What Is a Grade Beam?
A grade Beam is a beam that is built at Grade level (earth level) mostly used for buildings with piles and to connect pile caps to each other.
Grade Beams are reinforced concrete members which are constructed to act as horizontal ties between footings or pile caps.
Its main function is to transmit the load from a bearing wall into spaced foundations such as pile caps or caissons.
These types of beams are generally used when soil bearing capacity is less than the anticipated design loads.
It may have been designed to either directly rests on the soil or above the soil spans between piles. In case, when it is required to the extent the foundation is deep into the soil the grade beam would be the right choice.
It is not the same as wall footing, as the grade beam is designed for bending and typically spans between pile caps or caissons, while a wall footing bears on soil and directly transfers the weight of the wall to the foundation soil.
Also, it is not the same as strap footing, as the grade beam is reinforced to distribute the weight of a wall to separate foundations, while a strap beam is utilized to redistribute the weight of a column between footings.
It can be used as a combination with spread footing, in the case of large moments from lateral loads, in order to reduce the size of each spread footing.
Grade Beam Foundation?
The Grade Beam Foundation is used to transfer all superstructure load to subsoil strata safely.
The depth and size of the beam depending on the intensity of the load coming and the bearing capacity of the foundation soil on the construction site.
The grade beam depth should be kept at a minimum of up to 150. Grade beams are stronger compared to plinth beams. They also carry the load of the above masonry walls.
Concrete consumption in grade beam foundations is less compared to conventional foundations. The major disadvantage of using a grade beam foundation is that it cannot allow the construction of the basement.
The reinforcement used for the grade beam is a minimum of 3 bars of 10 mm diameter at the top and bottom of the beam.
Grade Beam Construction
Following are the steps involved in the construction process of the grade beam,
1. Preparation and Excavation for Grade Beam
First of all preparation and excavation for grade beams should be done. Excavation of trenches is executed for the beams on the basis of their level. The beams can be constructed on the ground directly and in this case, the ground surface is leveled and prepared.
2. Install a Framework for Grade Beams
After the preparation and excavation are finished, then according to the dimensions of the beam forms are placed. If we have constructed these beams on the ground, then the bottom of the forms is placed earlier to its sides.
The reinforcement cage is kept on the flat soling brick before we fix the side shuttering. The construction of the framework is the same as that of conventional beams when the grade beam is constructed above the ground. Hence, we must place shutters for the bottom and both sides of the grade beam.
After the finalization of the beam framework, the designated grade beam dimensions should be supplied which should contain enough reinforcement cover.
3. Reinforcement Placement for the Grade Beam
The reinforcement for the grade beam is placed as per the structural drawing. The reinforcement detailing is provided in structural drawings like the size and number of longitudinal reinforcements and the required length, number, and spacing of stirrups.
The number and size of the top, bottom, and extra reinforcements, lap length and placement, spacers, hooks, and clear reinforcement cover must be checked.
4. Pouring of Concrete for Grade Beam
At last, concrete is poured into the grade beam. A ready mix concrete or on-site machine-mixed concrete both can be used for concreting work.
The side support of the grade beam can be 24 hours after pouring concrete. But, the bottom formwork should be removed only after concrete gains its strength.
Depending upon the time span of the beam, we can determine the time duration for removing the bottom shutter.
Read More: Standard Height Of Window From Floor Level
Advantages of Grade Beams
1. Forms Easily
These beams are constructed in any size and shape. So, Grade beams are flexible in nature.
2. Excellent Support for Both Concrete and Soil
These beams are capable to support both the soil before the pour and the concrete during the pour.
3. Easily Penetrated
They can easily allow the penetration of other materials such as rebars, conduits, pipes, or dowels.
4. Less Excavation is required
Its installation requires less excavation work which saves time and money.
5. Saves Time and Money
It required less time for construction and less labor cost hence saving both time and money.
Grade Beam Design Example
Usually, Grade Beam is Designed to withstand the weight of the wall.
First of all, you have to calculate the loading of the wall as load per meter .then calculate the self-weight of the beam. Generally, we assume the depth of the beam is equal to the length/10 approximately.
Next to that, you have to analyze your beam if it is simply a supported or continuous beam you have to get a moment and shear force diagram.
For a simply supported beam, you have one maximum moment at mid-span and you have the formula to calculate the area of steel required for this longitudinal reinforcement.
The main reinforcement will be at the bottom and there is min reinforcement at the top always we but 2 bar .then you have to design for shear, also you have the formula to calculate the distance between stirrups that depend on with code you use.
For continuous beam, you follow the same procedure the difference here is that we have a negative moment at support, and the main reinforcement here is placed at top of the support.
Consideration such as soil investigation, potential impacts of external force such as earthquake, ground water level, should be taken into account during the design and construction of grade beams.
Adequate reinforcement, appropriate curing techniques are essential for achieving the desire strength and performance of grade beams, and deep foundation. Their specific project requirements and site condition and installation must be tailored to the specific project requirements and site condition.
In summary, the grade beams are essential components of foundation construction, providing support and load distribution for structure and their proper design, installation, construction are crucial for the stability, durability and overall performance of building.
By following industry best practices, working with experienced professionals and adhering to building codes, grade beams can contribute to the long term success and safety of construction projects.
What is a grade beam?
A grade beam is a reinforced concrete beam that runs along the perimeter of a building’s foundation. It sits on the ground and supports the weight of the building’s walls and columns.
How is a grade beam constructed?
A grade beam is typically constructed by excavating a trench along the perimeter of the foundation and pouring a concrete beam into the trench. The beam is reinforced with steel bars to provide additional strength and durability.
What factors affect the design of a grade beam?
The design of a grade beam is affected by several factors, including the weight of the building, the soil type and stability, the water table, and the local building codes and regulations.
What are the disadvantages of using grade beams in foundation construction?
The disadvantages of using grade beams in foundation construction include higher costs compared to other types of foundation construction, and the need for skilled labor and specialized equipment to install the beams. Additionally, grade beams may not be suitable for all building sites and soil conditions.
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