By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.May 6 2024A recent article published in Buildings has proposed a novel twin traction system to vertically lift elevators with a maximum load capacity of 50 tons or up to 300 people in a single trip. With multiple safety features, this elevator design can ensure workforce safety and enhance the productivity of various industries.
Illustration of twin traction drives, where each component is colored and labeled on one side. Image Credit: https://www.mdpi.com/2075-5309/14/5/1244
Background
Construction projects often require super-heavy objects to be lifted up to extreme heights, which has been a topic of concern due to incidents that have resulted in fatalities.
Large cargo elevators with high transport efficiency are essential to ensure the safety of thousands of workers in these dynamic work environments. Tower cranes, hydro cranes, crawler cranes, and winches are commonly used for lifting heavy objects at construction sites. However, they are slow and unsuitable due to high accidental risks during night-time and adverse weather operations.
Despite several studies on elevators for cargo and emergency rescue, an elevator with a maximum load capacity of 50 tons, the modern industry-standard equivalent to 300 passengers, has not yet been designed.
Most commercial elevators for buildings with more than four stories use a single cable-driven traction system. However, a much larger system would be required to securely transport a 50-ton load, posing several installation challenges. The resulting increased rope fatigue also requires frequent maintenance and raises safety concerns.
To this end, the authors of this study set out to develop a twin traction elevator (TTE) system that has the capacity to overcome some of the above mentioned challenges associated with conventional elevator systems.
Methods
The researcher's proposed a TTE featuring a vector drive and a rope-type design. This innovative system consists of four primary components: a three-phase induction motor, which powers the system by transmitting torque through a worm and worm gear setup to rotate the traction sheave. This sheave engages the rope to facilitate movement.
A strategically placed brake between the motor and the worm gear provides essential operational control. The elevator's twin hoisting mechanism is built on a robust steel beam structure, with twin driving motors enhancing the system's reliability and performance. The traction wire rope, which suspends the substantially sized boarding car, ensures stability at eight separate points. The design incorporates patented Z-shaped roping and ABBA-sequenced roping methods to optimize efficiency and safety.
This design helped establish a tilting safety device, which can detect and signal eccentric loads in case of large and heavy loads. Other safety features include a load cell display monitor, an anti-creeping device, a brake fall safety device, and an all-weather operation system (workable during rain, wind, snow, and icing).
In addition to the car's various safety features, three critical devices were integrated to enhance security: an independent wire rope emergency stop brake, an anemometer with a preset maximum wind speed threshold, and an overspeed safety device to prevent falls and uncontrolled acceleration.
This holistic approach to safety, encompassing load cell technology, rope brakes, an overspeed governor, and wind speed monitoring, has been designated as the Load Cell-Rope Brake-Overspeed Governor-Wind Speed Meter and Control (LROW) method.
Results
The authors verified the safety and practical application of the proposed TTE system through performance tests (including load tests, brake performance, and landing errors) conducted by the Korea Industrial Safety Association (KISA).
The newly developed elevator boasts the capability to lift 50 tons of equipment up to 60 times per day, significantly outperforming traditional crane capacities, which are limited to just 8 lifts daily. Precision testing revealed an impressive average landing error of 1.12 mm across five tests, far surpassing the industry standard of 10.0 mm.
Additionally, the main brake system, employing the LROW method, demonstrated swift and effective braking power, with no abnormalities detected in withstand voltage and residual voltage tests.
The proposed TTE elevator has already been installed and operates at nine sites worldwide, reaching heights of up to 110 meters and depths of 500 meters. It plays a crucial role in transporting extremely heavy equipment and materials, and can accommodate approximately 300 individuals simultaneously, in line with its design specifications. Moreover, this elevator provides a significantly improved ride experience and higher passenger satisfaction compared to existing rack and pinion-driven small lifts, which are commonly plagued by noise and vibration issues.
Conclusion
The primary objective of this study was to significantly enhance elevator loading capacities, achieving an unprecedented 50 tons with the TTE system. This innovation has markedly improved construction work efficiency and safety protocols by providing a viable alternative to traditional cranes.
Additionally, it has had a positive impact on labor health and safety, particularly under adverse weather conditions. The elimination of manual stair climbing further promotes the well-being of the workforce, ensuring safer and more efficient operational conditions.
The significant reduction in wait times for conventional elevators using the twin traction system can enhance the overall productivity in various industries such as large offshore plants, semiconductor display manufacturing facilities, underground high-speed railway stations, radioactive waste storage sites, and high-rise building construction sites.
However, the proposed TTE system still has certain installation limitations, such as the essential temporary use of a crane, which would require a significant amount of space for its operation. Additionally, excavation of a pit with a robust foundation beneath the intended location is mandatory, which becomes impractical in locations with marine-like terrains. Thus, alternative access methods like ramps for forklifts or staircases are required.
Following on from this preliminary study, the researchers plan to develop an 80-ton capacity elevator capable of transporting 500 people, an elevator specifically tailored for shipping containers, and multi-cage and double-deck elevators to address evolving industry needs.
Journal Reference
Kim, G.-Y., & Jang, S.-H. (2024). Elevating Innovation: Unveiling the Twin Traction Method for a 50-Ton Load Capacity Elevator in Building and Construction Applications. Buildings, 14(5), 1244–1244. https://doi.org/10.3390/buildings14051244, https://www.mdpi.com/2075-5309/14/5/1244
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