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