Overview
of Precast Concrete Buildings and Role of Structural Engineers
Precasting is not new to mankind and there
are many examples of its use since the ancient times.
However, Use of factory made mass produced
and high strength concrete components is rather a new development, essentially
a result of Vision, and daring of few notable Engineers.
The early pioneers from North America
developed new ideas, conceived new materials, and invented new devices, all
with a focus on mass production techniques.
In 1940 ,
construction of a 160 feet span
Pre stress bridge, known as “Walnut Memorial Bridge“ , using linear pre
stressing when hardly any experience was available, was indeed a major event
and generated strong confidence about the behavior of materials. This triggered many new ventures and by 1950, 7
wire strands pre stressing with long line beds, new admixtures, steam curing,
etc. were developed to create impressive variety of structures.
By 1970, low relaxation strand was
developed to reduce loss of pre stress due to creep in strands which made it
possible to design long span members with smaller sections. In 1980, Durability
of these structures was a focal topic and several admixtures with required
properties were developed.
In Europe and America, The growth of
precast buildings and related technologies contributed in creating several
infrastructure projects with complex Architectural shapes and with beautiful
surface finishes. In fact, some of the projects and their aesthetical appeal
was possible only with Precast.
In India, between 1970 and 1985, in spite
of having no infrastructure, Senior Structural engineers in Mumbai, did some
magnificent residential towers and Industrial projects with total precast
components including modular toilets in precast, and even today these projects
are the standing examples of the confidence and knowledge of Indian Engineers
and their vision of how the structures would behave.
The Precast initiative of 1970 was somewhat
lost till about 2008 and since then we have been witnessing a boom in transfer
of knowledge and processes from Europe. Today, we have at least a dozen
manufactures with large production facilities for Hollow Core slabs, Large
Panel walls, and very soon We will have Architecturally textured exterior
panels. We now have large capacity cranes and improved transportation
facilities. In fact in one case we could design and transport, precast roof
girders of about 25 m span in Pune. Considering the technology now at the
disposal of Design Engineers, We are already dreaming about projects which no
one would have thought to be possible any time in India.
From a designers perspective, Precast
buildings offer complete flexibility and one can be as creative as one wants.
with the options offered by today’s technology regarding long spans , complex
shapes , variations in textures and finishes , creativity will have no barriers
. For the constructor, Precasting offers
speed , control over quality and ability to deliver precise project needing
less manpower and less maintenance together with aesthetically pleasing land
marks which is what the developed
countries have achieved. We , in India are not very far away in terms of
knowledge about the technology and what we need now are systems coupled with
dedicated working to take us to the level of developed nations.
Precast projects are not easy and the
success of any precast project depends largely upon the integral and cohesive
efforts taken by the team of Precaster,Architect, And the Structural Engineer.
The role of Structural Engineer is very
vital in transforming the Architects vision in given time, cost and other
technological or logistical constraints.
Along with the Architects and Structural
Engineers, the conviction and resolve of the pre caster is very very important to transform the ideas to reality.
The process of design development for a
precast project is rather different than the conventional concrete building
project and The Structural Engineer is needed to have experience, exposure and
vision of the project as a whole including its requirements of utilities and
future developments.
He also has to have basic awareness about the available equipment’s and cranes , Production
capacities available , Sequence of erection and probable problems in joining of
components.
The Structural Engineer needs to be
involved at every stage and has to guide the process of Architectural design,
along with the process of designing Structural framing and other members in
conformity with prevailing codes, Aesthetical as well as service’sneeds, impact
of erection capacities on design, and suggest modifications in design so that
the project cost and time is under control. He also has to study the loads
getting transferred while concreting cast in situ components and overall
stability during erection.
Precast projects are like making a large
scale Lego model. The making of detailed
shop drawings is another major mile stone. These assembly drawings are required
to have every small detail about services , cut outs , bolts , sleeves , ducts
, erection points and for success of the project , the Structural Engineer has to check ,
comment and approve all such drawings with careful study of manufacturing and
erection tolerances.
During Manufacturing stage, the structural
engineer is required to visit and ensure that the design ideas are properly
embedded and quality assurance procedures are followed since everything is of
high strength. During erection stage, it
very essential that before start of erection, Structural Engineer gives a detailed
briefing to the site about the design requirements and check list of important
points.
On completion of the project, Structural
Engineer has to certify the work and also has to maintain record of various
technical parameters used in the project.
Today’s projects are demanding in terms of
Time,Cost, Planning constraints,and Logisticissues. All these issues are to be
kept in mind by the Architects and the Structural Engineer while planning a
building and although it looks like a demandingprocess, with My limited
exposure of projects done so far, I feel that with conviction of giving what is
imagined coupled with systematic approach, dedication to detailing, and close
interaction of all stake holders, a Precast building project has the greatest
potential of giving you satisfaction of creating a wonderful building.
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