Grillage Foundation: Types and Construction Details

What Is A Grillage Foundation?

A grillage foundation is a type of foundation that consists of a series of interconnected steel beams and concrete footings. It is commonly used for heavy structures, such as bridges, towers, and large buildings, where the loads are too heavy for traditional foundation systems.

Grillage foundations are designed to distribute the load of the structure evenly across the soil, reducing the risk of settlement or differential settlement.

This is accomplished by transferring the load to a larger area of soil through the use of steel beams and concrete footings.

Types of Grillage Foundation

There are two main types of grillage foundations:

1. Steel Grillage Foundation.
2. Timber grill foundation.

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1. Steel Grillage Foundation

The Steel Grillage foundation is composed of beams and steel joints assembled in one or more layers, and its name reflects its primary function as it is made from steel beams known as as-rolled steel beams.

A minimum coverage of 10cm is maintained on the external face of the outermost beams, which is higher than the highest flanges of the topmost tier, while the concrete depth should be at least 15cm.

During the leveling of the base and pouring of the concrete, it is essential to ensure proper compaction of the concrete and maintain a minimum spacing between the materials.

The presence of steel in this type of foundation provides protection against groundwater that can potentially corrode the steel used in the foundation.

Next, the primary layers of beams are placed over the concrete, maintaining a minimum distance of 150mm to 350mm using a temporary pipe separator.

Concrete is poured around the main beam layers with proper supervision and compaction to ensure no steel is left exposed.

Once the concrete has gained sufficient strength, the second layer of steel beams is positioned in the same location as the pipe separators used previously. Concrete is again poured to encase the beam from all sides.

The second layer of beams is connected to the upper steel column footing using angle brackets and base plate assembly.

Concrete is poured over the joint between the base plate and upper steel column footing to conceal it.

The Steel Grillage Foundation is constructed using steel beams known as rolled steel joists (RSJ) provided in two or more tiers.

In the case of a double-tier grillage, the top tier of beams is positioned perpendicular to the lower tier.

The beams of each tier are secured in place using twenty-millimeter diameter spacer bars and twenty-five-millimeter diameter pipe separators.

2. Timber Grillage Foundation

Timber Grillage Foundation is a cost-effective solution for supporting load-bearing walls in areas with waterlogged or permanently soft soil.

It can support low-loading buildings with a soil load capacity of up to 5.5 tonnes/sq.mt. Instead of using a concrete block below the load-bearing wall, Timber Platforms are used to construct the foundation.

mm to support load-bearing walls in areas where soil is waterlogged or permanently soft. These platforms are placed in two layers, one extending longitudinally across the foundation and the other extending beyond the footing base by 45cm to 60 cm on both sides.

To ensure stability and support, the bottommost layers of planks are 50 mm to 100 mm thick, based on site conditions and loading on the walls.

The two layers of timber planks are separated by a rectangular timber section, with a spacing of no more than 380 mm. The depth of each section is approximately 0.75 times the width of the section.

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Construction Process Of Grillage Foundation

Constructing a grillage foundation requires careful planning and execution. Here’s a general overview of the construction process:

Soil Investigation: Before constructing a grillage foundation, it’s important to conduct a soil investigation to determine the load-bearing capacity of the soil. This will help determine the size and spacing of the steel beams and concrete footings.

Excavation: The site is excavated to the required depth, and the footings are laid out according to the design specifications.

Steel Beam Placement: The steel beams are placed on top of the footings, and they are connected by welding or bolting.

Steel Plate Placement: If using a grillage slab, the steel plate is placed on top of the footings, and it is welded or bolted to the steel beams.

Concrete Placement: Once the steel beams or steel plate are in place, concrete is poured into the voids to create a solid foundation.

Curing: The concrete is left to cure for a specific amount of time, according to the manufacturer’s instructions.

Design

Grillage foundation design is a crucial aspect of constructing a building or structure that requires a strong and stable foundation.

A grillage foundation is a type of foundation made up of steel or timber beams and concrete, and it is typically used in areas where the soil is not stable enough to support a regular foundation.

The design process involves taking into account various factors such as the load requirements of the structure, the soil conditions, and the type and spacing of the beams to be used.

A structural engineer typically carries out the design process and determines the size, depth, and spacing of the beams required to provide sufficient support for the structure.

Once the design is finalized, the construction process involves preparing the site, excavating the area, and laying the foundation. The beams are then laid out and assembled, and concrete is poured around them to provide additional stability.

Proper grillage foundation design and construction are essential for ensuring the safety and stability of any building or structure.

Installation of Grillage Foundation

The followings are the steps of grillage foundation installation,

1. First, for solid monolithic grillage, we’ve got to provide and construct a framework. We tend to like this grillage as a result of its lot of dependable.
2. Formwork is formed from border boards within the type of rectangular troughs. Its height is one linear unit and its breadth is up to the least wall thickness. It should be set concerning a 6-8 inches gap in between every grillage.
3. Inside the formwork, we’ve got to line a framework of reinforcement connections victimization binding wire. The minimum distance between the frame to the face of the formwork required is similar.
4. Next, reinforcements are joined with a similar binding wire used before.
5. Then, the Concrete should be ready to victim the concrete mixer. It’s poured within the formwork of an exceedingly continuous cycle. Fittings must be done on the level of 25-30mm so it fully immerses in concrete.
6. Concrete ought to be fastidiously poured to restrict the cavities. When concrete pouring surface, these surfaces must be finished well and kept dry for some time. Once it’s dried, the formwork is removed. the muse is prepared currently.

Advantages of Grillage Foundation

The following are the Advantages of Grillage Beams,

• Grillage foundations can be constructed in low time and the materials used are also low compared to other foundations.
• The 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 the grillage Foundation. It has the capability to reduce a significant amount of vibrations.
• Grillage foundations are mostly used for important structures such as heavily loaded columns, Piers, Piles, and scaffolding work.
• The most important benefit of a grillage foundation is that it is capable of transferring heavy structural load on a larger area of the foundation.

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Disadvantages of Grillage Foundation

The 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 between the steel beams is essential to be heated and filled. hence skilled laborers are required.
• In the construction of grillage, foundation excavation is to be done on the larger area which increases the construction cost.
• The heavy uplift pressure can distribute this type of foundation.
• The structural arrangement of the column bed is changed sometimes in grillage foundation construction.

Conclusion:

In Conclusion, a grillage foundation is efficient and versatile solution for supporting heavy structure and distributing loads to the underlying soil, by utilizing a network of interconnected girders and beams the load is spread all over the larger area, reducing the pressure on the sol and minimizing the risk of settlement.

Grillage foundation offers numerous advantages including high load carrying capacity, flexibility in design and ease of construction, they are commonly employed in the construction of bridges, industrial facilities, and large building, however proper design and construction techniques are crucial to ensure the stability and longevity of the foundation, ongoing research and advancement in construction technology continue to enhance the performance and efficiency of grillage foundation making them a reliable choice in various engineering projects.

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