Description
This paper outlines a method of assessment for the Freyssinet concrete hinges present at the existing structures on the A465 Heads of the Valleys Section 5 & 6 Scheme in the UK beyond that provided by National Highways’ Design Manual for Roads and Bridges (DMRB) document CS468, which does not provide a sufficient mechanical model to demonstrate either safety or previous acceptable performance of the hinges in service.
Until the release of CS468 Assessment of Freyssinet concrete hinges in highway structures (Nov 2019), no assessment standard was available for Concrete Hinges. The previous standard, BE 5/75, covered design only and was withdrawn as the use of concrete hinges in new design in the UK is no longer permitted, unless in exceptional circumstances.
CS 468 undertakes assessment at the Serviceability Limit State on the basis that cracking and spalling to the concrete in or around the throat will lead to the ingress of water and subsequent corrosion to the reinforcement. However, recent application of the CS468 SLS assessment approach to the existing bridges on the A465 has identified that it will typically not be possible to satisfy the resistance to cracking check it contains at the Serviceability Limit State. The resistance to end block splitting is also often not satisfied due to low reinforcement in the hinge end block.
It is noted that the existing Freyssinet concrete hinges on motorway and all purpose trunk road bridges in England have generally been found on site to perform well at SLS and be structurally reliable to date and therefore a mechanical model based on ULS strength is presented here to provide justification of their acceptable performance and safety.
