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Reuse of 1950s concrete encased steel at Cundy Street Quarter – HTS and Innovate UK project

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This blog details of a project aiming to reuse concrete encased steel frames from a 1950s building.

Heyne Tillett Steel are the structural engineers on the redevelopment of Cundy Street Quarter, a Grosvenor Estates project in London. The project involves the demolition of four existing residential blocks to allow for redevelopment of the site.

As soon as it was determined that the existing buildings could not be retained, the team started undertaking research to find opportunities to recover the frame for reuse. The frame dates back to the early 1950s, which is twenty years beyond the limit set by the current SCI P427 protocol for steel reuse. It is also concrete-encased steel, which is currently not seen as economically viable to reuse due to the potential for damage sustained by removing the encasement.

Heyne Tillett Steel received Innovate UK funding to evaluate a sample of concrete-encased steel from one of the demolished buildings on site. The project aims to take the current methods of validating steel for reuse and test their applicability to an older steel frame, as well as understanding what happens to steel when concrete encasement is removed. It is estimated that 50% of steel in London is concrete encased which could make the results of this research significant for a large stock of steelwork in the capital.

Steel samples will be taken from throughout one of the buildings and materials-tested according to the SCI P427 testing protocol. A set of steel elements will then be deconstructed from the building and stored on site. The concrete encasement will be removed by two different methodologies to evaluate the difference between methods, both in resulting steel damage and time taken.

The main aim is to understand the impact of concrete encasement removal on the dimensional tolerances of reused steel. Currently, if the reused element is to receive a UKCA mark, the geometric properties must be the same as brand new steel and the allowance for any small deviations or damage is minimal. Given the fact that the steel must go through a deconstruction process in order to be salvaged, it is highly unlikely that the sections will meet the quality requirements of brand-new steelwork. We are looking to put numbers to this damage and consider engineering judgement alongside code requirements when evaluating how much damage is acceptable.

In Heyne Tillett Steel’s understanding, there is no provision in the design standards prohibiting the reuse of steel members with localised damage such as dents, grooves, bends etc., as long as the damage is reflected by a reduction in cross section properties. The only exception to this is member bow imperfections (lack of straightness) which must be corrected.

The value of limiting damage is being able to use the resulting section to its full capacity – without having to downgrade it to a smaller equivalent section and thereby “wasting” some of the self-weight which won’t be able to be considered as contributing to the design resistance. At some threshold (estimated around 30% extra mass) this is an inefficient use of material, and the steel is better off being reused elsewhere, or ultimately scrapped and recycled in an electric arc furnace. A balance is needed between economical forms of deconstruction and potential for efficient material reuse. This project aims to put numbers to that balance.

The funding period runs until the end of March 2023. Site works are commencing imminently, and results and insights will be shared as the project progresses.

 

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