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Advances in post-installation anchoring challenge cast-in’s dominance
L
IEBIG Ultraplus heavy duty anchors have demonstrated in a project to create a new lifting bridge over the
River Yare in Great Yarmouth that post- installation anchoring can offer performance equivalent to that of cast-in anchors, whilst also being better suited to the complexities of modern construction processes. The £121m Herring Bridge project is an excellent example of how the application of innovative products is enabling major civil engineering projects to be delivered more effi ciently in a shorter timescale. The twin bascule bridge’s
construction
process involved building cofferdams on both banks of the river. These house the machinery and mechanism required to lift, hold and lower each leaf of the bridge, all of which had to be securely anchored to the concrete. As with many major civil engineering projects involving the kind of ‘design and build’ process used here by main contractors BAM Farrans, the team did not have the luxury of the ‘ideal world’ approach where anchors are cast-in to the concrete. Construction of the cofferdams had to commence as soon as the project received the green light, which meant there was no scope for the extended design time that cast-in anchors would have demanded.
How three recognised anchoring approaches compare – left to right: a standard undercut anchor provides compression of the concrete by partial expansion forces being created at the bottom of the anchor. A typical cast-in place anchor allows compression of the concrete to be achieved between the cast-in washer plate and the concrete. With a LIEBIG Ultraplus Anchor, compression of the concrete is achieved between the undercut and the concrete surface.
The design team, therefore, explored the potential for a post-installation anchoring solution to attach the baseplates of the bridge’s operating mechanism. Crucially, any anchors would have to be suitable for the concrete
conditions within the cofferdam design and offer a very high load capacity. Yorkshire-based engineering specialists Qualter Hall were consulted to help identify a post-installation anchor that would meet this demanding criteria, which they found with LIEBIG Ultraplus anchors. For the Herring Bridge project,
concrete extremely effectively. It also does this in a way that differs signifi cantly from ‘normal’ post-installed anchors and other undercut anchors, including those intended to work like cast in anchors.
the
design required EJOT to produce and deploy possibly the largest post installed mechanical anchors ever used in a civil engineering project. Two lengths of M36 size Ultraplus anchors were produced, with the longest being 1.45 m in length and the shortest 1.09 m, with both lengths being used on the same baseplates in an unconventional yet successful design approach. It was an approach that,
despite
LIEBIG Ultraplus anchors securely angled to support the hydraulic mechanisms of the bridge decks as well as the tail locks that hold the Herring Bridge in its raised and open position.
being incompatible with the product’s ETA (European Technical Assessment), satisfi ed the requirements of the globally respected ACI (American Concrete Institute) Building Code.
The Ultraplus anchor’s design is unique in the way that it transfers stress into the
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Demonstrating compliance with the ACI Building Code enabled Ultraplus anchors to be deployed in this bridge construction project with confi dence and ensure a post- installation approach could be utilised. The advantages that stemmed from this meant the bridge’s design and construction time could be reduced, with subsequent cost benefi ts.
01977 687040
www.ejot.co.uk/cast-in_vs_post-install_anchors
17/07/2024 10:55
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