As an engineer, there are certain projects which continue to impress even after they’re completed. For me, Toybox is one of those, it combined both stunning looks with an ingenious design that delivered a successful project.
Toybox was built on the former site of the Nautical Club on Bishopgate Street. The building’s design, by architects Corstophine + Wright, was inspired by the metalworking, goldsmithing and silversmithing workshops that produced small items that were considered ‘toys’.
Torsion Group, the developer, wanted a quality student apartment block that provided desirable accommodation, by clustering en-suite study space cum bedrooms around a central living area, with security and excellent on-site amenities. However resident occupation needed to be maximised to ensure the project was commercially viable which was why the structural design was so important.
The site had several limiting factors, an existing underground railway tunnel and a deep cutting located to the south eastern boundary of the site meant the tunnel had to be protected from both the construction work and the building’s final structural load, creating a 10 metre exclusion zone.
We focused on delivering the client brief, which we eschewed designs that simply reduced the footprint away from the exclusion zone, (reducing the number of student apartments), nor did we design foundations within the exclusion zone, which would have caused significant additional expense for the developer.
Instead, we were able to use our experience to design a 15 storey, 290 bed student apartment block that avoided all below ground construction within the exclusion zone by using two post-tensioned cantilever beams. One of these was in the ground and the other visibly holds up 14 storeys of the building. By designing an over-sail above the pavement and away from the exclusion zone the design maximised the overall floorplate even though the ground floor entrance was set back from the road.
Offsetting the vertical load of the cantilevered section away from the central core, it meant our design of the post-tensioned transfer beam and wall needed to reflect the significant tensile and compressive forces. The post-tensioned elements provided the tension while the compression struts transferred the loads to the core.
We also designed piled foundations to support the resulting increased loads in the sub structure. This allowed us transfer loads from the superstructure back into the site away from this tunnel.
The structure has a central 15 storey block with two 10 storey wings that comprise a reinforced concrete frame with pre-stressed flat slab construction, one main central shear core in the 15 storey block and two planar walls situated within the 10 storey blocks.
To achieve the elegance and height of the design required some real engineering feats, such as the 14m cantilever beam which is part buried in the ground. As is often the case though, the engineering excellence gets hidden away by facades or superficial facings. The lack of visibility means a lack of appreciation for this remarkable engineering solution.
The design was developed using the Design2e design approach, utilising three key elements:
- a rigorous understanding of engineering
- an application of engineering science
- the most advanced computational techniques to eliminate the possibility of numerical and philosophical errors
This ensures the overall safety of our distinctive designs and allows us to assess and compare the values and merits of various design alternatives in terms of time, money, quality and sustainability.
For the Toybox project we ensured that the balance of the superstructure of the building remained economic and standardised to facilitate the most rapid construction. This, combined with the project team’s successful collaboration meant that the building was completed in 69 weeks, on time and within budget. Resulting in the client being able to let the whole block by the start of the 2019/20 academic year.
Looking back on the Toybox project two years after its completion, it’s possible to see that the architectural vision is still being appreciated; it was shortlisted in the Student Accommodation Awards 2019 for Private Halls of Residence of the Year for its design and imaginative use of materials.
The Toybox project provided a number of challenges for us from an engineering perspective, but it allowed us to provide engineering ingenuity in the design. As Torsion Group said: “Design2e are the people to go to for innovative and proactive solutions.”