Question 1

How is a RC stair flight modeled for structural design?

Accepted Answer

The stair flight is modeled as an inclined one-way slab spanning between supports (beams or walls). The equivalent horizontal span is used for load calculation: span = L/cos(α), where α is the inclination angle.

Question 2

What loads are applied to a concrete staircase?

Accepted Answer

Stairs carry: dead load (self-weight of waist slab + steps + finishes) and live load (typically 4.8 kN/m² for public stairs or 3.0 kN/m² for residential per ASCE 7-22 Table 4.3-1). Loads are applied on the horizontal projected area.

Question 3

What is the waist of a staircase?

Accepted Answer

The waist is the structural slab thickness of the stair flight, measured perpendicular to the soffit. It is the primary structural member that carries bending. Treads and risers are non-structural above the waist.

Question 4

How is the self-weight of a staircase calculated?

Accepted Answer

Self-weight per horizontal meter = γc × (t/cos(α) + 0.5 × R × T/L), where t is the waist thickness, α is the slope angle, R is the riser height, T is the tread width, and γc is concrete density.

Question 5

What reinforcement is typically required in RC stairs?

Accepted Answer

Main flexural bars run along the flight length (in the direction of span). Distribution bars (typically 20–25% of main steel) run transversely. Standard covers are 25 mm for interior stairs and 40 mm for exterior.

Step	Formula	Substitution	Result
Rise	R	175	175 mm
Going	G	275	275 mm
θ	atan(R/G)	atan(175/275)	32.5° °

Step	Formula	Substitution	Result
wu	factored load	18.46	18.46 kPa
Mu	wu·L²/8	18.46·L²/8	25.13 kN·m/m

Step	Formula	Substitution	Result
As,req	As,req	457.86	457.86 mm²/m
As,prov	As	753.98	753.98 mm²/m	✓

Step	Formula	Substitution	Result
Rise	R	175	175 mm
Going	G	275	275 mm
θ	atan(R/G)	atan(175/275)	32.5° °

Step	Formula	Substitution	Result
wu	factored load	18.46	18.46 kPa
Mu	wu·L²/8	18.46·L²/8	25.13 kN·m/m

Stair Design

RC Stair Design

Loads

Geometry

Material

Reinforcement

Stair Design

Given:

Loads

Reinforcement

DCR

Stair Design

RC Stair Design

Loads

Geometry

Material

Reinforcement

Stair Design

Given:

Loads

Reinforcement

DCR