At 22 Bishopsgate in London, WSP Parsons Brinckerhoff has used RAM Concept and RAM Structural System from Bentley in an integrated modelling approach that incorporates existing elements from a previous, unfinished building
The conceptual design for 22 Bishopsgate, envisaged as ‘London’s first vertical village’, comes from PLP Architecture and features 120,000 square metres of office space, retail shops and restaurants, fitness centres and educational facilities, as well as an open viewing terrace and observatory.
WSP Parsons Brinckerhoff (WSP) meanwhile, was retained to manage the structural modelling and design, as well as provide multi-discipline engineering services to ensure sustainability. In particular, the firm is aiming for a BREEAM ‘excellent’ rating for 22 Bishopsgate and for it to be the first building in London to adopt the WELL Building Standard, for the health and wellbeing of its 12,000 occupants.
The £1.5 billion project requires that 22 Bishopsgate be built on the site of a previous, unfinished building, the Pinnacle, for which the foundation, basement and partially constructed core (the ‘stump’) remained. Thus, the new tower needed to incorporate the Pinnacle’s foundation and three storeys of basement.
From the start, there were numerous challenges here. There are site constraints, given the site’s location in that cluster of other buildings, as well as a tight timeline and budget constraints. At the same time, there was the need to design an efficient building that would be larger than, and completely different from, the Pinnacle design.
“The challenge was to marry the superstructure, which did not correspond to where the foundations were,” explains WSP structural engineer Diego Padilla Philipps. Here, WSP used RAM Structural System and RAM Concept from Bentley to provide it with an integrated BIM solution.
Recycled foundations
Working with local structural specialists, WSP chose to demolish the seven-story Pinnacle stump and analysed the interaction between the new design and the existing basement and foundation elements to determine what could be salvaged.
As Philipps explains: “We used RAM Concept to analyse the complicated geometry and export the spring reactions from the piles from the geotechnical analysis, and tried to make them compatible and interpret how the foundation was going to work.”
Since the core footprint of 22 Bishopsgate is larger than that of the Pinnacle, the team determined that if it added new raft and pile caps to adapt the existing supports to transfer the structure’s weight, they could establish the additional foundation capacity for the bigger building, while still using 100% of the former Pinnacle’s foundation. This would not only reduce costs but also minimise impact to the environment.
The team also decided that the basement was the best location for the substructure load transfer elements. Using RAM Concept, WSP analysed and modelled the three basement floors to determine how to build around and through them, to optimise the transfers. On the north side of the structure, there were three big columns to support the 62 storeys. WSP designed a raft to spread the loads for the three columns into the existing foundations. However, it found that the loads were so gigantic that the new raft was failing. In order to appropriately distribute the weight, the project team used A-frames.
Due to a waste management implementation on the south side of the structure, the team could not use a vertical column going down to the foundation. Rather, WSP needed to incorporate an inclined column on this side of the structure, with high-strength cables to tie the column to the core.
Similar to the basement transfers, the superstructure also required some elements to be transferred using inclined columns. However, while the basement inclined column was tied to the core, the superstructure did not lend itself to this type of support, because the high-strength cables would interfere with the services running through the openings at these levels. To resist the lateral forces generated by the inclination spanning 50 storeys high, WSP used RAM Structural System to analyse and design a horizontal transfer system, where the floor plates behaved horizontally.
Having columns at different positions throughout the superstructure, without corresponding foundations in the substructure required WSP to design concrete walls all the way around to transfer the huge loads involved. Integrating RAM Concept with RAM Structural System provided WSP with innovative design solutions that salvaged the existing basement structure.
BIM advances
To design the floors and determine the optimal shape of the overall structure, WSP linked RAM Structural System with Fabsec and Revit. “At some point in the design of the project, it was requested that we transfer all the elements to Fabsec,” Philips explains.
The team used RAM Structural System to analyse the steel frame for the floors and exported all the elements to Fabsec for design. Linking the two technologies allowed for the integrated design of the steel-plated floor beams and facilitated seamless collaboration and information mobility with the client to meet the project’s changing demands.
The team conducted up to 70 iterations to achieve the required design. With each iteration taking one or two engineers one week to model, WSP used Revit integrated with RAM through Bentley’s Integrated Structural Modeler to produce drawings and model simultaneously. This integrated approach accelerated the structural design process, reducing engineering and modelling time from 70 weeks to 43 weeks — a reduction of almost 40%.
Interoperable RAM drives design
WSP used RAM Structural System for much of the steelwork design to generate and analyse multiple design schemes, conduct fire assessments (such as the effect of fire on steel beams), and optimise the design in accordance with the site and structural constraints. RAM Concept was used to design the basement raft foundation and floor slabs of the substructure, in order to retain all of the existing foundation and much of the basement construction.
RAM’s interoperability simplified the complex calculations and structural modelling required for lateral stability and load analyses, in both the substructure and superstructure, for effective use of inclined columns.
And integrating Bentley technology with Revit and Fabsec provided an intelligent model for 3D visualisation, drawing production and material takeoffs, as well as accelerating information mobility to meet the imposing deadlines.
Using Bentley’s interoperable applications for schematics through to construction design provided efficient and economical solutions within the tight timeframe, as well as ensured strict compliance with European regulations.
The final design for 22 Bishopsgate includes a structural steel frame that is not only 15% lighter than that of the Pinnacle design, but also boasts 30% more floorspace.
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