7 Concrete Frame Structures: Roofs & Floors

Concrete Frame Structures: Roofs & Floors Cast In-Situ

• Concrete frame structures, specifically roofs and floors, are cast directly on-site.
• Slabs are horizontal load-bearing members.
• One-way slabs: length/width ≥ 2
• Two-way slabs: length/width ≤ 2
• Waffle slabs are used for large spans.

Post-Slab Structural System

• Members: Columns, Slabs
• Slab: horizontal structural member
• Post: vertical structural member

Classification of Post-Slabs

• Flat Plate (A)
• Flat Slab (B): with capital, with drop, with capital & drop

Effective Span

• Horizontal distance between center points of two vertical supports.
• Clear span: horizontal distance between internal faces of two vertical supports.

Cantilever

• Floor slab can extend across the span, and will be 1/3 of it.
• Maximum cantilever is 33-50% of span.

Position of Walls

• Walls can be placed freely in various floors.
• A recommended approach is building along column strips

Flat Slabs

• Supported directly by concrete columns, without beams.

Drop Panels

• Concentrated shear load from the slab onto the columns.

Types of Flat Slab Construction

• Simple flat slab
• Flat slab with drop panels
• Flat slab with column heads
• Flat slab with both drop panels and column heads

Uses of Column Heads

• Increase shear strength of slab.
• Reduce moment.
• Decrease clear span.

Uses of Drop Panels

• Increase shear strength of slab.
• Increase negative moment capacity of slab.
• Stiffen slab and reduce deflection.

Advantages of Flat Slabs

• Quick construction; simplified structure; diminished framework.
• Reduced floor-to-floor height by avoiding false ceilings.
• Reduced costs in cladding and prefabrication.
• Flexibility in room layout; allows for partition walls.

Slab Thickness

• Increased floor-to-ceiling height and reduced cladding costs are made possible by thin slabs.
• Sufficient reinforcement is crucial for design issues.
• Room for accommodating future architectural changes.

Benefits of Using Flat Slab Construction

• Flexibility in room layout.
• Savings in building height.
• Shorter construction time.
• Easy installation of M&E services.
• Prefabricated welded mesh use.
• Better constructability score.

One-Way vs. Two-Way Ribbed Slabs

• Classified as one-way if ribs in one direction only.
• Classified as two-way if ribs in two directions.

Wall-Slab Structural System

• Transfer external loads through continuous or linear support.
• Load-bearing walls transfer loads to the foundation.

Structural Member: Walls

• Cellular wall arrangement.
• External walls form building boundaries, and internal walls divide into cells or rooms.

Double Cross-Wall Structure

• Limits building depth for effective daylight.
• Suitable for buildings like hostels or hotels with multiple, similar rooms.

Simple Cross-Wall Structure

• Suitable for hostel or hotel buildings.

Complex Wall Arrangement

• All hybrid arrangements using cellular and cross-walls.