Precast Construction In India And Its Future Ahead
C. A. Prasad
President, Pre-engineered Structures Society of India (PSI)
Director, Metey Engineering & Consultancy Pvt. Ltd., Hyderabad
Precast is fast adopting itself into the construction sector, as skilled labour availability is diminishing day by day in India, and the construction demand is on the rise in the country. Builders and Developers are looking at ways of adopting the precast into the construction and achieve speeds and quality.
As the skilled labour availability is diminishing day by day, the projects delivery schedules are getting affected with delays. This has prompted the developers to think of alternative construction technologies to speed up their construction and meet the delivery demands.
More and more developers are departing from the conventional construction and transforming their construction into advanced construction technology like monolithic construction using aluminium formwork. As aluminium formwork repetitions are limited and needs to go for new form work for new projects, they are moving forward to Precast Construction Technology duly setting up their own precast set up, and some developers are giving orders to the precast industries.
The developers who have set up their own precast factories in order to meet their delivery requirements with less dependency on the labour are as follows:
In Hyderabad: Janapriya Developers, Aurobindo Reality, My Home Constructions Pvt. ltd., Pooja Craft Constructions
In Bangalore: Brigade and Shobha Developers
In Ghaziabad: Bharat City Developers
The demand for precast systems is rising day by day. The developers and Govt. institutions have felt the necessity of completion of projects faster and thus pass on benefits to the customers early as well as for themselves. Precast construction is fast catching up and is establishing itself as the construction technology of the future. Both the State and Central Governments are insisting for the new construction technologies to be adopted into construction. Taking note of this, the Govt., institutions are calling the tenders for construction of buildings using precast construction technology in the locations wherever the precast units are available.
The DRDO is constructing the apartment buildings required for them using the Precast Construction Technology. MES Dept., is also promoting the precast construction technology for faster delivery of their structures. The Telangana State (TS) Govt. has constructed the affordable houses using Precast Construction Technology, Monolithic Construction Technology and Tunnel Form Technology in the city of Hyderabad and around. Now, the TS Govt. has taken up the construction of medical universities and the buildings in it using the prefabricated Construction Technology such that the buildings can be completed faster.
The overall development of precast units set up across India and the machinery supplied by various manufacturers is as indicated in the table below:
Precast Advantages
Factory condition production, all weather working, better quality, finish and accuracy.
Less labour requirement, less wastage and less cost based on repeatability of items.
Faster cycle time, scalability and repeatability.
Offsite working and parallel working, standardisation of design, engineering and execution.
Precast Housing
Precast Limitations
Volumes are required for viability of precasting.
Equipment intensive in terms of transportation, lifting and erection.
Types Of Precast Systems
Depending on the load-bearing structure, precast systems can be divided into the following categories: Large-panel systems, frame systems, slab-column systems with walls and mixed systems.
Large-Panel Systems The designation large-panel system refers to multistorey structures composed of large wall and floor concrete panels connected in the vertical and horizontal directions so that the wall panels enclose appropriate spaces for the rooms within a building. These panels form a box-like structure. Both vertical and horizontal panels resist gravity load. Wall panels are usually one story high. Horizontal floor and roof panels span either as one-way or two-way slabs. When properly joined together, these horizontal elements act as diaphragms that transfer the lateral loads to the walls. Depending on wall layout, there are three basic configurations of large-panel buildings: Cross-wall systems, longitudinal wall systems, and two-way systems.
Precast Frames Precast frames can be constructed using either linear elements or spatial beam column sub-assemblages. Precast beam-column sub-assemblages have the advantage that the connecting faces between the sub-assemblages can be placed away from the critical frame regions; however, linear elements are generally preferred because of the difficulties associated with forming, handling and erecting spatial elements. The use of linear elements generally means placing the connecting faces at the beam-column junctions. The beams can be seated on corbels at the columns, for ease of construction and to aid the shear transfer from the beam to the column. The beam-column joints accomplished in this way are hinged. However, rigid beam-column connections are used in some cases, when the continuity of longitudinal reinforcement through the beam-column joint needs to be ensured. The components of a precast reinforced concrete frame are:
Slab-Column Systems With Shear Walls These systems rely on shear walls to sustain lateral load effects, whereas the slab-column structure resists mainly gravity loads. There are two main systems in this category:
– Lift-slab system with walls
– Prestressed slab-column system
In the Lift–slab system, the load-bearing structure consists of precast reinforced concrete columns and slabs.
Precast columns are usually two stories high. All precast structural elements are assembled by means of special joints. Reinforced concrete slabs are poured on the ground in forms, one on top of the other. Precast concrete floor slabs are lifted from the ground up to the final height by lifting cranes. The slab panels are lifted to the top of the column and then moved downwards to the final position. Temporary supports are used to keep the slabs in the position until the connection with the columns has been achieved. The prestressed slab-column system uses horizontal prestressing in two orthogonal directions to achieve continuity. The precast concrete column elements are 1 to 3 stories high. The reinforced concrete floor slabs ft the clear span between columns.
After erecting the slabs and columns of a story, the columns and floor slabs are prestressed by means of prestressing tendons that pass through ducts in the columns at the floor level and along the gaps left between adjacent slabs. After prestressing, the gaps between the slabs are filled with in situ concrete and the tendons then become bonded with the spans. Seismic loads are resisted mainly by the shear walls (precast or cast-in-place) positioned between the columns at appropriate locations.
Precast Concrete Structural Elements Which Are Used In The Industry Are As Follows:
Precast Load Bearing Walls with Precast HCS Building Of Stilt+ Parking
+ 9 Story Buildings At Dundigal, by Inventaa Industries, Hyderabad
Wall Panels: Wall Panels could be precast as two types, viz:
(i) To full thickness as one panel, or
(ii) Two leaves as a double precast concrete panel of typically 2 x 50 – 100 mm thickness with integrated structural reinforcement and special lattice girders.
In the case of a first system, the wall panels would be cast horizontally on a flat bed made of steel mould, and after sufficient steam curing the bed is lifted to a 60 degree angle, then is carried away by gantry girders to one end for loading on to a truck and further to precast yard or site.
This could also be cast in the vertical position with number of moulds and after sufficient curing can be lifted of and stored in a precast yard for further curing and eventual transportation to the site.
Precast Staircases
Stair cases are too cumbersome to provide shuttering and pour concrete in the case of conventional construction and Precast stairs are the easiest to cast in vertical moulds, lift and erect in position as can be seen in the following pictures.
Industrial Structures
Lots of Industrial Structures are now turning into precast construction. Predominant in this field are Pharma Industry, electrical Sub stations, etc. Sai Life Pharma Industry in Hyderabad and Bidar (Karnataka) have resorted to precast construction for their buildings, such that the existing facility is not affected with dust and other construction related pollution, and a neat and clean construction will happen.
Pre Engineered Buildings (PEB) using structural steel is well established in the country. PEB Structures do provide large column free structures which are beneficial to the industry set up to place their machines, etc. inside. However, for the external walls, the brick wall is constructed for a height of 3 m and thereafter sheeting is provided upto the roof so far. Sheeting durability lasts for 10 to 15 years and thereafter it requires replacement again. Considering this, the external walls are now proposed with Precast RCC walls. The external precast RCC walls also provide for fire resistance too in addition to long lasting durability. The precast RCC wall panels area provided with fixity at bottom over a beam connecting the column pedestals and over the height, it is connected to the structural steel elements of the PEB with angles.
Photos below show the wall panels of width 3.6 to 4 m and height of 7 m, 16 m and 19.3 m high panels being erected and placed in position for the Industrial Structure at Hyderabad, by Inventaa Industries.
Car Parking Structures
Precast is one of the best options and ideal for the car parking structures, as the Precast Hollow core slabs can span upto 12 to 15 m and the double tee slabs can span upto 22 m. With such long spans of precast floor slabs as a possibility, large column free space structures are possible and car parking can be efficiently planned with it. Precast RC frame structure (precast columns and precast beams) with precast oor slabs is the type of construction which could be used for car parking structures.
Infrastructure
Precast can be used in the infrastructure in various ways. Culverts, Drain channels, Man holes, Boundary walls Underground Tunnels, etc., can be made of using precast construction technology.
Summary
For multi story residential buildings, load bearing RCC Precast wall panels with Precast HCS as flooring is the best option. The load bearing RCC precast walls will also give more resistance against the lateral forces due to earthquake and wind forces.
For car parking, shopping mall buildings, commercial structures and structures which need large column free space, precast RCC framed structures with precast columns and beams plus precast HCS is an ideal solution.
Precast is the most suited to the Industrial structures, as large column free space structures can be provided which is needed for them.
In the Infrastructure field too, precast can be efficiently utilised for most of the elements like Culverts, Abutments, Retaining walls, Drain channels, etc.
Precast Construction Technology is entering into the construction sector on fast pace with number of developers themselves setting up the precast units, and more and more entrepreneurs will set up the units in the future. PSI (Pre Engineered Structures Society of India) is making its efforts to create awareness about Precast Construction by conducting workshops in the name of PEPSCON and details of workshops conducted so far and the papers presented there in can be downloaded from the web site www.pesssi.in. Architects need to be aware about precast construction and its modularisation such that they can conceptualise the precast into the planning right from the beginning.
Architects Harrysons and Consultants Pvt. Ltd., Noida, have conceptualised the DRDO apartment buildings considering the Precast Construction Technology. Structural designs are carried out by the author.
Sumit Maity Architects, Delhi have done over 40,000 units of 3BHK, 2BHK and EWS structures for DDA, utilising Precast Construction Technology.
There are number of other architects who are considering Precast Construction Technology into their planning and Precast design and construction is set for big growth in this country which will meet the demands of faster construction.
Any structure can be designed to suit to precast construction and reap the benefits of speedy construction and durable structures.
