1. PREFABRICATED STRUCTURES

2. UNIT 1- INTRODUCTION NEED FOR PREFABRICATION ADVANTAGES MATERIALS
MODULAR COORDINATION
STANDARIZATION
TRANSPORTATION
ERECTION

3. DEFINITION
Prefabricated building is the completely assembled and erected building of which the structural parts consist of prefabricated materials

4. AIM To effect economy in cost To improve quality
To speed up construction since no curing is necessary
To use locally available materials

5. ADVANTAGES Work time is reduced Less workers needed
Work done with better technology
Interruption in connection can be omitted

6. Materials of Construction
Materials like concrete,steel,treated wood,aluminum etc…
Special characteristics while choosing materials
Easy available
Economy
Easy workablity
Light weight
Durablity

7. MODULAR COORDINATION
Modular coordination is a concept of coordination of dimension and space in which buildng components are positined in terms of MODULE(M)
1M= 100mm

8. Dimensions of pre fab components
Flooring and Roofing
Length- multiple of 3M
Width – multiple of 1 M
Thickness – multiple of M/4
BEAMS
Length – multiple of 3M
Width – multiple of M/4
Depth – multiple of M/4

9. Thickness – multiple of M/4 Staircase
Column
Height – multiple of 1M for ht up to 2.8M and ht above 28M is multiple of 2M
Lateral dimension- multiple of M/4
Wall
Thickness – multiple of M/4
Staircase
Width – multiple of 1M

10. lintels Sunshade Length – multiple of 1M Width – multiple of M/4
Depth – multiple of M/4
Sunshade
Projection- multiple of 1M

11. STANDARDIZATION Factors influencing :
Reducing the number of joints by using largest type of elements
To select the suitable type of member for each element from the point of production,assembly ,economy
To limit the size there by reducing the transportation and by reducing the over all weight

12. ADVANTAGES Easier in design Easier in manufacture
Makes repeated use of specified equipments in erection and completion easier and quicker

13. Types of pre cast RC elements
i) precast concrete foundation structures
Use of pads should permit larger loads and poorer soil condition
Load bearing walls consist of wall blocks,wall panels,shell units….
Entire scheme should be simple in design and easy construction

14. Prefabrication pad locks

19. Isolated column footing

20. Combined footing under two columns

21. Cross section of completed prefab footing

22. Precast RC slab units 1.slabs with precast funicular shell units
Funicular shells are ideal for shell roofs
These precast shell are also called waffle shells, can be either square,rectangular or triangular
They can be cast in a factory or at site with simple moulds with concrete or surki mortar
No reinforcement is req in body of shell since no tensile stress is developed
However 6mm mild steel bar is used in edges of ribs to take care during transportation

24. Section of shell units

25. Slabs with RC joists and hollow clay blocks
In this joist with bottom flange of width slightly greater than web width are precast in site and laid over support
Space bwn them is adjusted by providing clay blocks
The precast joist are provided with reinforcemnt to take shear and flexure tension.

27. Celcrete slab units
Natural light wt agg is not available in india so autoclaved aerated concrete is used to produce slab units
Also called foam or cellular concrete
Density is kg/m3
C.s is 3MPa-5MPa
This foam concrte is used in prefab bldg

28. Pre cast concrete column
Bldg constructed by using precast columns and beams are generaly designed as framed structures
Connection bwn column and beam is designed in such a way shear force and moments are transferred through structural embers
Connection can be done by placing insitu concret or welding of projectng steel renforcements
In some case bolted connection also used to connect precast columns later coverd wit insitu concrete

32. Precast water tank elements
Water tank can be cast either as part or whole
Large water tank cannot be prefab at factory bcoz of over wt .
Small segemnts are precasted and bolted together at site
In order to avoid corrosion stainless steel bolts are used
Tanks up to 2.5m ht and 40m in dia have been built using such segments

34. Precast pavement slabs
Pressed pavement slabs can be made from palin concrete for covering large open lands
These elelments can be pressed to obtain smooth finish and also enhance durablity
Excess strength is achieved by pressing by squeezed out in wet state

36. Precast retaining wall
Cantilever type retaining wall itself can be pre casted if the ht is with in 1.5m
Normally in railway platform, verandah in residential bldg are provided with retaining walls of about this ht
These retaining wall can be bwn 1.5m-2m length depending up on facility available
Weep hole are provided on vertical face to drain water from fill.

39. Transportation
Transportation of precast elements inside the factory and to the site is based on not only economy but also design aspect to avoid jerk as it s placed in final position
Inside the factory
its based on method of production selected for manufacture

40. Transport from factory stacking yard to site of erection
It s planed based on traffic rules
Size is restricted by the availability of suitable transport equipments such as tractor cum trailer
While transporting through wagons, trucks , bullock cart etc care should be taken such that excessive cantilever is avoided
Also care should be seen at sharp bends and uneven roads

41. Erection Factors to be considered Precast element position
Crane capacity
Crane rotation radius
Cleaning of elements and site for erection

42. Types of crane 1.stationary erection 2. cranes on rails
Guyed derrick
Climbing carne
Tower crane with fixed base
2. cranes on rails
Portal crane
Tower crane
3.Mobile crane moving on ground
Truck mounted
Crawler mounted

43. Stationary cranes A.guyed derrick
Used on framed buildings for errection of floor panel ,columns .
Lighter in weight
Can be shifted from floor to floor operating from an erected floor.

44. b.Climbing crane
Tall building over 20storeys are constructed this type crane is used
Horizontal jib and balancing counter weight is placed on top of shaft
It operates around 360 degree and can be lifted up to new position as buldg goes on completion and dismantled
This is used in longest areas

45. C . Tower cranes with fixed base
Places were rail mounted and climbing cranes are not possible tower cranes can be installed
These cranes are fixed at base and braced horizontally to the building portion already completed as building go up ,the vertical mast can be hoisted up by special hydraulic jack.

46. 2. Cranes on rails A. portal cranes
In storage yards and in buildings where the travel distance is short portal crane is used
Consist of two vertical legs and horizontal beam
Travelling trolley is attached to bottom flange of beam tht carries load horizontally
It is very stable

47. Mobile cranes moving on ground
A . truck mounted crane
For quick movements from place to place cranes are mounted on track with operating cabin and separate chassis
Chassis will have generator and motor
Before operating the crane with loads,crane is taken off from pneumatic tyres and load transferred to the ground by simple hydraulic legs

48. Crawler mounted cranes
It s used in excavation ,dredging and material handling.
Should be used on a hard and compacted soil
On loose soil it is difficult to move the crane with load
It can operate 360 degree

49. Methods for manufacture of pc elements
factory prefabrication
Site prefabrication

50. Factory pre fabrication
Done in centrally located plant
High level of mechanization
Preparation of Moulds
Concreting
Vibration
curing

51. Major disadvantage Extra cost –transportation from plant to site
Shape and size is limited due to lack of transportation

52. Site prefabrication Manufactured at site or near the site
Normally done in open space with local labours
Reduction of transport cost
draw backs:
Not suitable for high degree mechaniztion
Continuity of work is not available

53. Process involved
Main process
Auxiliary process
Subsidary process

54. Main process Assembling moulds Placing reinforcements in position
Fixing of tubes if necessary
Pouring of concrete
Vibrating
Demoulding
curing

55. Auxiliary process
It s necessary for successful completion of process covered by main process
Testing products

56. Subsidary process Storage of materials
Transport of cement and aggregate
Transporting and stacking the precast elements
Repairs and maintenance of tools,machines etc…

57. Various methods of manufacture of precast unit can be broadly classfied in two methods
Stand method
Flow method

58. Stand method Moulds remain stationary at factory
Various elements required for work is casted in factory itself and then transported to site

59. Flow method
Precast unit under consideration is in movement according to the various process involved in it.
Moulds are transported to site for required elements

60. Cycle of precasting Preparation of concrete
Preparation of reinforcement
Preparation of moulds
Assembly of reinforcement in mould
Casting and compaction
Curing