View source for Tamesis One Redevelopment, Egham, Surrey

==Article in [https://www.newsteelconstruction.com/wp/wp-content/uploads/digi/NSCMarch17digi/pubData/source/NSCMarch17digi.pdf#page=16 NSC March 2017]==
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'''Floodplain development'''<br>
A new [[Multi-storey_office_buildings|commercial block]] close to the River Thames has been redesigned as a steel structure that will sit above any potential flood waters.<br>

Located at Egham in Surrey, close to the River Thames, the redevelopment of Tamesis One involves the [[Construction|construction]] of a new five-storey [[Multi-storey_office_buildings|office block]] to replace a previously demolished building. Client Royal London Asset Management has pre-let the offices to technology research company Gartner, who also occupy the adjacent Tamesis Two building. The scheme also includes the [[Construction|construction]] of a dedicated four-storey [[Braced_frames|steel-framed]] [[Car_parks|car park]] to the rear and new landscaping throughout.

[[Concept_design|Initial designs]] considered both concrete and [[Braced_frames|steel-framed]] options. Main contractor BAM opted to go with the steel solution as it offered a [[Multi-storey_office_buildings#Speed of construction|quicker programme]]. A cost saving was also gained as [[The_case_for_steel#Take a load off your foundations|shallower foundations]] were required, while more slender columns were attainable with steel giving the project a more aesthetic look. “The top floor was always going to be built with steel because it has 15m-long spans, however we redesigned the entire scheme as a steel structure during Stage 3,” explains Heyne Tillett Steel Project Engineer Szymon Lukas.

The site has historic flooding issues as it is close to the River Thames. This was a key consideration in the [[Design|design]] of the new development. A comprehensive sustainable urban drainage system has been incorporated in the works. Supported on up to 25m-deep CFA piles, the [[Braced_frames|steel-framed]] [[Multi-storey_office_buildings|office building]] has been raised above the flood plain to create a 800mm void under the building that could be used, in the event of a deluge, as a flood water reservoir.
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The flood zone void has been created with a suspended ground floor structure comprising a beam and block floor system spanning between RC beams. Steel columns are sat directly on the pile caps and are encased in concrete below ground floor level. The encasement was introduced to protect columns from [[Corrosion_of_structural_steel|corrosion]] and to provide structural bearing for the RC beams. “We’ve designed the scheme for a one in 100-year flood plus 20%,” explains BAM Project Manager John Rabey. “The [[Car_parks|car park]] has also been included in the flood design as its lowest level has been constructed so that it can accept flood water.”

Space is at a premium on this confined site and so logistics have played an important role in the [[Construction|construction]] process. As the two structures take up most of the site, leaving little room for material storage or plant equipment, a phased sequence was adopted with the [[Multi-storey_office_buildings|office block]] [[Construction#Steel erection|erected]] first.
Once this was up and the envelope nearly complete, the adjacent [[Braced_frames|steel-framed]] [[Car_parks|car park]] was [[Construction#Steel erection|erected]].

The five-storey structure will provide 11,600m<sup>2</sup> of office space and measures approximately 60m × 50m. It is a [[Composite_construction|composite]] steel frame with in situ concrete slabs cast on profiled [[Steel_construction_products#Decking for floors|metal decking]].
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Steelwork contractor H Young Structures [[Construction#Steel erection|erected]] the 800t of structural steelwork for the [[Multi-storey_office_buildings|office building]] as well as [[Construction#Installation of metal decking|installing metal decking]], stairs and lift shafts in an 11-week programme. “We [[Construction#Steel erection|erected]] the structure in a multi-phased sequence as it had to be handed over at various stages to allow follow-on trades to get started to keep the overall programme on schedule,” says H Young Structures Managing Director Ian Peachment.

The structure is generally on a 7.5m × 9m [[Concept_design#Floor grids|grid]] except for the uppermost floor where internal columns have been omitted to create a large open-plan area with 15m clear spans. “The idea was to create a statement for the top floor as it also benefits from having good views over the surrounding countryside,” explains Mr Lukas.
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Internally a full-height [[Steel-supported_glazed_facades_and_roofs#Atrium Roofs and Sky lights|atrium]] splits the building in half. Topped with glazed rooflights the [[Steel-supported_glazed_facades_and_roofs#Atrium Roofs and Sky lights|atrium]] allows natural light to penetrate the inner parts of the building and also accommodates the main reception areas and entrance. Steel link [[Bridges|bridges]] on each floor span across the 12m-wide central [[Steel-supported_glazed_facades_and_roofs#Atrium Roofs and Sky lights|atrium]] providing access between the two sides of the building.

Structurally, the entire building is one large [[Braced_frames|braced frame]] deriving all of its [[Concept_design#Structural options for stability|stability]] from strategically positioned [[Braced_frames#Vertical bracing|bracing]]. Westok [[Service_integration#Composite beams with web openings|fabricated beams with large web openings]] have been used at roof level to provide flexible [[Service_integration|services distribution]] within the depth of the structural roof zone.

Externally, the [[Multi-storey_office_buildings|offices]] feature a series of perimeter cantilevers of 1.5m, with a larger 3m cantilever to the front [[Facades_and_interfaces|façade]]. As well as helping to increase the available floorspace, the cantilevers provide a stand-out architectural feature to the building. The larger 3m-deep cantilever is located on a raking [[Facades_and_interfaces|façade]] which occupies half of the building’s main eastern elevation. Adjacent to the main entrance, the raking columns slope outwards by 10 degrees to the rest of the frame and had to be temporarily propped until the floors were cast, which then gave them the necessary [[Concept_design#Structural options for stability|stability]].

Adjacent to the raking elevation the building also features an angled [[Facades_and_interfaces|façade]] which cuts in on plan to form the entrance. The exterior of this angled zone is topped by a [[Facades_and_interfaces#Solar shading systems|brise-soleil]] at roof level formed with 400mm × 200mm × 10mm [[Steel_construction_products#Structural hollow sections|RHS sections]], which cantilever out from the main frame by up to 7m.

Steelwork for the stand-alone [[Car_parks|car park]] was completed by H Young in a separate six-week programme and required the [[Construction#Steel erection|erection]] of 300t of fully [[Metallic_coatings#Hot-dip_galvanizing|galvanized steel]]. The four level [[Car_parks|car park]] measures 80m long × 21m wide, including exterior ramps, and provides 240 parking spaces. There are no internal columns, which creates 16m clear spans for maximum flexibility.
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The project’s [[Construction|construction]] programme has recently completed and it is expected to achieve a [[BREEAM|BREEAM]] “Very Good’ rating. “We‘ve recently been awarded the fit-out programme for the [[Multi-storey_office_buildings|offices]] which means our hand-over date has been extended to August,” sums up Mr Rabey.

{|class="wikitable" width="400"
|-
|'''Architect'''||Scott Brownrigg
|-
|'''Structural Engineer'''||Heyne Tillett Steel
|-
|'''Steelwork Contractor'''||H Young Structures
|-
|'''Main Contractor'''||BAM Construction
|-
|'''Main Client'''||Royal London Asset Management
|}

[[Category:Case studies - Multi-storey office buildings]]