1.2 Forces on Civil Engineering Structures_Note1

1.0 INTRODUCTION OF CIVIL ENGINEERING

1.2 Forces on Civil Engineering Structures

1.0 INTRODUCTION OF CIVIL ENGINEERING

1.2 Forces on Civil Engineering Structures

FORCES ON CIVIL ENGINEERING STRUCTURES

Learning Outcomes;

(a) Describe action on civil engineering structures due to physical forces;
i) Permanent action(self weight, superimposed dead load)
ii) Variable action:
 Traffic loads
 Imposed loads
 Hydrostatic pressure; and
 Earth pressure

(b) Describe actions on civil engineering structures due to environmental factors:
i. wind
ii. Earthquake
iii. Waves
iv. Flood
v. fire
vi. pollutant

Describe action on civil engineering
structures due to physical forces

i) Permanent action

Permanent actions (known as dead load) are permanent or
stationary loads which are transferred to structure throughout

the life span.

Permanent action is primarily due to

- self weight of structural members

- superimposed dead load such as permanent
architectural component; exterior cladding, partitions
and ceilings

i) Permanent action

i) Self-Weight

❑ is the weight of the structure acting with gravity on the foundations
below.

❑ Include the weight of the structure, all architectural
component such as exterior cladding, partitions and ceilings.

❑ The weight of structure does not change in value and location of its
action.

❑ Characteristics of action load
a) its value is fixed and simply determined by its
density and dimension ( size)
b) its point of action is fixed

i) Permanent action

ii) Super Imposed Dead Load

❑ Super imposed dead load is load from applied
finishes and building services.

❑ is the load that always applied on the finished
element or structure that is not transferring
to the ground.

❑ Equipment and static machinery when permanent fixtures
are also considered as part of dead load

Dead load
The action of dead load on a bridge

Here shown, the weight s of some common materials used in
construction of building

ii) Variable action

Variable actions (live loads) are those actions that
can change over time

Live loads are temporary or moving load
Load that acts on structural component
These load are more difficult to determine

accurately. Estimates done on standard codes of
practice or past experience

ii) Variable action

Imposed Load

imposed loads(live load) on floors and roofs consists of
all the loads which are temporarily placed on the
structure.

 For example, loads of people, furniture, machines etc.
Imposed loads keep on changing from time to time.

EXAMPLE

Towers: Live and Dead Loads

 Towers serve many purposes. Radio, TV and wireless
communication signals are transmitted from towers. Forest rangers
keep a vigilant eye peeled for signs of forest fires from observation
towers. Skyscrapers serve an important role in the world’s urban
areas.

 Like other structures, towers are subjected to dead and live loads. In
the case of a skyscraper, dead loads are comprised of steel columns
and beams, concrete, and glass – the weight of the structure itself.
Live loads include the people milling about on the floors and
ascending the elevators; plus furniture, materials, and goods that
move into the building.

 Another important live load acting on a skyscraper is the force of wind
blowing against the exterior surfaces. Because the buildings have an
enormous amount of surface area, the force of wind on a skyscraper
can be extremely powerful.

Imposed load acting in structures

ii) Variable action

Traffic Load

Also known as dynamic load, moving load, impact load

The standard measurement for vehicle traffic load on a
section of road, bridge and the basis for most
decisions regarding transport planning.

Example : load from vehicles such as cars and busses
on the road

Traffic load on Bridge

FA FB

ii) Variable action

Hydrostatic pressure

In a fluid at rest, the weight of the liquid will create
a pressure on the surface of a body.

This pressure is defined as the hydrostatic pressure
Its depend on density of the liquid and depth.
Normally consider for marine structure and

dam structure.

ii) Variable action

Hydrostatic pressure increase in proportion to
depth measured from surface because of the
increasing weight of fluid exerting downward force
from above.

Force on a Submerged Surface- Examipi)leVariable action

The pressure distribution on the wall

ii) Variable action

Dam Structure

Arch Dam Cross Section

ii) Variable action

Lateral earth pressure

Lateral earth pressure is the pressure that soil exerts in the
horizontal plane.

The common applications of lateral earth pressure theory are
for the design of ground engineering structures such as
retaining walls, basements, tunnels, and to determine the
friction on the sides of deep foundation

Example : for design a retaining walls, basement, tunnels

ii) Variable action
Action of lateral earth pressure on a retaining wall

 Retaining walls and their attachment to mudsills and floor
joist must be design properly to withstand this load.

ii) Variable action

Soil Nailing

Soil nailing is a technique in which soil slopes, excavations or retaining walls
are reinforced by the insertion of relatively slender elements - normally
steel reinforcing bars. The bars are usually installed into a pre-drilled hole
and then grouted into place or drilled and grouted simultaneously.

Actions on civil engineering structures due to
environmental factors:

i. Wind
ii. Earthquake
iii. Waves
iv. Flood
v. Fire
vi. pollutant

ii) Environmental factors

i) Wind load

positive or negative pressures exerted on a house when it
obstructs the flow of moving air.

generally act perpendicular to the surfaces of the building.
Wind loads depends upon the velocity of wind, shape and

size of the building
The design wind speed is determined

from historical record to protect
future extreme wind speeds.

Direction of wind forces





27

Shanghai World
Financial Center

The trapezoidal notch at the top of the
building reduces wind loading.
(Source: emporis.com)

ii) Environmental factors

ii) Earthquake

Earthquakes are the result of sudden release of energy in the
earth crust that causes seismic waves.

@

natural vibrations of the ground caused by movement along
fractures in Earth’s crust, or sometimes, by volcanic eruptions

It causes shaking of the ground, so building resisting on it will
experience motion at its base

The engineering intention is to make buildings earthquake
resistance, such buildings resist the effects of ground shaking,
although they may get damaged but would not collapse during
strong earthquake.

30

Earthquake force

ii) Environmental factors

iii) Wave load

A wave is a disturbance (an oscillation) that travels
through space and time.

Waves travel and the wave motion transfers energy
from one point to another.

Commonly used in the analysis of offshore structure,
piping and an engineering platform.

 Wave loads are those loads that result from water waves propagating
over the water surface and striking a building or other structure.



ii) Environmental factors

iv) Flood

Flood is an overflow or accumulation of an expanse of
water that submerges land.

Flood load is the pressure exerted on a house when it obstructs
the flow of moving water.

The forces produced from flood can damage any type of
structure, including bridges, cars, buildings, sewerage systems,
roadways, and canals.



ii) Environmental factors

v) Fire

Defined as a thermal stress (steady-state upper
layer temperature) resulting from a fire within a
building space.

The energy needed to produce the target
temperature is a function of the geometry, heat
losses, and ventilation of the space and can be
estimated in a number of ways.

Example : heat release from fire, occupants and
building requirements.

ii) Environmental factors

vi) Pollutant

A pollutant is a waste material that pollutes air, water or soil,
and is the cause of pollution.

Smog, coal dust and other chemicals in the air have
deleterious effects on people, plants and animals, and these
chemical pollutants also have effects on our buildings and
structures as well.

Dust

• Air pollution most noticeably affects buildings by depositing
dust and filth on them.

• Though we have different forms of air pollution today, the
deposits that soil buildings and structures is one of the most
common effects, often staining buildings a permanent
colour with the dirt.

Acid Rain

 It refers to rain that has been affected by pollution so that it is more
acidic than it should be.

 The acidic nature of this rain can cause major damage to buildings and
structures over time.

 This is especially true of limestone buildings, which are particularly
sensitive to the effects of acid rain.

Figure : Acid rain damages buildings



CONCLUSION

As an structural engineer, you should have
to consider all off physical and

environmental forces in your calculation
design to determining location, material,
and size of structural elements to resist

forces acting in a structure

Mohd Suhaimi bin Ahmad is a Senior Lecturer of Civil Engineering at Kolej Matrikulasi Kejuruteraan
Kedah, Pendang, Kedah. He graduates B. Civil Eng. from UTHM and MSc. Civil Engineering from
UNIMAP. He also obtained Diploma & Cert. in Civil Eng. (Construction-Polytech) and Edu. Diploma
(Domestic Water Supply-MPBP). His Registered as Graduate Engineer with BEM and Graduate
Technologist with MBOT. Have an experience in civil engineering field and teaching since 2004.

Nor Azah binti Aziz is a Senior Lecturer of Civil Engineering at Kolej Matrikulasi Kejuruteraan Kedah,
Pendang, Kedah. She obtained B. Tech. & Edu. (Civil Eng.) & Diploma Civil Eng. from UTM and
M. Edu. Tech. from USM. Have an experience in teaching Civil Engineering since 2001. She is actively
involved in the Civil Engineering syllabus drafting program at the matriculation division level