PSI - Issue 64

Chris Hendy et al. / Procedia Structural Integrity 64 (2024) 206–213 Hendy C/ Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Until the release of CS468 (2019) no assessment standard was available for Freyssinet Concrete Hinges in the UK. The previous BE 5/75 (1986) was a design standard that was no longer directly applicable as the use of concrete hinges in new design is no longer permitted in the UK, unless in exceptional circumstances. CS 468 (2019) provides an assessment methodology for use in the assessment of concrete rectangular and circular concrete hinges. CS 468 (2019) requires 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. Recent application of the CS468 (2019) SLS assessment approach to real bridges has identified that it will sometimes not be possible to satisfy the resistance to cracking check (Eq. 3.15). This was found to be due to typically low vertical loading through the hinges. The resistance to end block splitting check (Eq. 3.18) 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. A simple mechanical model, based on ULS strength, is therefore presented here to provide justification of their acceptable performance and safety. Markic and Kaufmann (2023) undertook destructive testing of hinges and proposed more general resistance equations covering moments and forces in three perpendicular directions. Their proposed model generally provides even greater resistance than proposed in this paper but, crucially, they tested new specimens without defects and deterioration and assumed bars crossing the hinge throat were intact. These assumptions may not be realized for assessment of a deteriorated hinge and the methods in this paper do not assume that bars across the throat are intact. Hinges that are non-compliant with CS 468 (2019) should therefore satisfy the requirements in this paper of either: i. Section 2 for rotation at SLS and section 4 for splitting at ULS, or ii. Section 3 for rotation at ULS and section 4 for splitting at ULS A method for hinges that do not comply with the shear resistance requirements of CS468 (2019) is also provided in section 5. 2. Alternative resistance to cracking validation model at SLS: hypothetical throat reductions This approach considers a hypothetical reduction of the throat width (Fig. 1), which could represent spalled or deteriorated concrete should cracking occur at the serviceability limit state. The application of the SLS assessment equations CS 468 (2019) Eq. 3.15 are then to be undertaken using the reduced throat width. First, the throat width is to be reduced sufficiently to meet the Resistance to Cracking limits (CS 468, Eq 3.15), with the reduced throat value subsequently used to check that the Compressive Resistance limits (CS 468, Eq 3.14) are also satisfied. Second, the minimum throat width is to be checked against the Resistance to Compressive Resistance limits (CS 468, Eq 3.14). Where the over-utilisations in Cracking at SLS are due to low vertical loading through the hinge throat, it is typically found that there is sufficient compressive resistance capacity within the restricted hinge throat to demonstrate that the hinge is adequate to the SLS limits. If this revised check still does not show adequate SLS performance, then increased inspection of the details on site can be employed to check that the actual details are performing satisfactorily in conjunction with satisfying the ULS check given in section 3.