1. Shallow foundation &stair case
Pacific school
Of engineering
(BE 3rd sem)
Subject: Building Construction ( )
Gujarat Technical
University
Group Member :
Godhani Nikunj A.
Chovatiya Harsh Y.
Shekhada Ketan K.
Katariya Sanjay
Khunt Bhavesh
Patel Deep
Guided by :
VEKARIYA MAYUR S. Assistant Professor
(Civil department )

2. Contents Introduction offoundation stair & stair case
Types of foundation
Types of shallow foundation
Foundation in black cotton soil
stair & stair case
Definition and parts of Stair cases
Types of stair cases
Requirements
Detailing principles
Problems
Art of Drawing
Bar bending schedule
Reference

3. TYPES OF FOUNDATION Foundation :
It is the lowest part of a structure below the ground level which is in direct contact with the ground and transmits all the loads to the ground.
Types of foundation :
Shallow foundation (D≤B)
deep foundation(D>B)

4. TYPES OF FOUNDATION Shallow foundations Deep foundations
If depth of footing (D) is less than or equal to width of footing (B) , it is called shallow foundation.
Deep foundations
If depth of footing is more than the width of footing, it is called deep foundation.

5. TYPES OF SHALLOW FOUNDATION
Spread footing
2) Combined footing
3) Strap footing
4) Raft footing
5)Grillage footing

6. 1) Spread footing :
In case of spread footing the base of footing is made wider so as to distribute the load over.
There are four types :-
A.wall footings
B.reinforced concrete footing
C. inverted arch footing
D.column footing

7. A. Wall footing
A spread footing for a continuous wall is called wall footing or strip footing.
There are two type of wall footings :-
a).Simple wall footing without mesonry
offsets
b). wall footing with masonry offsets.

8. a) Simple wall footing
When the wall carries light loads or when the safe bearing capacity of soil is very high, is called as simple wall footing. Its shown as fig. (a)
b) Wall footing with masonary offset
when the wall carries heavy loads or when the safe bearring capacity of the soil is less the base width required will be more than ( 2t+2p) is called as wall footing with masonary offset. Its shown as fig.(b)

9. Rainforced concrete footing :
In place where the walls are subjected to heavy loads and the bearring capacity of soil is the low .
A 7 to 8 cm thick bed of lean concrete is usually provided below the rain forced concrete footing

10. C) Inverted arch footing :
One of the drawblacks in this type of construction is that the and columns must be strong enough to resist the outward pressure caused by the arch action.

12. D) Column footing : They are used to support individual columns.
Generally , 15 cm offset is provided on all sides of concrete bed.

14. 2) Combined footing :
A combined footing supports two columns. It may be rectangular or trapezoidal in shape.
When the two columns are so close to each other that their individual footing would overlap.
When the property line is so close to one column that a spread footing would eccentrically loaded when kept entirely within the property line.

15. Combined &strap footing

16. 3) Strap footing :
A strap footing consists of two isolated footing connected with a structual strap or a lever as shown fig.
The strap is designed as rigid beam.
A strap footing is mmore economical than a combined footing when the allowable soil pressure is relatively high and the distance between the columns is large.

17. 4) Raft footing :
A raft or mat foundation is a large slab supporting a number of columns and walls under the entire structure or a large part of the structure.
When the allowable soil presuure is low.
When the structure loads are heavy.

18. Foundations in Black Cotton Soil :
Black cotton soil is dangerous for the building on account of its volumetric changes with the change of atmospheric conditions.
The variation in thevolume of the soil is to the extent of 20 to 30 percent of the original volume.
This tendancy of soil is on account of the presence of fine clay particles which swell when they come in contact with water.
precautions for the safety of foundation in black cotton soil :
1) The raft and pile foundation should be adopted
2) The construction work should be carried out in dry season.

19. Types of foundation in black cotton soil :
Strip or pad foundation
Pier foundation
Under reamed pile foundation
Strip foundation :
For medium loads , strip foundation and pad foundation may be provided , along with special design features as discussed below.
Method-1:- This method is suitable when the soil, though expansive , has little sweeling pressure.
Method-2:- Its used for soils of high swelling pressure and having high shrinkage properties .

20. 2) Pier foundation :
Pier are dug at regular interval and filled with cement concrete. The pier may reston good bearing strata. This gap would permit free vertical movement soil during swelling and shrinkage operation.

22. 3) Under- Reamed Pile Foundation :
An under reamed pile is a board casting situ concrete pile having one or more bulbs rounder reams in its lower portion.
The Under reamed pile Diameter 20 to 50 cm and length 3 to 8 meter. Than spacing of piles is 2 to 4 meter.
A single under reamed pile has only one bulb at the bottom. When two or more bulbs are provided at the base ,it is known as multi bulb under reamed pile.
The vertical spacing between two varies from 1.25 to 1.50 times the diameter of bulb..

24. Precast Concrete Piles

25. Shallow Foundations Requirements Suitable soil bearing capacity
Undisturbed soil or engineered fill
Basic types or configurations
Column footings
Wall or strip footings

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

28. Type of steps: Filer Bullnose step Round ended step Splayed step
Commode step
Dancing step
Winder

30. Types of stair cases Based on shape Quarter turn stair Straight stairs
Dog legged stairs
Open well or open newel stairs
Geometrical stairs such as spiral, circular, etc.
Bifurcated Stair
Three Quarter turn Stair

31. Dog legged SC
Straight SC
Geometric SC

32. Straight Stair :

33. Bifurcated Stair :

34. Dog legged Stair :

35. Geometric stair :

36. Spiral stair:

37. Three Quarter turn stair :

38. CLASSIFICATION Based on type of span
Horizontally spanning or transversely spanning SC
Longitudinally spanning SC.

39. Guide lines for fixing the dimensions
Rise (R) : 150mm to 180mm
Tread (T) : 220 mm to 250 mm- for residential buildings.
Rise (R) : 120 to 150 mm
Tread (T) : 250 mm to 300 mm – for public buildings
[T + 2R] : Between 500 mm to 650 mm
The width of the stair
0.8 m to 1 m for residential building and
1.8 m to 2 m for public building.

40. Guide lines for fixing the dimensions Contd…
The width of the landing is equal to the width of stairs.
The number of steps in each flight should not be greater than 12
The pitch of the stair should not be more than 38 degrees.
The head room measured vertically above any step or below the mid landing shall not be less than 2.1 m.

41. 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 a conventional slab.
All rules regarding the detailing are similar to that of slab.
Enough development and anchorage lengths for steel should be provided.

42. EFFECTIVE SPAN FOR LONGITUDINALLY SPANNING STAIRCASESLe
LANDING
WAIST SLAB
WALL
EFFECTIVE SPAN FOR LONGITUDINALLY SPANNING STAIRCASES
WAIST SLAB SUPPORTED AT THE ENDS OF LANDINGS
Case (a)

43. EFFECTIVE SPAN FOR LONGITUDINALLY SPANNING STAIRCASES GOING=G LeX Y
EFFECTIVE SPAN FOR
LONGITUDINALLY
SPANNING STAIRCASES Le
Case (b)
Le=G +[ X +Y], X ≤1m AND Y ≤1m Le
Case (c)
Le=c/c of beams

44. Longitudinally spanning SC
Detailing
Steel at bottom longitudinally-tension
Anchorage and development steel
Distribution steel
Row of chairs
Nominal foundation for ground flight

45. Exercise A dog legged stair case is to be detailed with the
following particulars:
Clear dimension of stair case room=4.48 m x 2.1 m
The floor to floor height is 3.2 m
Width of each tread =250 mm
Width of each rise = 160 mm
Thickness of waist slab = 150 mm
Width of flight =1m
All round wall = 230 mm

46. Exercise contd., Both flights are supported at the ends of
landing on 230 mm wall.
(Landing and flight spans in the same direction)
The first flight starts from the plinth level
Main steel for each flight =
Distribution steel for each flight = 200
Use M20 concrete and Fe 415 steel.
Draw to a suitable scale
The plan of stair case
Sectional elevation of the Ground flight
Sectional elevation of the First flight
Bar bending schedule

47. Solution Dimensioning: R=160 mm, T= 250 mm
Floor to floor height = 3200mm
No of rises = 3200/R = 20. Each flight has 10 rises.
No of treads per flight=10-1 =9
Width of landing along flight
= (4480-9x250)/2 = 1115mm.
Going of flight=9x250 =2250mm
Development length = 47φ= 47 x 12 = 564 mm

48. Exercise Plan of stair case 2100 PLAN
1115 mm
2250 mm
Le = 4710 mm
Gap=0.1m
2100
Clear dimension of stair case room=4.48 m x 2.1 m

49. Estimation of quantity of concrete
Volume of concrete = L x B x D
L= length along the central line in m-measured
B=Breadth in m
D=Thickness of slab in m
Plus concrete in footing
Weight of concrete, kg = Volume x density

50. Conclusion Types of staircases. Effective span concept.
Requirements of staircase.
Detailing of steel.
Importance of development length and anchorages.
Drawing to scale and bar bending schedule.

51. Reference :- www.whereisdoc.com www.authorstream.com
Dr. R.P.Rethaliya, “ Building construction, “ Atul prakashan

52. The end
Thank you very much