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P R O J E C T
P R O F I L E
P R O J E C T
P R O F I L E
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All advice or information from the Br itish Cement Association is intended for those who will evaluate the significance and limitation of its contents and take responsibilityfor its use and application. No liability (including that for negligence) for any loss resulting from such advice or information is accepted. Readers should note that all BCA
publications are subject to revision from time to time and should therefore ensure that they are in possession of the latest version.
97.324
First published 1992
ISBN 0 7210 1444 5
Price Group C
British Cement Association 1992
Published by the British Cement Association on behalf of
the industry sponsors of the Reinforced Concrete Council.
British Cement Association
Telford Avenue, Crowthorne, Berkshire RG11 6YS
Telephone (0344) 762676
Fax (0344) 761214
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P R O J E C T P R O F I L E
2
Merchant House and Woodchester House are
two office buildings that form a significant part of
the City Harbour development in the heart of
Londons Docklands.The site adjoins the east side of Millwall Docks
and is at the centre of an expanding communications
network - only minutes from City Airport and
immediately adjacent to Crossharbour Station on the
Docklands Light Railway.
The scheme for the five-acre development
includes three major office buildings (totalling some
240 000 ft2), individual office units, a luxury hotel, a
multi-storey car park and other ancillary buildings.
The architecture and planning take full advantage of
the sites extensive dockside frontage, creating a
modern working environment with attractive views.
Merchant House and Woodchester House overlook
the water and border a tree-lined piazza called
Watermans Square.
The development of City Harbour was divided
into five phases, the first of which consisted of
Merchant House and the smaller Woodchester
House. For these two buildings, the development
team chose precast concrete frames. Neither
structural steel nor in-situ concrete frames could
meet the exacting lead-in time and erection
programme requirements; neither could theyprovide the economy and quality of precast concrete.
THE PROJECT
The City Harbour development is on the former Olsen 3 site
of Milwall Docks
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Description
Merchant House and Woodchester House offer
high-quality office accommodation in a central
London location, but with much lower occupancy
costs than those in the City. Their design offers the
flexibility for changing the layout to accommodate a
wide range of future uses.
Each building may be used as a self-contained
office headquarters, with its own entrance, servicing
and car parking, or may be sub-divided into separate
tenancies. The two buildings incorporate varied
floor plans, with balconies and terraces that form a
distinctive stepped profile and provide unobstructed
views across the water.
The buildings have the following principalfeatures:
Eight levels of office accommodation in MerchantHouse and six in Woodchester House.
Ground floor reception lobbies with high-speedautomatic passenger lifts to all floors.
Flexibility for open-plan or cellular office layouton a 1.5m grid.
Raised access floors for electrical and communi-cations installations.
Fully accessible suspended ceilings allowingpartition-head fixings on a 1.5 m module.
Knock-out panels in floors for additional verticalservices distribution.
Fixed sealed double glazing with tinted solar-control glass.
Full air conditioning. Terraces, conservatories and balconies. Dedicated parking with additional visitor spaces in
Watermans Square.
BUILDING SPECIFICATION
P R O J E C T P R O F I L E
The distinctive dockside elevations
Office adjoining one of the terraces
Conservatory office
Terraces on Woodchester House
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P R O J E C T P R O F I L E
4
Space provisions
The net floor area of Merchant House is 55 000 ft2,
with typically 7000 ft2 per floor from ground to fifth
floor levels, and 6000 ft2 and 5000 ft2 respectively at
sixth and seventh floor levels. Woodchester House
has a net floor area of 37 000 ft2, typically 7000 ft2 perfloor; but reducing at the third, fourth and fifth floor
levels. Because of the high water table, the buildings
have no basements.
The internal clear height, from finished floor
level to underside of ceiling, is 2.6 m for all office
areas. A 700 mm deep ceiling void and 150 mm deep
floor void are provided for installing services.
Structure
The superstructures consist of precast reinforced
concrete columns, shear walls, beams and stairs, andprecast prestressed hollow-core floor units. The
precast frames are based on 6.0 x 6.0 and 6.0 x 7.5 m
grids, and are supported on piled foundations.
The floors were designed to carry an imposed
load of 5.0 kN/m2 (including 1.0 kN/m2 allowance
for partitions) plus 0.4 kN/m2 for services.
Cladding
The aluminium cladding system is based on
top-quality products and workmanship, and the
elevations feature dark grey glazing units usedfull-height or within colour-coated panels.
Services
The buildings have full variable air volume (VAV) air
conditioning, with individually controlled terminal
boxes in each structural bay, at all levels, to provide
an efficient and highly flexible system.
Precast concrete frames were specified for both buildings
Details of the curtain wall cladding
Typical office floor section
showing precast concrete frame
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P R O J E C T P R O F I L E
5
Facilities for power, telecommunications and data
wiring are provided within the 150 mm raised floor.
The ceilings have integral light fittings and the lighting
zones can be rearranged to suit future requirements.
Each floor is served by ten-person automatic lifts,
and additional lifts, also serving as firemens lifts,adjoin the goods entrances.
The east
elevations
The dockside setting of the two buildings
Architecture
The site encompasses a landscaped setting on the
former Olsen 3 site, to the east of Millwall Docks on
the Isle of Dogs. The City Harbour masterplan
integrates three separate self-contained headquarters-
style office buildings, seven smaller terraced frontdoor office units, a major hotel, a multi-storey car
park, a health centre, restaurant, and wine bar.
Merchant House and Woodchester House occupy
the east and north sides of Watermans Square - a
paved and tree-planted piazza. The elevations take
full advantage of the sites extensive dockside
frontage to make a strong visual impact.
The exteriors are clad with a high-quality
colour-coated aluminium curtain wall system, the
solid panels having outer panels that act as a
secondary rain screen to the fully weatherproofed
inner system.
In addition to its attractive appearance, the
curtain wall system allows for future refurbishment
or alterations without disturbing the integrity of the
inner system. At ground level the outer cosmetic
panels are a slate-stone-composite material that
provides a more robust and vandal-resistant surface.
Tinted solar-control double glazing complements
and mirrors the surrounding waterside. Plant con-
tainers on terraces and balconies provide visual relief.
DESIGN
Watermans Square
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P R O J E C T P R O F I L E
6
The internal lighting, fittings and finishes in the
offices are all of the highest standard. The interior
design fully anticipated that occupiers would require
flexible internal layouts, and the scheme benefited from
a full space-planning exercise at its conceptual stage.
Structure
A number of different frame designs were considered
and reviewed to determine which would best suit
the project requirements. Least cost and minimum
time were paramount. Flexibility, quality and ease of
erection were also crucial.
Only precast concrete could meet all these
criteria. It was found to be cheaper and quicker to
erect than either steelwork or in-situ concrete
frames, and it beat steelwork on lead-in time.
The use of precast, prestressed concrete floorunits obviated the need for transverse internal floor
beams and kept the floor plate thickness to a
minimum. This in turn generated the maximum
depth of ceiling void. The flat soffits of the floor
units, and the clear longitudinal runs, made it easier
to install services. They also allow for future
alterations to services and office layouts.
The floor units in Merchant House were 150 mm
and 200 mm thick, and 200 mm thick units were
used in Woodchester House. Small service
penetrations were formed in situ through the voids
of the hollow-core floor units. Major penetrationswere preformed within the floor layout, and
knock-out panels are provided to allow for possible
future modification of the services.
The precast reinforced concrete internal spine
beams were restricted to 500 mm deep overall to suit
the distribution of services. The precast spandrel
beams are generally 900 mm deep, with a downstand
providing a fire break in the ceiling void below, so no
time-consuming blockwork was needed. Upstands
for roof balcony and terrace details are provided by
1350 mm deep spandrel beams.The versatility of precast concrete easily enabled
the stepped profile, irregnlar-shaped terraces, and
curved balconies to be produced. A late change in the
location of the lifts was also easily accommodated.
The components are durable and quality assured,
and have immediate structural loading capacity. They
also have in-built fire resistance, both in service and
during construction.
The in-situ concrete slab at ground level is
supported by precast concrete beams resting on the
pile caps.
Lateral stability is provided by a minimum number
of precast concrete shear walls located around the stair
The simplicity of the precast concrete frames
Floor units span onto l ongitudinal beams
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wells and lift cores. Thus the structure behaves as a
braced frame, which permitted economy of
column design. As the building was over five storeys
high, full provision against progressive collapse was
provided by simple horizontal and vertical ties.
The design of the precast columns took fulladvantage of high-strength concrete and the quality
control available under factory conditions. The use
of grade 50 concrete resulted in 450 mm square
internal columns at the ground floor of Merchant
House. The column sections were cast up to
11.4 m long to support three storeys, with cast-in
rectangular hollow section billets to carry the shear
forces from the beams.
The precast concrete stair units, with cantilevered
half-landings, are supported by precast mid-storey
beams and floor landings.
Generally the connections were made, and the
ties installed, by stitching-in with in-situ concrete.
Channel and other fixings, as required for the
following trades, were cast into the precast units to
speed construction on site.
The detailed design, manufacture and erection
of the precast frames were carried out by the
manufacturer. This single-point responsibility was seen
as another benefit of precast concrete construction.
Services
The services were designed for an office occupancy
level of 10 m2 per person with a fresh air supply of
12 litres per person per second and an interual tem-
perature of 21C 2C with 30 to 70% r.h.
The warm air supply of the air conditioning serves
the perimeter wall panels and is controlled from the
rooftop plant room. Each panel is individually isolated
and the system is zoned, with thermostatically
controlled circuits.
The principal feature of the heating system is that
the cold radiation and downdraught effects of the
glazing are offset by the strategically placed heating
panels in the flush under-sill panels. This arrangementensures that the heaters do not encroach upon usable
floor or wall space.
The gas boilers and all other major plant are
contained within plant rooms and screened
compounds at roof level.
The lighting level was set at 500 lux average and
was achieved using continuous twin tube low-glare
recessed luminaires which incorporated return air
slots. On-floor power requirements were assessed at
25 w/m2 with outlets provided in the raised floor.
Other services included hot and cold water, lifts,sanitation, drainage, fire alarms, and facilities for
telecommunications and data wiring.
P R O J E C T P R O F I L E
7
Precast walls for the lift shafts
and stairs act as shear walls
The pland room -
Woodchester House
Precast column units are up to 11.4 m long
Flush under-sill heating
panels in office areas
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P R O J E C T P R O F I L E
8
General
A straightforward approach to construction was
adopted, and met the principal requirements of cost
and speed.
The buildings are founded on a combination of
driven and bored piles. The precast frame proceeded
quickly, with a floor being completed every two
weeks, on average.
No fire protection, either in the form of sprays or
boards, was required. No scaffolding was needed for
the cladding, and access on foot was gained via the
precast stairs. No drying-out period was necessary
which, together with minimal propping requirements,
gave following trades rapid and clear access.
Substructures
Generally, the driven piles have a nominal diameter of
400 mm and a safe working load of 110 tonnes, but
vibration during construction close to the existing dock
wall and sewers was identified as a potential problem.
Therefore, bored continuous-flight-augured piles
(CFA), with a nominal diameter of 600 mm and a
safe working load of 90 tonnes, were used within a
distance of 24 m from the existing dock wall and
within 10 m of the main sewers. Ground vibrations
were monitored for both forms of piling.
Where necessary, the pile caps were restrained
laterally by the precast concrete ground beams.
Holding-down bolts for the first section of the precast
concrete columns were cast direcdy into the pile caps.
Superstructures
Delivery of the frame components was carefully
scheduled so that they could be lifted directly from
the delivery vehicles and placed into position using a
rail-mounted tower crane. This had the capacity to
lift the heaviest component, which weighed 6.2
tonnes, and was supplemented by mobile cranes asrequired. Erection of the frame was unaffected by
weather, and the required storage area was minimal.
The columns were usually erected in three-storey
lifts and temporarily propped. They have bolted steel
base plates and the splice joints were formed with
loose continuity reinforcing bars inserted in
preformed ducts in the ends of the units. When the
units had been lined and levelled, the voids were
filled by pressure grouting.
The main precast concrete beams were securely
seated on projecting RHS steel billets cast into the
columns, and the tops of the beams were fixed in
position by an angle cleat. Generally the beams sitThe first lift of columns
for Merchant House
Column base detail
CFA piling in progressCONSTRUCTION
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P R O J E C T P R O F I L E
9
between columns with a nominal 10 mm gap left at
each end to allow for production and erection
tolerances. The gap was pointed with cement mortar
to enable the remaining void around the billet and
seating cleat to be enveloped in poured grout.
Curved edge-beams were temporarily propped untilthe floor was completed.
The prestressed concrete floor units span from
edge spandrel beams to internal spine beams. They are
seated on wide nibs which are an integral part of the
precast beams. These nibs not only provide ample
bearing for the floor units, but also allow space at the
ends of the units for the longitudinal ties. These consist
of unstressed 12.7 mm prestressing strands anchored
by right angle returns at each end of the building.
Transverse ties were formed by loose
reinforcement placed and concreted into open
hollow cores, and hooked over reinforcement leftprojecting from the top of the precast beams. The
floor units were delivered with the concrete above
every third core already removed at each end. Similar
details were used at the sides of the floor.
The joints between prestressed concrete floor
units, and the stitching between floor units and
beams, were completed using a grade 40 concrete
with 75 mm slump and 10 mm aggregate. This
ensured the diaphragm action of the floor against
lateral loads. No formwork was necessary as the
precast units completely surrounded the voids. The
plant room floor units have a 100 mm thick30 N/mm2 structural concrete topping to carry an
additional imposed load.
The precast concrete shear walls were inter-
connected by vertical lacing bars threaded through
the projecting link reinforcement allowing the joint
to be finished with 40 N/mm2 in-situ concrete.
The stair units were lifted into position on to
simple halvingjoints at floor level, and on to
dowelled bearings at mid-storey height. Flights were
precast to finished floor levels, but landings were
screeded. The cantilever semicircular half landings
were tied with steel channels that also provide lateralsupport for blockwork.
The efficient and disciplined approach to design
resulted in the precast concrete subcontractor being
able to use cross-sections with a high repetition
factor, thus minimizing costs. The resulting
construction is accurate and well within the specified
tolerances. The choice of precast concrete provided
rapid and easy construction to give a robust structure
with economy of design.
The frames contain 1100 precast concrete column,
beam, wall and staifflight components, plus 9400 m2
of precast floor units. The entire structural frame of
Merchant House was erected in 16 weeks at a rate of
Floor/beam/perimeter column
connection detail
Precast stair unit being lifted into position
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P R O J E C T P R O F I L E
10
approximately 95 precast units per week. The surface
finish throughout was ex-factory type A in accordance
with BS 8110. During production, strict quality control
procedures were maintained under a BSI-registered
Quality Assurance Scheme. The units were also
inspected by the design team before despatch to site.
Following trades
The inherently dry construction and total absence of
formwork allowed safe, clear and rapid access for
following trades using the precast stairs. Fixings for the
cladding, temporary handrails, and the conservatory
and plant room steelwork were cast into the factory-
produced units to speed following trades. For
example, the aluminium curtain walling on
Woodchester House was fixed only two floors
behind the precast concrete frame.The curtain walling is an aluminium stick
system and the two-or three-storey high mullions
were fixed before infliling with transomes, and the
solid and glazed panels.
Meanwhile internal concrete block walls were
being constructed just ahead of first-fix services and
joinery. The absence of transverse beams or drops
encouraged the prefabrication and fast installation of
M & E services. Small service holes were formed in
situ through the easily locatable voids in the hollow-
core units. Supports for the services and suspended
ceiling grids were fixed directly into the concretesoffits using drilled and self-tapping devices.
Suspended ceilings and raised floors were installed
before final decoration. Wet trades were confined
mainly to the stairs, lobbies and toilets.
Flat roofs and terraces are of inverted roof con-
struction laid to falls, and were made weathertight
before first fixing began. The waterproof membrane
is covered with 100 mm insulation board protected
by concrete paving slabs.
Merchant House was completed ahead of
programme in 22 months and Woodchester Housewas completed in 20 months.
THE PRECAST CONCRETE SOLUTION
The frames for both buildings were quality assured
Curtain walling
during erection
Paving on the
completed terraces
Merchant House and Woodchester House clearly
demonstrate the advantages of using precast concrete
construction to meet clients requirements for the
following:
Speed and economy - the precast concrete framewas the least-cost solution with the lowest storeyheight, and had a shorter lead-in time than a steelwork
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P R O J E C T P R O F I L E
11
frame. It gave rapid erection with less contractor
preliminaries and quicker returns on investments. It
also gave rapid, clear and safe access for following
trades. High repetition factors and the use of high-
strength concrete produced further cost benefits.
Simplicity - the disciplined approach to design ledto repetitive elements of design, detailing,manufacture and construction. Construction was
uncomplicated, with simple connections, no form-
work, no weather problems, cast-in fixings for
following trades, and minimal storage and propping
requirements. Flat soffits and preformed holes made
services quick and easy to install.
Quality - the robust and rigid frames were builtfrom quality-assured factory-produced components,
to give accurate and durable structures. The quality
of construction was further assured by one-point
responsibility for the detailed structural design,
manufacture and erection.
Flexibility - the precast concrete frames accom-modated balconies, terraces, curves and irregular
shapes, and also permitted a late design change. The
precast floors allow for flexible future office
planning. The flat soffits and large ceiling voids
permit alterations to services, ceilings and office
layouts. Knock-out panels are provided for possible
future large service penetrations. Smaller holes can
be made through the easily locatable hollow cores in
the floor units.
Precast concrete was the only structural frame
material that could meet the cost, speed, quality and
versatility requirements for Merchant House and
Woodchester House. The result is two prestigious
buildings which are a credit to all those involved in
their design and construction.
January 1988: frame of Merchant House
well advanced, cladding in progress
at Woodchester House
May 1987: piling commenced
April 1988:
cladding to
Woodchester House
nearing completion,
internal walls and
cladding in progress
on Merchant House
Woodchester House was handed over in January 1989 and Merchant House in April 1989
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P R O J E C T P R O F I L E
12
Developer Brunel Centre Limited
Architect, structural Building Design Partnership
engineer and quantity
surveyorServices engineer Ralph T. King Associates
Main contractor John Laing (London)
Frame contractor Crendon Structures
Flooring supplier Bison Floors
THE PROJECT TEAMA P P E N D I X
CONSTRUCTIONCOSTS /m2 gross
WoodchesterHouse
Enabling works 15
Piling 15
Substructure 25
Frame 100
M & E 295
Cladding/roofing 335
Finishes 215
External works 35
Preliminaries 125
Sundries 30Total 1190
Merchant WoodchesterHouse House
Gross floor area 6540m2 4500m2
Net lettable area 5100m2 3500m2
Number of storeys 8 6
AREAS
THE PROGRAMME
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P R O J E C T P R O F I L E
13
Woodchester MerchantHouse House
Start May 1987 May 1987
Finish January 1989 April 1989
Duration 20 months 22 months
CONSTRUCTION TIME
TYPICAL FLOOR PLANS
WoodchesterHouse
Floor one
MerchantHouse
Floor one
MerchantHouse
Floor seven
WoodchesterHouse
Floor five
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PROJECT PROFILE: MERCHANT HOUSE AND WOODCHESTER HOUSE
C.H.Goodchild and P.Seilen
BRITISH CEMENT ASSOCIATION PUBLICATION 97.324