Stair Flight and Landing Design (BS 8110)

This design sheet presents a complete structural analysis and reinforcement design for a reinforced concrete stair flight and its associated landings, complying with BS 8110:1997 – Structural Use of Concrete. The analysis includes both ultimate limit state (ULS) and serviceability limit state (SLS) checks.

1. Structural Safety (Ultimate Limit State - ULS):

• Loading combinations are calculated using factored values for imposed loads, finishes, and self-weight.
• Maximum design moment is calculated to be 41.64 kNm, which occurs approximately 2.15 m from the left support, i.e., where shear is zero. This is critical for main reinforcement design.
• Support reactions are calculated as:
• R1 (left support): 47.08 kN/m
• R2 (right support): 37.81 kN/m

These values demonstrate a stable and correctly supported stair slab subjected to standard loads per BS 8110.

2. Reinforcement Design:

• Required reinforcement area (As): 599 mm²/m
• Provided reinforcement (As prov): 670 mm²/m using T16 bars @ 300 mm centers, which satisfies the structural demand.
• Span reinforcement (top steel): T10 @ 300 mm is provided for continuity and shrinkage/crack control.
• The provided steel ratio (0.401%) exceeds the minimum code requirement (0.13%), ensuring ductility and crack control.

This confirms that the stair is adequately reinforced against bending and cracking.

3. Deflection and Serviceability (SLS):

• The effective depth (d) is 167 mm.
• Calculated span-to-depth ratio (L/d) is 25.749, which is less than the allowed limit of 26.375.
• An enhancement factor of 8.5% has been applied to improve deflection control, likely based on tension reinforcement and compression zone checks.

4. Detailing & Construction Considerations:

• Cover: 25 mm (satisfies durability and fire resistance requirements).
• The flight waist thickness of 200 mm is typical for this type of stair and supports both strength and constructability.
• The rake angle of 34.64° indicates a steep but acceptable stair slope.
• Continuity steel is recommended where appropriate for structural integration with landings or adjacent structures.

5. Design Efficiency:

• Material usage is optimized—steel is provided only where needed, and the slab thickness is appropriate for the span and loading.
• Simplified simply supported design is used, but with notes advising the provision of continuity reinforcement—an important consideration in practice.
• The design reflects good engineering practice, balancing safety, serviceability, and economy.

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