The annual Year in Infrastructure conference was recently held in London, UK. This conference, hosted by Bentley Systems, is the home of the Be Inspired Awards, which bring together experts from across the architecture, engineering and construction (AEC) industries.
The winner of the Innovation in Structures category for 2016 was a tricky project indeed. Imagine a 62-story, 912-ft tower in the heart of London’s financial district, designed to be a vertical village replete with restaurants, retail, fitness centers and more.
Now, imagine building it on the basement of a completely different building. Think of the analysis that would be required to determine what could be kept, what had to go and how best to transfer the structure’s weight.
This was the essence of the 22 Bishopsgate project.
Designing a New Building Over an Old One
The finalist nominated for the 22 Bishopsgate project was WSP Group of WSP Parsons Brinckerhoff (WSP), which, in addition to features such as the building’s acoustics, façade, geotechnics and fire protection, was responsible for the structural design.
Now, this ended up being a bigger issue than it is for most buildings. The site for 22 Bishopsgate had previously been the site for what was called the Pinnacle, another tower project approved for construction in 2006.
However, in 2012, the project was halted in part due to issues with a pre-lease. With six floors of the core and three floors of basement already built, a complete redesign was ordered. In 2015, when the site changed hands and the building was redesigned, WSP got the task of designing the structural system for a building that would be larger than and completely different from the original Pinnacle design while still using the built foundation and basement levels.
All About Structure
With this massive task at hand, the team at WSP had to do extensive analysis of the basement levels to see what could be salvaged and what needed to be demolished.
The new design required the team to run through several iterations—70, in fact. Ordinarily, according to WSP, this would take approximately a week per iteration. However, the team linked Bentley’s RAM Structural System with Revit to speed up the process and reduced the estimate to 44 weeks, a 40-percent reduction from the original.
The design the team settled on required partial demolition of the existing basement, as well as complex pile caps with plunge columns to adapt the existing supports. With these caps and columns in place to transfer the structure’s weight, the team could start building above and below ground at the same time.
The final result was a structural steel frame that was 15 percent lighter than the Pinnacle design while using an efficient shape to create an overall larger building. It reused 100 percent of the existing foundation and 50 percent of the existing basement levels.
For more information on 22 Bishopsgate, check out the WSP Parsons Brinckerhoff website.