Interspan Delivers Structural Innovation for Barnfield College Redevelopment

Interspan is proud to play a key role in the redevelopment of Barnfield College in Luton, UK, bringing our expertise in post-tensioned slab design and construction to this important project. The second phase of this transformation focussed on creating a state-of-the-art, four-storey teaching block dedicated to construction and engineering education. With a focus on enhancing educational facilities, this project represents a significant investment in the future of education in the region.

Project Scope and Overview

Barnfield College’s new teaching block spans 5,780 m² and is designed to accommodate modern educational needs. It provides cutting-edge facilities for construction and engineering courses.

Working alongside the Summit Group, Interspan was entrusted with designing and constructing the post-tensioned slabs that form the structural foundation of this innovative building.

The project began on September 20, 2023, and practical completion was scheduled for December 2024. The use of post-tensioning methods was central to meeting the building’s aesthetic and functional requirements while also aligning with sustainability targets.

Design and Engineering Innovations

Interspan collaborated with main contractor Gilbert-Ash and structural engineer BW Murray during the tender phase to refine and optimize the inherited structural design. Originally, the design specified 350 mm thick post-tensioned slabs spanning a 9 m x 9 m grid, supported by a deep edge beam measuring 450 mm x 600 mm.

However, using advanced Ram Concept analysis software, Interspan proposed a value engineering solution that reduced the slab thickness to 300 mm.

This adjustment maintained the required structural integrity to support the high load demands – 0.95 kN/m² dead load and 8.7 kN/m² live load – while reducing material usage, contributing to cost efficiency and environmental sustainability.

Addressing Structural Challenges

One of the key challenges for this project was the internal columns, which measured 550 mm square and posed a potential risk for punching shear failure. To mitigate this, Interspan implemented proprietary shear rails over the columns, a solution that avoided the need for additional reinforcement and allowed the edge beam to remain unchanged. This approach was structurally sound and helped maintain the building’s visual and functional integrity.

Environmental Benefits and Sustainability

Sustainability was a core focus for the Barnfield College redevelopment, and Interspan’s involvement contributed to significant environmental savings. By reducing the slab thickness from 350 mm to 300 mm, the project reduced concrete usage, saving an estimated 98 tonnes of CO2 emissions across the 5,800 m² of post-tensioned slabs installed.

The post-tensioning system’s pre-compression significantly reduced the risk of cracking, ensuring the building’s fair-faced soffit finishes met the high aesthetic standards required for the college. This alignment of functional performance, aesthetic quality, and environmental impact highlights the benefits of post-tensioning in modern construction.

Innovation and Sustainability

The redevelopment of Barnfield College is a prime example of how structural innovation and sustainability can coexist. Through close collaboration and value engineering, Interspan delivered a solution that not only met the project’s demanding technical requirements but also contributed to its long-term sustainability goals.