Smithfield Market, Farringdon

Project: Smithfield Market, West Smithfield

Main Contractor: PAYE Stonework & Restoration Ltd.

BACKGROUND

JDC Scaffolding have been involved continuously with this project since 1Q 2017 when we originally tendered the project for Sir Robert McAlpine. The works involve remedial works to the historic Smithfield Meat Market – the last ruin in London, which in many areas was in an extremely bad state of repair or nearing collapse. The works have involved shoring, protection and general access in the building which ultimately is being transformed into the new Museum of London when it moves from its current location at Barbican.

The original enquiry, as with all tenders since, included a raft of specific design requirements from the Clients engineer, AKT-2. McAlpine lost the project to PAYE Stonework who tendered the successful bid. We submitted our price which was accepted and commenced our, now long standing, relationship with PAYE.

Two previous phases have been completed and a third is currently in progress running alongside the new Phase 2 & 2A.

JDC received the tender package for Phase 2 & 2A in May 2020 and tendered the scheme. The previous phases were region £250K in value but the new phase is in excess of £1 Million. We tendered the scheme competitively against six other scaffolding companies and after a final round of negotiations and tender queries were finally awarded the contract in July 2020.

The works are split into two phases across the internal footprint of the market building which is approximately 60.00m x 60.00m, the second phase of works started later due to a package of works, carried out by Dyer and Butler, to remove and replace the existing ground floor slab of the building working over a live railway tunnel below.

SCAFFOLD BRIEF

Design General

The works are extremely design intensive and the design itself is based on the very specific “Constraints Document” which has been produced by AKT 2. This document sets out the allowable parameters in the design with respect to acceptable loadings on the ground floor slab and permissible forces against the surrounding walls. The document sets out the construction of the existing building internally which is generally a heavy rivetted steel frame which is supported on cast iron “Phoenix Columns”. JDC were instructed early to develop the scaffold design to enable works to commence on site in October 2020.

The scaffold design was carried out by JDC Scaffolding with supporting calculations and Design Statement by IDH. PAYE are acting as Temporary Works co-ordinator with Wentworth House as their Third-Party Cat 3 checking engineer. The completed collaborative design would finally be presented to AKT 2 for final sign off. The design process to date has been challenging due to the ongoing Covid restrictions. All parties have been communicating via email, telephone etc. with regular Teams meetings. These by nature have not been ideal due to connection problems etc.

The design to date produced by JDC comprises a suite of twenty-six drawings for Phase 2 and sixteen drawings for Phase 2A.

The designed scaffolding works comprise generally of the following:-

  • Construction Deck to whole internal area.
  • Internal and external access to the existing roof dome.
  • Temporary roof coverage to the whole internal area – comprising six separate temporary roofs.
  • Full height and full-length access to the existing roof lanterns to allow timber repairs and glazing replacement.
  • Temporary bracing to the existing trusses during remedial works.
  • Lateral restraint to the existing steel frame whist it is decoupled from the external walls during the demolition/new construction process.
  • Access to the existing cast iron Phoenix columns

Design – General

The works are extremely design intensive and the design itself is based on the very specific “Constraints Document” which has been produced by AKT 2. This document sets out the allowable parameters in the design with respect to acceptable loadings on the ground floor slab and permissible forces against the surrounding walls. The document sets out the construction of the existing building internally which is generally a heavy rivetted steel frame which is supported on cast iron “Phoenix Columns”. JDC were instructed early to develop the scaffold design to enable works to commence on site in October 2020.

The scaffold design was carried out by JDC Scaffolding with supporting calculations and Design Statement by IDH. PAYE are acting as Temporary Works co-ordinator with Wentworth House as their Third-Party Cat 3 checking engineer. The completed collaborative design would finally be presented to AKT 2 for final sign off. The design process to date has been challenging due to the ongoing Covid restrictions. All parties have been communicating via email, telephone etc. with regular Teams meetings. These by nature have not been ideal due to connection problems etc.

The design to date produced by JDC comprises a suite of twenty-six drawings for Phase 2 and sixteen drawings for Phase 2A.

The designed scaffolding works comprise generally of the following:-

  • Construction Deck to whole internal area.
  • Internal and external access to the existing roof dome.
  • Temporary roof coverage to the whole internal area – comprising six separate temporary roofs.
  • Full height and full-length access to the existing roof lanterns to allow timber repairs and glazing replacement.
  • Temporary bracing to the existing trusses during remedial works.
  • Lateral restraint to the existing steel frame whist it is decoupled from the external walls during the demolition/new construction process.
  • Access to the existing cast iron Phoenix columns

Construction Deck

We were asked to provide a Construction Deck, in the form of a fully boarded birdcage throughout the whole internal area. This 53.00m x 53.00 deck would be both a working platform for all the works above 6.00m as well as supporting the required temporary roof structures. We also incorporated Safelinks board retainers throughout to ensure the 3,000 boards remain in place, do not warp and form trip hazards for the other trades.

Roof Dome

Internal and external scaffold access were designed and installed to the existing concrete roof dome to enable internal repairs and replacement of the external copper facing.

Temporary Roofs

To enable the required works to be carried out the whole internal area, excluding the dome, had to be designed to be covered with temporary roofs. The roofs themselves had to be designed to fit in with PAYE’s construction programme and specific phasing therein. This has meant three separate roofs designed for Phase 2 and a further three roofs for Phase 2A.

View though Haki temporary roof
Interface between roofs in differing directions

Each roof would have to be able to be erected and struck separately without any reliance on the other standing roofs. Due to our past experience with the Hakitek 750 roofing system we opted to use this method, adopting the “Roll Out” method of installation due to the speed of erection and the safe method of installation without the requirement to work at height. We also feel that the finished product is aesthetically pleasing against a traditional beam and ci sheet solution.

Roof Lanterns

At roof level there is a total of 224.00m run of glazed lantern structure which is being refurbished. JDC have designed and developed an access solution/strategy to suit the specific requirements of the following trades.

Built from the Construction Deck traditional access and birdcage scaffolding are being built through the roof structure – to the perimeter of the building this also incorporates the temporary roof support scaffolds. This scaffold gives access to remove and replace existing louvres and access the underside of the lantern.

Access around roof lanterns

These scaffolds are then box tied around the existing steel structure, inclusive of additional modular beams, which in turn is designed to restrain the steel structure and to provide restraint from thrust from the existing timber arches.

A further beamed detail has then been designed which is mechanically fixed to the timber arch which will restrain and support the existing timber structure whilst repairs are made to the historic features.

Lateral Restraint

A system has been designed utilising modular beam cassettes to tie the existing steel frame to the original masonry walls.

Modular beam walers have been designed at Construction Deck level which are mechanically tied to the Inner Crust walls with a series of drilled fixings at each connection point. From the walers the beamed cassettes extend to and ae fixed to the main construction deck.

Phoenix Columns

Part of the works required in this scheme is refurbishment of the existing decorative, cast iron Phoenix Columns. JDC have developed a design to give access to the columns which will also allow for excavation at the base as set out in the Constraints Document.

SKILLS AND EXPERTISE

The project highlights our design capabilities and the depth of our engineering knowledge, the design development has been an intense process and carried out in difficult communication circumstances during the pandemic with a very large design team – with many different ideas.

The parameters with regards to both vertical and horizontal loadings, set out in many areas looked unachievable but with time, thought and with the tacit knowledge of our management team we have solved most issues. 

We have always suggested practical, workable and cost-effective solutions to all areas of the works. Our workforce has adapted well to changing working practices and processes and the end product on site is well constructed and aesthetically pleasing.

We have erected some huge scaffolds on this project to suit the programme requirements.

We pride ourselves at all times on our attention to detail in both our design drawings and final delivery on site. The completed scaffold on this project is testament to both these attributes.

CHALLENGES

Covid 19

As with the tender process and the design development, 50% of the on-site works were carried out during the Covid 19 Pandemic. Our operatives and management have worked to the strict site rules and updated policies implemented by PAYE with regards to Social Distancing, breaks, welfare use, face coverings, testing etc. as well as adhering to the JDC Scaffolding SSOW and Covid 19 rules.

JDC Scaffolders wearing Face Masks during the height of the Covid Pandemic

Exclusion Zone

Under a portion of the Construction Deck a clear exclusion zone had to be left 30.00m x 13.00m (Extreme dimensions) to allow for a future demolition package to take place below.

Together with this the existing PAYE welfare area is situated in the centre of the site – 20.00m x 20.00m (Extreme dimensions).

Both of the above areas were required to be clear spanned utilising modular scaffold beams whist also supporting the imposed loads of the temporary roofs/dome scaffold above. To achieve what was required in these two areas a total of 1,300.00m of modular beams were installed. Including the above items meant that the imposed loads were not spread equally over the whole footprint but with the above configuration many legs had massive leg loads which were way over and above what AKT 2 had specified/requested in the original constraints document.

30.00m x 13.00m clear exclusion zone over future demolition zone. Deck to support imposed loads of temporary roofs.

To spread the loads and to achieve what was required a series of steel spreader beams were designed and approved. Unfortunately, JDC had been instructed to commence works prior to the steel design being finalised so a large part of the deck was based out on adjustable screw jacks which were altered/adjusted to allow the steel beams to be located. Carrying out the installation in this

manner was extremely labour intensive. At either side of the main exclusion zone, in lieu of the steel spreaders, JDC designed an alternate system using rows of steel unit beams connecting along the main deck supports.

Temporary Roof Support over Exclusion Zone

During design it was discovered that the main support for the first Temporary roof would fall within the required exclusion zone so to ensure compliance with the constraints a modular beam cassette with heavy duty tower supports at either end was designed to support the and spread the required loads.

Padstone & Steel Installation

A further request from the PAYE team was that the roof supports be erected in separate towers to leave sufficient space for installation of new padstones, steel beams and CLT structures. Heavy duty, fully braced towers were designed and to enable this request we, again, had to design and introduce paired modular X-beams at high level to join the towers and to allow the roof above to roll out above, a further 1,230.00m of modular X-Beams.

Heavy duty, fully braced towers and continuous beam lengths supporting Haki roof above.

Haki Roof Tie Chords

The use of a standard Haki tie chord system, tube and fittings or a beamed arrangement could not be utilised in this location due to the existing roof projections – chimneys and the like. To achieve the die chord JDC have designed a system of wire bonds connected with shackles, jaws and rigging screws to all roofs.

Bespoke tie chord arrangement to Haki roof

Lateral Restraint

A lateral restraint system had been developed over a number of months between the whole design team. It has transpired at a late date that some of the loads produced are greater than the permissible loads in the Constraints Document. With this in mind JDC have worked with RDG Engineering to produce computer modelling which has proved that the whole structure can actually be free standing without the requirement to tie to the walls which will negate the issue with imposed loads.

Continuation of Works

The separate contract of replacing the concrete slab has overrun and the client has concerns about project overrun. We met with the ultimate client, and the design teams to to develop and value engineer a scaffold design to bridge over the works below to allow the main works to continue.

Budget

The continually developing design has raised a number of budgetary challenges. We have worked closely with the PAYE commercial team to ensure transparency and best value at all times. We have also strived to ensure that any items of variance are priced in a timely manner to enable works to be agreed early with the client wherever possible.

Design

Section through construction deck, a temporary roof, welfare exclusion zone and central internal dome access

Testimonials

“JDC have a wealth of experience and knowledge which puts them in good stead to generate solutions to design problems. They have an in-house design team lead by Adam Callow and they partner with various engineering companies that provide the expertise in overcoming design hurdles. West Smithfield has been particularly complicated with design loading constraints that have occasionally thrown up problems at site level requiring rapid response to design solutions to avoid project delays. JDC have been committed to overcoming these throughout.” Rod Palmer, PAYE

“JDC are vigilant in reviewing design options and practical solutions to overcome site constraints and health and safety concerns. They pursue industry best practise.” Rod Palmer, PAYE

Images by Gary Britton

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