Building Construction 3: Columns

Building Construction 2: Elements of Skeleton System - Columns

• Column Definition: A vertical structural member that supports the load of beams, slabs, and the entire building. It is adjusted based on client needs.
• Column Design Considerations: Column dimensions, the amount of concrete, sand, and aggregate, the number and spacing of steel bars, and the spacing of stirrups are all determined by the structural designer considering the safety factors of the actual load on the column.
• Load Bearing Mechanism: Columns primarily resist compressive loads acting along their longitudinal axis.
• Bending Moments: Wind, earthquakes, and accidental loads can create bending moments on columns.
• Load Transfer: Columns transfer loads from above (slabs and beams) to the supporting foundation, typically the soil below.
• Column Placement: Placing columns should be strategically situated to be partially or fully hidden within structural walls.
• RCC Column Construction Methods:
  • Column Layouts: Marked using ropes in grid lines.
  • Reinforcement Work: Reinforcement bars are checked based on number, diameter; spacing, and proper connection (lappings). Lapping shouldn't extend into beams or slabs. Stirrups should be correctly hooked and spaced apart according to plans.
  • Formwork: Plywood or steel sheets with supporting stiffeners establish the shape. Proper alignment is crucial to maintain verticality.
  • Concreting: Poured up to slab level. Thorough support of the formwork. Vibrated after pouring to ensure proper compaction, horizontal and vertical alignment.
• Shuttering: Concrete pads (starters) are first cast to support and align the shuttering. The thickness of the starter ranges from 45 to 60 mm, matching the column dimensions. The starter should cure for a day or two. The shuttering should be lined with grease to facilitate removal. Gaps should be sealed, and careful removal is critical to avoid damage.
• Concreting Process:
  • Method: Manual or machine (pump).
  • Concrete Quantity: Smaller quantities often involve machine-mixed concrete while larger quantities require ready-mix (RMC).
  • Pouring: Poured up to the slab bottom; the remaining portion is poured during slab or beam placement. The height of concreting shouldn't exceed 1.5 meters.
  • Compaction: Proper vibration to ensure compaction of each layer.
  • Finishing: Verticality and horizontality need to be checked after concreting.
• Types of Columns:
  • Tied Columns: Reinforcement bars are tightly bound within closely spaced ties. Found in 95% of buildings.
  • Spiral Columns: Reinforcement bars encased by a helix pattern, enhancing compressive strength.
  • Composite Columns: Combine concrete and steel, for higher strength and reduced cross-sectional size.
  • Axially Loaded Columns: Loads act on the center of gravity.
  • Uniaxial Eccentric Loaded Columns: Eccentric loading on one axis.
  • Biaxial Eccentric Loaded Columns: Eccentric loading on both axes.
• Column Classification: Based on reinforcement type, loading type, slenderness ratio, shape, and materials (reinforced concrete, steel, timber, brick, block, or stone).
• Short and Long Columns: Classified by the ratio of effective length to least lateral dimension (less than 12 for short, greater for long). Short columns fail due to crushing; long columns to bending or buckling.
• Column Shapes: Square, rectangular, circular, L-shaped, and T-shaped are typical column shapes.
  • Other: steel columns shapes (I, channel, equal angle, and T-shape)
• Importance of Shuttering: Shuttering needs to be strong enough to handle concrete pressure and maintain its position.

This quiz focuses on the elements of the skeleton system, specifically columns used in building construction. Participants will explore key concepts like column definition, design considerations, load bearing mechanisms, and placement strategies. Understand how columns play a critical role in supporting structures and ensuring safety.