St Pancras Square is a public realm area including new homes, offices, cafes, restaurants, retail space, 20 new streets and a terraced water feature, all forming an important part of the huge King’s Cross development that has radically changed the former rundown industrial site in central London into a new and vibrant neighbourhood.
The development consists of commercial and retail buildings situated around a central public square.
How it started
To facilitate construction of the seven buildings, a 4,0000m2 podium had to be formed. The large steel podium provided a shared delivery basement for all the buildings as well as a level platform for the landscaped public realm. During construction the podium also served as a robust two level working surface for the project’s many project teams.
The podium was the catalyst for the construction of Pancras Square and the choice of materials to achieve this was crucial. With speed of construction a main driver for the project, steel was the ideal solution. Access for the adjacent buildings was via the basement of the podium and vital to the work starting on time.
What we did
A steel frame supporting precast planks was the best way to achieve the tight deadlines required on the project. Due to very tight spaces to manoeuvre and for storage on this city centre site, it was also essential for a co-ordinated delivery programme to achieve the phased erection sequence.
“Originally the design was for an in-situ concrete structure, but this would have been too slow and the amount of formwork needed would have restricted access below the podium and to the surrounding building sites,”
“We changed the design to a steel frame supporting precast planks as this is the fastest method and the best way of meeting our deadlines”, said David Carter, BAM Design Director.
The steelwork programme was so quick and efficient and once work was completed at one end of the site, the other end of the podium was already in use for material storage on the top deck and vehicle access on the lower deck. To facilitate large trucks and utilities that serve the buildings, the basement level of the podium had a 9m floor to ceiling height.
To achieve this floor to ceiling height of 9m with concrete would have been extremely difficult, blocking the restricted site up with formwork and preventing follow on trades gaining access so quickly, all adding to the construction time. As the lower level of the podium would be used as a delivery yard for the surrounding buildings it required large open column free spaces, achievable with steel, large enough for trucks to turn around in.
Some of the spans were up to 18m in places and fabricated steel beams were the best way of forming these large spaces. The beams not only form the necessary basement spaces, but they also support some heavy loads on the podium’s top level, including construction traffic, building loads of the realm and the public square itself.
As the northern end of the site is around 3.5m higher than the southern end, a series of steps located along the structure were created using a steel braced frame to cater for the slope. The steps were created using a series of girders and deep beams which were designed with a double lip configuration. These large steel elements accept 200mm deep planks which on one side sit on a midpoint stiffened shelf plate and at the other end the planks sit on the top flange, creating the step.
As greenery focuses in the public realm’s future and include a number of trees and large shrubs, large pre-fabricated pits were installed within the podium’s upper slab. The pits were formed similar to the steps.
Using steel we’ve actually saved at least six weeks on our programme.
David Carter, BAM Design Director.