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SUSTAINABLE PRECAST CONSTRUCTION METHODS FOR TALL
OFFICE BUILDINGS IN HONG KONG
Corum K L Ip
Hsin Chong Construction (Asia) Ltd
Abstract: According to an informal survey of the past 10 years records of tall office buildings,
structural precasting construction method was adopted only once and it was one of the
“Swire Properties” office buildings in Tai Koo place – Cambridge House completed in April
of 2003. One of the major reasons for structural precasting not having been widely adopted
for high rise office construction could be the lack of practice notes and relevant codes of
practice (COP) providing the necessary guidance on development of such works. The
Buildings Department did not publish a relevant COP to the practitioners in the industry as
the formal guidance until October 2003. The absence of proven experience and track record
in the market for successful adoption of precast concrete frame structures and construction
methods might have further deterred the designer’s desire to explore and select this system as
a cost-effective and efficient alternative to the common insitu concrete casting and steel
method. A four day construction cycle was achieved on the Cambridge House project using
structural precast construction and at a competitive price. Such speed of construction had
only previously been achieved by insitu construction method in housing and could normally
only have been considered using steel frame for commercial buildings with their clear and
open span typical design. It is therefore hoped that the precast construction method can be
promoted to the practitioners in the local construction industry for building sustainable
developments. It is not necessary to compromise the primary concerns of the developers and
designers, as capital expenditure levels, architectural requirements, and operation efficiency
can be maintained whilst seeking to develop and construct sustainably.
INTRODUCTION
Background
Tall buildings are an inevitable form and part of the contemporary landscape in metropolises
nowadays. This has been sufficiently reflected in Hong Kong with immense population
heavily concentrated in certain urban districts. Under the market driven force of supply and
demand, super high rise residential buildings are abundantly visible in seafront areas, such as
West Kowloon, while the “skyscrapers” of commercial developments are readily available in
Central and neighbouring areas. With the tremendously high land acquisition cost in Hong
Kong, construction time, in addition to the architecture, and functional requirements of the
development become the primary concerns for determining its most desirable structural
system. There are many ways to construct tall buildings and in practice it is the desired use
of buildings which predominantly determines their design. The determination on adopting a
certain construction method is always responsive to the selected structural design system,
which is particularly significant in traditional “design-tender-then construct” form of
procurement contract arrangement.
Clients’ Desire for Internal Layout of Office
Flexible types of structure are a requirement from commercial building developers in an
increasingly fluid property market. More and more new buildings need to be designed to be
adaptable to changes throughout their lifetime.
In high-rise structural engineering, there are essentially three building materials: structural
steel, reinforced concrete, and a composite of the two. Within each material, there are a very
large number of options that one could choose. According to Chris Luebkeman (1996)7, the
design process is both a process of elimination as well as creation. Options must be
eliminated so that the best value can be determined. At the same time, creative solutions to
the specific site constraints should be considered. There are many cases in which both a
complete structural steel design and reinforced concrete design will be developed. At that
point, and only at that point, can the accurate cost of the final structure be analyzed? The
evaluation criteria for the choice of a structural system can vary. However, the following
items shall generally be included as the compiled list 7:
(1)
(2)
(3)
(4)
(5)
(6)
Economics
Length of Construction (Time is Money)
Construction Risk
Convergence of architectural desires and structural needs
Convergence of structural and mechanical needs
Local Condition (such as site constraints)
Most structural design schemes for a development are generated from different use or various
combinations of such materials and supplemented by other advancing techniques, like
prestressing. The most desirable structural system for a development would be determined
on the ultimate efficiencies of achievement to meet the clients and designers’ desires.
It is quite apparent to note in Hong Kong that the primary design concern for many tall
buildings is their operational efficiency rather than their environmental impact. A balance
needs to be struck between two factors. Inefficient energy use is a particular concern.
Progressive developers and designers would seriously look at the environmental impacts
together with the economic factors in the selection of structural systems. Speculative office
developers have less interest in their buildings’ environmental performance than the
companies that lease their offices. Whilst energy use is currently a relatively minor financial
cost, it is associated with major environmental costs, particularly climate change. Life cycle
assessment of buildings and construction materials is now gaining credence. Some 10-20 per
cent of the energy used in buildings over their lifetime is in the form of embodied energy
incorporated in materials and the process of building itself 10. Lifecycle analysis shows that
much can be done to reduce the embodied energy of buildings, particularly in tall buildings
with repetitive floor plans and large areas of façade. The potential for improving the
sustainable development of new high rise buildings is immense.
As there is quite a lot of study and research publications on the precast techniques adopted in
residential building, this paper explores the use of different construction methods responding
to some common structural design systems for tall office buildings in Hong Kong.
COMMON STRUCTURAL SYSTEMS AND CONSTRUCTION METHODS FOR
TALL OFFICE BUILDINGS IN HONG KONG
Design for Flexible Use Required for Office Building
The design life of buildings in Hong Kong is 50 years, whereas the average length of
occupancy is about 6-9 years from discussions with some property agents of a renowned
office buildings owner in Hong Kong. Similar to the situation in London, the vast majority of
tall buildings in Hong Kong are often initially financed by commercial developers and leased
to the occupiers for a number of years. As the socio-economic drivers change throughout the
lifespan of a building, so the demands on the building alter. A change of occupants often
leads to sub-division of the building internally, with partitioning of floors and zoning of
several floors together for a single lease-holder. Open plan offices are more common now.
Designing new buildings for flexibility of use and the potential for future changes helps
ensure their usefulness throughout their design life.
The change in demand and the requirement for flexibility has led to an increase in span of the
floor beams of offices. Whereas column grids were previously laid out with spacing of the
order of 5-8m, new buildings today are constructed with clear floor spans of 10-15m 10. To
improve the efficient use of materials to accommodate the increasing spans, construction
methods have been adapted and new techniques developed in the last decade. There has been
an obvious trend in using longer span steel beam floor systems in the past 10 years,
particularly in those super high-rise buildings with post-modern architecture and extremely
fast-tracked programmes. Advantages of the composite action between a concrete floor slab
and its supporting steel beams has also led to a reduction in the depth of beams and hence
weights of steel by up to 30 per cent 10.
Efficiencies in the design and construction of office towers can make a significant difference
to both economic and environmental burdens. Engineers strive to find savings in materials
through efficient design, making best use of concrete and steel in floors and structural frames.
However, the environmental impacts of their decisions are not always clearly understood.
Popular Structural Systems for Tall Office Buildings
The most common structural system for tall office buildings since the last decade is still
reinforced concrete. This is despite everyone recognizing that structural steel enables
designers to have a long span design with relatively smaller dead weight and member sizes
which contribute to higher head rooms and clear spaces. Recent development in reliable
production of high strength concrete and application of prestressing technology has made
concrete design more versatile to suit the contemporary architecture and flexible client’s
requirements. The inherently better resistance to fire also makes concrete more immediately
compatible with design codes and less sensitive to quality of construction.
In America and U.K, the early development of steel led to its use as the favoured material for
high rise structures. In general, reinforced concrete systems are three to eight per cent more
expensive than the steel options 4 in U.K. However, in other parts of the world, like Hong
Kong, that situation is reversed. Steel is not so readily available and its material cost has
been substantially higher than concrete. The difference has reached the peak at about 90% in
2005 (refer to an informal survey by “Arup” as attached in Appendix I). The total
construction cost of using steel framed structures (taking into account of its smaller weight
and resulting foundation saving) is 15% to 40% higher than that of concrete structures (from
inquiries with some local cost consultants) disregarding the time cost derived from any
difference in the construction programme. The wide range of variance is accounted by the
project specific features/requirements, particular site constraints, and fluctuation of material
cost, etc.
Combinations of concrete and steel structures are often the most efficient form, utilizing the
best characteristics of each material. In the UK, the most common form of structure in
buildings up to 50 storeys comprises a reinforced concrete shear core, used to stabilize the
building against wind and for fire escape, with lighter composite concrete floor slabs on a
steel frame, used to carry the building’s gravity loads to the foundations. The choice of
materials for the structural frame is determined primarily to satisfy those requirements, with
comparisons made of the most economical form that will do the job.
The structural systems popularly adopted for most tall office buildings in Hong Kong are in
form of rigid frames comprising a concrete core (to withstand high wind load, provide rigid
lift cores, and fire restrained stair cores) and steel composite mega columns at the perimeter
(carry the building’s gravity loads to the foundation). Concrete floor slabs on either steel
beams and metal deck or concrete beams are then used to transfer lateral loads to the mega
columns. It is very seldom in the market that a precast concrete structural system has been
used.
Construction methods for tall office buildings have also been developed according to the
popular structural systems. A survey has been carried out for the structural design and
construction method adopted by for tall office building development in the last 10 years.
Over 80 % of the buildings have adopted the insitu concrete design and method while there
has been a trend in the popularity of using steel frames recently. The result is indicated in
Table 1. The details of the office developments included in the survey are shown in
Appendix II.
Table 1 Survey on the Structural Systems and Construction Methods for Tall Office
Buildings Completed from 1996 - 2005 in Hong Kong
Floor Schemes (2)
Year of completion
Insitu
Steel
Precast
Total
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1
5
1
1
3
2
7
5
4
2
1
0
1
0
0
0
1
2
0
0
0
0
1
0
0
0
0
0
0
0
2
5
3
1
3
2
8
7
4
2
31 (83.8%)
5 (13.5%)
1 (2.7%)
37
Total (%)
Remarks:
(1) Tall Office buildings are defined as those office buildings with 30 storeys or more
(2) The floor schemes are referring to the main beams involved in typical floors
(3) Buildings completed within 1996 - 2005 but with unknown structural systems adopted is
not included in the above table
COMPARISON OF DIFFERENT STRUCTURAL SYSTEMS AND CONSTRUCTION
METHODS
Each structural system and construction method brings its own particular merits to a
development in favour of the client and designer. There is no definite conclusion that one
system and method is totally outweighing the other. The performance of insitu concrete,
precast concrete, and steel design is evaluated in the following aspects:
(1)
(2)
(3)
(4)
(5)
Cost
Time
Environmental Impact
Logistic Constraints
Flexibility for Design/Use
The detail comparison is shown in Table 2.
Insitu concrete design, with its significant merits of easy availability, relatively cheaper cost
and flexibility for design changes, is still the major structural system and construction method
favoured for most tall office buildings. With the increasing building height or number of
floors required for skyscrapers, structural steel frame system, which can result in less
sophisticated foundation design and lower foundation cost, and faster construction speed,
becomes more popular. Most practitioners in the industry believe that the steel construction
method is more environmental friendly in particular with off-site prefabrication in efficient
factory conditions, and bolt and nut assembly design minimizing on-site welding and cutting
activities. However, when we take into account the embodied energy and the extra fire
proofing and decorative encasement required for the structural steel frames, the
environmental impact from using steel is not obviously reduced in comparison with the
concrete systems. Among the major building materials including steel, concrete and timber,
the embodied energy for steel is the highest while timber is the least and concrete is in
between 10. Where architecture requires extensive use of conventional timber formwork,
insitu concrete begins to loose its environmental benefits and therefore use of steel/metal
system forms with highly repetitive and recycled use has been more and more desirable.
The precast concrete structural system is rarely adopted in office buildings because of the
typical open plan design and long spans which give rise to deep beams and heavy weight of
each individual member. The feasibility or constructability of using precast concrete
structural system and construction method, especially for office buildings located in high
value urban districts usually with highly constrained site areas, is not well ascertained by
most designers. As a result, the precast concrete system and method, especially one that
involves structural precasting, is not popular in Hong Kong notwithstanding its merits in
minimizing construction waste and environmental impacts.
Table 2 Comparison of Different Structural Schemes and Associated Construction Methods
Evaluation on the Relative Performance of Different Structural System and
Associated Construction Method
Relative Performance of Different Structural
Aspects of Concerns
System and Associated Construction Method
Categories
Items
Insitu
Steel
Precast
Foundation Cost
High
Medium
High
Material Cost
Low
High
Low
Transportation Cost
Medium
High
High
Installation Cost
High
Low
Medium
Cost
Protection Cost
Low
High
Low
Decoration Cost
Low
High
Low
Maintenance Cost
Low
High
Low
Overall
Low
High
Low
Design Finalization Lead Time
Short
Long(1)
Medium
Short
Long
Medium
Procurement and Procurement Lead Time
Preparation Time Fabrication Time
Short
Long
Medium
Overall
Short
Long
Medium
Installation Time
Long
Short
Medium - Short(2)
Fire Protection Application Time
Nil
Long
Nil
Construction
Time
Finishes Application Time
Medium
Long
Short
Overall
Medium
Medium
Medium-Short
Embodied Energy
Low
High
Low
Insitu Formwork Requirements
High
Low
Low
Noise Pollution
High
Low
Low
High
Low
Low
Environmental Air Pollution
Impact
Water Requirements
High
Low
Medium
Wastage Generations
High
Low
Low
Difficulties in Recycling
High
Medium(3)
High
Overall
High
Low
Low
Off-Site Storage
Low
High
High
On-Site Storage
Low
High
High
Site Access Requirements
Low
High
High
Effect from Site Surroundings
Low
High
High
Logistic
Requirements
Off-site Transportation
Low
High
High
Vertical Transportation on site
Low
Medium
High
Just In time Requirements
Low
High
High
Overall
Low
High
High
Resistance to Design Change
Low
High
Medium
Difficulties in Finishes Application
Low
High
Low
Constraint on Headroom Requirements
High
Low
High
Flexibility
Constraint on Column Spacings
High
Low
High
Constraint on Services Penetration
Low
High
Low
Overall
Medium
Medium
Medium
Remarks:
(1) For bolt and nut connections
(2) Depends on the area of floor plans
(3) Normally with fire protection paint
USE OF PRECAST CONCRETE STRUCTURAL SYSTEM IN “CAMBRIDGE
HOUSE PROJECT”
Background
To support the development of sustainability in construction industry, a renowned
progressive property developer in Hong Kong – “Swire Properties” explored the use of
structural precasting system in one of their tall office buildings in Tai Koo Place – Cambridge
House, in 2001. Same as the general design feasibility and optimization process, the engineer
had investigated different structural systems with various combinations of concrete and
erection system. Ultimately, a prestressed concrete structural frame system, with composite
steel and concrete columns at the perimeter, was found to be the most efficient scheme to
meet the client’s requirement. The client had considered a preference for a precast concrete
system but since the market lacked proven record as well as experience in precast
construction, the engineer prepared two design schemes – insitu and precast concrete, and a
construction advisor was employed to evaluate the constructability and construction
programme for these two options at the pretender stage for the superstructure contract. On
pretender stage, it was believed that the precast design and construction could be of about 2
months faster than the insitu scheme. When the tenders returned, the results indicated that
the cost to client for adopting the precast method was very close to that for insitu one and the
anticipated programme gains of 2 months time could be achieved. The precast concrete
structure and construction method was therefore eventually adopted.
Project Particulars
Cambridge House is a Grade “A” office building erected in Tai Koo Place. The building,
with total construction floor area of about 31,000m2 , consists of 36-storeys of offices sitting
on two levels of podium floor. The floor plate of the tower is designed in an octagonal shape,
and the columns are about 11 m apart. The longest primary beams are 16 m span. The
primary beams, secondary beams and slabs were designed as prestressed and semi-precast.
The staircases in typical floors were also designed in precast concrete. Each typical floor
from 3/F to 21/F has 11 precast beams, 44 precast planks and 3 stair modules (see Figure 1).
On the floors of 22/F to 36/F, 1 more beam and 4 more planks were involved because larger
office floor area was obtained from omission of the low zone lift cores.
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of of
Cambridge
House
The superstructure contract mainly consisted of the structural works from the pile caps
upwards and included all internal finishing and M&E installation. The scope also included
the construction of link bridges and alteration of some building services connecting to an
existing building – Devon House adjoining to the site.
To enable proper planning and sufficient preparation to use the precast construction method,
the superstructure contract was awarded with lead-in period of about two and a half months
before the actual required works commencement. This allowed the contractor sufficient lead
time to design and fabricate the system forms and moulds for precast elements and carry out
trial assembly before the actual installation works started on site.
Special Design for Semi-precast Beams
To reduce the weight of the semi-precast beams, the cross-section of the beams was designed
with a prestressed U-shape (see Figure 2) rather than the traditional half-beam. As a result,
the heaviest member of 16m long, weighed about 13 tonnes. With the conventional half beam
design, the dead weight of the heaviest member would be over 21 tones, i.e. about 61%
heavier. This would have required the use of a rare and expensive heavy duty tower crane for
the installation of the precast elements.
Figure 2 Two Design Section of Semi- Precast Beam
Construction method
The building was situated in an urban district location surrounded three sides by existing
property and with, on its fourth side, a heavily-traffic carriageway – Kings Road (see Figure
3). The podium floor footprint occupied nearly the whole site area, and no open area could
be allowed for any precast element storage. Only one site entrance was allowed from the
King’s Road. To cope with such site constraints, an off-site storage was designated at a
nearby location, at about 10 minutes travel distance from the site. The local off-site storage
was sufficient for holding the required precast elements for three storeys construction. In
addition, on site, a temporary unloading area was provided at a late cast portion of the
podium structure outside the tower footprint. A luffing jib tower crane with lifting capacity
of 16 tones at 25m was provided for installation of the precast elements.
Figure 3 Location of Cambridge House
To minimize the environmental impacts arising from construction activities upon the
neighbouring areas, the construction works were carried out within a full perimeter enclosure.
No transportation plant was erected outside the tower footprint and a three-storey high
external climbing metal platform was provided at the working floors (see Figure 4). In
addition, the number of construction joints was minimized as far as possible.
Figure 4 External Climbing Working Platform
The precast concrete frame system was used for the open office area (front of house) but the
services core (back of house), including lift shaft, lift lobby, stairway and other plant rooms,
was in insitu concrete design. The construction of a typical floor was split into two portions,
namely insitu and precast, accordingly (see Figure 5). For the insitu portion, contrary to the
traditional method of using self-climbing slip or jump forms for construction of the lift shafts
Figure 5 Typical Floors Construction (4 Days Cycle) Split into 2 Portions
only, the contractor built the whole services core on a complete floor basis, i.e. walls, beams,
and slabs together. This method introduced the merit of providing safe worker access to the
working levels and also eliminated any unnecessary construction joints from late cast
elements which would always gave rise to risk of quality and environmental problems. To
implement such method, the contractor adopted large panel metal forms for the external walls
of the services core and aluminum handset panel forms for the internal walls, beams and slabs.
For the precast portion, special modular metal scaffold (falsework) was used to support the
precast elements until they had gained sufficient strength after concreting. This type of
scaffold can be pre-assembled in a modular form (see Figure 6) which allows easy and fast
erection and transportation. The contractor specially designed an internal small gantry
hoisting device (see Figure 7) for moving the scaffolds up from the lower floors to the
working level. The mobile scaffolds could be efficiently moved to the required location and
assembled together with fixing of the additional bracing and ties among different modular
units.
Figure 6 Modular Metal Scaffold for
Supporting Precast Elements
Figure 7 Gantry Hoisting Device for
Modular Metal Scaffold
With optimized utilization of the craneage time, the luffing jib was the only mechanical plant
used for the execution of the structural works activities, including installation of the precast
elements, fixing of the steel forms as well as the concreting. No placing boom and pumping
concrete was used and hence least concrete wastage has been achieved.
As no mechanical plant was erected at the external face of the building, the curtain wall
panels could be completed on an entire floor basis in line with the superstructure progress so
that there were no left out openings at the façade throughout the whole construction stage.
Early achievement of watertightness enabled the early commencement and completion of
internal finishing as well as building services installation.
4-Days Construction Cycle Achieved for Typical Office Floors
To meet the 18 months construction period requirement for the project, a 4-day construction
cycle must be achieved for the structure of each typical office floor. The structural
construction activities for respective insitu and precast portion should be well scheduled to
enable completion within the cycle time. To validate that the planned schedule for each
activity was practical, an off-site trial assembly was carried out before the production of the
precast units and the system forms. In addition, any necessary modification of rebar details
and minor dimensions of the precast units enabling the achievement of the tight construction
cycle time should be identified through the trial assembly. The detailed schedule for carrying
out the construction activities is explained as below (see Table 3). Photos showing the
activities carried out in the 4 –day cycle is attached in Appendix III. This construction speed
was same as that given by the use of structural steel method.
Table 3 Detail Schedule of 4-Day Cycle Activities
Area
Activities
Semi-precast Concreting to Semi-precast Portion (9:00am to 4:00pm)
Delivery of Semi-Precast Beams to site (9:00am to 4:00pm)
Portion
Day 1
Day 2
Day 3
Day 4
Delivery of Semi-Precast Planks (9:00am to 4:00pm)
Erection of False-work Support (8:00am to 6:00pm)
Raise Up External Working Platform (4:00am to 6:00pm)
Steel Fixing of Columns (8:00am to 12:00pm)
Installation Steel Column Formworks (1:00pm to 4:00pm)
Concreting to Columns (4:00pm to 7:00pm)
Hoisting and Installation of Semi-Precast Beams (8:00am to 12:00am)
Hoisting and Installation of Semi-Precast Planks (1:00am to 6:00pm)
Steel Fixing to Beams and Slabs (7:00am to 5:00pm)
Installation Steel Stanchions (4:00pm to 6:00pm)
In-situ Portion Steel Fixing to Core Wall (7:00am to 3:00pm)
Striking of Steel / Aluminium Formwork (8:00am to 12:00pm)
Raise up lift shaft wall form and working platform (by Tower Crane) (8:00am to 9:00am)
Erection Aluminium Wall formwork (1:00pm to 6:00pm)
Hoisting and Install of precast staircase (4:00pm to 6:00pm)
Erection Aluminium Slab Panel (8:00am to 5:00pm)
Raise up external steel working platform (2:00pm to 4:00pm)
Installation of Steel wall mould for external Lift Shaft and Staircase (5:00pm to 7:00pm)
Hoisting Reinforcement from Storage yard to working floor from (7:00am to 8:00pm)
Fix Beams and Slabs Reinforcement from (8:00am to 5:00pm)
Cast in Curtain Wall embeds from (3:00pm to 6:00pm)
Concreting to Core Walls beams and Slabs from (8:00am to 4:00pm)
The insitu portion was constructed two floors ahead of the precast portion in order to allow
the appropriate airspace for operation of the large panel metal system forms to the core walls
and also installation of the steel stanchions for the composite columns. Since the largest
concrete pour to the typical floor only involved about 230 m 3 and the heavy duty tower crane
had some spare craneage time, crane and skip method was adopted for placing concrete. A
large skip of 2.2m 3 capacity aided the process with a total weight of 6.5 tonnes with fresh
concrete per crane lift.
“Just on time” delivery of the precast elements was the critical factor for achieving the tight
construction cycle where on-site storage was highly restricted. Success on the logistic
arrangements has direct bearing on the achievement of the required fast track programme.
Other Environmental Friendly Measures Adopted associated with the Construction
Method
Two jump lifts were used, being an internal transportation system making use of the
permanent lift shafts. This provision can help to avoid the use of temporary hoisting facilities
normally erected at the external face of a building or inside a building. Jump lifts avoid the
need for numbers of left-out floor and wall openings and therefore cause the least
environmental impacts to the surrounding regions.
With the contractor’s method of constructing the whole service core, including the lift shaft,
lobby, plant rooms and staircase, at the same time, maximum benefit was demonstrated by
the use of jump lifts which could be installed and put in use for vertical transportation
purpose up to only a few floors below the working levels with structural works in progress.
Two jump lifts were used in this project for both building materials and passengers.
As mentioned above, a 3-storey high external climbing platform was adopted for the
structural works progress. After the structural works had been finished to certain upper floors,
the curtain wall panels were installed by means of gondola starting from the lower floors
upwards. The use of conventional scaffold to the external face of building has therefore been
omitted.
Benefits of Using Precast Construction for Cambridge House
The construction cost to the client for using precast construction was almost the same as that
for total insitu concrete system. The 2 months saving in the shorter construction programme
achieved by using precast method (derived from 4-day construction cycle of precast method
against 6-days cycle of insitu method) has also enabled the client to take over and lease out
the buildings earlier with extra financial gain.
The use of precasting methodology in Cambridge House enabled the contractor to deliver a
better quality product than using insitu casting. As the concrete elements were manufactured
in an off-site precast yard with well planned and equipped factory conditions, the production
process was closely controlled and monitored to achieve the required standard satisfactorily.
Concrete tolerances and surface finishes were improved, providing savings in follow on
trades for the shell and core finishes and MEP installations. Material wastage and rubbish,
with their associated safety concerns, were minimized in avoiding site cutting and insitu
concreting activities. The client was able to review and accept the quality of the products
before their delivery and incorporation in the project, and ahead of any risk of abortive works
or programme delays.
The prefabrication method also helped to reduce the demand for skilled trades labour on site
for the project during the construction stage because significant parts of the works had been
executed off-site. Reducing the range and skill level of workers required on site, the
contractor not only reduced the impact of fluctuation in the labour market availability and
price upon the tight erection programme, but was also able to be more selective with his site
team, developing a disciplined work force for optimum safety and quality. In summary, the
quality and environmental performance of the construction has been effectively raised to a
higher standard.
The project has gained an excellent grade award by the HKBEAM and a number of other
environmental related awards, such as “Innovative Practice” and “Green Office” of EcoBusiness from the Environmental Protection Department, and “Good Housekeeping”
commendation award from the Labour Department.
CONCLUSIONS AND RECOMMENDATIONS
In current practice, economic factors tend to outweigh the social and environmental factors in
commercial developments. Very rarely do commercial buildings developers and designers
place serious thoughts and attention on determining a structural system with high
environmental concern, particularly in absence of incentive schemes or legislation of relevant
standards, or guidance for sustainability. However, pressures to redress that balance are
increasing and new developments are going to be more sustainable in future.
For sustainable development to become common practice, legislation is needed to ensure
further measures are taken to safeguard the environment. While best practice and guidelines
are helpful in raising awareness of opportunities for improvements, “the bottom” line is the
dominant factor in procuring buildings. Property development is a market driven business
and tall buildings are financial instruments to most developers and clients
The use of precast concrete construction in private developments and other projects requiring
approval by the Buildings Department (BD) was limited. One of the main reasons was the
lack of practice notes and relevant codes of practice providing the necessary guidance on
such works 1. The use of precast concrete construction can significantly reduce the amount of
construction waste generated on construction sites, reduce adverse environmental impact on
sites, enhance quality control of concreting work, and reduce the amount of site labour. To
assist in promoting precast construction, the BD commissioned a consultancy study on
precast concrete construction and the drafting of the Code of Practice. The Code was first
published by BD in October 2003. The code gives recommendations and guidelines on the
design, construction and quality control of precast structural and non-structural elements. It
was drafted following an extensive review of international standards and other published
literature and based, where applicable, on local experience and practices. It is intended to be
used in conjunction with the new code of practice for reinforced concrete covering the
following areas1:
-
Design including stability, durability and water-tightness of joints;
Construction of precast elements ranging from factory production, transportation and
handling through to site erection;
Quality control during both production and erection
Another major reason for the lowest popularity of precast concrete design and construction in
tall office buildings is lack of proven experience and track record in the industry. The
logistic constraints, including the use of heavy duty mechanical plant required for the
installation of the precast elements, transportation facilities for vehicular access to site, and
the construction speed, create lots of uncertainties to the designers and developers.
There is no conclusion that the merits of a concrete structural system and construction
absolutely outweigh those of the steel system or vice versa. The determination is based on
the evaluation on the efficiencies of the system in meeting the design and client’s
requirements. In general, steel with significantly higher construction cost could be adopted in
circumstances where lighter structural dead weight was required to suit the practical
foundation design, and where longer span of structural frame with smaller member sizes was
required to achieve the fundamental architectural requirements or client’s desires. A lot of
research papers suggest that precast concrete planks should be used instead of metal decks on
the steel framed structures for both better functional efficiency and environmental
performance. If speed of construction is the predominant factor for the determination, the
successful use of precast construction technology achieving a 4-day cycle in Cambridge
House project should give an indication to the Hong Kong industry that precast design can be
a competitive alternative to steel system.
When a concrete structural system is chosen, precast design and construction can be really
considered as economical alternative to the insitu method with its potential to achieve faster
programmes. Although the production and transportation cost for precast concrete elements
is generally higher than that for insitu casting, this can be offset by the resultant smaller site
preliminaries from a shorter construction period and reduced waste, rubbish clearance, and
housekeeping. As indicated in the Cambridge House case, the contractor’s price or the
construction cost to the client was almost the same in using either insitu or precast method.
In addition, the client has gained an extra financial benefit in taking over the building earlier.
Of course, the critical transportation as well as logistic issues, which are prerequisites for
adopting the precast method, should be properly addressed in addition to its efficiency of
meeting the client’s desire. It also worth noting that a relatively longer preconstruction lead
time is generally required for the precast method if fast-track programme and smooth
progress is to be the returned. Modular architecture, dimensional co-ordination and
standardized concepts should be widely adopted for the architecture to facilitate the re-use of
precasting moulds and for fabrication of the elements to be cost effective. This concept is
significantly important for the use of a precast design where such as progressive changing
floor plates or irregular structures are involved.
It cannot be concluded that the precast construction method should prevail over other systems
in all cases with different project specific requirements and site constraints, particularly
where the current market has no clear standards and guidance for the relevant design and
practice in structural precasting.
However, as well as generating a return on capital expenditure, primary concerns of designers
include the need for new buildings to enhance their environment, to be aesthetically pleasing
to the eyes of observers, and to be effective and comfortable to the senses of their occupants.
But these main aims need not be compromised in seeking to develop and construct
sustainably. With the successful completion of the Cambridge House project, we believe a
desirable balance between economic, social, and environmental effects can be achieved by a
holistic approach to the whole building design. Increased awareness of the issues is needed
throughout the industry to give impetus to improvements and potential savings in practice.
Appendix I
Material Cost Trend for Concrete, Reinforcement and Structural Steel
Appendix II
Particulars of the Office Buildings Completed from 1996 to 2005 of the Survey
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
Building Name
AIG Tower
8 Fleming Road
Langham Place Office Tower
May House (Police Headquarter)
Enterprise Square 3 (Kowloon Bay)
Three Pacific Place
Skyline Tower (Kowloon Bay)
Two International Finance Centre
Cambridge House
One Peking Road
Chater House
The Centrium (Wyndham Street)
148 Electric Road
Enterprise Square 2 (Kowloon Bay)
333 Lockhart Road
88 Hing Fat Street (Gordon Road N.P.)
Cheung Kong Centre
AIA Tower
The Westpoint (Connaught Rd. W)
Oxford House
Dah Chong Hong Commercial Building
Man Yee Building
MLC Millennia Plaza (King's Road)
1063 King's Road
The Center
Cosco Tower (Queen's Road)
Manulife Plaza (Hysan Avenue)
One International Finance Centre
Standard Chartered Tower (Millennium City)
Grand Millennium Plaza
28 Marble Road
Henley Building (Queen's Road Central)
Citic Tower
China United Plaza
Western Harbour Centre (Connaught Rd. W)
Laws Commercial Plaza
Bank of Communication Tower
Year of Completion
2005
2005
2004
2004
2004
2004
2004
2003
2003
2003
2002
2001
2001
2001
2000
2000
1999
1999
1999
1999
1999
1999
1999
1999
1998
1998
1998
1998
1998
1998
1998
1997
1997
1997
1997
1996
1996
Storey
40
30
59
47
41
40
38
88
36
30
30
41
41
33
52
37
62
44
41
41
31
31
30
30
73
53
52
38
38
30
30
36
33
30
29
34
33
Structural Floor Scheme
Steel
R.C.
R.C.
R.C.
R.C.
R.C.
R.C.
Steel
Precast
R.C.
R.C.
R.C.
R.C.
R.C.
R.C.
R.C.
Steel
R.C.
R.C.
R.C.
R.C.
R.C.
R.C.
R.C.
Steel
R.C.
R.C.
Steel
R.C.
R.C.
R.C.
R.C.
R.C.
R.C.
R.C.
R.C.
R.C.
Appendix III
4-Day Construction Cycle for ‘Cambridge House’
DAY 1
In-situ Portion
Rebar Fixing for Corewall
(7:00am – 3:00pm)
Precast Portion
Concreting for Topping Semi-precast
Beams and Slabs (120 m3)
(9:00am – 4:00pm)
Striking of Steel/Aluminium Formwork
(8:00am – 12:00pm)
DAY 2
In-situ Portion
Hoisting and Installation of Steel/
Aluminium Formwork and Working
Platform (2:00pm– 4:00pm)
Hoisting and Installation of Precast
Staircase (5:00pm – 7:00pm)
Precast Portion
Delivery of Semi-precast Planks
(9:00am – 4:00pm)
Delivery of Semi-precast Beams
(9:00am – 4:00pm)
Day 2 (Cont’d)
Precast Portion
Erection of Modular Metal Scaffold
(8:00am – 6:00pm)
Lifting & Installation of Working
Platform (2:00pm – 6:00pm)
Precast Portion
Rebar Fixing for Columns
(8:00am – 12:00pm)
Installation of Column Formwork
(1:00pm – 4:00pm)
Concreting Columns (22 m3)
(4:00pm – 7:00pm)
DAY 3
In-situ Portion
Rebar Fixing for Beams and Slabs
(8:00am – 5:00pm)
Precast Portion
Hoisting and Installation of Semi-precast
Beams (8:00am – 12:00pm)
Hoisting and Installation of Semi-precast
Planks (1:00pm – 6:00pm)
DAY 4
In-situ Portion
Concreting Core Wall, Beams & Slabs
(220 m3) (8:00am – 4:00pm)
Precast Portion
Rebar Fixing for Beams and Slabs
(7:00am – 5:00pm)
Installation of Steel Stanchions (Max. 8
m High, Max. 11 Tons) (4:00pm –
6:00pm)
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1.
Albert W.K. Leung & Allen Spring: “The new concrete and precast concrete
codes – their development and essential features”, The Structural Engineer – 18
October 2005, P.30-33
2.
Angela Tam: “Sailing into the gap of the Furama”, Hong Kong Engineer
October 2005
3.
Angela Tam: “Structural Precasting gets thumbs up in Tuen Mun”, Hong Kong
Engineer – Cover Story August 2005
4.
Corus Construction & Industrial: “Supporting the Commercial decision –
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buildings”, 2004
5.
C.S. Poon, Lara Jaillon (Department of Civil and Structural Engineering, The
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Prof. Dr. Chris H.Luebkeman: “Structural Systems Selection - Resources on the
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