Grillage foundation is a type of foundation that consists of more than one extra layer of beams which are usually steel placed on a layer of concrete to distribute and transfers the structural load on a big area of soil below the foundation.
These types of foundations are used for heavily loaded columns. Grillage foundation has various layers of the beam which are cover into concrete and each arranged 90 degrees to the other. This foundation type is mostly used for scaffolds, heavily loaded structures, and column construction.
Though other types of foundations and grillage footing look similar they’re completely different. Wherever the foundation takes the structural load and transfers it to the bottom, the footing grid spread it over a large area of soil below the foundation.
Types of Grillage Foundation
Following are the Grillage Footings types,
- Steel Grillage Foundation.
- Timber grill foundation.
1. Steel Grillage Foundation
Steel Grillage foundation is made up of beams and steel joints or they are assembled in one or more layers. Its name indicates its function because it is manufactured from beams that are mare made up of steel. It is also called as-rolled steel beams.
A minimum cowl of 10cm is unbroken on the outside face of external beams furthermore is higher than the higher flanges of the tallest tier. The concrete depth ought to be a minimum of 15cm.
When we tend to level the bottom and concrete pouring, we have to always make sure if concrete compaction is finished properly and minimum cover should be left between. The steel provided in this type of grillage foundation provides a safeguard against the groundwater which may cause corrosion of steel used for the foundation.
Thereafter, main layers of beams are spread over concrete keeping a minimum distance of 150 mm to 350 mm by using a pipe as a temporary separator. Concrete pouring is done around the main beam layers with proper compaction and supervision such that no steel is left out of concrete.
After the concrete is gain sufficient strength, the 2nd layer of steel beams is placed in the position used pipe separators. The concrete pouring is again done to cover the beam from all sides.
Then the 2nd layer of the beam is connected to the upper steel column footing with the help of angle cheats and base plate assembly.
The connection of base plate and upper steel column footing is poured with concrete to hide the joint between them.
Steel Grillage Foundation is built of steel beams, structurally referred to as rolled steel joists(RSJ.), provided in 2 or additional tiers. Within the case of double tier grillage(which is usually provided), the highest tier of grillage beams is arranged at right angles to a very cheap tier.
The joists or beams of every tier are commands in position by twenty-millimeter diameter spacer bars with twenty-five-millimeter diameter pipe separators. Fig. 3.10 shows the arrangement and section of such a foundation. The grillage beams are embedded in concrete.
2. Timber Grillage Foundation
In a place where the soil is found to be waterlogged or permanently soft in nature, load structural walls can be economically supported by the proper design of Timber Grillage Foundation.
Timber Grillage foundation can be used to construct a low-loading building by minimizing the load on soil up to 5.5 tonnes/sq.mt. In the construction of the foundation, a concrete block that is placed below the load-bearing wall is replaced by the use of Timber Platforms.
The Timber Platforms used in this foundation is generally having a thickness of 80 mm to 100 mm. These platforms were placed in 2 layers, one longitudinally across the foundation and other the placed extending beyond the footing base in a range of 45cm to 60 cm on both sides.
The bottommost layers of planks are kept 50 mm to 100 mm thick by considering site conditions and loading on walls.
Timber planks two layers are divided with help of a rectangular timber section which is spaced not more than 380 mm. The depth of each section is kept around 0.75 times the width of the section.
Grillage Foundation Design
The grillage foundation design is done by calculating the load coming on the column and the moment on the structure and superstructure. Also, finding out the minimum base area required with considering tolerable soil bearing capacity and pressure condition on construction site.
For this construction, it is required to calculate the magnitude, quantity, and dimension of each and every grillage steel beam is essential. Steel beams tiers are then designed to cantilever or projected from tier border which helps to select the dimension of the beam to contract balance the bedding moments and shear forces.
As per design requirements for grillage which is covered in concrete, various construction techniques can be implemented considering the loading condition. This combined action of steel beams and concrete is used to settle the load within the limits.
Installation of Grillage Foundation
Followings are the steps of grillage foundation installation,
- First, for solid monolithic grillage, we’ve got to provide and construct a framework. We tend to like this grillage as a result of it’s a lot of dependable.
- Formwork is formed from border boards within the type of rectangular troughs. Its height is one linear unit and breadth is up to the least wall thickness. It should be set concerning a 6-8 inches gap in between every grillage.
- Inside the formwork, we’ve got to line a framework of reinforcement’s connections victimization binding wire. The minimum distrance between frame to the face of the formwork is required is similar.
- Next, reinforcements are joined with a similar binding wire used before.
- Then, Concrete should be ready to victimization the concrete mixer. It’s poured within formwork of an exceedingly continuous cycle. Fittings must be done on the level of 25-30mm so it fully immerses in concrete.
- Concrete ought to be fastidiously poured to restrict the cavities. When concrete pouring surface, the these surface must be finished well and kept dry for some time. Once it’s dried, the formwork is removed. the muse is prepared currently.
Features of Grillage Foundation
- The Steel Griallage foundation is connent the the whole structure togther which helps in distribution of structural load evenly on entire foudnaiotn.
- In many case, Grillage foundation is constructed as monolithic slab foundation which is cover with concrete.
- The clearance between steel beams kept around 8 cm which is allows easy pouring of concrete. The concrete is filled between gaps to cover all steel beams and protect them of corossion.
- The main function of concrete in steel grillage foundation is to combine all beam together and make it single strucuture body.
- Bottom cover is below the steel beam is kept around 15 cm from the soil base.
Advantages of Grillage Foundation
Following are the Advantages of Grillage Beams,
- Grillage foudnation can be constructed in low time and material used are also low compare to other foudnations.
- Evocation of heat is been kept in control with the help of such foundations.
- Vibrations caused in a house because of some disturbances are taken down by grillage Foundation. It has the capability to reduce a significant amount of vibrations.
- Grillage foundation are mostly used for important structure such as heavy loaded column, Piers, Piles and scafflofing work.
- The most important benifit of grillage foundation is that it capbleof transfer heavy strutural load on largert area of foundation.
Disadvantages of Grillage Foundation
Disadvantages of Grillage Foundation are listed below,
- Piles Required for this foundation are needed to be inserted to a large depth.
- The empty space left betewen steel beam are essential to be heated and filled. hence skilled laborers are required.
- In construction of grillage foundation excavation is to be done on larger area which increase the construction cost.
- The heavy uplift pressure can distrib this types of foundation.
- Structural arragement of columb bedd to be changes sometimes in grillage foundation construction.
A foundation that consists of more than one additional level of beams which are usually steel, which is covers in a layer of concrete to distribute the load over a large area is called a Grillage foundation
Is Grillage foundation economical?
For the construction of a structure to transfer heavy structural load from a column to the soil which is having low bearing capacity a Grillage Foundation is one of the most suitable foundations. In this scenario Grillage Foundation is the most economical one. It distributes the load over a larger area and resists the occurrence of shear failure.
Where are Grillage foundations used?
Use of Grillage Foundation,
1. Grillage foundations are used at the bottom of the columns.
2. This type of foundation is usually used for significant structure, column piers, and scaffolds.
3. In case of transferring heavy loads from columns to the soil of low bearing capacity Grillage Foundation is used.
4. It is used to disperse the load over a large area in a foundation for grilling.
What are the reasons for recommending Grillage foundation?
Reasons For Recommending Grillage Foundation
1. The installation process of Grillage Beam requires less time and materials.
2. Evocation of heat is been kept in control with the help of such foundations
3. It has the capability to reduce a significant amount of vibrations.
4. This type of foundation can be used for significant structures such as column piers, and scaffolds.
5. It is capable of transforming load over a larger area.
Grillage foundation is a type of foundation that consists of one, two, or additional levels of beams which are usually steel, superimposed on a layer of concrete to distribute the load over a large area.
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