detailing of steel in stair cases

7/27/2019 Detailing of Steel in Stair Cases

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DETAILING OF STEEL IN STAIR CASES(For class held on 12th March 07)

Dr. M. C. Nataraja,

Professor, Civil Engineering Department,

Sri Jayachamarajendra Collge of Engineering, Mysore-5a70 006

Phone: 0821-2343521, 9880447742

e-mail: [email protected]

Stair case

Stair cases are used for the purpose of giving access to different floors of a structure.

Parts of stairs

There are two main parts namely flight and landing. Series of steps are provided in the flight.

The vertical height of the step is called the rise and the horizontal distance between the

vertical faces of risers is known as going. The horizontal distance available on the step is

called tread. The horizontal length obtained by deducting going from the tread is called

nosing. These parts can be seen in the Figure 1.

Figure 1. Parts of stair case

G

T

N

R

W


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Types of stair cases

The different types of stairs may be classified under the following main heads:

Straight stairs

Dog legged stair

Open well or open newel stairs

Geometrical stairs such as spiral, circular, etc.

Classification based on span

Based on type of span, following are the two types of stair cases;

Horizontally spanning or transversely spanning stairs. Figure 2

Longitudinally spanning stairs. For details refer IS: 456-2000 and SP (34).

Transversely spanning stair cases can be seen in figure 2. Here the main steel is provided

transversely and the distribution steel is in the longitudinal direction.

Figure 2. Transversely spanning stair cases

STEPS

STRINGER

BEAMS STRINGER

BEAM

0.5 Ast

0.1L-0.15L

L

Ast


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Longitudinally spanning stair cases:

Here the main steel in provided longitudinally and the distribution steel is in the transverse

direction.

Effective span

The effective span is defined as follows based on the type of support.

Where flight supported at the ends of the landings in such a way that both landing and flight

spans in the same direction, the effective span is the distance between the center to center of

the supporting beams or wall. Refer Figure 3.

Where spanning on the edge of a landing slab which spans parallel with the riser, the effective

span is the distance equal to the going of the stairs plus at each end either half the width of thelanding or one meter, whichever is smaller. Refer Figure 4.

Where supported at top and bottom riser by beams spanning parallel with the riser, the

distance center to center of the beams is the effective span. Refer Figure 5.

Figure 3. Flight supported at the ends of the landings on walls

Le


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Figure 4. Flight supported at the sides of the landings on walls

Figure 5. Flight supported on landing beams

Le

Le

X Y

X

Y


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Guide lines

Guide lines to be followed for fixing the dimensions of component parts of stair.

1. Rise (R) is 150mm to 180mm and tread (T) is 220 mm to 250 mm for a residentialbuilding.

2. For public building rise is kept between 120 to 150 mm and tread between 250 to 300

mm

3. Sum of tread (T) and twice the rise (2R) should be between 500 mm to 650 mm

4. The width of the stair is dependent on the usage and is between 0.8 m to 1 m for

residential building and 1.8 m to 2 m for public building.

5. The width of the landing is equal to the width of stairs.

6. The number of steps in each flight should not be greater than 12

7. The pitch of the stair should not be more than 38 degrees.

8. The head room measured vertically above any step or below the mid landing shall not

be less than 2.1 m.

Design of stairs

Design for maximum bending moment and check for maximum shear force. The depth is to

be fixed from deflection criteria. Stair case slab is designed as slab. All rules regarding the

detailing are similar to that of slab. Enough development and anchorage lengths for steel

should be provided.

Worked out problem

A dog legged stair case has to be provided for a residential building with the staircase

room size 2.1 m x 4.48 m (internal). The following details are given:

Vertical distance between the floors = 3.2 m

Waist slab thickness=160mm

Wall thickness =230

Main reinforcement= 12mm dia @ 120 mm c/c

Distribution steel = 8 mm dia @ 200 mm c/cGrade of concrete used =M20

Grade of steel used =Fe415

First flight starts from foundation level.

Assume that the flights are supported at the ends of landing or landing spans in the same

direction as that of flight.


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Draw to a suitable scale the following

a. Plan of staircase

b. Sectional elevation of first flight

c. Sectional elevation of second flight

d. Prepare the bar bending schedule 20 Marks

Solution:

Data: As above

Let Rise= R=160 mm and Tread= T= 250 mm

T + 2R=570 mm ok

Number of risers=H/R= 3200/160 = 20

Number of risers in each of the two flights= 20/2=10

Number of treads per flight= 10-1 =9

Going = 9 x 250 = 2250 mm

Width of landing in each flight= (4480-2250)/2= 1115 mm.

Width of stairs = 1000mm leaving a gap of 100 mm between the flights.

With this drawing can be made.

See details at the end in Figure 6

Exercise Problems:

A dog legged stair case is to be detailed with the following particulars:

Clear dimension of stair case room=5.5 m x 2.8 m

With of each tread =250 mm

With of each rise = 150 mmThickness of waist slab = 150 mm

Landing 1.4 m x 1.4 m

All round wall = 230 mm

Main steel for each flight = #12@120

Distribution steel for each flight = #8@ 200


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Intermediate Landing is supported on 230 mm wall. The second flight rests on rectangular

beam of 230 mm x 350 mm.

Beam consists of 4-#16 at bottom out of which 2-#16 are curtailed up.

Two hanger bars #12 at top is also provided. Two legged stirrups #8 at 150 mm c/c up to750 mm from the face of supports and the spacing is increased to 200 mm c/c near the

center.

Draw to a suitable scale

The plan of stair case

Sectional elevation of first flight

Sectional elevation of second flight

Beam details

Bar bending schedule

Solution: All details are given. First draw the rough sketch and then the final drawing and

detailing. For bar bending schedule, measure the length of bars on the drawing sheet and

use it for the calculation.

December/January 2007

A dog legged stair case has to be provided for a public building with the staircase room

size 2.6 m x 5.4 m (internal). The following details are given:

Vertical distance between the floors = 3.6 m

Waist slab thickness=160mm

Wall thickness =230

Main renforcement= 12mm dia @ 120 mm c/c

Distribution steel = 8 mm dia @ 200 mm c/c

Grade of concrete used =M20

Grade of steel used =Fe415

Draw to a suitable scale the following

e. Plan of staircase

f. Sectional elevation of first flight

g. Prepare the bar bending schedule 20 Marks


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Figure 6. Detailing for stair case when supported at the ends on landing on walls

ROW OF CHAIRS

500 mm

500 mm

GL

Wall

FOUNDATION

GROUND FLIGHT

MAIN STEEL# 12 @ 120

DIST. STEEL

# 8 @ 200

150

Ld =564

REINFORCEMENT

FROM BM

Ld =564 FLOOR LEVEL

LANDING FIRST FLIGHT

R=160

T= 250

LAP L

PLAN

1115 mm 1115 mm2250 mm

Le = 4710 mm


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Figure 7. Detailing for stair case when supported on landing beams.

Y=0.3 l or Ld

LANDINGBEAM

500

500

GL

FOOTING

GROUND FLIGHT

FIRST FLIGHT

PLAN

MAIN STEEL # 12 @ 120

DIST. STEEL # 8 @ 150

LANDINGBEAM

Le

150

X

l

Y

Y

150

INTERMEDIATE

LANDING

ROW OF

CHAIRS

X = 0.15 l or Ld

MAIN STEEL

DS

150

detailing of steel in stair cases

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