Engineering practice lecture no 05 Lecture-05.pptx

Engineering practice lecture no 05

1. Engineering Practice Lecture 05

2. Mass Concreting ACI Concrete technology defines Mass concrete as; “Any volume of concrete in which a combination of dimensions of the member being cast, the boundary conditions can lead to undesirable thermal stresses, cracking, deleterious chemical reactions, or reduction in the long-term strength as a result of elevated concrete temperature due to heat from hydration.”

3. Mass Concreting

4. Applications of Mass Concreting In Columns and Foundations oh high rise buildings Dams Reservoirs Retaining Walls

5. Mass Concreting Mass concrete should be properly designed, placed, and cured to obtain a durable structure. In mass concrete work, the major problem is temperature shrinkage. Cracks my cause loss of structural Integrity, excessive shrinkage, loss in durability.

6. Methods of Temperature Control Use of low heat materials. Pre-Cooling of concrete Post Cooling of Concrete Surface Insulation.

7. Methods of Temperature Control Use of low heat materials . Select low heat of hydration cement. Use low cement content. Use of fly ash generates half as much heat as the cement that it replaces and is often used at a replacement rate of 15-25%. Ground granulated blast furnace can be used. Use large sized aggregates to reduce heat of hydration.

8. Methods of Temperature Control Pre cooling of Concrete . Use of chilled mix water. Sometimes mix water can be replaced with ice. Efforts to cool aggregates have pronounced effects on concrete temperature. Liquid Nitrogen can also be used to precool concrete. But this method significantly increase the cost of concrete.

9. Methods of Temperature Control Post cooling of Concrete . Cooling pipes in mass concrete are sometimes used to reduce the maximum concrete temperatures. This methods can have high initial and operating costs. It is important to emphasize again that significant thermal and internal cracking can result if post cooking is improperly performed.

10. Methods of Temperature Control Surface Insulation: Insulated formwork is often used to warm the concrete surface and reduce the temperature difference , which in turn minimizes the potential of thermal cracking. Insulation often has to remain in place for longer period of time. Removing it too soon can cause surface to cool quickly and crack.

11. Methods of Temperature Control Surface Insulation:

12. Pre-Stressed Concrete In conventional reinforced concrete, the high tensile strength of steel is combined with concrete's great compressive strength to form a structural material that is strong in both compression and tension. The principle behind pre-stressed concrete is that compressive stresses induced by high-strength steel tendons in a concrete member before loads are applied will balance the tensile stresses imposed in the member during service.

13. Pre-Stressed Concrete Pre-stressing removes a number of design limitations conventional concrete places on span and load and permits the building of roofs, floors, bridges, and walls with longer unsupported spans. This allows architects and engineers to design and build lighter and shallower concrete structures without sacrificing strength.

14. Pre-Stressed Concrete Conventional Concrete Pre-Stressed Concrete

15. Methods of Pre-Stressing Pre-Tensioning: In the pre-tensioning process, the steel is stretched before the concrete is placed. High tensile steel wires or tendons are used between two ends and stretched to 70-80% of ultimate strength. After that, concrete is poured around the tendons and allowed to cure. Once the concrete gains the desired strength, the stretching forces are released. When the highly stressed steel attempts to contract, concrete gets compressed and in a permanent state of maintaining pre-stressed strength.

16. Methods of Pre-Stressing Post-Tensioning: In post tensioning, the steel is stretched after the concrete hardens. Post tensioning is carried out at the project site. Concrete is cast and allowed to cure. When the concrete reaches its required strength, tendons are stretched. The excess ends of tendons are cut away. Examples: Roads, Bridges, Railways, Tunnels. Dams, Foundations, Reservoirs,

17. Advantages of Pre-Stressed Concrete Consumption of materials like concrete, steel is reduced. Longer beam spans and girders can be constructed which gives untroubled floor space. It has long term durability. Possibility of steel corrosion and subsequent concrete deterioration is reduced because concrete is crack free. Pre-stressed concrete offers greater load resistance and shock resistance. The compressive strength of concrete and tensile strength of steel is used to their fullest.

18. Masonry Construction Masonry consists of building structures from single units that are laid and bound together with mortar. Brick, stone and concrete blocks are the most common materials used in masonry construction.

19. Advantages of Masonry Construction Masonry is non-combustible, so improves  fire protection  for the building and its occupants. Fireplaces are commonly made of masonry for the same reason. Offers a high resistance against rotting, pests, weather, and natural disasters such as hurricanes and tornadoes. Provide an attractive rustic or elegant look for a home or building, depending on the material used and the workers’ expertise. Durable and resistant, masonry can withstand large amounts of compressive weight loads. Masonry doesn’t rot, and insects such as ants and termites can’t destroy its structure. Using this method in construction costs less in terms of labor and materials as compared to using wood.

20. Disadvantages of Masonry Construction Masonry construction involves heavy materials such as bricks, stone and concrete blocks. These cannot be transported in conventional vehicles, and in some cases they must be ordered from special catalogs, especially stones. The stability of masonry structures depends completely on their foundation. If any settling of the foundation occurs, cracks are likely and they must be repaired to prevent moisture infiltration and damage. Masonry activities cannot be done during heavy rain or freezing conditions, since mortar will be severely affected. Masonry construction requires a good amount of time and adequate  project planning . Depending on the type or masonry, specialized manpower may be necessary.

21. Commonly Used Materials: Brick Masonry: Advantages: Brick masonry does not require highly skilled labor, since the shape and size of the masonry units is uniform. Bricks are also lightweight (lower dead loads), easy to handle and transport, and cheaper that stones and concrete blocks. Brick walls are thinner, and units can be adhered with different types of mortar, depending on structural requirements.

22. Commonly Used Materials: Brick Masonry: Disadvantages : Bricks have a low resistance against tension and torsion loads, making them more susceptible to seismic damage. Compared with stone and concrete blocks, bricks are also less strong and durable, and limited in sizes and colors. Plasterwork is required as finishing, which raises  construction costs .

23. Commonly Used Materials: Stone Masonry: Advantages : Stone masonry is the most durable, strong and weather resistant. One of the main advantages of stone is its aesthetic look, with a variety of colors, sizes and textures - the design possibilities are endless. Stone masonry requires little maintenance and repairs.

24. Commonly Used Materials: Stone Masonry: Disadvantages : Stone walls are thick and heavy, reducing floor space. It also has a high self-weight, combined with low flexural strength, tensile strength and seismic resistance. Stone masonry is time-consuming and it requires skilled workers, since it cannot be altered, repaired or relocate easily.

25. Commonly Used Materials: Concrete Block Masonry: Advantages : Concrete blocks are resistant against weather, pests, mold, and fire. Transporting concrete blocks can be quite expensive, but this material can be found locally in most cases. Concrete blocks are available in many sizes, finishes and colors. These units can also be manufactured to meet any set project requirements, and some concrete blocks are made using recycled materials. Concrete blocks have good insulating properties against heat, sound and moisture.

26. Commonly Used Materials: Concrete Block Masonry: Disadvantages : Large concrete blocks are heavy and difficult to handle, requiring more manpower. Concrete blocks also increase the amount of steel required in reinforced cement concrete structures. The price of concrete blocks can vary depending on the region, cement costs and availability.  Plumbing issues  are harder to solve when they occur in a concrete masonry structure, since they can cause internal flooding. An effective drainage system is very important when dealing with concrete block masonry.

27. Stone Masonry: Rock that is removed from its natural site and generally cut or dressed and then finished for building purposes is called stone and the art of building the structure with stones as constructional units is called stone masonry. Types of stone masonry: Rubble Masonry Ashlar Masonry

28. Stone Masonry: Rubble Masonry: The stone masonry in which either undressed or roughly dressed stones are laid is called “Rubble Masonry”. In this masonry, the joints of mortar are not of uniform thickness, The strength of rubble masonry depends on; Quality of mortar The proper filling of mortar between the spaces of stones.

29. Stone Masonry:

30. Stone Masonry: Ashlar Masonry: The stone masonry in which finely dressed stones are laid in cement or lime mortar, is known as ashlar mortar. In this masonry, all joints are regular, thin and of uniform thickness. This type of masonry is costly in construction. This masonry is used for heavy structures, arches, architectural building etc.

31. Stone Masonry:

32. Composite Walls: When Walls are constructed with two are more types of building materials, it is known as composite masonry. The composite masonry is adopted due to following reasons; Reduces overall construction cost. Improves appearance of structure. Use of locally available materials to obtain optimum economy.

33. Cavity Walls: Cavity walls consist of two skins separated by hollow space. The skins are commonly masonry such as bricks or concrete blocks. Masonry is an absorbent materials and will slowly draw rainwater or even humidity into the wall. The cavity serves as a way to drain this water out through weep holes at the base of wall system or above windows.

34. Function of Cavity Walls: Strength Stability Thermal Insulation Weather Exclusion Sound Insulation Durability Fire Resistance.

35. Lintels: A horizontal structural member which is placed across the opening. Types of Lintels: Timber Lintels Stone Lintels. Brick Lintels Reinforced Concrete Lintels