Important Points For Civil site Engineer

Basic Points

A)     Bricks

1)      Bricks should be soak in water for 1 hour and spary water before use.

2)      For masonary work – 1 part cement and 6parts sand.

3)      The bricks should be laid alternate header and stretcher pattern

For block only stretcher pattern

The vertical joints should be staaaered

4)      The joints in bricks bulky filled with morter of 10-12mm

5)      For half partition bricks wall or 100mm thik wall place 6mm diameter rebar in every 4^th course

6)      The masonary wall should not raise 1 m height in day.

7)      Masonary wall cured for 10 days.

B)     Aggregate

1)      The size between 4.75mm to 80mm are coarse aggregate

2)      The rougn and non glacy surface aggregate are considered best for construction

3)      Angular aggregate assure high compressive strength in concreate because of the inter locking the angular aggregate due to their hisher specific surface area .

4)      The aggregate should not absorb water more than 10% of their weight (after 24 hr)

5)      Flaky/ thin, elongate / long aggregate not more than 35% by weight of total quantity.

6)      For RCC works 20mm and down size of aggregates.

7)      For 20mm and 10mm the combined ratio is 60:40 or 70:30

Development length:

“The embedded length in concrete is called development length. The minimum length of steel bars necessary on either side od section to develop bond is called as development length.”

Note: for HYSB steel bars increase value for mild steel by 60%

Overlapping length:

The lap of bar needed to transfer the stressen to other bar. Lap length is provided for overlapping two rebars in order to salely transfer the load from one bar to another

1)      Beams and slabs: 60d

2)      Column                : 45d

Bend:

The anchorage value of bend shall be taken as for each 45degree bend, 4 times diameter of bar to maximum upto 10 diameter of bars

What is Foundation

What is Foundation in Construction? Purpose and the Functions of Foundations

What is a Foundation in Construction?

Foundation is the lowest part of the building or the civil structure that is in direct contact with the soil which transfers loads from the structure to the soil safely. Generally, the foundation can be classified into two, namely shallow foundation and deep foundation.

A shallow foundation transfers the load to a stratum present in a shallow depth. The deep foundation transfers the load to a deeper depth below the ground surface.

A tall building like a skyscraper or a building constructed on very weak soil requires deep foundation. If the constructed building has the plan to extend vertically in future, then a deep foundation must be suggested.

Fig.1.Building Foundation in Construction

To construct a foundation, trenches are dig deeper into the soil till a hard stratum is reached. To get stronger base foundation concrete is poured into this trench. These trenches are incorporated with reinforcement cage to increase the strength of the foundation.

The projected steel rods that are projected outwards act as the bones and must be connected with the substructure above. Once the foundation has been packed correctly the construction of the building can be started.

The construction of the foundation can be done with concrete, steel, stones, bricks etc. The material and the type of foundation selected for the desired structure depends on the design loads and the type of underlying soil.

The design of the foundation must incorporate different effects of construction on the environment. For example, the digging and piling works done for deep foundation may result in adverse disturbance to the nearby soil and structural foundation. These can sometimes cause the settlement issues of the nearby structure.

Such effects have to be studied and taken care before undergoing such operations. Disposal of the waste material from the operations must be disposed properly. The construction of foundation has to be done to resist the external attack of harmful substances.

The foundation for each structure is designed such that:

• The underlying soil below the foundation structure does not undergo shear failure
• The settlement caused during the first service load or have to be within the limit
• Allowable bearing pressure can be defined as the pressure the soil can withstand without failure.

What is the Purpose of Foundation?

Foundations are provided for all load carrying structure for following purposes:

• Foundation are the main reason behind the stability of any structure. The stronger is the foundation, more stable is the structure.
• The proper design and construction of foundations provide a proper surface for the development of the substructure in a proper level and over a firm bed.
• Specially designed foundation helps in avoiding the lateral movements of the supporting material.
• A proper foundation distributes load on to the surface of the bed uniformly. This uniform transfer helps in avoiding unequal settlement of the building. Differential settlement is an undesirable building effect.
• The foundation serves the purpose of completely distributing the load from the structure over a large base area and then to the soil underneath. This load transferred to the soil should be within the allowable bearing capacity of the soil.

Functions of Foundation in Construction

Based on the purposes of foundation in construction, the main functions of the foundation can be enlisted as below:

1. Provide overall lateral stability for the structure
2. Foundation serve the function of providing a level surface for the construction of substructure
3. Load Distribution is carried out evenly
4. The load intensity is reduced to be within the safe bearing capacity of the soil
5. The soil movement effect is resisted and prevented
6. Scouring and the undermining issues are solved by the construction of foundation

Requirements of a Good Foundation

The design and the construction of a well-performing foundation must possess some basic requirements that must not be ignored. They are:

1. The design and the construction of the foundation is done such that it can sustain as well as transmit the dead and the imposed loads to the soil. This transfer has to be carried out without resulting in any form of settlement that can result in any form of stability issues for the structure.
2. Differential settlements can be avoided by having a rigid base for the foundation. These issues are more pronounced in areas where the superimposed loads are not uniform in nature.
3. Based on the soil and area it is recommended to have a deeper foundation so that it can guard any form of damage or distress. These are mainly caused due to the problem of shrinkage and swelling because of temperature changes.
4. The location of the foundation chosen must be an area that is not affected or influenced by future works or factors.

Why Clear cover is provided in RCC ? and How much clear cover is provided ?

 Why Clear cover is provided in RCC :

The result is going to be something like this. In order to protect the reinforcement from this phenomenon called corrosion and to provide fire resistance to bars embedded in concrete, nominal cover is provided for Reinforced Concrete Structures.

Concrete cover is the least distance between the surface of embedded reinforcement and the outer surface of the concrete.

Why do we provide cover then?

1. To protect the reinforcement steel from environment in order to prevent the corrosion
2. To give reinforcing bars sufficient embedding to enable them to be stressed without slipping
3. And to provided insulation from fire or heat.

However each national code suggests different cover depths like American code suggest for 40-50 mm cover where as UK code suggest for 25-50 mm.

You may think now like this " the more cover is the safer the reinforcement is". However this is not true, because as the cover depth increase it leads to increased crack width in flexural RCC members and crack width greater than 0.3 mm permit ingress of moisture and chemical attack to the concrete, resulting in possible corrosion of reinforcement and deterioration of concrete. Therefore, thick covers defeat the very purpose for which it is provided. There is a need for judicious balance of cover depth and crack width requirements

Item-wise clear cover provided in RCC as Below :

sr no                 Item                                                                  Cover Provided.
  1                   Raft foundation Bottom and side                   75 mm
  2                   Raft Foundation top                                         50 mm
  3                   Footings                                                              50mm
 4                    Beam                                                                   25 mm
 5                    Column                                                               40 mm
 6                    Slab                                                                     15-20mm
 7                    Staircase                                                             15 mm
 8                    Retaining wall                                                  20-25 mm

Note : In Order to protect R/f from this phenomenon called corrosion and provide fire resistance to bar embeded in concrete

Basic Questions asked in Interview for fresher of civil engineering

What are the steps involved in the concreting process, explain?

The major steps involved in the process of concreting are as follows:
1. Batching
2. Mixing
3. Transporting and placing of concrete
4. Compacting.

> Batching: The process of measurement of the different materials for the making of concrete is known as batching. batching is usually done in two ways: volume batching and weight batching. In case of volume batching the measurement is done in the form of volume whereas in the case of weight batching it is done by the weight.
> Mixing: In order to create good concrete the mixing of the materials should be first done in dry condition and after it wet condition. The two general methods of mixing are: hand mixing and machine mixing.
> Transportation and placing of concrete: Once the concrete mixture is created it must be transported to its final location. The concrete is placed on form works and should always be dropped on its final location as closely as possible.
> Compaction of concrete: When concrete is placed it can have air bubbles entrapped in it which can lead to the reduction of the strength by 30%. In order to reduce the air bubbles the process of compaction is performed. Compaction is generally performed in two ways: by hand or by the use of vibrators.

Describe briefly the various methods of concrete curing.

Curing is the process of maintaining the moisture and temperature conditions for freshly deployed concrete. This is done for small duration of time to allow the hardening of concrete. The methods that are involved in saving the shrinkage of the concrete includes:
(a) Spraying of water: on walls, and columns can be cured by sprinkling water.
(b) Wet covering of surface: can be cured by using the surface with wet gunny bags or straw
(c) Ponding: the horizontal surfaces including the slab and floors can be cured by stagnating the water.
(d) Steam curing: of pre-fabricated concrete units steam can be cured by passing it over the units that are under closed chambers. It allows faster curing process and results in faster recovery.
(e) Application of curing compounds: compounds having calcium chloride can be applied on curing surface. This keeps the surface wet for a very long time.

What do you understand by “preset” during the installation process of bridge bearings?

During the installation of bridge bearings the size of the upper plates is reduced to save the material costs. This process is known as preset. Generally the upper bearing plate comprises of the following components:
> Length of bearing
> 2 x irreversible movement.
> 2 x reversible movement.
The bearing initially is placed right in the middle point of the upper bearing plate. No directional effects of irreversible movement is considered. But since the irreversible movement usually takes place in one direction only the displaced direction is placed away from the midpoint. In such cases the length of the upper plate is equal to the length of the length of the bearing + irreversible movement + 2 x reversible movement.

Why are steel plates inserted inside bearings in elastomeric bearings?

In order to make a elastomeric bearing act/ function as a soft spring it should be made to allow it to bulge laterally and also the stiffness compression can be increased by simply increasing the limiting amount of the lateral bulging. In many cases in order to increase the compression stiffness of the bearing the usage of metal plates is made. Once steel plates are included in the bearings the freedom of the bulge is restricted dramatically, also the deflection of the bearing is reduced as compared to a bearing without the presence of steel plates. The tensile stresses of the bearings are induced into the steel plates. But the presence of the metal plates does not affect the shear stiffness of the bearings.

What reinforcements are used in the process of prestressing?

The major types of reinforcements used in prestressing are:
> Spalling Reinforcement: The spalling stresses leads to stress behind the loaded area of the anchor blocks. This results in the breaking off of the surface concrete. The most likely causes of such types of stresses are Poisson`s effects strain interoperability or by the stress trajectory shapes.
> Equilibrium reinforcements: This type of reinforcements are required where several anchorages exist where the prestressing loads are applied in a sequential manner.
> Bursting Reinforcements: These kinds of stresses occur in cases where the stress trajectories are concave towards the line of action of load. In order to reduce such stresses reinforcements in the form of bursting is required.