Engineering Against The Elements: A 25-Tonne Semi-Portal Crane For Twin Hills Gold Mine
We were tasked with the turnkey design, manufacture, and structural validation of a highly specialised, 25 ton capacity semi-portal double girder crane. Engineered and built entirely in house at our Germiston facility in Gauteng, South Africa, this massive asset was designed to operate outdoors 365 days a year under some of the most punishing climatic conditions on the African continent.
Our core lifting objective was to provide continuous, high capacity material handling across an open yard. However, the site’s physical footprint and severe weather dictated unprecedented structural parameters. While the crane features a 12m span, its overall width extends to 15.8m to incorporate safe walkways and cat ladders for routine maintenance access. Most notably, the total structure height reaches a staggering 20.8m, ranking it with some of the tallest portal cranes we have built.
Overcoming the structural physics of a 20.8m high moving portal frame under immense environmental forces, whilst navigating extremely tight physical space constraints on site, required us to completely rethink our standard design approach to ensure absolute stability and lifting efficiency. Following the successful completion of the manufacturing phase at our factory, we delivered the machine in July 2026 alongside a broader fleet of cranes commissioned for the development. The semi-portal crane is currently en route to its final destination in Namibia, where our expert technical team will directly supervise the complex on-site installation and commissioning of this amazing piece of engineering.
Innovation & Enhanced Solutions
Faced with a 20.8m vertical structure, standard structural profiles would have created an immense “sail area,” leaving the crane highly vulnerable to the violent wind vectors typical of Namibian mine sites. To optimise the design, our engineering team introduced an innovative structural pivot: fabricating the specialised semi-portal legs out of high tensile structural pipe profiles rather than conventional box girders or beams.
This rounded, aerodynamic geometry radically altered the wind drag coefficient of the crane. By allowing high velocity winds to flow smoothly around the structure rather than slamming into flat metal faces, we drastically reduced wind loading. This aerodynamic efficiency allowed us to limit the structural steel deadweight to 17 tons, with mechanical components making up an additional 7 tons.
Furthermore, to accommodate the client’s severe spatial and physical restrictions on site, we designed and integrated specialised U-shaped drives. These feature vertical motors coupled with custom-engineered gearboxes, which dramatically reduced the physical footprint of the drive assemblies without compromising torque or operational performance.
By saving deadweight and optimizing space through advanced geometry and compact mechanical packaging, we delivered a highly cost-effective and energy efficient solution that successfully bypassed the client’s on site clearances and safeguarded daily operations against structural deflection.
Planning & Control (Risk Management)
Operating a 24 ton deadweight structure at a height of nearly 21 metres outdoors meant that risk management had to be seamlessly integrated into our mechanical engineering from day one. Because this is a semi-portal configuration, riding on an elevated gantry runway on one side and a ground rails on the other, the physical dynamics under wind load are highly asymmetrical.
To mitigate the catastrophic risk of high-wind structural instability, derailment, or runaway events, we implemented a multi-layered control matrix:
Asymmetrical End Carriages: To address the starkly different loading profiles and structural behaviours of the semi-portal setup, we engineered two completely different end carriage lengths. The ground level portal leg side features an extended wheelbase of 10m to distribute the massive vertical and lateral loads over a larger footprint, while a shorter, optimised end carriage was designed for the elevated overhead runway side.
Anti-Derailment Systems: We engineered heavy duty anti-derailment brackets directly into both long travel assemblies, physically locking the crane to its tracks and ensuring absolute containment under maximum wind speed scenarios.
Active Environmental Monitoring: We integrated an on-board anemometer that provides continuous, real-time wind velocity data.
Secondary Mechanical Braking: In the event of extreme wind thresholds being breached, we equipped the crane with specialised, secondary storm brakes. These heavy duty auxiliary braking systems automatically engage to mechanically anchor the crane safely to the rail, eliminating the threat of wind driven runaway tracking.
Outcome & Engineering Legacy
Our decision-making process for this project revolved around balancing sheer scale with extreme site safety regulations and spatial restrictions. While alternative options considered utilising heavier, standard box-girder leg designs with massive counterweights and standard horizontal drive arrangements, our engineering team rejected these approaches. They would have increased manufacturing costs, failed to meet the tight site clearance limits, inflated transportation logistics across the border to Namibia, and put excessive wheel-load stresses on the civil foundations.
Our final aerodynamic, pipe leg semi-portal configuration, complete with asymmetric end carriages and compact, vertical U-shaped drives, proved to be an outstanding success. Because of the unprecedented physical size of the crane and the punishing environmental conditions it faces daily, we subjected the entire design to exhaustive third party validation, achieving full certification by a registered Professional Engineer (Pr.Eng).
By delivering this optimised machine in 2026 and stewarding it through to on site commissioning, we continue to demonstrate our true OEM capability. By managing the entire lifecycle, from the initial mathematical stress models in Germiston to eventually overseeing the actual installation on the mine, we have successfully pushed the boundaries of portal crane engineering, proving that heavy lifting assets can be simultaneously massive, safe, physically compact, and highly aerodynamic.
Condra,
+27 (0) 11 776 6000,
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