The foundation of a building is one of the most crucial aspects of civil construction. It has the function of transferring the loads of the structure to the soil safely and efficiently. Among the various types of foundations, the foundation slab stands out as a viable and widely used solution in small and medium-sized constructions.
What is a foundation slab?
Sapatas isoladas. (Escola Engenharia/Divulgação)
The foundation slab is a structural element that serves to evenly distribute the weight of the construction over the soil. It is characterized by a reinforced concrete base, designed to support the loads transmitted by the pillars or walls. This solution is common in soils with good bearing capacity, as it prevents differential settlements and provides stability to the structure.
Main types of slabs and their applications
Diagrama ilustrando os principais tipos de sapatas utilizadas em fundações rasas. Fonte: BATISTA, Joicy Alves et al. Fundações Rasas Tipo Sapatas e Blocos – Ensaio SPT, Procedimento, Execução. (Revista Científica Multidisciplinar Núcleo do Conhecimento/Divulgação)
Foundation slabs can be classified into different types depending on the soil conditions, the weight of the building, and the loads transmitted. The main types are:
Isolated slab: is used to support individual pillars and is common in buildings with moderate loads. Its main advantage is the material savings and ease of execution. However, it requires soil with good bearing capacity and is not recommended for areas with large variations in moisture.
Continuous slab: ideal for distributing linear loads, such as in structural walls and retaining walls. Its elongated shape allows for uniform load distribution along the length of the structure. This type of slab is widely used in residences and small buildings, being essential to avoid differential settlements in variable consistency terrains.
Combined slab: used when two or more pillars are close together and their isolated slabs would overlap. In these cases, a larger slab is designed to support the loads of the pillars, ensuring stability and avoiding wasted space. This type of slab is an efficient alternative for optimizing load distribution in more compact projects.
Lever slab: used when a pillar is very close to the property line and it is not possible to construct the slab symmetrically. To compensate for this asymmetry, a lever beam connects the slab to another support point, ensuring proper load distribution. This type of foundation is commonly used in urban constructions, where space for the foundation may be limited.
Rigidly connected slab: employed when a more uniform distribution of loads between two or more structural elements is required. It is commonly used in buildings that require greater rigidity and control over settlements, ensuring that the structure supports loads in a balanced and efficient manner.
How to calculate the ideal foundation for each project
Diagrama de distribuição de forças em uma estrutura com sapatas isoladas. (Celere/Divulgação)
To determine the ideal foundation, it is necessary to consider factors such as:
Soil capacity: The bearing capacity of the soil is one of the most important factors in foundation sizing. A geotechnical study must be conducted to assess the bearing capacity of the terrain, identifying its characteristics and preventing differential settlements that may compromise the structure.
Structure load: The total weight of the building and the loads exerted on the structural elements must be calculated accurately. This includes permanent loads, such as the structure and cladding, and variable loads, such as occupancy and furniture. The choice of slab must ensure that the load is safely distributed over the soil.
Dimensions of the slab: The size of the slab must be sized to adequately distribute loads in the soil without exceeding its bearing capacity. The calculation takes into account factors such as the area of the slab base and the allowable stress of the soil, ensuring stability and preventing differential settlements.
Foundation depth: The depth at which the slab will be installed depends on the characteristics of the soil and the size of the building. More resistant soils allow for shallower foundations, while unstable terrains require greater depth to reach firmer layers and prevent undesirable displacements. A structural engineer should be consulted to calculate and design the best solution for each case.
Materials used in the construction of slabs
Duas formas mais usuais de sapata isolada. (Dantas Neto/Divulgação)
The most common materials for constructing foundation slabs are:
Reinforced concrete: composed of cement, sand, gravel, and water, ensuring strength and durability.
Steel CA-50 or CA-60: used in the reinforcement of the slab to increase its strength.
Gravel and sand: essential for composing the concrete.
Cement: key element for binding the aggregates and steel. The quality of the materials is essential to ensure the safety and durability of the foundation.
Tips to avoid structural problems
Sapatas associadas. (Housing/Divulgação)
To ensure a safe foundation and avoid failures, some practices are essential:
Conduct a soil study: Before defining the type of slab to be used, it is essential to conduct a geotechnical study to understand the composition and strength of the soil. This survey helps prevent differential settlements and future structural problems.
Follow the structural calculations correctly: The slabs must be sized correctly to support the loads of the building without compromising its stability. Using accurate structural calculations, made by a specialized engineer, is essential to ensure the safety of the construction.
Use good quality materials: The strength of the foundation directly depends on the quality of the materials used. Concrete, steel, and aggregates must meet current technical standards to ensure durability and safety of the structure.
Ensure the correct execution of reinforced concrete: The concrete work must be done properly, respecting the spacings and arrangement of the reinforcements. Poor execution can compromise the strength of the foundation, leading to serious structural failures.
Observe soil moisture and plan adequate drainage: Excessive moisture can compromise soil stability and cause differential settlements. Installing efficient drainage systems helps control moisture and protect the foundation of the building. CASACOR Publisher is a content creator agent, developed by the CASACOR Technology team based on the knowledge base of casacor.com.br. This text was edited by Yeska Coelho.
