lecture 1 building structures(2)

8/18/2019 Lecture 1 Building Structures(2)

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Lecture 1:INTRODUCTION TO

BUIILDING STRUCTURES


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Contents:

• Nature of Buildings

• Building Superstructures

• Solid Superstructures

• Skeleton Superstructures

• Surface Superstructures

• Advantages of Frame Structures• Classification of Frames

• Materials for Building Frames


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Function of Buildings

• As a shelter / envelope

• To meet primary physical needs

• Must be well-designed as well as constructed

• Building technology and building techniques are interrelated


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Functions of building

• Enclose space so that the satisfactory internal environment may

be created relative to the purpose and intended function of the

building

• The space within the building must be suitable for the

activities to take place with it

• Comfortable, safe, stable

• Must be designed in terms of size and shape, and environmental

factors


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Building Superstructures

• General Definition - portion of a building that is above theground.

• In Malaysian construction – refers to the building ‘primaryelements’ that transfers the building load to the sub-structure(foundations)

• Mainly as the main building structural component or BuildingPrimary Element of the building


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Building Primary Elements

Roof

Beam(Roof Beams)

Suspended Beam(B)

Ground Beam(GB)

Column(C)Slab(S)

Footing(F)


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Purpose of Primary Elements


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Building Superstructures (Building

Primary Elements)Design:

1 . better use of structural materials (steel, brick, timber, concrete etc)

2. an easier method of construction and erection/expansion

3. reduce cost

4. answer to a particular problem (such as provision of a clear floor area for

a warehouse or a factory)

5. conform with the requirements of the designer (architect) in search of

visual appeal ( aesthetic )

6. withstand the forces that the building will carry i.e. does not move in any

manner under loads


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Types of Superstructures

3 basic types of superstructure:

i) Solid

ii) Skeleton

iii) Surface


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Solid Superstructures

• Combines the load-carrying function with space enclosure

• The loads are transferred to and spread through the

walls/building frame to give a distributed load on the

substructure

• The common types of solid structures:

i) cellular/box frame

ii) igloo

iii) cross wall


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SolidSuperstructure

Types Box Framed Structures Load-bearing Walls Cellular Box Structure

Cross Wall Structure

Igloo

Load bearing wall


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Cellular Box/Frame

• the loads are transferred to the walls of the cells,

each wall being rigidly jointed to its neighbor

• arrangement – where both the internal and external walls are load-bearing and arranged to form a

cellular system

• resulting structure is rigid and stable, suited

applications where large areas are not required or

alteration in layout are unlikely


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Cross-walls

• A generic method of building

construction using a series of division or

party walls which transfer the floor loads

through the building to foundation or

transfer slab level.

• The walls are ususlly built at standardised

centres and spacing thus allowing other

elements aslo to be standardised

division or party walls


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Load bearing walls• A load-bearing wall (or bearing wall ) is

a wall that bears a load resting upon it

• Its weight is then transferred directly to the

foundation structure.

• The materials most often used to constructload-bearing walls in large buildingsare concrete, block, or brick.

• Depending on the type of building and thenumber of stories, load-bearing walls aregauged to the appropriate thickness to carrythe weight above them.


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Skeleton Structures

• Comprise of a framework through which theloads are concentrated and transferred to the

supporting structure or substructure

• The strength of the members of the

framework and their connections plays an

important part in the transmission of the

applied loads

• Common materials: timber, steel and

Reinforced concrete (RC)


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Skeleton Structures

• Apex Frame

• Rectangular Frame

• Truss Frame

• Portal Frame

• Shed Frame

• Grid Frame

• Geodesic Frame

• Suspension Frame


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Skeleton Structures Apex Frame

• Framework of poles is jointed at or near one end to provide the

framework of a conical shape


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Apex Frame


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Skeleton StructuresRectangular Frame

• A series of uprights and cross-members set up in mutually

perpendicular planes

•Provides the framework for support to the floors, walls and roofs


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Skeleton Structures

Truss Frame • The truss frame a structure comprising one

or more triangular units

• Constructed with straight members whose

ends are connected at joints referred to

as nodes.

• External forces and reactions to those forcesare considered to act only at the nodes and

result in forces in the members which are

either tensile or compressive forces.


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Skeleton Structures

Portal Frame • Portal frame construction is a method of building

and designing simple structures, primarily

using steel or steel-reinforced precast concrete

• Similar to an arch, but consisting of two uprights

rigidly jointed by a horizontal, sloping or curved third

member

• Each frame requires lateral support, usually in the

form of bracing


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Skeleton Structures

Shed Frame

• Similar to portal

frame, but the third

member is in the

form of a roof truss


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Skeleton Structures

Grid Frame (Space Frames) • Used for lightweight roof structure covering large

open floor areas

• The frame comprises a series of triangular frames

set out in the form of a grid

• The grid may be in the form of one, two or three

layers or of a space grid which comprises a six-

member frame joined to other similar frames

forming a strong rigid framework


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Skeleton Structures

Geodesic Frame • Formed in the shape of a dome and comprising a

network of triangular frames in the form of spherical

triangles

• i.e. portions of a sphere formed by the intersections

of great circles (great circles has a diameter equal to

that of the sphere it is drawn on)

• The greater the number of triangles used in the

structure, the less the chance of collapse


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Skeleton Structures

Functional Requirements • The primary function of a skeleton frame is to carry all the loads imposed on the

building, without deforming excessively under load as a whole or in parts

• Transfers all these loads to the building sub-structure (foundation)

• To meet this function efficiently, it must have adequate design and construction

regarding:

i) strength and stability - appropriate materials & stiffness of joints

ii) fire resistance - for a period long enough for occupants to escape


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Surface Structures

• Load carried by the roof and has thin skin

which is:

i. Sufficiently rigid to be self-supporting when

shaped and the shape provides additional

strength

ii. Sufficiently strong but flexible enough to support

load when stretched across a supporting

framework


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Surface Structures

• Shell Dome


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Surface Structures

Barrel Vault

• Both structures above use

their curved shape to obtainstrength e.g. principle of an

egg, when pressed by fingers

it will not break


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Barrel Vault

Surface Structures


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Surface Structures

Suspension Roofs & Tents

• The membrane stretched over some other skeleton framed

• Form a structural component itself


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Air-Supported Structures

http://www.alibaba.com/catalog/11161717/Air_Supported_Structure.html


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Advantages of Skeleton

Frame Structure Advantages over solid & surface structures:

1. Save in floor space

2. Flexible in plan and building operations (because of the

absence of the load bearing walls at any level)

3. Reduction of dead weight


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Classification of Frames

The building frames may be classified according to the stiffness or

rigidity of the joints between members (especially in columns andbeams)

Non-rigid frame

• The nature of the joints is such that the beams are assumed to

be simply supported and the joints are non-rigid

• Rigidity in the frame structure as a whole is ensured by the

inclusions of some stiffening elements in the structure, often inthe form of triangulating members – bracing (normally in steel

and pre-cast concrete frame)


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Semi-rigid frame

• Where some or all jointsachieved some degree ofrigidity

• Normally used in steel framedbuildings where connection areof both bolt and weld)


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3. Fully Rigid Frame

- Where all joints are rigid

- Normally in steel where joints are

welded & conc. frame where

members are cast monolithically


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Choice of Structural Materials for

Building Frames1. Concrete

- Strength varies according to the mix

- Strong in compression weak in tension

- Compressive strength – 1/16 of steel

- Tensile strength 1/10 of its compressive strength

- Stiffness is low compared to steel

2. Steel

- Very strong and stiff- Strong both in compression and tension

- Relatively economical –

- Non-combustible; but at 427 C – 482 C it will lost strength


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Factors that Influence the Choice of Building Frame

Structural Materials

i. Availability of materials and labours

ii. Cost

iii. Speed of erection

iv. Possibility of standardizing the size of structural members

v. Size and nature of site

vi. Fire resistance required

lecture 1 building structures(2)

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