2.0 ANALYSIS AND DESIGN

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15 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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PREPARED BY :

NOR AZAH BINTI AZIZ

KOLEJ MATRIKULASI TEKNIKAL KEDAH

2.0 ANALYSIS AND DESIGN

2.2 STRUCTURAL ELEMENTS

Load Paths




The
load path

is simply the direction in


which each consecutive load will pass


through connected members.



The sequence commences at the highest point


of the structure working all the way down to


the footing system, ultimately transferring the total


load of the structure to the foundation.



Load Paths




Ultimately, the lowest structural member must


be strong enough to support all members above it.



This is why engineers often design the uppermost


members first and progressively work their way


down the structure following the load path.



RAFTER

PURLIN

GROUND SLAB

STUMP

FOUNDATION

COLUMN

ROOF BEAM

ELEVATED
SLAB

ROOF SHEET

GROUND BEAM

WALL

Load analysis distribution and path

Load Path Components in a Concrete
structure



Part of the load


path in a typical


multi
-
storey


reinforced concrete
structure is made up
of the following
components.



MAIN BEAMS

COLUMN


FLOOR SLABS

SECONDARY
BEAMS

Load Path in a Domestic Structure



The direction that loads are transferred through


a structure is important and must be identified.



A simple domestic structure works on similar


principles as a large concrete structure although


the components are different:


-

the foundation supports the footings


-

the footings support the flooring structure which


consist of bearers, joists and flooring


-

the stud walls and bracing transfer their load to the flooring


-

the roof trusses support the battens which support



the roof cladding and this load is transferred to the walls.



Load Path




A diagram shows the
framing of the roof, wall,
floor, footing and
foundation of a building.


The load of the path is
shown in the diagram.


ROOF

WALL

FLOOR

FOOTING

FOUNDATION

Load Path

STRUCTURAL

COMPONENT

LOAD PATH

Roof


Roof load are transfer to roof
beam

Wall


Wall load is transfer to beam



Floor
Slab


Carry direct applied load and
transfer it to
beam

Beam


Carry load from floor slab and
transfer it to column

Column


Carry load from beam and
transfer it to foundation

Foundation


Carry and distribute building
load to soil beneath

Nature of Load
-

Point Load



A point load


-

often abbreviated to
P

or
L


-

is a load acting at a single point.


-

sometimes called a concentrated load.



Example;


-

Roof truss supported on a top plate


-

As the contact area of a truss on the top plate is small,



the load is assumed to be concentrated at a point.


Nature of Load
-

Point Load


A diagram shows a plank of timber
appearing horizontally above a
roof truss.


At the end of the plank is an arrow


showing the information P or L
units kN.


On either side of the roof truss is a
top plate.


Where the top plate and roof truss


intersects is a an arrow indicating
P or L.


Nature of Load
-

Uniformly Distributed
Load


A uniformly distributed load (UDL)


-

is a load that is evenly spread along a length



or across an area.


For example, the loads supported by a


typical beam include:


• the beam’s own weight


• the weight of the floor slab it is supporting


• the live load supported by the floor slab.


Nature of Load
-

Uniformly Distributed
Load


These loads are consistent along the entire


length of the beam.



The load may be represented as ;


i) rate per linear metre (kN/m) for beams


ii) rate per square metre (kN/m
2
) for slabs.


Nature of Load
-

Uniformly Distributed
Load


A diagram shows a beam with
the load distributed all along
its length.


The load is labelled UDL with
units shown as kN/m or
kN/m
2
.


A reinforced concrete beam is
displayed and labelled with
UDL equal to 4.3 kN/m.


A reinforced concrete slab is
displayed and labelled 2.7
kN/m
2
.

Nature of Load
-

Uniformly Varying
Load


A uniformly varying load


-

is a load that is distributed along the length



of a linear element such as a beam,



but instead of the load being evenly spread it



varies in a linear fashion.



Example ; Retaining wall.


-

is designed to hold back earth, which exerts a



horizontal force on the back of the retaining wall.

Nature of Load
-

Uniformly Varying
Load


A diagram shows a vertical
section through a retaining
wall.


The retaining wall is in the
shape of an upside down
‘T’. The earth to the left of
the wall is labelled ‘retained
earth pushes horizontally at
back of wall’.

Nature of Load
-

Uniformly Varying
Load


A diagram shows a symbolic
representation of a uniformly
varying load on a retaining wall.


This shows a number of arrows
pointing to the right. The length
of these arrows indicates the
strength of the load on the wall
at different heights.


The load is smallest at the top of
the wall and greatest at the base
of the wall.


A right angled triangle is drawn
around these arrows to further
illustrate this point.



Moments are a
measure of the turning
effect of a force around
a specified turning point
or pivot.


A moment is a
force

times a
distance
. The
unit used to measure a
moment is newton
metres (Nm).




Nature of Load
-

Moments







M = F x d


M = 10 N x 5 m


M = 50 Nm


Note that the units are Nm (
newton

metres
)


not N/m (
newtons

per
metre
).


Nature of Load
-

Moments








The direction of a moment is
opposite



to the direction of the force



Nature of Load
-

Moments








The convention is that:


clockwise

moments are positive


anti
-
clockwise

moments are negative.


Nature of Load
-

Moments



MAIN BEAMS

ARE SUPPORTED BY COLUMN

BACK



COLUMN

ARE ARRANGED IN A GRID PATTERN

BACK



SLABS

ARE SUPPORTED BY THE MAIN BEAMS

BACK



SECONDARY BEAMS

ARE SUPPORTED BY

THE MAIN BEAMS

BACK

Roof

The roof load path flows
down through the walls to
the foundation.

BACK

Wall

The wall load path flows
down through the floor to
the foundation.

BACK

Floor

The floor load path flows
down through the footing
to the foundation.

BACK

Footing

The footing load path
flows down through to
the foundation.

BACK

Foundation

The foundation
supports the footings.

BACK