Bridges, Tunnels and other Transportation Structures
Full Session with Abstracts
Description of Presentation
The Mersey Gateway Bridge, opened in late 2017, was procured under a design, build, finance and operate contract, one of the largest of its type in the UK. Key aspects of the design and construction will be explained. The crossing is 2.25km long and includes a 1km long three tower cable stayed bridge across the River Mersey estuary together with approach viaducts to the north and south. Main spans are 294m and 318m, approach viaduct spans are around 70m each. Carrying six lanes of highway traffic, the deck features a single central plane of cables and a continuous single cell concrete box girder 4.6m deep. Both internal and external post tensioning is used in the longitudinal direction together with transverse deck slab post tensioning.
Relatively simple spread footing foundations were used for the pylons whereas deep piled foundations were required for some of the approach spans. Crossing an area that included legacy contamination, these foundations included innovative provisions to prevent contaminants leaching to deeper sandstone aquifers.
Extensive testing was undertaken to prove the design of wind shields provided on the deck edges. The probabilistic requirements and prevailing wind directions resulted in an unusual wind shield arrangement. Results of the reduction in over-turning moment in each lane will also be presented.
An innovative "buffer" system was developed to protect piers from vessel impact based on absorbing energy through yielding of reinforcement. Results from scaled model tests to prove the design will also be presented.
In order to achieve a demanding construction programme, much of the reinforcement was pre-assembled at ground level and this dictated the detailing requirements but enabled a 5 day cycle time to be achieved for each 6m long cable stayed bridge deck segment. Construction of the cable stayed bridge is based on the balanced cantilever principle and the approach viaducts are built using full span in-situ casting on a self-propelled moveable scaffold system. Details of the construction will be presented.
The audience will hear about an interesting recent case study of an all-concrete cable stayed highway bridge with a description of the design evolution and construction. In addition, the presentation will cover a number of special aspects and innovative ideas.
Keywords: cable stayed bridge, post-tensioning; construction methods; moveable scaffold, marine foundations.