76 Southbank | IBM Buildings | Wentworth House Partnership

76 Southbank | IBM Buildings

Aerial shot of construction project at 76 Southbank, London showing construction work and cranes

Client: Keltbray (Demolition Contractor)
Architect: Allford Hall Monaghan Morris (AHMM)
Structural & civil Engineer Heyne Tillett Steel

76 Southbank is the transformation of Sir Denys Lasdun's 1983 IBM Building on the South Bank, one of Britain's finest examples of Brutalist architecture. The project retained 80% of the existing concrete frame while creating 300,000 sq ft of modern office space, targeting net zero carbon development. We provided construction engineering support to Keltbray, designing bespoke lifting systems for listed façade panels, implementing observational methods for basement propping adjacent to Thames Water infrastructure, and coordinating structural steel connections within the retained concrete frame.

30,000

sq ft of modern office space

80%

of the existing structure retained

Our Role

Wentworth collaborated with Keltbray to detail the structural steelwork, including designing steel-to-steel connections and providing comprehensive fabrication details. We generated 3D models in Tekla Structures, produced general arrangement and fabrication drawings, and resolved remedial issues, including a hanging column 30mm out of plumb. Additional scope included designing bespoke lifting brackets for Grade II listed façade panels, implementing observational methods for basement propping to minimise temporary works, and designing constrained welfare office foundations, protecting the underlying Thames Water sewer.

Capabilities

Buildings
Demolition
Adaptive Re-use
Cut and Carve
Structural Engineering
Geotechnics
Construction Method Engineering
Temporary works

Buildings
Demolition
Adaptive Re-use
Cut and Carve
Structural Engineering
Geotechnics
Construction Method Engineering
Temporary works

Designing bespoke lifting systems for façade panels

The Grade II listed precast concrete façade panels needed to be removed, stored off-site during demolition and structural alterations, then re-fixed to the modified structure. The listed status meant the panels had to remain undamaged, requiring precise lifting studies and connection designs that could handle the weight and geometry of Lasdun's distinctive Brutalist panels without cracking or permanent deformation.

We designed bespoke lifting brackets specifically engineered for each panel type, conducting detailed lifting studies to determine safe load paths and stability during crane operations. Our fixings design accounted for the existing concrete conditions, panel weights, and the subsequent re-fixing methodology after the structural frame modifications were complete. Each bracket was detailed to distribute loads without concentrating stresses at vulnerable points in the 40-year-old concrete.

This enabled Keltbray to safely remove and store the iconic façade elements, protecting the heritage character while the building was comprehensively remodelled behind the retained elevation.

A wide-angle, eye-level shot captures a large, rectangular pre-cast concrete panel suspended in mid-air by a crane at a construction site.

Grade II listed façade panel removal and reuse

Precast concrete façade panels from Lasdun's distinctive Brutalist elevation needed removal, off-site storage during demolition, and subsequent re-fixing after structural alterations. The buildings’ listed status had to be carefully handled to prevent damage to the 40-year-old elements.

We designed bespoke lifting brackets engineered for each panel type, conducting lifting studies to determine safe load paths and stability during crane operations. Our fixings design enabled Keltbray to safely remove and store the iconic façade elements, protecting the heritage character while the building was comprehensively remodelled.

Maintaining stability during core replacement

The structural alterations required demolishing the existing cores and part of the surrounding floors, then replacing them with new reinforced concrete core clusters and a composite steel-concrete floor system. We needed to maintain vertical and lateral stability of the retained structure throughout this temporary stage, while also accounting for two tower cranes operating on the upper levels.

We initially proposed temporary X-bracing embedded in the retained concrete framing to compensate for the absent cores. However, we built a full 3D finite element model simulating the complete demolition sequence and accurately modelling all sources of residual stiffness in the frame. This analysis proved that at the stage of maximum demolition, the structure had sufficient strength and stiffness to remain stable, eliminating the need for temporary bracing.

Structural steel coordination within retained concrete frame

A wide-angle interior shot of a construction site within a concrete building. Massive, dark grey steel beams form a series of large "X" shaped braces between thick white concrete columns and the ceiling. The floor is unfinished grey concrete, and large wi

New structural steel had to connect to a 40-year-old concrete frame with accumulated tolerances and as-built positions differing from the original drawings. A hanging column at Level 02 was 30mm out of plumb, structurally sound but required remedial work. Level 3 hanging steel needed continuous adaptation as surveys revealed actual concrete positions.

We produced 3D Tekla models updated as surveys to reveal the reality on site. Wentworth proposed a welded plate-to-plate splice for the out-of-plumb column and resolved the steel-to-concrete connection alignments through iterative coordination. This adaptive detailing maintained programme momentum, giving Keltbray fabrication packages matching site reality.

Basement propping adjacent to a Thames Water sewer

The existing basements were directly adjacent to a major Thames Water sewer that had to remain operational throughout construction. Traditional propping would have restricted site access for months while imposing unnecessary costs on this reuse-focused project.

We implemented an observational method approach, installing strategic monitoring on the basement walls and designing propping installations triggered by actual movement thresholds rather than worst-case predictions. This monitoring-led strategy minimised temporary works quantities and duration, speeding up construction and decreasing costs, while maintaining wall stability throughout demolition and alterations.

Outcomes

This project is a great example of how Wentworth's construction engineering knowledge can help to deliver predictable outcomes for specific challenges on one of London's most complex heritage reuse projects on the South Bank.

Key results:

Heritage protected: Bespoke lifting systems enabled safe removal and re-fixing of Grade II listed façade panels
Programme efficiency: Observational method minimised basement propping, speeding construction and reducing costs; construction stage finite element analysis minimised bracing requirements
Infrastructure safeguarded: Foundation designs protected the Thames Water sewer during constrained site operations
Contractor confidence: Real-time coordination and adaptive Tekla modelling maintained Keltbray's fabrication programme despite as-built variations
Sustainability contribution: Construction solutions supported retention of 80% of the existing structure, contributing to the net-zero carbon target

76 Southbank was completed in July 2025.

This project demonstrates the value of sustained early involvement across a major programme. Our 10-year engagement with the project gave us a thorough understanding of each site's history, allowing us to integrate solutions and take advantage of existing features rather than work around them.

Key results:

Long-term partnership: continuous involvement from early design through construction completion, built deep project knowledge
Risk management: 3D geotechnical modelling identified and resolved potential issues before construction, preventing costly site delays
Heritage protection: Victorian structures remained operational and undamaged throughout complex adjacent works
Construction confidence: bespoke temporary works designs tailored to each site's specific conditions enabled safe, efficient delivery
Collaborative approach: open communication and proactive problem-solving with the CVB JV, other designers, contractors and stakeholders resolved complex multi-party challenges.

The Thames Tideway Tunnel East Section was completed successfully in 2025 after 10 years of construction, with Wentworth's construction engineering knowledge helping deliver predictable outcomes across some of London's most challenging underground construction sites.