01 jsb551 introduction to design of multi storey buildings
TRANSCRIPT
Hailane Salam & Noriati Mat Som FSPU
Lecture 01
JSB551 Advanced Construction Technology 2
Introduction to Design of Multi Storey Buildings
Multi-Storey Buildings
The term multi-storey refers to structures with more than one storey and covers building used for many different purposes including:
•Apartments
•Office developments
•Shopping centres
•Car parks
•Schools and universities
•Hospitals
Although the basic anatomy of each building is similar, they may have different requirements for column grid, services, and internal/external finishes.
The structure will generally be more economic if large-spans are avoided, hence providing a shorter path between the point of application of loads and the ground.
The speed and economy of construction can also be increased by the large degree of vertical and/or horizontal repetition common in the structural systems of multi-storey buildings.
The individual contributions of major components to the overall building cost can vary significantly with building function, size and architectural treatment. However they are generally within the indicative ranges given below:
Foundations 5% to 10%
Steel Skeleton 10% to 20%
Floor Structure 5% to 10%
Cladding/Finishes 15% to 40%
Services 15% to 40%
Multi-Storey Buildings
Structure of multi-storey
buildings composed of:
1.Foundations
2.Framework
3.Floor slabs
Design of Multi-Storey Building
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The most common types of foundations are:
a) Pad Footings,
where an individual base of mass or reinforced concrete is provided under each column is the simplest option, where the supporting ground is good
1. Foundations
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1. Foundations
b) Raft footings.
For greater loads, or poor ground, the individual pads may be connected to form a continuous raft. This system may also provide improved resistance to water.
c) Pile footings.
Where ground conditions are poor the load carrying capacity of the individual pads or raft may be increased by installing piles to create individual pile caps or a piled raft
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Structural frame transmit vertical and horizontal
loads from their point of application to the
foundations by the most efficient path with the
minimum impact on the economy and function
of other elements of the building.
Stabilize the building by resisting horizontal
actions (wind & seismic)
Structural frame consists of:
I.Columns
II.Beams
III.Vertical and horizontal bracings
2. Framework
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2. Structural Frame
Vertical Load-Bearing Elements
The floor slab usually spans one way and is, either simply supported or continuous.
It is supported by 'secondary' steel beams, typically at 2,5m to 3,5m centres.
Several different types of slab can be used, most of which can be designed to act compositely with the supporting beams if adequate shear connection is provided.
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1. Columns - load transmission
Columns are the structural components which transmit all vertical loads from the floors to the foundations.
The means of transmission of vertical load is related to the particular structural system used for the framework.
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I. Columns
Load transmission from floors to
columns may occur directly from floor
beams to the column , or it can be
indirect involving the use of major
`transfer beams`, which resist all loads
transmitted by the column above
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1. Columns
The location of columns in plan is
governed by the structural lay-out.
The most common grid
arrangements are square,
rectangular, or occasionally
triangular, according to the choice
of the global structural system
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I. Columns
Column spacing depends on
building function, but is usually
between 5m and 10m.
Closer centred columns may be
used in an external 'tube'
stability system for a tall
building
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Fire Protection
The steel skeleton must be protected against fire. Typical solutions of protection are shown in Figure 6.
Columns filled with cast concrete can be designed for composite action (Figure 6a).
Beams can be protected in different ways (Figure 6b): by sprayed vermiculite, by concrete encasement, by filled concrete or by box-shaped cladding.
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II. Beams
Beams support the floor elements
and transmit their vertical loads to
the columns.
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II. Beams
In a typical rectangular building frame the beams comprise the horizontal members which span between adjacent columns; secondary beams may also be used to transmit the floor loading to the main (or primary) beams.
In multi-storey buildings the most common section shapes for beams are the hot rolled I (Figure 6a) or H shapes (Figure 6c) with depth ranging from 80 to 600mm. In some cases channels, (either single or double) can also be used (Figure 6b).
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II. Beams - accommodating building services
Sometimes openings in the webs of beams are required in order to permit the passage of horizontal services, such as pipes (for water and gas), cables (for electricity and telephone), ducts (for air conditioning), etc.
The openings may be circular (Figure 6h) or square with suitable stiffeners in the web.
castellated beams (Figure 6i),
which are composed by welding together the two parts of a double-T profile, whose web has been previously cut along a trapezoidal line.
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Floor are required to resist vertical loads directly acting on
them.
They usually consist of slabs which are supported by the
secondary steel beams
Supported by beams so that their vertical
loads are transmitted to the columns
Consist of:-
•Reinforced concrete slabs
•Composite slabs using profiled steel sheets
3. Floor Slabs
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3. Floor Slabs
Vertical Load-Bearing Elements
The floor slab usually spans one way and is, either simply supported or continuous.
It is supported by 'secondary' steel beams, typically at 2,5m to 3,5m centres.
Several different types of slab can be used, most of which can be designed to act compositely with the supporting beams if adequate shear connection is provided.
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3. Categories of Structural Floor Slabs
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3. Floor slabs
The structural arrangement of
multi-storey buildings is often
inspired by the shape of the
building plan
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3. Floor slabs
Floor slabs may be made from
pre-cast concrete, in-situ concrete
or composite slabs using steel
decking. A number of options are
available:
conventional in-situ concrete on
temporary shuttering (Figure 7a).
thin precast elements (40 - 50mm
thick) with an in-situ structural
concrete topping (Figure 7b).
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3. Floor Slabs
thicker precast concrete elements which require no structural topping (Figure 7c).
steel decking acting as permanent shuttering only (Figure 8b).
steel decking with suitable embossments/indentations so that it also acts compositely with the concrete slab (Figure 8c).
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3. Floor Slab Construction
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3. Structural System
Moment resisting frame system
(column-to-beam connection)
To provide resistance to the combined effects of horizontal and vertical loads in a multistorey building, two alternative concepts are possible for the structural system.
The first, so-called 'moment resisting frame system', is a combination of horizontal (beams) and vertical (columns) members which are able to resist axial, bending and shear actions. In this system no bracing elements are necessary.
The moment resisting frame behaviour is obtained only if the beam-to-column connections are rigid, leading to a framed structure with a high degree of redundancy
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3. Column-to-Beam Connections - rigid frame
Typical details of beam-to-column
joints for rigid framed systems are
shown in Figure 12.
They are called 'rigid joints' and their
task is to transfer bending moment
from the beam to the column.
Type (a) can transfer limited bending
moments only because the column
web can buckle due to local
concentration of effects.
The presence of horizontal stiffeners
in the column web (Type (b))
recreates the cross-section of the
beam and the column web panel has
to resist the shear force only.
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3. Column-to-Beam Connection - pin ended
Pin-ended connection are used to avoid the practical problems of rigid frame construction of site welds
a simple frame composed by beams pinned (bolted) together, which is capable of transferring the vertical loads to the foundation
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III. Vertical & horizontal bracings
Bracing systems are often identified with triangulated trusses or with concrete cores or shear walls which present in buildings to accommodate shafts and staircases.
Bracing systems are used to resist horizontal forces (wind load, seismic action) and to transmit them to the foundations.
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III. Vertical & horizontal bracings
When a horizontal load F (Figure
9a) is concentrated at any point
of the facade of the building, it is
transmitted to two adjacent
floors by means of the cladding
elements (Figure 9b).
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III. Vertical & Horizontal Bracings
The vertical supporting elements are
called vertical bracings; the horizontal
resisting element is the horizontal
bracing which is located at each floor.
Where horizontal bracings are
necessary, they are in the form of
diagonal members in the plan of each
floor, as shown in Figure 9c).
If steel decking is used, the diagonal
bracing can be replaced by
diaphragm action of the steel
sheeting if it is fixed adequately.
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a. Single diagonal
b. Cross-braced (X-shaped
bracing)
c. Inverted V-shaped bracing
d. Unsymmetrical portal
e. Symmetrical portal
f. V-shaped bracing.
III. Vertical & Horizontal Bracings
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III. Vertical & Horizontal Bracings
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References
ESDEP LECTURE NOTES