The newly completed Ashton Arch Bridge in the Western Cape is South Africa’s first concrete tied-arch bridge constructed using the transverse launching method.
Using state-of-the-art bridge analysis software, key considerations for the upgrade were to minimise river flow restriction and improve the available free board within the restrictions of adjacent properties and road alignment levels.
The bridge comprises a cable-supported concrete deck which spans 110m between supports, with arching ribs rising 22m above the roadway. It has a single tied-arch structural configuration, where the typical cross-section of the arch-bridge deck provides for four 3,4m traffic lanes and two 2,4m sidewalks.
The structural complexities
To install the sliding and permanent bearings, the 8 000-ton deck had to be vertically lifted and lowered by H&I Construction. This was done in phases by installing the bearings at one abutment before repeating the process at the next.
To achieve a higher level of stability and safety on the temporary concrete support columns, the temporary works engineers specified SikaWrap®-300 C for additional structural strengthening. It is a high-quality unidirectional woven carbon-fibre wrapping system, which was used to encapsulate and confine the head of the concrete support columns, using Sikadur®-330, a structural impregnating epoxy-resin adhesive.
SikaWrap®-300 C has a high load capacity, is easy and quick to install, saving time and money on the project. The Sika®CarboDur® FRP Design software, a state-of-the-art external structural strengthening design programme, was an exceptional added benefit.
Final installation and community involvement
The launching of the bridge from its constructed position to its final position required a perfectly levelled surface. This was achieved by using Sikadur®-42 ZA, high-strength epoxy grout with its high compressive strength and high abrasion resistance. Tests with other products were performed prior to application and Sikadur®-42 ZA met all the stringent requirements set out by the project engineers. It not only met the levelling requirements but could also be applied in a thin layer, over a wide area, without having any shrinkage or cracking.
The successful completion of the new Ashton Arch Bridge resulted in a proud monument for the region. Furthermore, the manner and techniques used were a first for the country and a wonderful achievement.
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