TOPIC 1.0 FORCE IN CIVIL ENGINEERING PROJECT

1
TOPIC 1.3
RESPONSE OF CIVIL ENGINEERING PROJECT
BY NOR AZAH BINTI AZIZ KOLEJ MATRIKULASI
TEKNIKAL KEDAH
2
Learning Outcomes
Identify and describe material response of modes
primary failure due to A) Concrete i. Structure
failure ? Compressive ? Tensile ? Shear. ii.
Performance failure ? Creep ? Shrinkage
3
CONCRETE
4
CONCRETE

• Concrete is a construction material composed of
  cement (commonly Portland cement), coarse
  aggregate, fine aggregate, water and admixture.
• The cement and water form a paste that hardens
  and bonds the aggregates together.
• Concrete is the most widely used construction
  material in the world.

5
CONCRETE

• Concrete has strength, durability, versatility,
  and economy.
• It can be placed or molded into virtually
• any shape and reproduce any surface texture.

6
Concrete Structure Failure

• i) Compressive
• ii) Tensile
• iii) Shear

7
What is the Compressive Strength(CS)?
8
Introduction

• Compressive strength is the capacity of a
  material or structure to withstand axially
  directed pushing forces. When the limit of
  compressive strength is reached, materials are
  crushed. Concrete can be made to have high
  compressive strength.
• When a specimen of material is loaded in such a
  way that it extends it is said to be in tension.
  On the other hand if the material compresses and
  shortens it is said to be in compression.

9
Introduction

• On an atomic level, the molecules or atoms are
  forced apart when in tension whereas in
  compression they are forced together. Since atoms
  in solids always try to find an equilibrium
  position, and distance between other atoms,
  forces arise throughout the entire material which
  oppose both tension or compression.
• the compressive strength of a material is that
• value of uniaxial compressive stress reached
  when
• the material fails completely
• usually obtained experimentally by means of a
• compressive test.

compression
10
Introduction

• The major difference between the two types of
  loading is the strain which would have opposite
  signs for tension (positiveit gets longer) and
  compression (negativeit gets shorter).
• Another major difference is tension tends to pull
  small sideways deflections back into alignment,
  while compression tends to amplify such
  deflection into buckling.

11
What is the Compressive Strength(CS) of Concrete?

• Concrete mixtures can be designed to provide a
• wide range of mechanical and durability
  properties
• to meet the design requirements of a structure.
• The compressive strength of concrete is the most
  common performance measure used by the
• engineer in designing buildings and other
  structures.
• CS is measured by breaking cylindrical concrete
  specimens in a compression-testing machine.

12
compression tests of cylinders of concrete which
are crushed 28 days after they are made.
13
What is the Compressive Strength(CS) of Concrete?

• CS is calculated from the failure load divided
• by the cross-sectional area resisting the load
• (pound-force per square inch (psi) in US) and
  Customary units or megapascals (MPa) in SI units.
• Concrete CS requirements can vary from
• 2500 psi (17 MPa) for residential concrete to
• 4000 psi (28 MPa) and higher in commercial
  structures.
• Higher strengths up to and exceeding 10,000 psi
  (70 MPa) are specified for certainapplications.

14
What is the Compressive Strength(CS) of Concrete?
Compressive strength. The amount of force a
material can support in a single impact
15
Why is Compressive Strength(CS) Determined?

• Compressive strength test results are primarily
  used to
• determine that the concrete mixture as delivered
  meets the
• requirements of the specified strength in the
  job
• specification.
• Strength test results from cast cylinders may be
  used for
• quality control, acceptance of concrete, or for
  estimating the concrete strength in a structure
  for the purpose of
• scheduling construction operations such as form
  removal
• or for evaluating the adequacy of curing and
  protection
• afforded to the structure.

16
Why is Compressive Strength(CS) Determined?

• Fractured Test Specimen at Failure

17
Why is Compressive Strength(CS) Determined?

• Concrete structures, except for road pavements,
• are normally designed on the basis that concrete
  
• is capable of resisting only compression, the
• tension being carried by steel reinforcement.

18

What is Compressive Stress?

• applies to materials resulting in their
  compaction (decrease of volume).
• When a material is subjected to compressive
• stress then this material is under compression.
• Usually compressive stress applied to bars,
• columns, etc. leads to shortening.

19
Component action
20
Modes of failure of standard concrete cylinders
21
What is Tensile Strength?

• Concrete has substantial strength in compression,
  but is weak in tensile.
• The Tensile strength of concrete is roughly 10
  of its compressive strength
• Nearly all reinforce concrete structures are
  design on the assumption that the concrete does
  not resist any tensile forces.
• Tension will create cracking of the concrete.

22
What is Tensile Strength?

• Importance in design of concrete roads
• and runways.
• E.g, its flexural strength or modulus of
  rupture(tensile strength in bending) is
• utilized for distributing the concentrated
  loads over a wider area of road pavement.

23
What is Tensile Strength?
Tensile strength. The amount of stretching force
a material can withstand
24
What is Flexural Strength?

• FS is one measure of the tensile strength of
  concrete.
• Measured on unreinforced concrete beam or slab to
  resist failure in bending.
• Is expressed as Modulus of Rupture(MR) in psi
  (Mpa)
• Flexural MR is about 10 to 20 percent of CS
  depending on size, type and volume of coarse
  aggregate used.

25
What is Shear Strength?

• Shear strength in engineering is a term used
• to describe the strength of a material or
• component against the type of yield or
  structural failure where the material or
  component fails in shear.
• A shear load is a force that tends to produce
• a sliding failure on a material along a plane
• that is parallel to the direction of the force.

26
What is Shear Strength?

• the shear strength of a component is important
• for designing the dimensions and materials to
• be used for the manufacture/construction of
• the component (e.g. beams, plates, or bolts).
• In a reinforced concrete beam, the main purpose
  of stirrups is to increase the shear strength.

27
What is Shear Strength?
Steel in place in a abeam
Stirrup and column ties
28
What is Shear Strength?

• Shear strength is the maximum shear stress that a
  material can absorb in one impact before failure
  ness of the material tested.

Shear strength. The maximum shear stress a
material can absorb in one impact
29
Concrete Performance failure

• Spalling
• Shrinkage
• Creep

30
Spalling Concrete ( concrete cancer)

• Concrete cancer can affect any building in
• which reinforced concrete is used.
• This includes floor slabs, stairs, balconies,
  walls, columns, beams and pathways.
• Essentially, the steel responsible for
  reinforcement has begun to rust.

31
Spalling Concrete ( concrete cancer)

• Spalling concrete is concrete which has broken
  up, flaked, or become pitted.
• This is usually the result of a combination of
  poor installation and environmental factors which
  stress the concrete, causing it to become
  damaged.
• On a low level, concrete spalling can be purely
  cosmetic in nature. However, it can also result
  in structural damage such as damage to
  reinforcing bars positioned inside the concrete.

32
Spalling Concrete ( concrete cancer)

• Spalling concrete is largely due to a natural
  deterioration process called carbonation.
• Carbon dioxide in the air diffuses into the
• concrete and reacts with the alkalis in it.
• The concrete becomes carbonated and this allows
  the embedded steel bars to corrode.
• These corroded steel bars expand and exert a
  force on the surrounding concrete causing the
  concrete to bulge and crack.

33
Spalling Concrete ( concrete cancer)

• The early stages of spalling concrete will
• not affect the safety of the building. However,
  the spalling concrete should be repaired as soon
  as possible before the steel bars corrode further
  and damage larger areas hence the term 'concrete
  cancer'.

34
Spalling Concrete ( concrete cancer)

• Spalling Concrete - Concrete Cancer
• - Corrosion in Reinforced Concrete

35
Spalling Concrete ( concrete cancer)
36
Concrete Shrinkage

• Shrinkage of concrete is defined as the
  contraction due to loss of moisture.
• Due to the shrinkage of concrete, the prestress
  in the tendon is reduced with time.
• Prestressed concrete
• concrete with stresses induced in it before use
  so as to counteract stresses that will be
  produced by load often contains stretched steel
  bars or wires called tendons

37
Concrete Shrinkage

• Due to water loss to atmosphere (volume loss).
• Plastic shrinkage occurs while concrete is still
  wet (hot day, flat work, etc.)
• Drying shrinkage occurs after concrete has set
• Most shrinkage occurs in first few months (80
  within one year).
• Reinforcement restrains the development of
  shrinkage

38
Concrete Shrinkage

• As concrete harden there is reduction in volume
• It caused a shrinkage
• - Absorption of the water by the concrete and
  the aggregate
• - Evaporation of the water which rises to
  concrete surface.
• This contraction can lead to cracks or breaks in
  the surface of the concrete, or in tiles and
  other floor finishes installed over the slab.
• To minimize cracks associated with concrete
  shrinkage, builders place control joints at
  specific intervals along the concrete.

39
Concrete Shrinkage

• A wet mix makes pouring easier but it also
• tends to encourage shrinkage.
• The more shrinkage the higher chances
• of finding cracks later.

40
Restrained shrinkage cracking
Parallel cracking perpendicular to the direction
of shrinkage
40
41
Concrete Creep

• Creep of concrete is defined as the increase in
• deformation with time under constant load.
• Due to the creep of concrete, the prestress in
  the
• tendon is reduced with time.
• Basically, long term pressure or stress on
  concrete
• can make it change shape.
• This deformation usually occurs in the direction
  the force is being applied.

42
Concrete Creep

• Like a concrete column getting more compressed,
  or a beam bending.
• Creep does not necessarily cause concrete to fail
  or break apart.
• Creep is factored in when concrete structures
  are designed.
• creep deformation does not occur suddenly upon
  the application of stress. Instead, strain
  accumulates as a result of long-term stress.
  Creep is a "time-dependent" deformation.

43
(No Transcript)