5 Concrete Frame Structures: Foundations

Concrete Frame Structures: Foundations

• Foundation Definition: A structure that transfers the load of a building to the soil.

Choosing a Foundation Type

• Factors influencing foundation choice include:

  • Ground conditions
  • Groundwater conditions
  • Site and surrounding buildings
  • Building structure requirements

• Requirements:

  • Structural safety (ability to bear building load)
  • Constructional feasibility (schedule, resource availability, cost)

• Foundation Special Considerations:

  • Repair cost and difficulty
  • Foundation location (often underground)
  • Potential for damage if improperly applied

Foundation Types for Frame Structures

• Spread (Shallow) Foundations:
  • Beam (Grillage) Foundation: A grid of beams supporting the load.
  • Pad Foundation: Isolated concrete pads to spread the load.
  • Mat Foundation: A large concrete slab supporting the entire structure.
  • Slab Foundation: A continuous slab used as the foundation.

Pad (Footing) Foundation Detail

• Description: Square or rectangular concrete pads spreading concentrated loads.
• Typical Use: Commercial and residential buildings (ground level to medium rises).

Foundation Examples and Plans

• Pad (Footing) Foundation Example: Illustrated in plans (different scales). Includes specific dimensions and details for the design.

• Types of Foundations in Frame Structures: (Illustrated with diagrams).

  • Combined pad foundation
  • Brick column
  • Concrete column
  • Concrete pad

Raft (Mat) Foundation

• Description: Monolithic structure covering the entire building area.
• Usage Considerations: Medium to high-rise buildings, where the soil has poor bearing capacity, to control differential settlements.
• Types:
  • Solid slab raft
  • Beam and slab raft
  • Cellular (void) raft

Beam and Slab Raft Foundation Details

• Description: A monolithic concrete slab supported by beams.
• Diagrams illustrate:
  • Cross-sectional views
  • Floor plans

Cellular (Void) Raft Foundations

• Description: A concrete slab with openings (voids), lighter and structurally efficient than a solid raft. - Illustrated with diagrams.

Balanced and Cantilever Foundations

• Balanced (Strap) Foundations: Two or more separate footings connected by a strap beam. Used when one footing lacks sufficient space. - Transfers loads effectively.
• Cantilever Foundations: Transfer loads by cantilever action from one footing to another. Used in situations like adjacent building construction.

Application Conditions for Balanced and Cantilever Footings

• Insufficient Ground Area: Useful in cases where the footprint is too small for sufficient load transfer.
• Adjacent Buildings: Employed when constructing near existing structures, to accommodate limited space.
• Soil Capacity Issues: Useful to overcome if the soil supporting the foundation has a lower load capacity.

Combined Footings

• Description: Used to support multiple columns, especially when the distance between them is extensive.
• Inefficiency Concern: Less effective than a strap beam when space constraints are high between foundation columns.