RCC Dog-Legged Staircase Design with Reinforcement Details, Section & Plan

Dog-legged Staircase Design: Details on the Full Section, Reinforcement, and Plan

It is important to recognize that the staircase is one of the most vital structural and architectural components of any building. It provides a safe means of vertical movement between different floors. Staircases must be designed with comfort, safety, structural integrity, and building regulations in mind to prevent future accidents; given its critical role, the design process should involve a structural engineer.

The staircase shown in this drawing is a dog-legged Reinforced Cement Concrete (RCC) staircase featuring intermediate landings. This type of staircase is commonly used in residential, commercial, and institutional buildings because it is space-efficient and facilitates easy movement between floors.

Staircase Type

1. Dog-legged staircase
2. RCC waist-slab staircase
3. Two flights connected by an intermediate landing
4. Suitable for residential and apartment buildings

Floor-to-floor height

• Ground floor level = ±0'-0"
• First floor slab level = +11'-6"
• Total height (rise) = 11'-6" (138 inches)

Calculation of Riser and Tread

Riser

The riser is the vertical distance between two consecutive steps.
Given:

• Total height = 138"
• Number of risers = 23
• Calculation:
• 138 ÷ 23 = 6
• Therefore,
• Riser height = 6 inches

This measurement ensures a comfortable climb and complies with standard specifications for residential staircases.

Tread

The tread is the horizontal surface upon which a person places their foot.
Given:

• Tread width = 11"

The selected tread dimension facilitates comfortable walking and safe movement.

Stair Proportion Rule

To build a comfortable staircase, the following formula is generally used:

• 2R + T

Where:
R = Riser (height of the step)
T = Tread (the part of the step where the foot is placed)
Plugging in the values:

• 2 × 6 + 11 = 23 inches

Since the result falls within the acceptable range of 22 to 24 inches, this staircase is easy and comfortable to walk on.

Staircase Layout Details

The staircase consists of the following components:

1. Lower Flight

• Starts at the ground floor level.
• Comprises the first set of steps.
• Leads up to Landing-1.

2. Intermediate Landing

• Serves as a resting area.
• Changes the direction of travel by 180°.
• Enhances safety and convenience.

3. Upper Flight

• Starts from Landing-1.
• Ascends to Landing-2.
• Connects to the first-floor slab.

4. Top Landing

• Directly connects to the floor slab at the +11'-6" level.

Structural Components of a Staircase

1. Waist Slab

The inclined RCC slab that supports the staircase is called the waist slab.
Functions:

• Supports the stair steps.
• Transfers loads to landings and supporting beams/walls.
• Safely carries live and dead loads.

2. Landing Slab

The horizontal slab situated between flights of stairs is called the landing.
Functions:

• Provides a resting point while climbing.
• Changes the direction of movement.
• Transfers loads to supporting components.

3. Steps

Each step consists of:

a. Tread

• The horizontal walking surface.

b. Riser

• The vertical surface between adjacent treads.
• Together, these elements form a safe and ergonomic staircase.

Reinforcement Details

The reinforcement shown in the section details includes the following:

Main Reinforcement

• 10 mm diameter steel bars.
• Placed along the slope of the staircase.
• Located in the tension zone.

Purpose:

• Resists bending moments.
• Provides tensile strength to the staircase.

Distribution Reinforcement

• 10 mm diameter bars, spaced at 6 inches center-to-center.

Purpose:

• Distributes the load uniformly.
• Controls shrinkage cracks.
• Improves structural integrity.

Stirrups

• 8 mm diameter stirrups, spaced at 6 inches center-to-center.

Purpose:

• Holds the reinforcement in place.
• Provides shear resistance.
• Maintains the spacing between bars.

Load Transfer Mechanism

Staircases transfer loads in the following sequence:

• Self-weight of the stair steps.
• Weight of people (live load).
• Load transferred to the waist slab.
• The waist slab transfers the load to the landing.
• The landing transfers the load to supporting walls/beams.
• Walls and columns transfer the load to the foundation.

Advantages of Dog-legged Stairs

1. Space-saving

Requires less floor area compared to straight-flight stairs.

2. Cost-effective

Uses fewer structural components.

3. Better privacy

The upper floor is not directly visible from the lower floor.

4. Comfortable movement

The intermediate landing reduces fatigue.

5. Ease of construction

Simple reinforcement and shuttering arrangements.

Construction Guidelines

a. Formwork

• Ensure proper alignment and slope.
• Provide adequate support for the shuttering.
• Reinforcement (Rebar) Placement
• Maintain the specified spacing.
• Install correct cover blocks.

b. Concrete

• Use at least M20 grade concrete.
• Ensure proper compaction and vibration.

c. Curing

• Cure the concrete for at least 7–14 days.
• Prevent rapid moisture loss.

Conclusion

As shown in the drawing, this is a well-proportioned RCC dog-legged staircase. It serves a floor height of 11'–6" and comprises 23 risers, each 6 inches high, with a tread width of 11 inches. This design ensures comfortable movement and efficient space utilization.

 Additionally, it offers robust structural integrity thanks to a well-engineered reinforcement system featuring 10 mm main bars, 10 mm distribution bars, and 8 mm stirrups.

This type of staircase is highly suitable for residential buildings, duplex homes, apartments, and commercial structures, where efficient space utilization, safety, and structural strength are key design considerations.