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Presentation on theme: "CIVIL ENGINEERING PROJECT KOLEJ MATRIKULASI TEKNIKAL KEDAH"— Presentation transcript:


2 ii. Performance failure ● Creep ● Shrinkage
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 2


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. 4

5 CONCRETE Concrete has strength, durability, versatility, and economy.
It can be placed or molded into virtually any shape and reproduce any surface texture. 5

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 (positive—it gets longer) and compression (negative—it 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 Loads Tension Compression 19

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? Stirrup and column ties
Steel in place in a abeam

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)
- 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 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 43


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