Allnorth was responsible for the construction solutions at the Self Anchorage Span (SAS) of the San Francisco Oakland Bay Bridge; the concept, design and engineering of the pushing frame, crossbeam erection gantry and the 1,500 tonne lifting frame.
During construction, deck segments (weighing up to 1,500 tonnes) were lifted onto scaffolding using the lifting frame. The scaffolding provided pedestals with Teflon pads for sliding where the segments were pushed into position by the pushing frame, followed by the crossbeam erection gantry that slid crossbeams longitudinally while cantilevering its nose 30m beyond the scaffolding, before planting the gantry support onto the opposing deck, to slide the crossbeams transversely into their final position.
The challenges these tasks created were magnified by the weight of the deck segments and the changing of C.G. from segment to segment. The cables used during the lifting process were 9 part 3’’ braided cables. Imperfections in the length of individual strands of the cable made the lifting process a highly non-linear problem, where the elongation of strands and the rotation of blocks had to be taken into account in the load redistribution process.
Advanced structural analysis and construction sequencing was required for the project in conjunction with analysis software including SAP2000, Solid Works and COSMOS.