The case of precasting



The major difference between traditional cast-in-place reinforced concrete structures and precast structures is that the latter is composed of various members cast at a place different from their final position in the structure; therefore the structure consists of a set of “elements” and “connections”.
Thus, the main structural issue in precast construction is related to the connections between the precast members and to the extent to which the connections affect the response of the total structure under seismic actions.
In this regard, the following issues need to be discussed:

  • The stiffness of the structure
  • Structural Integrity of precast structures. Ties.
  • Ductility properties of the structure 

For all types of structures built in seismic areas, it has to be verified that both the structure as a whole and its constituent structural elements possess adequate ductility, taking into account the expected ductility demand, which depends on the characteristics of the particular structural system.
In addition to other requirements which apply to all structures built in seismic areas, in the particular case of precast structures,  the effect of the connections on the energy dissipation capacity of the structure has to be properly considere.
In this respect the following distinctions should be made for the connections 
connections that are located well outside  the critical regions of the structural  members, not affecting the energy dissipation capacity of the structural system, 
connections that are located within critical regions but are adequately over-designed with respect to the rest of the structure, so that in the seismic design situation, they remain elastic while inelastic response occurs in critical regions adjacent to the connections,     
connections that are located within critical regions and are provided with substantial ductility,
hinged beam–to–column connections (in frames with fixed column-to-foundation connections)
How can precast concrete be a boon for Indian construction

The use of precast concrete in construction is widely regarded as an economic, durable, environmentally friendly, structural sound and architecturally versatile form of construction. The precast concrete industry is continuously making efforts to keep on line with the demands of modern society: economy, technical performance, safety, labour circumstances and environmental friendliness.
The evolution of building construction and civil engineering works during the next decades will undoubtedly be influenced (in greater extend than today) by the developments in information processing, global communication, industrialization and automation. These are already certain to be implemented in prefabrication. However, when looking into the efficiency of present building processes, there must be a smoother transition from the design of the construction to its completion. The only way to move forward from the traditional labour intensive methods (which characterizes the building construction in India up to date) to the modern approach of prefabrication is to apply an industrial philosophy throughout the entire building process (including design and relevant Codes).
Sustainability is a major issue in any industrial activity today. In the building industry, prefabrication is able to provide the best approach to this end. In fact, the whole life-cycle can be better controlled. Industrialized production of elements allows for saving materials and energy when constructing.
Compared with traditional construction methods and other building materials, prefabrication as a construction method, and concrete as a material, have a number of positive features. It is an industrialized way of construction, with inherent advantages: factory made products, optimum use of materials, prestressing, quality, architectural freedom, structural efficiency, flexibility in use, adaptability, fire resistance construction, environmentally friendly way of building, appearance and surface finishing, building services e.t.c.
  For the case of India, the only way to face the demand of constructions of every type which is expected to increase dramatically in the near future, is the use of precasting in the construction process, for the sake of increased quality, (including aesthetics, safety and lifetime) together with economy (including reduction of onsite working personnel and speed of erection) of the structures.
  However, between else, conditions for the above are:
-  Encouragement of the Indian state to precast industry e.g. by means of: special laws, financial support: reduced taxes,soft and/or subsidized loans etc.
There is also need to develop a “unified Indian precast code” to comply with the existing body of the Indian Standards.
 - Changements on approach to designs:
In precast concrete construction some changes on the methodology on the production of the design should be envisaged. That means that from the first step of the design process several decisions have to be taken, in addition to the functional and aesthetic needs of the project, in order to satisfy the demands of the prefabrication. This in turn leads to the recognition that, from the very beginning of the project, for the entire design process (conceptual design, analysis, dimensioning, verifications) a “unique” prefabrication design team is needed including the precasting engineer to ensure that the input by the precaster is properly integrated into overall design.