devolved into chaos without clear communication with all the parties involved. DHC was happy to be a part of this complex project.