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INTEGRATION WITHIN THE STRUCTURAL SYSTEM
Introduction
To discuss about the total building performance, it is crucial to deem a building as a
system, comprising four distinct subsystems.
They are namely, structure, envelope,
mechanical and interior. This chapter focuses on the structure of the building and
describes the integration within the structural system itself.
The structure consists of the substructure (foundation and basement with retaining walls)
and superstructure. The superstructure in this case draws most of the attention. The
characteristics of the structural system are based on the decisions made in the design
process. The physical features and specifications are taken from the drawings and on-site
information.
One of the primary motivating forces for systems integration is performance. The various
design characteristics of the structural system can have a critical affect on the systems
performance. By analysis of these aspects, the structure’s performance can be obtained on
six performance mandates.
Structural System
The structural system of this 37-storey building gives it the ability to withstand all natural
and programmatic loadings. In short the structural system can be described as follows:
General system type:
The main loadbearing system consists of slabs, beams and columns, together with the
core walls.
Stability of the structure:
The beams and columns are a semi-rigid frame, supported by the core walls. The floors
transport the horizontal wind loading to the core walls. Stability is ensured in all
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directions by the core walls and through the partly stiff connections of the columns with
the beams.
Structural elements of the superstructure:
a) Floor slabs:
The floor slab is of cast in situ reinforced concrete on a steel deck
(bondek). Normal depth of slab is 175 mm, but in lift area the slab
thickness is 140 mm (smaller span) and on certain storeys it is increased
up to 230 mm.
Cast in situ concrete slab
h = 175
mm
Steel deck
hmax = 610mm
Secondary steel beam
Primary steel beam
Figure 1: Structural Floor Elements
b) Beams:
Steel plate girders or UB form the beam system. For the primary beams
the maximum height is about 610 mm and maximum length is 12m.
c) Columns:
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The reinforced concrete columns have a steel H-section inside. The
maximum diameter of concrete column is 1200 mm.
d) Core Walls:
Core walls, consisting of 500mm thick concrete, also form the walls for
the lifts. These walls are located at the west of the building, forming a
closed façade.
Critical Implications for Integration within the Structural System
The structural system is examined with reference to following six performance mandates:
1. Spatial Performance
2. Thermal Performance
3. Air Quality
4. Acoustical Performance
5. Visual Performance
6. Building integrity
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The following table shows what design characteristics of the structural system can have a
critical affect on the systems performance.
General system type
System Materials and
Properties, Steel, Concrete
Span, Bay Sizes, Column
Spacing
Floor to Floor Height
Cross-section structural
elements (height, width, depth)
Building Form: Plan, section
Expansion Capabilities
Connections to/
Accommodations of Other
Structural Components



















Integrity
Building
Visual
Acoustical
Spatial
characteristics
Thermal
Structural design
Air Quality
Checklist for critical Implications



















Table 1: Checklist for critical Implications
Key:
 Critical Implication for the delivery of the performance mandate.
 Some Implication for the delivery of the performance mandate.
The table above is used to analyse the performance of the various characteristics of the
structure.
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Relevant Information on the Structural System
To analyse the structural system on it’s performance, the relevant information is stated
below:
 System materials and Properties: Steel, Concrete etc.
 Span, Bay size Column spacing
 Floor to Floor height
 Cross-section of structural Elements (height, width and depth)
 Building Form
 Capability of horizontal and vertical expansion
 Connections to /Accommodations of other structural components
All these physical features and specifications can be taken from the drawings and onsight information.
To obtain extra insight, the building manager was asked the following questions:
1) What general type of system is used for this building?
2) Is there anything in special to say about the construction of the structure?
3) Is there anything special about the materials and components used?
4) Do tenants complain about the structure? (e.g. sway, sloping floors, etc)
5) Did the tenants complain about the structural system when planning for interior
layout?
6) How well do you think the structural system has fulfilled the acoustics criteria of
the building?
7) How often is the maintenance for the structural system carried out?
8) Are there any major repairs, modifications or additions to building’s structure?
The building manager could not give answers to all these questions. Extra information
can still be obtained from the structural engineer (Steen Consultants Pte Ltd.)
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Impact on Performance Mandates
Before giving an evaluation of the different subsystems, the general system can be
analyzed on its performance.
General Systems
General Information: It is an open frame system.
Implications on the performance mandates
1) Thermal: The structural system has small amounts of materials and only walls at
the lift core area. This means that the amount of thermal mass is low.
2) Indoor Air Quality: The open system ensures free flow of air.
3) Acoustics: The open structure blocks little sound, except for the core walls.
4) Building Integrity: The structural elements are designed to accommodate above
average floor loadings, resulting in a high safety-factor.
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In general also the material used in the structure can be evaluated.
Materials
General Information: Concrete and steel are the main materials used in the
construction of the building.
Implications on the performance mandates
1) Thermal: Concrete has low heat conduction characteristics.
2) Indoor Air Quality: Concrete has minimum outgassing effect to the occupants.
3) Acoustics: The lift walls are of 500 mm concrete, the floor slab is at least 175 mm
thick (with dropped ceiling). Both of these are more than sufficient.
4) Visual: The smooth texture and light colors of the materials result in a large
amount of diffuse light.
A) Columns
General Information:
The columns are of reinforced concrete and are spaced at 11.2 m by 12.0 m.
Implications on the performance mandates
1) Thermal: The large diameter of the columns gives less thermal conduction (low
surface to volume ratio). The columns outside are isolated to minimize thermal
loss due to thermal bridging.
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2) Spatial: There is almost column-free area with the large column spacing. There is
only small amount of columns and lift core is at the side of the building. This will
give flexibility to the office layout for the tenants. In terms of column spacing,
Hitachi Towers offers the tenants a highly efficient open plan floor space with
maximum column-free design to allow for greater flexibility, adaptability and
suitability for tenants’ activities. (See Diagram). Spatially, the tenants find this
ideal for their future activities and that it increases the flexibility of rentable
space. This was shown by the tenants designing each interior layout differently,
as observed from the expert walkthrough.
3) Indoor Air Quality: The round cross-section of the columns gives a small surface
to collect dust. The I-beam sections however can collect dust.
4) Visual: The columns are slender and rounded and blends in well with the whole
office building. They are also aesthetically pleasing. An almost column-free area
and large column spacing give a good visual performance. The small amount of
columns will not disturb the lines of sight.
C) Beams
Implications on the performance mandates
1) Building Integrity: Steel I beams are encased in fireproofing materials like
intumescent coating, which reduces heat conduction and resists fire.
2) Visual Performance:
As there are not beams in sight, it gives a good visual
performance and do not disturb the lines of sight.
D) Slabs
General Information: A typical floor slab is 175mm of reinforced concrete.
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Implications on the performance mandates
1) Spatial: The floor-to-floor height is above average. The large floor-to-floor height
gives a larger air volume that needs to be conditioned.
2) Acoustics: The large floor-to-floor height gives a larger acoustical volume. The
minimum slab depth is 175m and is thus able to provided good acoustical
performance.
3) Visual: The large floor-to-floor height gives a higher daylight factor
4) Building Integrity: Heavy equipment such as large transformers is placed on the
6th storey on the special heavy load areas. This was highlighted by the structural
floor plan of heavily reinforced slabs with a depth of 230mm and greater
dimensions of I beams used. This also applies to other heavily loaded floors.
E) Core Walls
General Information: The core walls are generally of 500 mm thick concrete.
Implications on the performance mandates
1) Acoustics: The core walls will cause sound to be absorbed and reflected. This will
have an impact on the acoustical performance.
2) Visual: The walls will block daylight and block lines of sight; this has a negative
impact on the visual performance.
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Summary:
The structural system employed by this building of maximum column-free space allows
improved daylight penetration and this enables better visual performance in the offices.
The materials of the system pose a very small problem and do not significantly influence
the indoor air quality and thermal mandates.
Design decisions about the building form and shape and properties of materials do have
influence on the acoustical performance. As mentioned above the whole building adopts
the maximum column- free design, thus neighbouring offices are partitioned by nonstructural materials. However the side of the building near the lift core, insulation needs
to be provided for the (indirect) noise of the lift. The thickness of 500mm of core wall
also contributes to the acoustical performance.
Decisions about the structural system also significantly impact the building integrity. As
this is an 8-year-old building, there are signs of degradation as shown by cracks on the
walls located at the car parks.
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This picture shows an office space in empty condition.
Notice:
Column free
No beams in
sight
Free height of
2.7 meters
High daylightfactor
This picture shows part of the floor structure shown from underneath.
Steel deck
I-beam with
fire-resisting
coating
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The Element of Time: Units of Evaluation for Building Performance
The performance goals can be evaluated and compared in terms of suitability, reliability
and flexibility.
Suitability
Spatial performance is considered as being the most important mandate. The structure
affects the spatial performance in different ways.
The suitability of the structure is a measure of degree in which the structure of Hitachi
Towers serves the tenants’ spatial needs in the present and near future. In terms of
column spacing, Hitachi Towers offers the tenants a highly efficient open plan floor
space with maximum column-free design. The tenants can design each interior layout
differently, as shown from the expert walkthrough. This open plan office suits the needs
of the tenants and will continue doing this in the near future.
IAQ performance is affected to the extent that it allows airflow, volume of air, emits
particulates into the air, and the air tightness between the structural elements.
The open plan structural system ensures free airflow and the large floor-to-floor height
gives a large air volume for good ventilation, which enhances the IAQ performance of
the building. Therefore, the structure is suitable in the respect of IAQ performance.
Moreover, the connections between structural elements are airtight, thus suitable in
enhancing the IAQ performance of the structure. Also, the low outgassing characteristic
of concrete makes the structure suitable.
However, the fire-resisting coating for the steel elements emits particulates in the air,
which is not suitable for the IAQ performance of the building.
Thermal performance is least affected by the structural systems. Suitability on the
thermal performance of the structure can be stated not to be critical. As mentioned, the
airflow and air volume are related to the structure, which will have minor impact on
thermal performance. The structure sets no boundaries on the internal temperature
behaviour. The thermal performance will be handled by means of conditioning and any
methods of conditioning that will suit with the structure.
Acoustical performance is affected to the extent that the system materials and properties
used will affect the insulation of sound and therefore the transmission of sound in the
building.
For Hitachi tower, the core walls are of 500mm concrete and the floor slab is at least
175mm thick. These are suitable in the acoustical performance of the building because
the level of sound insulation they provide is more than sufficient. The large floor-to-floor
height also gives a large acoustical volume, which enhances the suitability of the
structural system used with regards to the acoustical performance.
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However, due to the open floor plan from column-free structure, sound transmission is
high. Since acoustical performance of the building is 4th in priority of the TBP of Hitachi
Tower, as long as the basic acoustical performance is achieved for the function of the
office, other performance mandates such as spatial performance would be placed at a
higher priority.
For visual performance, the structural system is a transparent system with few walls,
which implies a large window/façade area-ratio. Thus, it is suitable for the purpose of this
building, which is mainly for offices. The offices are able to make full use of the natural
daylighting.
The steel and concrete structure of the building is able to give a smooth texture and light
colours of the materials, resulting in a large amount of diffused daylight. This is more
useful than direct daylight as glare is reduced.
The large floor-to-floor height of 3.7m gives a higher daylight factor, appropriate to the
use of this building. The plan, which comprises of 3 open facades out of the 4 facades, is
fairly compacted. Moreover, the maximum distance to the façade is only 12m, thus
ensuring the penetration of natural daylight for task purposes.
The large, open and column-free layout of the building is able to give a good visual
performance. Also, there are no beams in sight, which can affect this performance
mandate. The small number of columns also does not disturb the lines of sight of the
occupants. The round cross-section of the columns gives a nice view as it is slender and
casts minimal shadowing effects.
Reliability
The structure of the Hitachi Towers is a reliable system. Its impact on the Spatial
performance will remain constant throughout the life of the building.
The structure is relatively durable in its function of providing for the IAQ performance
with regards to air tightness, ventilation and airflow.
The structure is reliable because of the durability of the materials used, and thus the
permanence of its performance with regards to Acoustics. It is also reliable because of its
generally maintenance-free characteristic.
The system is made up of steel and concrete, for instance, the columns are a combination
of steel being encased in concrete. The steel, being encased in concrete, is thus protected
against fire. Moreover, the concrete protects the steel against corrosion. Hence, the
building is guaranteed of its Building Integrity, being able to be structurally sound over
time.
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In addition, as none of the structural elements are subjected to direct sunlight or the
weather elements, the structural elements are protected from degradation due to the direct
sunlight and weather, for instance, sealant degradation due to ultra-violet rays.
Flexibility
The large floor-to-floor height of 3.7m is able to give extra flexibility for Spatial
performance.
The large area of free, open office space also allows for future changes in the layouts of
the offices. For instance, for vast open office layout to closed office layout or vice versa
and the like. There is also flexibility in the size of the different office units should there
be a need to, for instance, combine two units together for bigger organizations. The
highly efficient open plan floor space allows again for great flexibility. As mentioned, the
tenants can form their own office layout. Spatially, the tenants find this ideal for their
activities.
The structure is not flexible because it cannot be altered to the changing needs of its
occupants with regards to IAQ performance due to the characteristic of permanence of
the system. However, this is not critical as flexibility is not important for this mandate
and it cannot be expected from a permanent structure.
The open structure provides all kinds of possibilities to condition the office space. The
Thermal performance can be said to be flexible.
The structure is not flexible in terms of Acoustical performance because it cannot be
altered to the changing needs of its occupants due to the characteristic of permanence of
the system. Once again, flexibility is not critical and cannot be expected as discussed
above for IAQ performance.
For Building Integrity, the structural elements are designed in such a way as to
accommodate higher-than-above average floor loadings, resulting in a higher factor of
safety. Thus, there is flexibility in loading as now, higher loads can be placed in this
building without running the risk of violating the high safety factor.
Also, there is a breakout panel on every floor for future use, thus providing for expansion
capabilities in future.