Project: Project Pegasus
Main Contractor: Sir Robert McAlpine
The Inner Temple Treasury Building has an interesting history and has had a building on this site since the 14th Century. The previous building was destroyed in enemy bombing in 1941. The building was rebuilt and was designed with a mansard roof across the whole building. Due to spiralling costs the War Damages Commission removed the project management and looked for cost savings – part of which was to omit part of the designed mansard roof and leave a flat roof to the remaining building. The new building was completed in 1958. The Temple library which contained over 70,000 books house in ornate shelves has been carefully demounted and stored off site for later reinstatement.
Project Pegasus involves significant works and remodelling to the Inner Temple Treasury building. The works include:-
- Construction of a new upper floor to the whole building with a new mansard roof to the whole building – as the original design.
- Creation of a break out and amenity space plus offices.
- Creation of a new plant room on the roof.
- Construction of a new double lift core internally.
- Construction of a new stair core externally.
- Remodelling and refurbishment of the Great Hall.
- Remodelling of Treasury library
JDC Scaffolding first became involved with this project in early 2014 when we received a tender for the works from Sisk. We produced a bespoke scaffold schedule for the Sisk requirements and had a number of meetings both on and off site to develop the scheme further. The project was then shelved for a number of years.
We were contacted by Sir Robert McAlpine (Special Projects) in September 2018 to ask if we would provide a tender for the proposed scheme. We informed them about our previous involvement in the project and our knowledge of the scheme and its requirements. McAlpine ultimately won the project in competitive tender and we developed our tender scheme and provided value engineering suggestions and proposed design solutions. After a final round of negotiations JDC Scaffolding were finally awarded the contract for the scaffolding works in June 2019.
- Independent scaffold to all faces of the main L shaped building complete with Monarflex Sheeting and a printed banner wrap to replicate the original building façade.
- Hoists and Haki Staircases to both the North and South Elevations.
- A bridged birdcage to the Great Hall with specific adaption sequence (Strike & re-erect top lifts) to suit the refurbishment programme of the fibrous plaster ornate ceiling.
- Hakitec 750 roof to cover the whole building inclusive of allowances to open and close the roof to allow crane lifting of materials into specific locations.
- Access scaffolding to enable the construction of new lift cores and new external staircase.
- Crash deck scaffold to the new library building inclusive of a designed beamed support to transfer loads to the external walls and internal spine wall.
- Crash deck scaffold to the underside of a new glazed roof over the break out space.
- Various localised access scaffold to enable demolition and later reconstruction of building elements.
SKILLS AND EXPERTISE
In the first instance this project highlights our design capabilities and the depth of our engineering knowledge especially with regard to the required temporary roof and the Great Hall birdcage.
The scheme is very high profile and the ultimate client has an office adjacent to the site. He is very hands on, visits the site every day and speaks to the operatives on site. It has been vitally important that we have found practical and workable solutions to all problems, we are working safely at all times and that our finished product is aesthetically pleasing. We have had extremely positive feedback on all counts to date.
Prior to commencement on site, and since, our In-House Design Department have worked alongside the McAlpine Design Department and our Consulting Engineers to find workable and practical solutions to all challenges we have met thus far. In a number of areas, we have suggested differing solutions and the final designs have ensured satisfaction for all parties involved in the design and these solutions have been communicated to our Contracts Department and operatives on site to ensure that risks are reduced.
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.
The route for delivery of materials was made quite clear to us in all the meetings prior to commencement on site. All materials had to be delivered one way via a designated route through Tudor Gate (restricted width and height) into the site and then to leave via a gate in Crown Office Row onto the Embankment. We were given the overall dimensions of Tudor Gate and had measured the gate prior to commencement. We were satisfied that our 26T Hiab vehicles could safely enter site. Unfortunately, we found on our first delivery that this was not the case due to a ground level obstruction through which the vehicles wheel nuts could not pass. We have solved this problem by delivering our materials to a nearby location and then using a 7.5T lorry to service the whole project. The scaffold and roof have been completed and we are ahead of programme.
Due to the access restrictions there is not a tower crane on site. The only access for the rear elevation was via an alleyway between our building and the neighbour’s property. The only vehicular access through this alley is for hearses for funerals held at the adjacent Temple Church. We have used trolleys and the like and have erected the required 1,000m2 of access scaffold (complete with Haki Stair and hoists) to suit the McAlpine programme.
At the western end of the main Treasury Building stands the remains of a 14th Century building which is Grade II* listed. The scaffold design had to ensure that no part of the scaffold bears or butts the structure of the buttery. To the south east side of the Buttery building there is a pedestrian access which is a pinch point. Our design ensure that the access was left clear for pedestrians and that no part of the scaffold touches the actual structure.
The required temporary roof was required to cover 1,300m2 of roof area to an L shaped building. The general method to erect this type of roof is to build a working platform at one end then safely construct each complete roof bay and then roll the completed roof bays away from the safe working area. With our knowledge of this method we know that our operatives can work safely without the need to access the high-level roof structure. With our knowledge from two previous schemes we decided to construct the roof from a central loading/working platform and to construct the roof in two directions with a final roof sheet and lacing frames to join both elements.
The main design issue we had to overcome was the covering of the adjacent roof at 90 degrees to the main building. We considered a number of possibilities but we were left with issues with both buildability and water management. Whichever solution we arrived at it was imperative that our design reduced risk and hazard to our operatives. If we utilised a traditional ci sheet roof in this location this would increase the potential risks and hazards.
After a number of solutions were considered we arrived at a final scheme. The main roof would follow one width and be constructed and rolled out traditionally. At the junction of the two roofs we designed a 25.50m beam span which supported the reactions of the rolling roof and the imposed loading of the adjacent roof. The beams to cover the adjacent roof were fixed in line to the main roof beams at one end and from a separate beam cassette on the opposite end. The required lacing frames were added working from a birdcage below and then complete 26.00m roof sheets were added to the whole bay.
The roof was originally designed with allowances for two specific loading areas. These areas were designed, as we have previously experienced, without lacing frames but with additional bracing, to give a designated 3.05m x 4.00m void to allow lowering of materials to the working area. The new mansard roof structure is to be formed in structural steel and the method suggested was agreed as the best method and that the steel elements would be moved into place once at roof level.
This methodology was later rejected by the steel subcontractor who wanted to lift all elements into place using a mobile crane. This led to a redraw of the scheme and using the standard Haki bay sizes we achieved the required layout.
We then pointed out that although this method suited the roof layout a problem arose with the actual lifting in that we would have to remove both the roof sheet and the lacing frames in a bay complete to allow the installation of the required elements then to replace on completion. To carry out this method we suggested either working from a man rider using our scaffolders qualified in this method of working or alternatively working from below in a MEWP (See Challenge 5 – Great Hall Birdcage below) which would be situated on our birdcage scaffold below. Following a number of meetings and collaboration between our own and McAlpine Safety Departments it was agreed that we would move forward with the MEWP method.
The beam span was designed in collaboration with our consultants, RDG Engineering. After a number of models had been considered the final solution of a beam cassette of nine lines of modular X beams was agreed on and constructed on site.
At the eastern end where the support for this beam cassette is ground founded there was concerns raised about the reactions near to an existing substation and the possible surcharge loads to the retaining walls. With this in mind we have designed and installed a Mabey propping system so safely shore the area working around the constraints of numerous pipes, windows and an existing cat ladder.
Once in place there was concern expressed about the visible deflection in the cassette overall. For due diligence we arranged for RDG Engineering to visit site to view the cassette in-situ. RDG prepared a report to prove that the visible 163mm deflection was quite normal in this situation.
Great Hall Birdcage
The original design brief was to build a bridged birdcage to the complete Great Hall to give access for refurbishment. The agreed sequence of striking, adapting and re-erecting were agreed prior to contract award. Access for all materials were through a small window at First Floor level
The scaffold was to be constructed with an independent scaffold to both long edges of the Great Hall, X Beams joined the supports at high level with a standard tubular birdcage built above the beamed level. This birdcage was to be struck later and the beamed deck would be boarded for the following trades.
Following the above changes to the temporary roof methodology the birdcage design now had to be altered accept the rolling load of a 2 Tonne MEWP. Calculations proved that the existing structure could not support the leg load of the bridged birdcage so the redesign included for additional legs going to ground over the whole birdcage area.
The independent scaffold as a whole is to be covered in a vinyl banner with artwork replicating the existing façade. We contacted our long-term supplier, Concorde Graphics, to price the works and get involved early in the project.
Concorde have historically worked, on previous projects, from existing architectural drawings and have replicated a number of building facades for us. The problem with this scheme was that the quality of the actual drawn information was not very good. Concordes art department have worked hard in collaboration with our own design department to produce a number of sample sections which have been attached to the scaffold for approval by both McAlpine management and representatives of the ultimate client – The Honourable Society of the Inner Temple. Colours of brickwork, stonework, windows and sizes of the actual visible brickwork have been altered and amended and the client has now accepted the proposed banner.
JDC Scaffolding have installed a banner frame to all element to accept the banner. The offset frame has Kee Klamp elements at all joint and junctions to ensure an aesthetically pleasing finish and to minimise any potential damage which could be caused by standard scaffold fittings.
The final banner wrap has been altered and extended to be seamlessly built around our Haki staircases, hoist installations and the new staircase and lift cores.
JDC’s Team is their greatest asset and everyone has proved to be honest, hardworking, conscientious and personable since joining Project Pegasus. With a low turnover of operatives, many of them are now known to the SRM Team and on first name terms, they are approachable with a willingness to listen, help and provide solutions.
Throughout the duration of the scaffolding works JDC’s Team have Interfaced with SRM at all operational levels; most notably SRM’s Engineering Team in the management of daily tasks and activities, which has led to the development of strong working relationships. This positive relationship has, in turn, helped drive efficiency and productivity throughout the Site.
Project Pegasus is fortunate to have had a significant presence from JDC’s Senior Management Team, who are regularly on site to review progress, provide advice, explore options and implement solutions, despite how uncongenial they may be.
Josh Murray – Construction Manager – Sir Robert McAlpine
JDC Scaffolding were shortlisted for the 2019 NASC Award for Project of the Year – £5 Million plus.
We were pleased to be recognised and achieve Highly Commended for our submission.