AUTONOMOUSTHE FULTON CENTER SYSTEMS WEALTH CREATION

A $1.4 billion project that created a new transit hub and improved links to six subway stations in Lower Manhattan was completed last year. The engineer and freelance writer Hugh Ferguson talked to Craig Covil, Principal of Arup and New York Project Director, to find out the main challenges and how they were overcome.

The Fulton Center is a $1.4 billion subway changing platforms had to use cramped glass pavilion, surrounding a giant eight- interchange in New York, that improves passages, or rise to ground level and cross storey dome structure capped with a connections between six subway stations in busy streets. Peak hour ‘dwell times’ for 53ft-diameter oculus, inclined to draw the Lower Manhattan and has regenerated an trains had become unacceptably high, maximum amount of sunlight down area badly affected by the 9/11 attack in reducing train frequency and increasing through the building to the lowest 2001 and the economic crisis of 2008. With congestion still further, and the system- subterranean level. It is lined with a large- Arup as lead consultant, the project wide knock-on effects could affect services scale installation, the Sky Reflector-Net, The northwest corner of the Fulton Center, showing the dome and the oculus rising above the steel and glass pavilion. At the rear is combined a wide range of engineering skills, all day. which involved a detailed collaboration the west end of the Corbin Building projecting on to Broadway, with the eight-storey ‘interstitial’ building in between © James Ewing from modelling pedestrian movements to A key to the solution was a new central between engineering, art and architecture. underground work in difficult ground and interchange building, the Fulton Center, on However, it was underground that the managing the project through a succession a site facing Broadway, through which most real engineering challenges lay. Some 30 m of stops and starts caused by uncertain of the 300,000 passengers using the below ground was sound bedrock, too deep funding. The Fulton Center opened in stations each day could be routed. This and too difficult to reach by piling. Near the November 2014, and was announced in facility was designed in conjunction with surface was a typical mixture of urban fill. In October 2015 as the winner of this year’s three architects: UK firm Grimshaw between, where almost all the work was to British Construction Industry International Architects; the preservation architect Page take place, was a treacherous mixture of Award. Cowley; and, HDR/Daniel Frankfurt. The sands and silts including Manhattan’s THE FULTON The principal purpose of the Fulton Center was required to be much more than notorious ‘Bull’s Liver’ soil, a vibration- Center project was to join up six stations on a functional transport interchange with sensitive stratified silt and fine sand. This is 11 separate lines that were expressly built by retail space above. New York needed an prone to consolidation, causing settlement competing private railway companies (1902– exciting, welcoming gateway building to under construction vibrations, and rapidly 1933) so that they would not join up. Lower Manhattan that would symbolise loses strength when disturbed or wetted: in Constructed in the early 20th century, the and catalyse the area’s regeneration. The its saturated state, it can quake like jelly CENTER, NYC entrances were narrow; passengers result is a simple three-storey steel and when shaken, and even flow like a liquid.

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testing and analysis, and combined this with excavated beneath the station, and the PROJECT PLAN its knowledge of the behaviour of cast-iron exposed mini-piles replaced with CLASSIC BUILDING RESCUED A lot of the construction work for the project Along the south side of the Fulton Center linings of a similar vintage in London tube permanent columns. Meanwhile train ran the risk of disturbing the existing tunnels stands the Corbin Building, which was tunnels. This was done to assess the ductility speeds on the Subway were restricted, to and stations, most of which had been scheduled for demolition at the start of the of the iron and the structural integrity of the reduce vibration but also to reduce the constructed by ‘cut-and-cover’ and all of project. The narrow eight-storey building, large horizontal forces caused by sharp which were ‘floating’ in the sands and silts, tunnels and, in particular, to determine the braking. wedge-shaped in plan built in the 1880s including the Bull’s Liver. At the start of the maximum deflection that could be tolerated It was early in one of these weekend was dull grey from a century and more of project, temporary station closures had been in the lining: fortunately, the iron proved less possessions that a serious loss of ground grime, its distinctive pepper-pot roofs long planned, but this was ruled out because of brittle than anticipated. was detected around one of the mini-piles gone and its façade littered with iron fire the transport disruption it would have Here, as elsewhere on the project, as it was being placed – so serious that the escapes and with air conditioning units caused. So, all the work had to be carried out potential movement was modelled and parts subway operator had to be informed that hanging from windows. The architect was around a live railway operating 24 hours a of the stations and tunnels were fitted with the work would not be complete for hand- Francis Hatch Kimball, described by day, with 300,000 passengers passing deflection monitoring equipment. Sometimes over and train operations at 5.00 am the contemporaries as ‘the father of the through each day, and with just occasional and in some places, the tunnel tubes were following Monday. Resources were brought skyscraper’. Although modest by modern weekend closures. tending to sink, at other times to float in from other sites and by concerted standards, at the time of its construction in On top of this, the team had very little How the new Fulton Center interconnects six subway stations on 11 lines. Running north-south is the upwards. Phasing of the work proved critical, oldest and busiest route, the 4 and 5 Lines, built in 1902, which separates the new Dey Street concourse efforts, the hand-over was only delayed by 1888-9 this was (briefly) Manhattan’s tallest space at ground level beyond the confines from the new Transit Center building with the Corbin Building in front. Running east-west is the newest not just to control deflection in the tunnel, half an hour, the biggest impact of any building. Kimball was a pioneer in the use of of the Fulton Center site itself, and no full and deepest, the A and C Lines constructed as cast iron tubes in 1933, with a large cut-and-cover but to cope at all times with pedestrians mezzanine above © Arup event during the project. ironwork and terracotta, both materials street closures were permitted. using the stations and mezzanine, and traffic The first challenge was the station with using Fulton Street overhead. the A and C tube lines beneath Fulton Street The new Fulton Center ‘floats’ on a which had been constructed in the 1930s in concrete box, built with secant (interlocking) an unusual way. First, the two running pile walls and a 1.7 m-thick raft laid directly tunnels had been driven, under compressed on the carefully prepared sands and silts. The air just below the ground water level, and walls were propped temporarily by heavy lined with cast-iron segments; then the steel struts and permanently by the space between had been opened up to diaphragm effect of the Fulton Centre’s form the platforms; and finally a long concrete floors. A similar technique was used mezzanine area had been built over the top for creating the new, wide passenger by cut-and-cover, for pedestrian ramps and concourse underneath Dey Street – see corridors. The mezzanine needed to be subway schematic. rebuilt to accommodate new lifts and The trickiest part was connecting the two, escalators, with an original line of columns by opening up the area under the 4/5 Line down the centre removed and a new steel station as a passage. First, some 120 steel A-frame roof installed to transfer loads to the mini-piles up to 30 m long were sunk to side columns. support the old station box, which was just The greatest concern was the effect all resting on the ground with shallow this work and the change of loading would insubstantial foundations. Most of the new have on the running tunnels beneath: if the mini-piles were sunk between the tracks cast-iron lining cracked, water would come during weekend possessions. Jet-grouting A 3D CAD/ BIM model used by different construction disciplines to look at the mechanical, electrical, in and the tunnel could flood. Arup used the structural, civil and plumbing elements of the Center. The model was uploaded into Bentley augmented was used to create two cut-off walls directly old as-built records, as well as taking cores of reality software and then used by engineers onsite with iPads to compare site conditions with ‘as-built under the station, forming the side walls of Looking across Broadway at the narrow west elevation of the Corbin Building, and the dome with its design records’ © Arup inclined oculus and skylight under construction to the north © Arup the original cast-iron lining for laboratory the new passageway. Then the soil could be

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Throughout the critical underground operations, the building was fitted with deflection monitoring equipment, the readings linked via software to hand-held devices so that MASSMOTION The Arup software MassMotion, though including doors, stairs and passageways. engineers on site could get instant warning of any untoward borrowing existing 3D models, has The agents themselves will then decide their movement, with a 6 mm shift sufficient to trigger an alarm. developed a completely new set of tools most appropriate routes across the based on individual, virtual ‘agents’ in order environment between the various origins to represent and understand people and destinations, their decisions based not movement. These agents could be just on distance, congestion and vertical programmed to mimic human behaviour, for movement but also on each agent’s example pausing at a café for a cup of coffee individual personality profile. Some agents further. Both were addressed by tying the sections of the perimeter of the or stopping at a travel information board, will walk slowly and always wait to queue for had to be tested, including contingency structure into the Fulton Center and dome underpinning zone had first to be stabilised passing through a turnstile or going up an the escalators; others will take the stairs at plans for each. If, for example, during a phase to the north via an ‘interstitial’ building - a by a system of contiguous jet-grouting. Then escalator, based on destination preferences. the first sign of congestion – and everything of construction, certain exits were closed and new eight-storey steel frame against the the remaining sections under the walls were They make their own choices about in between. passageways restricted in width, could ‘blind’ north wall of the Corbin Building, underpinned with mass concrete, using the appropriate actions based on the dynamics Agent profiles were based on existing people still be safely evacuated from the housing the new services and lifts. traditional method of hand-digging and of their environment. The agents were data on pedestrian behaviour, combined platforms in an emergency? Arup could find But this only partly solved the structural filling a series of narrow shafts no more than assigned attributes based on field surveys: for with real counts of passengers at the existing no software that would do the job problem. Analysis showed that the many 900 mm wide, a task which in itself took example, the ratio of men to women (who, stations. For calibration, the model was first adequately, and so designed their own – see new openings in the north wall created more than a year. on average, walk at a slightly shorter step applied to the existing layout, and the Mass Motion. stress concentrations in the masonry walls, Then the soils beneath the Corbin and slower pace than men), and whether weighting factors were tweaked to get a The model not only provided graphical particularly just above street level. The Building could be removed to create the they are commuters (who know where they better fit with survey results, and a 20% representation of where, for example, pinch solution was to encase the walls between escalator pit. The problem here, was are going) or tourists (who are not so sure). increase was factored in to represent growth points were causing congestion, but also level 2 and street level in a 100 mm-thick transferring the large below-ground Information from the architectural design during the construction period. allowed the design team to observe the real- shotcrete layer on each face, heavily horizontal loads between the retaining wall was used to develop a virtual environment Since the Fulton Center, MassMotion has time behaviour in realistic 3D as the agents reinforced to provide ductility and anchored to the south and the new floors of the based on a set of polygon mesh objects that been further developed by Arup’s software passed through the Center, replicating the to the masonry by resin-dowelling several Fulton Center. The solution involved a represent the walkable areas and house Oasys for a variety of other random and chaotic behaviour of humans thousand L-shaped reinforcing bars. massive ring beam within Corbin’s escalator obstructions within them. The walkable areas applications including mass evacuation of better than previous systems were able to Also it was difficult to provide lateral wellway. are then further broken down into circulation buildings, managing major venues and do. Movements were tracked of more than stability for the upper stories, since the Throughout these critical underground spaces, such as rooms, pavements or designing buildings, sports stadia and retail 48,000 people passing through the Center at platforms and connection elements, spaces. A jet-grouting rig stabilising the moving ground Fulton Center itself had limited stiffness operations, the building was fitted with any one moment. Now, designers were able beneath the ‘blind’ north wall of the Corbin above level 3. The remedy was to introduce deflection monitoring equipment, the to see how people would use their facility Building (on the right), to allow excavation to a concrete moment-frame into the upper readings linked via software to hand-held before it was actually built. proceed below the building’s foundations © Arup levels, near the narrow western end of the devices so that engineers on site could get The model proved invaluable in planning building, to transfer the lateral loads down instant warning of any untoward movement, the complex construction phasing of the used structurally and ornamentally, in the building. with a 6 mm shift sufficient to trigger an project. After opening the Center, the most realising his often extravagant designs. However the most challenging aspect of alarm. Total vertical movement of the south noticeable discrepancy between the model Research revealed a historical gem, and the the whole renovation was the work below wall was a little over 50 mm, and half that for and reality was caused by an unpredicted building has been painstakingly restored ground, which included sinking a new the north wall. change in land use of the area from offices and integrated into the Center – a task escalator shaft running along much of the towards housing: a higher proportion of local requiring the skills of the engineers as much length of the narrow building, from ground residents compared with incoming as the conservation architects. level to the lowest level of the new Center PEOPLE MOVEMENT commuters meant, in particular, that more Planning the movement of people through Two problems for the conversion both some 12 m below – and 6 m below the ticket machines were needed. Nevertheless the Fulton Center, with its network of stemmed from the narrowness of the Corbin building’s existing foundations – the modelling helped the project succeed in passages, stairs, escalators and lifts, was building: how to provide lateral stability, through notoriously difficult ground. greatly reducing congestion points: the particularly challenging. It was not just a particularly to satisfy earthquake and wind- This presented a challenge to support station ‘dwell times’ for trains on the busy 4/5 question of predicting movements after loading codes not mandated in the 19th the eight-storey building during and after Line were reduced down to about 20 opening day, passengers also had to be century; and how to include building construction, and required the whole of the Fulton Center – looking south. Analysing pedestrian movement in Lower Manhattan. The Center is seen seconds in peak times – to the delight of the accommodated throughout the 10-year services, including lifts and fire-escape stairs, building to be underpinned. To counteract in pale green-blue with the World Trade Center site to the right of the image. The green, blue and yellow Subway’s operator. construction, so hundreds of combinations blocks represent subway trains stopped at the station © Arup without reducing the usable floor space still potential issues with the liquefiable soils,

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to identify which were really ‘requirements’ Then, in November the project received its LESSONS LEARNED and which were just ‘desirements’”. Frequent 20th award to date – a winner at the World A key lesson from the project was that, for all funding delays, including a six-month shut- Architecture Festival in Singapore. the technical challenges that were identified down in 2005, required regular rescheduling. and resolved, the most difficult task of all on When Arup was appointed in 2003, a major project such as the Fulton Center completion of the project was targeted for was negotiating the mix of political, 2009. The project was repackaged in 2007 administrative and financial obstacles. BIOGRAPHY with a revised opening date for the end of Craig Covil is an engineer and Principal Funding was drawn from federal, state and 2014, which was met. of Arup based in the firm’s New York city funds, each with its own political The newly renovated Fulton Center now office. He obtained a BSc Eng Hons agendas and different political tenures. processes 300,000 daily passengers from the University of Surrey and an Not only the client – MTA Capital between 11 train lines. The improved Center MSc from Imperial College London. He Construction – but other bodies including not only simplifies transit connections, but worked on the Fulton Center from its the operator (New York City Transit) and the provides 65,000 square feet of retail and start in 2003, and was Project Director Federal Transit Administration had to be office space. Its design and engineering from 2008. Craig led a multidisciplinary satisfied. Differing requirements by different achievements have been recognised team of engineers, architects, planners bodies required complex design code worldwide and in October 2015 the British and scientists in the delivery of this reconciliation. As Craig Covil, the Project Construction Industry awarded the Fulton mega-project. Dorector, says: “Sometimes it was necessary Center project its International Award.

SKY REFLECTOR-NET As a result of a public art competition, US structure was sufficiently flexible, and light artist and designer John Carpenter checking that its movement would be was appointed as a collaborative artist for contained within prescribed limits. A key to an unusual art installation: an the former was the design of the cruciform interdependent reflective lining, offset from connectors, to ensure that any movements the interior of the Fulton Center’s dome, to did not transfer forces into the delicate direct sunlight down from the sloping, aluminium infill panels. This was achieved circular oculus at the top. The final design by providing a single, fixed connection at involved a steel cable-net structure the top of each panel, and oversized holes supporting nearly 1,000 coated aluminium at the sides and bottom to allow for the infill panels using flexible, universal node maximum amount of movement as well as connection assemblies. for construction tolerances. The cable net is suspended from 56 A full-scale mock-up of 13 panels was connection points round the compression built to test the system’s performance and ring of the oculus, and anchored to beams to validate the construction procedure. The at the bottom. The 3.2 mm-thick aluminium complete net was fabricated and panels are heavily perforated, not just to assembled, together with all the node reduce weight but also to permit interior connectors, in a town in Massachusetts, air currents to pass through and to control test-lifted by a crane in a field outside the the quantity of light reflected. They are assembly facility, and then rolled up and linked by cruciform connectors attached to delivered to the Fulton Center. There it was each corner and fixed to the cable’s nodes hoisted up and fixed to the oculus, and the by swaging – cold-forming to provide a infill panels inserted via suspended The new Fulton Center features open direct paths, firm connection. platforms and ‘cherry pickers’ over a period widened corridors, and new mezzanines to separate entering, exiting, and transferring customers. The artwork was visualised as a dynamic of about three weeks: a time-lapse video of The Sky Reflector-Net helps to draw light down structure, able to respond to forces varying the assembly can be seen at from the inclined circular oculus deep into the subterranean levels of the Center, greatly reducing over time. This meant ensuring that the tinyurl.com/nt4hgvy the costs of artificial lighting © James Ewing

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