Grillage foundations are a type of structural foundation composed of beams layered over concrete, often found supporting heavy building columns, piers, and scaffolds. Constructed as a monolithic reinforced concrete structure, they ensure even distribution of weight across the foundation.
Grillage foundations are made of beams superimposed on a layer of concrete. They can be found at the bottom of the columns and commonly supports heavy building columns, piers and scaffolds
Disadvantages
It requires the insertion of large-diameter piles; skilled personnel are needed to heat and fill the empty area between steel beams; The excavation of a bigger area is required to construct a grillage foundation, increasing the construction cost; It is susceptible to uplift pressureSometimes the structural arrangement of the column bed is subject to modification in grillage foundation construction
Advantages
It takes less time to install and uses fewer resources; It lowers heat transfer from the home via the foundation; It reduces the amount of vibration in the house; Installation of Grillage Beams takes less time and requires fewer resources; It may sustain significant structures like column piers and scaffolds; It can spread the weight across a larger area.
Types
- Steel Grillage Foundation: Steel grillage foundation consists of steel beams, also known as grillage beams, offered in single or double levels. The beams are spaced enough apart to allow the placement and compacting of concrete between them. The space between the beams’ flanges should be one and a half to two times the flange width.
- Timber Grillage foundation: A timber-type foundation is supplied for strongly heavy masonry walls of timber columns. This foundation is particularly effective in wet areas. Between the timber joints, no concrete is present. However, the steel grillage’s bottom concrete is replaced by a timber platform made of wood boards
Installation
The framework for solid monolithic grillage must be built and installed and the formwork comprises rectangular troughs made of edging boards. The minimum distance between the frame and the side of the formwork must be the same, and the reinforcement must be linked with the same binding wire. Also, a 6 to 8-inch space between each grillage must be established, and a framework of reinforcement connections must be established inside the formwork using binding wire.
Features
The grillage foundation is usually constructed as a monolithic reinforced concrete structure. Also, the grill joins the entire foundation to the single structure, ensuring that the weight of the house and all the piles are distributed evenly. It allows easy pouring and compacting of the concrete.
Design
The loads and moments from the superstructure calculate for the grillage foundation design. The critical foundation area for a sufficient allowed ground bearing pressure must be determined. Then this space is divided to determine the number and size of each grillage layer. The layer must be designed to cantilevers from the edge of the layer above it to determine how big the beams need to withstand the bending moments and shear forces.
Uses
Grillage foundations can be used when hard rock soil is unavailable and mat foundation is not an option; it is also cost-effective and allows safe transfer of heavy building loads. Additionally, it can be employed in the main project for an electrical transmission line and the foundation for a telephone tower.
