Balfour Beatty's extensive use of modular construction on the Madison skyscraper in London's Docklands has required a clever approach to access. Will Mann reports.
The Madison is one of the tallest buildings under construction in the UK at present. Balfour Beatty is building the 53-storey residential tower near Canary Wharf in London's Docklands, which will include 423 apartments plus leisure and business facilities.
Central to Balfour Beatty's approach is the modularisation of key components, including bathroom pods, unitised facade sections and services modules, which has led to "significant programme savings", according to project director Paul Smith. The wide use of offsite manufacturing has also required some clever access arrangements to lift the bulky and heavy products up the 187m-high structure.
Client LBS Properties
Main contractor Balfour Beatty
Structural engineer WSP
M&E engineer Hoare Lea
Cost consultant Core Five
Programme February 2017 to 2020
Balfour Beatty was awarded a £1m pre-construction services contract by client LBS Properties in January 2016 and the £150m main building contract followed in February 2017.
The project occupies a tight footprint with "ground conditions typical of a site near a river, with a high water table and a thick layer of made ground and alluvial deposits", says Smith.
The basement perimeter has been constructed using a cased secant pile wall, with 368 piles 900mm in diameter, driven to a typical length of 20m. Dividing walls were formed from 147 contiguous piles, 600mm in diameter. Beneath the tower itself and the basement raft slab, are a further 102 bearing piles, 900mm in diameter, with a typical length of 24m.
Logistics are challenging on the cramped site and during the basement construction Balfour created an access road to help vehicle movements. "We installed plunge columns to support a gantry slab, which provided vehicular access and separation from public traffic," explains Smith. "The gantry slab later formed part of the ground floor slab, and the plunge columns were removed."
The glass-clad tower, designed by Make Architects, is hexagonal on plan. "The structure is almost entirely in-situ concrete, although we are proposing to use a precast slab system to complete the lift shaft capping slabs," says Smith. "This design is currently in development."
The main staircase in the tower core was constructed using a Stair Master lightweight mould system. "It comprises a steel shell, which acts as permanent formwork with reinforcement already in place," explains Smith. "The stairs are completed with in-situ concrete. This system allows rapid installation of the stairs and limits the need for falsework in the landing areas."
The glazed facade is a unitised cladding system, comprising storey-height units repeated across each floor of the tower. Additional panels form the internal balconies and winter gardens.
"Typical units are 3.1m by 1m in dimension, and weigh 400kg, although larger panels - up to 8m across in some cases - are located at the ground floor level, amenity levels and between levels 15 and 17," explains Smith. "The cladding is being manufactured in China and the panels arrive around eight weeks from leaving the factory."
The bathroom pods represent one of the largest offsite packages. Originally the bathrooms were to be constructed in situ, and the switch required adjustments to the tower superstructure.
"Temporary openings in the shear walls were required to transport the pods to their final location on the floor slab," explains Smith. "These were filled in at a later stage. We identified the locations of these openings early in the project, in coordination with the access strategy."
The pods are constructed in Italy, complete with finishes, fixtures and fittings. "We have visited the factory regularly to ensure quality, with snagging undertaken before the pods leave the factory," says Smith. The pods are transported to site by lorry and given a further inspection on arrival, he says.
Typically, the pods' dimensions are 2.25m by 2.2m, weighing in at 1.8 tonnes. Larger, wheelchair-accessible pods - at least one is on each floor - are 2.75m by 2.75m across and weigh 2.8 tonnes. There are between six and 10 pods on each floor.
"The pods have a bespoke thin wall construction which has allowed them to be installed with minimal impact on the internal floor space," adds Smith.
Balfour also prefabricated elements of the building services. M&E modules, 2.4m long and almost 1m wide, and weighing 20kg, are being installed in the communal corridors. Within the apartments, the utility cupboards were redesigned to accommodate more prefabricated service modules.
"Pipework and ducting is fixed to suspended lightweight steel frames, allowing the modules to be lifted into position quickly and easily," says Smith.
Access has been a key consideration from the outset. During construction of the basement and ground floor, the site had two tower cranes in openings in the ground floor level. On completion of the ground floor, one crane was removed but the hole in the slab retained to allow delivery of the large M&E components.
The cranes were supplemented by a common user tower, Colossus hoist and twin passenger and goods hoists, supplied by Brogan Group. The Colossus, the largest of its kind in the market, is 5m by 3m in area and 3.1m high, with a capacity of 4,000kg. Importantly, it is big enough for the pods and the facade sections.
With little storage space on site, on delivery these units are transported straight to the floor slabs via the Colossus. "An online delivery booking system is in place so lorries do not have to wait on the roadside," says Smith.
The size of the facade units caused lifting challenges. "This has meant use of a tower crane and a bespoke counterbalance lifting frame, to install the units below the frame contractor's protection screens," Smith explains, adding that some complex lifts have required out-of-hours delivery due to wide load restrictions in the local borough.
Meanwhile, the two passenger hoists and the common tower allow access to upper floors, so the core stairs can be closed if needed. "This minimises the impact on the facade installation, and therefore apartment fit out, as multiple hoists provide access to the floor slabs," says Smith. "Small-time gains add up when fitting out over 450 apartments."
Construction work on the Madison is due for completion in 2020.
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