grillage foundation.pptx

building construction

1. Grillage Foundation

2. Use - Grillage Foundation design is applied for heavy structural loads from columns, piers or beams are required to transfer bearing capacity of a soil comparatively poor. The grillage foundation helps in distributing the load over a wider area of the subsoil. This foundation helps in avoiding deep excavations as the necessary base area is provided for the load of the transmission.  The depth of foundation is limited from 1m to 1.5m. Grillage Foundation definition – The grillage foundation consists of two or more tiers of beams laid at right angles to distribute the load over a large area.

3. This type of foundation is generally used for heavy structure columns piers and stanchions. Grillage consists of steel I I section (R.S.J) laid in single or double large . The second larger. The number of R.S.J.S and they’re distanced apart depend upon the load of the structure and the bearing capacity of the soil.

4. The depth of foundation is limited from 1m to 1.5m , as its a type of shallow foundation . However it should not be less then 90 cm .  Steel beams are provide in two or more tiers, the top tier of grillage beam is laid at right angles to the bottom tier.  The beam of each tier are held in position by 20 mm diameter spacer bars or with 25 mm diameter pipe separators.

5. To construct a grillage foundation, a trench of the required width and depth is excavated. The surface the trench is leveled and rammed . Over the rammed surface, a layer of cement concrete is spread and is well compacted so as to make if impervious . R.S.J.S are of desired dimension that are laid at regular intervals. The lower flanges of the R.S.J.S are embedded into the concrete by pouring rich cement mortar the R.S.J.S are connected together by pipes and bolts. The bolts are driven into web of the R.S.J.S. After levelling the base and pouring the concrete its should be checked that compaction is done properly and formed an impervious layer of thickness not less than 15 cm. This protect steel joist from groundwater, which can cause corrosion.

6. G.I. pipe pieces are placed between R.S.J.S, and a long bolt is pass through all the holes and pipes. This will connect the R.S.J.S together thereby forming a rigid mass.

7. PRECAUTION TO BE TAKEN  The depth of footing should not be less than 90cm .  The distance between the flanges should not exceed 30cm so that filled concrete acts monolithically with the beams.  The concrete filling should not carry any load ; its simply keeps the beams in the position .  A minimum gap of 10cm is kept on the outer side of the external beam, as well as the upper flanges of top tier .  The depth of concrete below lower tier should be atlest 15cm.

8. Grillage Foundations Advantages Steel grillage foundation gives more advantages for contractors than wooden grillage . The speed of Installation – Contractors can save time using a foundation of grillage . Convenience – grillage foundation uses to avoid poured concrete and saves time with easy installation . Costs effective method – Contractor can reduce cost through minimal disruption of transport infrastructure . Versatile foundation solution – the technology suits many different applications.

9. Timber grillage foundation   is provided for heavily loaded timber column or masonry wall . The foundation uses timber planks and timber beams in the place of steel joists. This foundation is specially useful in water logged areas where the bearing power of the soil is very low, and where the steel beams may get corroded due to subsoil water. The loading on the soil is limited to 50 to 60 kN /m2. No concrete is embedded between the timber joists. However, the bottom concrete (provided in steel grillage foundation is replaced by timber platform constructed of timber planks.

10. Timber grillage for column

11. Timber grillage for wall