Obsidian – Trinity way

Located in the heart of Salford, Obsidian is a 26-storey development providing 250 beautiful homes in one of Greater Manchester’s most bustling districts. Delivered for renaissance client, Salboy, the £49 million project will feature one-, two- and three-bedroom apartments and has been designed to meet high standards of functionality and architectural appeal.

Working with Domis as the main contractor and Studio Power as the architect, we were tasked with overcoming some interesting engineering challenges in the journey to bring this exciting new development to life.

The structural approach

Efficient Slab Design

One of the key structural approaches we took came in the form of an efficiently designed column grid, allowing for a 200mm slab thickness to be utilised across most of the project. This approach reduced the amount of concrete required while maintaining the necessary 120-minute fire rating for a building of this scale. This design choice significantly decreased the embodied carbon footprint of the project, making it more sustainable without compromising on any of the other design choices.

Simplified Terrace Construction

The building features stepped terraces starting from level four. To accommodate this design choice, we proposed a detail to maintain a consistent  slab soffit level across the threshold between internal areas and the terraces , simplifying the formwork required. This approach to detailing not only streamlined construction but also reduced material usage and waste.

Managing site constraints

Navigating Existing Services

The location of the site was no stranger to us, with renaissance having provided engineering designs for several nearby structures and some that even abutted the site. Given our prior knowledge of the location, it was no surprise that the site presented significant challenges, with high-voltage cables, BT lines, a water main, a gas main, and an adopted sewer all converging around or through the site.

These constraints required a carefully phased approach to construction and had to be considered in our designs.

How we strategically approached these issues

  • High-voltage cable rerouting – We optimised the timing of enabling works to avoid disruptions during peak demand
  • Foundation redesign – We adjusted the foundations to avoid encroaching on service easements, with column positions and pile designs reconfigured accordingly

Collaborating with Neighbours

The location of the tower crane posed logistical challenges. Placing it within the building footprint was unviable due to the implications it would have on cost and programme. To that end, the best option was to place the crane outside the building’s footprint. Of course, this required agreement from the neighbouring properties. Through dialogue and collaboration, a suitable offsite location was secured, minimising disruption and maintaining construction efficiency.

Addressing structural challenges

Mitigating Torsion in the Cores

Given the building’s elongated shape, we designed the building to incorporate two cores. Balancing torsion between these cores was critical to ensuring stability while limiting deflections. By strategically adjusting wall thicknesses within the cores, we minimised structural twist and enhanced overall building performance.

Vehicle Impact Resistance

The building is a Class 3 structure and is high risk in terms of disproportionate collapse and accidental loads.  Therefore, due to the close proximity of the structure to Trinity Way, a main road, we implemented additional measures to account for potential vehicle impacts. For example, we enlarged columns facing the road to withstand accidental loads, minimising risk wherever possible.

Carbon reduction and sustainability

The project used a lot of concrete throughout so can’t lay claim to being a truly sustainable build. However, as engineers we always look to design as efficiently as possible, removing needless excess at every opportunity. Every measure of carbon has to justify its existence.

On the Obsidian project, these design principles led to efficient slab designs, reduced core wall thicknesses, and optimised structural grids. With our design interventions, the project achieved a C-rating in embodied carbon assessments — a good outcome for a reinforced concrete frame of this scale.

The bottom line

By addressing complex site constraints and optimising designs for material efficiency, the team delivered a structurally sound and visually exciting building that will serve the people of Salford well.

As in all our projects, with Obsidian we proved that our ethos of simplifying complexity is not mutually exclusive with maximising value for clients and stakeholders.

Client: Salboy
Location: Salford
Value: £49 million