Precast Technology in Infrastucture Projects

Kapilesh BhateDy Manager Tendering,

Planning & Control Precast India Infrastructures Pvt. Ltd. Pune

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AbstractIn a scenario of largely scarce and expensive labour force, need of fast track projects and high quality, construction industry is slowly moving towards Precast Construction. This paper intends to highlight the strides, the precast industry has taken in infrastructure projects through three case studies. The first case study explains various concepts in precast for Concourse Level of a Metro Station that were arrived at to bring about uniformity in design of metro stations and to achieve stipulated timeframes for such projects. The proposed solutions emphasized on addressing on-site execution issues like traffic congestion due to large manpower and extensive staging.The second case study showcases the award winning Multilevel car park building of one basement plus ten floors, measuring around half a million square feet, parking around 1300 cars is located in Pune, India and constructed as a combination of cast in situ and prefabricated structural elements, and later on treated with an envelope of façade elements, which includes the combination of a unique methodology of prefabricating façade elements to be fixed on spandrels specially designed and assimilated with the precast structural elements, in a simple but effective manner. The case study also explains evolution of the design and integration of façade elements, structurally and aesthetically, with the main structure, and deals with production, transport and installation techniques, and deciphers the achievement of safety standards of the building necessary as an additional aspect by annulling use of additional steel grills or meshes, which would have been needed in local conditions and normsThe final study speaks about the scope for precast technology in other infrastructure domains in the form of irrigation, bridges, Pipe Lines, urban and marine infrastructure that leads to faster, neater construction with much less site labour, better site control, greater accuracy and quality of finish.

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Case Study I: Precast In Metro Projects

To cater to urban India's needs of transportation, new

metro systems are currently under construction and

bringing about vast changes in 15+ cities all over the

country at a breathtaking pace. India is well on its way to

bring a shift from private modes of conveyance to public

transport. Attempts are being made to enhance

technology with low initial cost and avoiding high O & M

cost.

Precast construction can thus well serve these aspects

effectively.

The typical design of metro stations includes entry, exits,

concourse and platform. The scope is generally limited to

cast in place rib-slab arrangement with Precast I girders

at concourse and platform level parallel to the viaduct.

Sighting the primary objective of infrastructure projects of

delivering the facility to public within a stipulated

timeframe, an attempt to convert this conventional design

of metro station to Precast was made by us, at Precast

India IPL.

We tried to dwell into the feasibility of precast in Metro

Stations, through a case study of Nagpur Metro which is a

3 coach metro of two alignments running for 19km each.

The design of superstructure by the client is a simply

supported between the portal piers. The beams are

connected to the diaphragm on either ends which is

further seated on the bearings supported by the portal

piers.

General arrangement of the superstructure with

bearing arrangement and typical cross section of the

superstructure is shown in Fig 1.

Fig 1a: Cast in situ T shaped Rib beam and slab

arrangement of 26m long.

Fig 1b: Cross section of Cast in situ T shaped Rib beam

and slab arrangement

Concourse level consists of T shaped cast in situ rib

beam and slab arrangement (Fig 1a) spanning 26m for a

station length of 77m (Fig 1b). The staging for cast in situ

works is to be removed only after 48 - 72 days as per the

construction methodology laid down by the consultant.

This adds to the duration of the project.

Precast India in an attempt to overcome short-comings of

the above design and ease off the site execution,

proposed various precast alternatives for the concourse

level framing.

The primary aim was to cash-in the advantages of

production in controlled environment ensuring superior

quality, uniformity in element design, saving in formwork

due to repetitive production cycles and to limit on-site

activities.

In option -1, we proposed to split 26m long rib slab-beam

girder (fig 2) into 2 numbers of 13m long Precast T

shaped ,3.8m wide girders weighing 60T each which will

be connected together by post tensioning at site. Cast in

place stitch will render the girders monolithic. Precast

staircase of stringer beam–tread slab arrangement with

deep beam serving as a parapet was proposed in place of

25m long cast in situ staircase that connected concourse

to platform level.

Fig 2: Cross section of Option-1 Precast I shaped girder

beam

In concourse floor slab, a 6.5 m escalator opening had

been a major constraint. Because of which, stitch at two

locations (between P4 P5& P5P6) would have been

required for a width 2.65 m.

This required introduction of temporary structural steel

members which will be supported at the ends in a manner

similar to typical precast units. Also, on P5, the precast

slab slab would be required to be supported on two

temporary steel trusses which will be supported at ends

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in a manner similar to typical precast units. The trusses

would only be removed once the slab is connected to

neighboring precast girders and main girders pre

stressed. The slab will have to be spanned for 8.25 m

because of escalator opening. Another challenge was to

maintain the thickness of this slab within 175mm.

Sighting transportation constraints due to large width of

the girder and to incorporate framing of elements around

the escalator opening in option 1, a girder-slab

arrangement was proposed with I girder weighing 80MT

each spanning 13m and 1.8 m width (Fig 3) .

Fig 3: Cross section of Option-2 Precast girder beam and

Inverted channel slab

The slabs were designed as inverted precast Channel

sections to rest on corbels of I girder. This arrangement of

channel slabs enabled flexibility to cater for escalator

opening.

In a step ahead to further minimize the complexity in

terms of weight of 13m long precast girders (fig 4) we

proposed to split the girder into two segments, each of

650mm width and total depth of 1750mm placed 700mm

apart so that they will be almost on grid line column,

perpendicular to the viaduct .These girders were

designed to support double Ts or channel sections or

Hollow Core slabs. This option would also take care of

escalator opening

Fig 4: Cross section of Option-3 Precast I girder beams

and Inverted channel slab or Hollow core slab

Precast elements were also suggested for Entry, Exit

buildings in the form of precast staircases (stringer beam-

treads arrangement), columns, beams, slabs (Hollow

core, solid slabs) parapet, walls panels, and closure

walls.

In a nutshell, a comparative can be derived based on the

following parameters.

Case II: Precast in Infrastructure for Car Parks

An Award winning project whose exposed surfaces

surpass all other material finishes for external facades,

while at the same time keeping sustainable factors of

unharmed air circulation and soft daylight factors for the

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the half million sqft spaces inside the building.

All the aspects of Architectural Design, Structural design

and detailing, façade design, integration of MEP

services, production, quality control, transportation, and

installation capabilities were tested to the limit in the

extremely challenging site conditions and the limiting

tolerances of +/- 20mm for each of the 4000 elements

forming the building, making it a truly challenging precast

structure, proving that “modularity” does not mean a

coarse repetitive sensation, but can be professionally

tweaked to generate a very interesting and eye catching

structure, which gives a constantly variable and different

visual sight as we pass by the structure.

The execution of this delicate but imposing project has

touched its life cycle at every point, beginning from the

experience of changing from conventional labour

oriented site executed projects to a mechanized /

industrialized path breaking technique. This session,

through this project will explain the thought process

behind how Precast India transformed itself into a leader

of the Indian Precast construction scenario including the

challenges of investing correctly into a precast facility by

knowing the existing market conditions and

requirements, while at the same time projecting future

real time scenarios, and finalizing factory layouts,

investments, site locations, type of automatic / semi-

automatic machineries, technology transfer etc. .

A short tour through the conception of the project, the

fundamental purpose of the structure, and the

justification of the cost of a stunningly simple but

articulate façade in prefabricated elements proves how

easily a professional Architect, Domingo Seminario;

transformed the “simple” and modular elements into a

disciplined and beautiful façade, attracting international

attention.

The challenges

The project originates from an International competition

of Architectural design managed by Precast India after

their appointment and requisite freedom granted by their

Client Infosys to create a “masterpiece” as a single

directive. After the winning entry was selected from 5

International and 3 Indian Architects by Infosys, started

the journey of changing mindsets of the Client, their

Consultants and Advisors, from going in for precast

technology instead of Conventional construction

methodologies.

The structural design of the project as conceived was a

super challenge, met very efficiently by the in-house

Structural engineers of Precast India, involving the

challenges of maintaining speed, quality and logistical

constraints of the site within city limits and for elements

ranging from 2 tons up to 28 tons for heights up to 45

meters, involving tower crane capacities of 50 tons and

moving on rails.

The detail of each structural / nonstructural precast

element, speaks volumes of the innovations and cutting

edge technologies that have been used for structural

design, production planning, production, transportation,

quality control, testing of mock ups, installation, and

handing over the completed structure.

There were special calculations of sustainability resulting

into excellent natural lighting and fresh ventilation

factors. There was a tolerance of only +/- 15 mm in the

structural arrangements of all the dowels / bolts of the

element and the sleeves provided in the other. The whole

structure was designed and analysed for Zone 3 seismic

conditions, and therefore connections and detailing in

structural design was a special consideration for raft to

basement walls, raft to columns, column to column,

column to beam, beam to spandrel, beam to slab, façade

to spandrel, and from façade to façade.

With a reputation for extensive integration and use of IT

systems into all processes of design, execution, and

installation, all project stages, Precast India created

accurate

production drawings through 3D BIM Tekla softwares, in-

house production Protrak software, integrated mould

booking systems, and tied up logistic software with bar

coded elements using mobile Android phones, to

address the challenging volume in a short time.

Therefore reducing the complexity of the project through

proper and systematic use of precast technology coupled

with latest IT systems and 3D BIM software, Precast India

IPL has opened its horizons to tackle further challenging

projects, and the many national / international

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recognitions plus awards won for this project in the

various Architectural, Structural, façade, and

prefabrication categories, have bolstered the morale.

Case Study III: Precast in other Infrastructure

Domains

Precast technology in bridges and flyovers is common all

over the world and consequently India has also leaped

into it in the form of segmental construction for bridges,

culverts, deck slab and segments for viaducts for metros.

Precast technology ventured into Pre-stressed bridge

planks, pre- stressed Double T Slabs(Fig 5) and I

girders, post tensioned girders, piles, modular deck

units, railway box girders, bridge piers, headstocks,

abutments, etc. and other heavy constructions.

3.1 Bridges and Flyovers

Most common prefabricated elements for bridge

connections are pre stressed elements such as I beam

(Fig 8a), box beam (Fig 8b), channel/U shaped elements

(Fig 8c) and other segments.

Fig: 6a, I beam Element for Bridge Construction

Fig: 6b Pre stressed box beam for bridges

Fig: 6c Pre stressed box beam for bridge construction

3.2 Irrigation:

Irrigation infrastructure generally comprises of water

retaining and regulating structures. The conventional

methodology at times proves uneconomical, with the use

of rapid strengthening admixtures and temporary water

barriers until the structure attains stability.

On the contrary, where Precast elements can be put to

use in Canal lining, culverts, channels, river intake

cabins, spillways, walkover bridges, sewage drains,

water storage tanks, ground irrigation , it can minimize

wastage and ensure quality and delivery of infrastructure

projects in stipulated time-frame .

Precast in infrastructure can also find its use in culverts.

They may be three sided or four sided. Three sided units

allow for stream crossings maintaining the natural

stream-bed. A four sided box culvert unit is generally

used as a permanent service tunnel or a carrier tunnel for

underground piping .Precast box culverts are superior

quality, require low maintenance and have large number

of applications including storm sewers, service tunnels,

or small bridges for stream crossings.

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Fig 7: Precast box culverts

As a part of external development works of the multilevel

car park, Precast India produced culverts to cater for

future provision of underground services of the state

Industrial Development Corporation, without the need to

excavate the newly laid concrete road at the main gate of

the Car Park.

The 250mm thick base was first cast, after which the

shuttering and reinforcement was in place to cast the side

walls. The walls were cast after the base attained

required strength.

The whole U shaped assembly measured 4.4m in length,

2.5m in width and heights varying from 1.53m to 1.8m

thus weighing 16.1 MT which was transported on the

trailer to the site.

The culvert was installed overnight so as to not disrupt

the employee traffic during the peak working hours of the

day. The hollow core slabs were then placed over the

culverts and cast in place screed was done

Fig 8: Precast culverts Cast in lengths up to 2.5m

weighing 16.1MT..

Fig: 9 precast elements in irrigation infrastructure

3.3 Pipe line infrastructure: Pipe lines are laid

across states for conveyance of different resources.

Where the alignment passes through the adverse

locations, the use of precast elements

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of precast elements simplifies the execution. Precast

pipes, precast pipe holders, pipe chambers are some of

such elements.

Fig: 10 precast elements in pipe line infrastructures

3.4 Urban infrastructure: As the concept of Smart

cities is being materialized in India, infrastructure is

expected in short time period with minimal maintenance

in the form of water drains, pathways, walkovers, service

ducts, underground chambers, Precast electrical poles &

their foundation, road dividers, Traffic barrier, etc.

Fig: 11 precast elements in pipe line infrastructures

3.5 Marine infrastructures: India having the longest

coastline, the requirements in marine infrastructure

cannot be ignored. Commonly used precast elements

are Tripods, tetra pods, and other break water elements.

In recent past for stability and longer life span quay walls

are also built using precast elements.

Fig: 12 precast elements in marine infrastructures

3.6 Tunnel infrastructure: Interlocking precast

segments has changed the face Tunnel construction

methodology which has achieved standardization by use

of Tunnel Boring machine

Fig: 13. Precast elements in marine infrastructures

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3.7 Building Infrastructure : It comprises of Pre-

stressed Kerbs,Tactile Tiles , Bollards, Tree Guards,

P r e c a s t P a v i n g S l a b , G r e a s e

interceptors,Headwalls,Road Medians, Precast Bicycle

Tracks, Precast Bicycle Tracks with storm water drainage

underneath, Precast Slabs with finishes, Storm Water

Channels,Signage,Precast Benches, Precast Steps,

Precast Reinforced Ramp System, Precast Traffic

Islands, Precast Planter Boxes. Precast elements like

trenches, road elements can be re-used in case of

change in service alignment with minimal damage to the

elements.

Fig: 14. Precast Kerb Stone, Electrical Trench, Road

Median, Storm water drain

CONCLUSION

Precast Construction has a wide scope to establish itself

in infrastructure as is evident from the case studies.

Presently, Metro rail infrastructure is of highest

importance in India. However, the construction is a

challenge, as the cities are highly populated and traffic is

increasing day by day. Precast is the best suitable option,

as it does not hinder the traffic flow with construction

taking place at a faster pace. The Governing authorities

must thereby encourage precast in infrastructure

tenders.

As the efforts to transform cities to Smart cities are

gaining momentum in the country, Precast satisfies the

requirements like Underground services, Subways,

Tunnels, Flyovers, and Stations etc. Airports as well as

well high-rise utilities. Precast facade elements of various

geometries can add to the aesthetic value of the

infrastructure projects

The conventional construction methodologies are highly

un-standardized even today. In case of complex projects,

probability of human error and accidents is high. Precast

Construction standardizes various construction

methodologies and work procedures both on site and off

site. Cost and Time, the two driving factors of every

project can be controlled efficiently in Precast

Construction. Need for huge construction labor, Cost and

Time overruns, accidents at site, time consumption,

resource wastage are alleviated to a greater extent in

Precast Construction.

The un-paralleled advantages of Precast in infrastructure

projects viz. superior quality due to controlled

environment , reduction in project duration, minimized

material wastage ,standardization of methodologies,

effective pre-engineering by use of BIM software for

modelling the structure at element level, reduction in on-

site activities definitely supersedes the additional cost

incurred in Precast in terms of machinery and

transportation of elements

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