Seminar on Pre Engineered Building on 14th Oct 13

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.