A shining example of bold engineering: The Shrine of the Mother of Mercy is not only a visually striking landmark, it is also a remarkable example of steel engineering and construction. 

Submitted by Tass Engineering, the project won the tubular category at the Southern African Institute of Steel Construction (SAISC) Steel Awards 2024. 

In its overview in support of the project’s award submission, Perception Architects states: “The Shrine of the Mother of Mercy is a sacred place for the Catholic Church in South Africa. A place of pilgrimage and meditation for its patrons.” 

Using biophilic design principles, the building design blends in with, and respects the surrounding environment.

Design inspiration 

The design includes a chapel and a multi-purpose hall. Positioned in a natural, mountainous site in Magaliesburg, it invited a special style of architecture using biophilic design principles. 

While calling the hall design a heavenly inspiration, Perception notes that the challenge and complexity of the building’s design were to achieve a large, open interior space housing approximately 1 500 people, which embraced the surrounding natural environment. 

The interior therefore needed to be column-free, which necessitated a bold engineering approach. 

Each of the seven walls have large sliding folding doors, with ventilated glass panels above.

Flower-like roof 

The roof design comprised of three layers: 

1. Centre roof. 
2. Glazing window petals. 
3. The lower roof of the main heptagon structure. 

Beyond the biophilic inspiration, the “seven-petalled” flower of the roof is a symbol of Mother Mary and speaks to the importance of the number seven in Catholic liturgy. 

This also informed the choice of a central heptagon, elevated above the ground and serving as the foundation for the building’s unique roof.

From steelwork through to completed structure, the unique roof is the distinctive feature of the project.

Heart of the structure 

To support this central heptagon, the team employed an innovative approach, utilising seven scaffold towers positioned at the corners to temporarily hold the roof in place during the construction process. 

As the team began to add the radial steel members that would form the “petals” of the flower-like roof, the complexity of the geometry became increasingly apparent. It was a critical component, requiring precise geometry and careful erection to ensure the stability and integrity of the entire structure. 

Traditional square hollow sections proved inadequate, leading the team to explore the use of circular sections that could better follow the required geometry.

Innovative fabrication 

The steel roof structure was envisaged with a massive concrete ring beam along the perimeter of the walls. With no parallel sides and constantly changing curvature, the fabrication of the intricate steel elements was a true test of the team’s skills. 

Traditional square hollow sections proved inadequate, leading to the exploration of circular sections that could better follow the required geometry. Another significant challenge was the transition from the central heptagon to the outer perimeter of the roof. 

In order to achieve the desired aesthetic and functional outcome, the team developed a unique detail involving a rolled, circular hollow section that spiralled to match the curvature. An additional rolled-angle section provided a surface for the roof cladding to attach to. 

The team methodically added the radial steel members working outward from the central heptagon, until the entire roof structure was in place.

Quality and precision 

The complex intersections and connections between the various steel members left little room for errors. Quality control measures and precise detailing were therefore vital throughout the fabrication process. 

The lack of a pre-assembly process further heightened the importance of this attention to detail. The team placed their trust in the accuracy of their shop drawings and fabrication to ensure a successful on-site erection. 

Rising to the occasion 

With the central heptagon supported by the scaffold towers, the radial steel members were methodically added, working outward until the entire roof structure was in place. 

A critical moment was the removal of the central towers, to see if the self-supporting design would hold true. Remarkably, the roof settled by only 10mm, which is a testament to the precision of the engineering and fabrication. 

The end result is a stunning architectural centrepiece that seamlessly integrates engineering ingenuity and design vision. 

The clerestory windows and glazing on the leaves allows natural light to illuminate the building from all angles.

Project highlights 

• Unprecedented spans: The structure achieves a remarkable 44-metres span with no internal supports, a testament to the innovative use of steel and exceptional engineering expertise. 
• Dynamic roof design: The multi-stepped roof adds a captivating visual element while also offering a practical solution. 
• Open to the elements: The design bravely embraces the wind load, creating a sense of openness and connection with the surrounding mountains. 
• Luminous ambiance: The uplighting on all seven sides of the structure not only illuminates the building but also highlights its unique geometry, creating a truly breathtaking spectacle. 

The case for steel 

Steel’s inherent strength and versatility were essential to bring this project to life. Overcoming significant geometric challenges, through innovative solutions and meticulous attention to detail, the project team is a testament to the capabilities of the steel construction industry. 

The seven petals are linked to a central, smaller heptagon rooftop with additional clerestory windows.

The Tass Engineering team explains: “The versatility of steel allowed us to design soaring ceilings that foster a sense of grandeur. This achievement stands as a celebration of human ingenuity and showcases the remarkable possibilities that arise when technology and creativity converge in the realm of construction.” 

Benefits of steel usage included: 

• Structural integrity with exceptional strength and loadbearing capacity allowed for creative and daring architecture. 
• Durability through resistance to corrosion, weathering and pests ensures the building’s longevity and reduced maintenance costs. 
• Intricate designs facilitated by steel’s malleability enabled the architects to experiment with complex shapes and forms. 
• Steel is recyclable, thus promoting sustainability, eco-friendly construction practices and reducing the building’s environmental footprint. 
• Prefabricated steel components sped up the construction process, minimising the project timelines. 
• Steel’s non-combustible properties enhance the building’s safety and compliance with fire codes. 

Project details 

Project name: The Shrine of the Mother of Mercy. 

Location: Cradle of Humankind, Kruitfontein, Gauteng. 

Client: Catholic Archdiocese of Johannesburg. 

Main contractor: Gaudi Construction. 

Steelwork contractor: Tass Engineering.  

Architect: Perception Architects. 

Structural engineer: BMS Baker Consulting Engineers/THS Consulting Engineers. 

Steel detailer: 3D Con Steel Detailing. 

Cladding manufacturer: ArcelorMittal South Africa. 

Cladding roll former and supplier: Pro Roof Pretoria. 

Cladding/roofing contractor: PA Steel Structures. 

Ceiling Contractor: Pro-fit CNP 

Steelwork: 72 tons. 

Cladding: 11 tons. 

Full thanks and acknowledgement go to SAISC, Perception Architects and Tass Engineering for the information in this article.