AULA 5 - FUNDAÇÕES (BEC - IFPB Cajazeiras)

Introduction

This tutorial provides a comprehensive guide on the topic of foundations, specifically focusing on "sapata submetida a ações excêntricas" (footings subjected to eccentric loads). The content is based on a lesson presented by Professor Lucas Pessoa at the Instituto Federal da Paraíba, making it highly relevant for civil engineering students and professionals looking to deepen their understanding of foundation design.

Step 1: Understanding Eccentric Loads

• Define eccentric loads as forces applied away from the center of gravity of a structure.
• Recognize the implications of eccentric loading on foundation design, including:
  • Increased moments that can lead to bending and shear.
  • Potential for uneven settlement.
• Consider the types of structures that typically experience eccentric loads, such as:
  • Tall buildings
  • Cantilever structures
  • Overhanging elements

Step 2: Analyzing the Footing Design

• Review the key factors influencing the design of footings under eccentric loads:
  • Load magnitude and direction
  • Soil bearing capacity
  • Footing geometry and dimensions
• Conduct a preliminary analysis to determine:
  • The required footing size
  • The depth of the footing based on soil conditions

Step 3: Calculating Moments and Shear Forces

• Use the following formulas to calculate moments and shear forces for the footing:
  • Moment (M) calculation:

    M = P * e
    

    where P is the load and e is the eccentricity (distance from the center).
  • Shear force (V) is generally equal to the applied load (P).
• Ensure to check both the ultimate and serviceability limit states in your calculations.

Step 4: Designing the Reinforcement

• Determine the type and amount of reinforcement needed for the footing:
  • Use standard reinforcement guidelines based on local codes or standards.
  • Calculate the required area of steel (Ast) to resist bending moments:

    Ast = (M / (0.87 * fy * d))
    

    where fy is the yield strength of the steel and d is the effective depth of the footing.
• Plan for distribution of reinforcement:
  • Use high-strength steel for increased performance.
  • Position reinforcement bars appropriately to resist tensile and compressive forces.

Step 5: Executing Construction Practices

• Ensure proper construction techniques to avoid issues:
  • Use appropriate formwork to maintain footing shape.
  • Pour concrete under controlled conditions to prevent cracking.
  • Allow adequate curing time for the concrete to achieve desired strength.

Conclusion

In summary, understanding and designing footings subjected to eccentric loads is crucial for ensuring structural integrity. This tutorial provided a step-by-step approach to analyzing loads, calculating moments and shear forces, and designing reinforcement for footings. For further learning, consider exploring advanced topics such as soil-structure interaction and the impact of varying load conditions on foundation performance.