New lift technologies could transform the design of tall and super tall buildings.
Skyscrapers became a reality only after American inventor Elisha Otis invented the “safety elevator” in 1852. Since then every tall building ever constructed included a cluster of vertical shafts, each one containing a single counterbalanced car suspended from steel cables and powered by an electric motor. Super tall buildings more than 300m tall, however, are pushing this basic technology to its limits - and beyond.
Lift manufacturers have responded by switching from steel to Kevlar cables, by developing double-decker cars, and by pushing lift speeds up towards 18m/sec. A successful strategy was the “Skylobby” transfer stop concept, where high speed lifts stop only every 50m to 100m, leaving passengers to transfer to other lifts that serve only the intermediate floors.
This minimises the floor area taken up by the lift shafts. Even so, on some buildings this can be as high as 40%, with all the obvious commercial implications. As buildings top 500m, the sheer number of lifts verges on the absurd – the 632m Shanghai Tower, for example, will contain no fewer than 126 lifts, 20 of them double-deckers, when completed later this year, with 40 individual lift shafts at ground floor level.
“Another problem is the spread of mixed use buildings,” said WilkinsonEyre Architects director Chris Wilkinson. ”Office workers, hotel guests and permanent residents have very different patterns of vertical movement, and it’s hard to reconcile the conflicting demands.”
At least two alternative approaches are now on the horizon. Both promise to liberate building designers from the constraints of the conventional technology, allowing structural engineers and architects to create dramatically different structures that will be practical and cost effective even when they reach beyond the 1,000m milestone.
From Germany comes ThyssenKrupp’s MULTI system, with prototypes due to begin trials in a new record-breaking test tower next year (see box). Swedish multi-disciplinary consultancy Tyréns is also promoting its “articulated funiculator” solution for deep underground stations as well as for buildings up to 1,000m tall.
Both options bear more than a passing resemblance to the old paternoster lift concept (see box), now largely abandoned on safety grounds. Both feature cars running in twin shafts, both offer the option of combining vertical, horizontal or even diagonal movement - and both normally use the Skylobby system. There are key differences, however.
ThyssenKrupp arrived at its MULTI concept via its TWIN alternative, launched more than 10 years ago. TWIN features two cars in the same shaft moving semi-independently, although one car is unable to overtake the other. Some complex cabling is involved along with sophisticated control systems. MULTI, however, is a major conceptual leap.
Popular from the late 19th century until the middle of the 20th, paternoster lifts featured a chain of open fronted cars moving continuously through two parallel vertical shafts.
As each car reached the top of the up shaft it swung over into the down shaft while retaining its original orientation. The first true paternoster lift was installed in Liverpool in 1868.
Passengers, usually a maximum of two per car, were supposed to jump on and off at their preferred floors. Although the vertical speed was only around 0.3m/sec, actual passenger moving capacity was significantly higher than conventional elevators, which contributed to their popularity.
However, they were inaccessible to the elderly, the infirm and the disabled, so in the UK they were most commonly found in further education buildings. It became something of a rite of passage for daredevil students to ride the cars through a complete cycle, although in 1989 a student attempting such a feat in Newcastle University’s Claremount Tower became caught in the drive chain and had to be rescued.
Safety concerns after a number of accidents, at least one fatal, led to the gradual replacement of paternosters with conventional lifts. Some still remain: the tallest in the UK, with 38 cars, is in the Arts Tower at the University of Sheffield, although the 78m tall building also contains two conventional lifts.
Gone are the cables and counterweights, gone are the traditional electric motors on top of the shafts. Instead, each car has its own linear induction motor and is fabricated from high strength carbon composites. ThyssenKrupp claims significant weight and space savings, with each car weighing in at 50kg instead of the normal 300kg, and requiring only 6m2 of shaft rather than the normal 9m2.
Without the restrictions of cables multiple cars can operate in the same shaft, moving almost independently in response to passenger demand. Horizontal or diagonal transits are no more taxing than the traditional vertical movement. With cars travelling at 5m/sec and a Skylobby transfer stop every 50m, passengers should have access to a car every 15 to 30 seconds, significantly reducing waiting times.
According to the manufacturer, the MULTI system can reduce “elevator footprint” by up to 50% in buildings above 300m. This implies either a significant increase in usable floor area for a given size of building - or a slimmer building for the same area, with lower façade and associated costs.
Similar claims are made for the articulated funiculator system, although this is cable-based. In its simplest form, trains of up to four “pods” circulate through two shafts, stopping only at Skylobby transfer stations, usually at least 100m apart. These can be either vertical or horizontal stations, as both horizontal and diagonal motions are possible.
Indeed, Tyréns makes much of the potential for “dynamic architecture”, where trains of panoramic pods spiral and twist around a super-tall building’s outer skin - these are said to have three degrees of freedom. Currently, the first project likely to feature the technology is the Nacka extension of the Stockholm subway, where the new stations will be 100m below ground in hard granite rock.
A conventional access solution would require 10 lift shafts to be blasted through the granite. An articulated funiculator solution would require only four, according to Tyréns.
Many tall buildings rely on the central service core for lateral stability, so slimming it down significantly might seem to be less desirable than at first sight. However, Wilkinson points out that for very tall buildings the contribution of the core to lateral stability is much less significant and other structural forms have to be adopted.
He adds: “These new technologies could have enormous potential and really liberate the designer. We’re currently looking at a TWIN installation in a tall building to minimise the number of elevators we need, and will certainly look closely at MULTI when it finally becomes available.”
Developing the MULTI system
First prototypes of the MULTI system will be installed in ThyssenKrupp’s new £29M, 244m tall test tower, currently under construction in Rottweil, Germany.
Main contractor Züblin is aiming to top out the tower in summer this year, a target which implies the reinforced concrete structure gaining height at around 3.6m a day - “three times faster than a bamboo plant’, according to ThyssenKrupp. Actual prototype testing is scheduled to begin next year, once the distinctive translucent polytetrafluoroethylene (PTFE) cladding is installed.
Supporting the tower is a 2m thick slab foundation 32m below original ground level.
There will be 28 floor levels above ground within the tower, and 11 lift shafts. Of these, two, the lift that will take tourists up to the viewing platform at the 232m level and the firefighters’ lift, will use conventional technology.
The remaining nine will be devoted to product development work, with the MULTI system on trial in three.
Three basement levels will contain dampers, energy recovery systems and safety equipment. Full height shafts will be used to test high speed lifts capable of topping 18m/sec. Also under investigation will be the next generation of double-decker lifts.
Once complete, the Rottweil tower will be significantly taller than the current world record holder for test towers, the 173m tall Solae tower in Inazawa City, Japan, owned by Mitsubishi Electric. Its viewing platform will be the highest in Germany.