A steel-built structural damping system could make tall buildings safer in earthquakes and reduce wind sway without taking up valuable floorspace
As real estate prices in expanding cities across the world continue to rise, developers have responded by building taller, slimmer buildings.
Central London, Hong Kong, New York, Toronto, Wellington, Manila; all have some of the highest value real estate in the world and with the appetite to live and work in the centre of these business hubs remaining high, developers have looked skyward.
Modern construction methods enable skyscrapers to be built on increasingly small plots and with a corresponding slenderness. But while these slender skyscrapers offer vital accommodation, they also tend to sway in the wind.
“The VCD modules are manufactured using standard Japanese SM490A structural steel which sandwich the 3M viscoelastic polymer. It is a super-durable material”
The effect is more noticeable towards the upper levels and although there are no safety implications it can cause occupiers to experience a form of motion sickness. To combat the sway, developers have called on engineers and designers to develop damping systems that help reduce this movement.
There are two favoured types of damper that are installed toward the top of the building; a tuned mass damper, which is a mechanical system that acts to absorb any movement, and a damper which uses a water filled tank to add weight and counteract any sway.
Both are bulky, requiring 100 square metres of space over two stories, and in cities where every square centimetre of floor has a high value that can be expensive.
The high cost of existing damping systems was one of the reasons why Toronto-based company Kinetica Dynamics, in conjunction with materials producer 3M and steel specialist Nippon Steel and Sumikin Engineering, has been developing a system that can dampen any wind sway or earthquake movement without taking up valuable floor space.
Its Viscoelastic Coupling Damper (VCD) utilises the combination of the shear and strain resistance of viscous materials and the stretch memory of elastic, combined in a viscoelastic polymer developed by the 3M team.
Manufacturer Nippon Steel and Sumikin Engineering takes several layers of this viscoelastic material, sandwiching it between layers of high-strength steel to create one of their VCD modules.
These modules are transferred to the job site where they are anchored to steel sections cast into the structural concrete of the skyscraper. These ‘embeds’ are manufactured locally by steel manufacturers with ‘templates’ that act as tolerance preservers which enable the VCDs to be fixed using high tensile steel bolts at a later date. This ensures the process can be taken off the critical path of the construction cycle, saving time and increasing efficiency during the build.
“It means that general contractors can carry out the work without bringing in teams of specialists. It is a simple enough to cast in the embeds which are standard structural steel sections from local producers,” explains Michael Montgomery, Chief Technical Officer and Managing Principal at Kinetica.
He has been working on the use of VCDs in tall reinforced structures with 3M and Nippon Steel and Sumikin engineering through the eight-year development and testing process at the University of Toronto and is now seeing this technology being deployed.
That testing regime included full-scale damper tests to validate the steel and viscoelastic technology, confirming the effectiveness and robustness of the damping. They indicated significant performance improvements over traditional structural setups for frequent wind and earthquake levels, as well as sterner tests of hurricane level winds and extreme earthquake scenarios.
“We have been working on these VCDs and making sure they are fully tested for many years now. The VCD modules are manufactured using standard Japanese SM490A structural steel which sandwich the 3M viscoelastic polymer. It is a super-durable material,” explains Montgomery.
“We found during testing that the damper performs better without any additional bonding layer added between the steel and the polymer. The steel bolts that provide the clamping force are standard Japanese produced A490 hexagonal steel bolts.”
Distribution and location of the dampers around the tower frame is dependent on the design by structural and seismic engineers. In areas of significant seismic activity not only can they reduce the level and ferocity of seismic vibration but also the amount of post-earthquake repair work.
“We found during testing that the damper performs better without any additional bonding layer added between the steel and the polymer”
If their capacity is designed to predefined loads the VCDs connecting elements act as ‘structural fuses’, preventing damage in adjacent structural elements. After an extreme earthquake, it is only necessary to inspect these fuses and replace or repair them if necessary.
The Kinetica, 3M and Nippon Steel and Sumikin Engineering VCDs have already been installed at prestigious developments in areas exposed to both high wind loads and seismic activity.
In Manila the Park Central Towers development features two towers 267m and 217m in height. They are located in a severe typhoon region and just a few kilometres from a major fault line. There are 32 VCDs in each tower reducing wind and seismic loading on each structure. And in Toronto the 62-storey Y+C Condominium development features 42 VCDs which have replaced steel coupling beams in the tower’s central section.
With the future of accommodation and office space in large cities increasingly looking to skyscrapers, the potential for this steel-built technology to improve safety and comfort while maximising floor space could prove invaluable.
Images: iStock, Kinetica