Number of Planks: 30
Number of Joists: 2
Materials
Unit
Quantity
Ba g s
7
S a nd
m3
0.5
Ag g re g a te 6 mm
m3
0.5
Ce me nt
3
Ag g re g a te 10 mm
m
0.5
Ag g re g a te 20 mm
m3
0.15
6 mm MS ba r
Kg
62
8 mm MS ba r
Kg
8
Ma s on
Ma n da ys
5
Labour
Ma n da ys
12
Ba r be nde rs
Ma n da ys
2
Plank and
Joist Roof
Labour
Plank and joist roof is a building system in which precast reinforced cement
concrete planks – rectangular slab elements – are placed on precast RCC joists.
The roof gets completed with in-situ concrete poured over the haunches in planks
and over the partially precast joists, thus ensuring monolithic action of individual
precast elements.
a p p li ca ti on
EWS housing (left) at Narela
(National Capital Region Delhi) and
Low-cost rural housing
at Bathinda, Punjab
Photographs courtesy:
EWS Housing – Building Materials and Technology
Promotion Council, New Delhi
Pre-cast RCC Planks
These are pre-cast concrete slabs, typically 30 cm wide x 1.5 m long, although the length can vary from
1.2-1.8 m (4 to 6 feet) depending on size of room. The planks are made partly 3 cm thick and partly
6 cm thick (as shown in the figure overleaf) with a 10 cm wide tapered concrete filling provided for
strengthening the haunch portion for shear during handling and erection. The plank uses nominal MS
reinforcement, typically 6 mm bar and concrete of grade not less than M-20.
Jointly published by:
TARA Nirman Kendra
Village Ghittorni
Mehrauli-Gurgaon Road
New Delhi-110030
India
Phone: 91-11-26801521, 26800398
TARA
Nirman
Kendra
Pre-cast Joists
Development Alternatives
World Headquarters:
Building Materials & Technology
Promotion Council
B-32, TARA Crescent
Qutub Institutional Area
New Delhi-110016
India
Web: www.devalt.org
Ministry of Urban Affairs & Employment
Govt. of India
Core 5-A, First Floor, India Habitat Centre
Lodi Road, New Delhi-110003
India
Phone: 91-11-24638096, 24638097, 24636759
Development
Alternatives
This is a beam which is part of the T-beam formed together with the joist and planks on both sides.
The width of the precast joist is equal to the required width of web of the T-beam (as per IS 13994) and
depth equal to the required overall depth of T-beam less the thickness of flange i.e 60 mm. Typically for
medium spans upto 4 metres, a 15 cm x 15 cm section can be chosen for the joist with stirrups
projecting out, so that the overall depth of the joist with in-situ concrete becomes 21 cm. The length of
the beam will depend upon the functional and structural requirement of structure.
Concrete Filling
Planks are placed on joists and in-situ concrete is poured over the haunches provided in the planks
and the gaps between the planks over the joists. Monolithic action of the slab elements is ensured by
leaving hooks projecting out of joists and providing reinforcement across the joists over haunch
portion of planks, tying them together and pouring in-situ concrete over it.
Technology Profile
Material and labour
requirement for
construction of plank
and joist roof of
size 14’ x 10’
150 mm
150 mm
Haunch of plank –
900 mm long and
30 mm thick
300 mm
100 mm
Length
upto 4 m
300 mm
30 mm thick
300 mm
Stirrups@
130 mm c/c,
minimum
distance
from edge of
joist 50 mm
1.5 m
Pre-casting of roof leads to substantial reduction in construction time
15 to 20% saving in cost possible because of no shuttering and reduction in steel quantity
Creates employment as the roof components can be locally produced and delivered through
a micro level enterprise
Much better quality control can be maintained during pre-fabrication
Tried, tested and validated by BMTPC as a technique for cost-effective construction
Moderate size of components which can easily be handled manually without mechanical handling
and erection equipment
Simple technology which can easily be adapted by semi-skilled labour
Reinforced
Concrete Plank
Size
Concrete Mix
Reinforcement
Pre-cast Reinforced
Concrete Plank
Partially Pre-cast Reinforced
Concrete Joist
Weight
Size
Reinforced Joist
Brick Wall
Floor finish 30 thk
Base Floor
6 mm dia MS Bars,
2 Nos. per plank
Raw materials
20
40
60
210 mm
overall
6 mm dia MS Stirrups
150 depth
as per design
of T-beam
Precast RC plank
In-situ concrete M15
50
Less than 1500
Installation of RCC Plank and Joist
150
In-situ concrete mix
Plank and
Joist Roof
Overall depth of in-situ
concrete
Bedding for joist
Design Load
Partially precast
joist
: M 15
: Nominal MS reinforcement 6 mm dia - 3 Nos. for main
reinforcement and @200 mm c/c in transverse direction
: 50 kg
: Length not more than 4 m, cross section 150 mm x 150 mm
For spans larger than 4 m, joist depth can be increased or
it can be designed as a doubly reinforced beam as per
IS: 456-1978
Reinforcement
40 70 40
: Length not more than 1.5 m, Width 30 cm ± 50 mm,
Thickness partly 30 mm and partly 60mm (see diagram)
: 6 mm dia, triangular MS stirrups @ 200 mm c/c
Longitudinal 3 Nos. 8 mm dia MS bar as per length of joist
: OPC 43 grade cement, sand of fineness modulus
: M 15 with 12 mm and down graded coarse aggregate
: 210 mm over joist
: 300 x 120 x 75 mm block of cement concrete 1:3:6
: As per BIS: 875
2
Load carrying capacity of Plank and Joist Roof is 250 kg/m
650 MJ /sq.m as compared to 750 MJ/sq.m for a 4” thick RCC roof
Embodied
Energy
MJ – Mega Joules