Precast has proven its safety
The modern building industry is constantly developing safer solutions to respond to safety demands. The precast building industry has been able to take on the challenge of making buildings safe during construction and after they are finished. In seismic areas, the advantages of precast are being recognized and this technique is taking over the business.
India is a good example of a fast developing market with particular safety demands. In this market, demand for affordable housing is increasing fast. At the same time, safety regulations are tightening. Particularly in seismic areas the standards and regulations regarding building materials and technologies are reinforced as more knowledge and scientific data becomes available.
New safety requirements changing the business
In many developing countries, such as India, traditional building methods still dominate the industry. On-site production is still the most used technology although it is facing increasing difficulties in meeting tightening safety and profitability demands. Rajala says that clinging to the traditional methods means the old mistakes are repeated over and over again. Many of the traditional techniques have been proven to be inadequate in resisting seismic forces.
As an example, Rajala names a so-called soft-story solution where the bottom floor of the building is used, for instance, as parking facilities. A soft story, by definition, is less than seventy per cent as stiff as the floor immediately above it, or less than eighty per cent as stiff as the average stiffness of the three floors above it. “Soft story leaves the base of the building vulnerable so that in case of an earth-quake the building can ‘kneel’ one floor down, causing a so-called soft-story collapse. This can cause severe structural damages to the whole building. Despite the clear disadvantage of the soft-story structure in seismic areas, it still remains quite a popular choice in the traditional Indian construction industry,” says Rajala.
Precast offers a stable and strong option also for a soft-story solution. "Buildings which have well-defined and continuous load paths from top to the foundation perform much better in earthquakes than structures that are lacking such features. The degree of symmetry has a significant influence on earthquake resistance. Sudden changes in sections cause stress concentrations and potential failure points," explains Rajala.
“In some countries situated on seismic areas, like New Zealand, there are already strong traditions in precast building. Hollow-core slabs are a common choice for building floors and the experiences have been very positive,” says director Lasse Rajala from Finnmap Consulting Oy. “Hollow-core slabs are very well suited to seismic areas because of their lightness. Hollow slabs lighten the total mass of the building compared to cast-in-situ concrete. Total mass is a critical issue in seismic areas as trembling will cause lateral movement of the buildings. The bigger the mass, the heavier the lateral movement of the structure,” explains Rajala.
Solid precast façades are an important safety factor in seismic areas. “In case of an earth-quake, the first thing to fall down is the brickwork, causing danger both inside and outside the building. Masonry is also an accident-prone phase in the construction process, which can be eliminated by precast technology,” points Rajala out.
Safety becomes a norm
However, as new demands and the need for large-scale investments enter developing markets, new technologies are being adapted rapidly. "Precast concrete is able to meet to the rapidly increasing demand for affordable housing. Traditional building technology has hard time meeting modern demands on safety and cost-efficiency. The socio-economic change in India has paved the way for precast technology," concludes Rajala. Large-scale building projects have made precast technology even more lucrative as the high initial investment costs can be covered in a reasonable period of time.
“Another indirect safety advantage that has followed the increased use of precast technology is that the safety conditions on the construction sites have improved in general. International construction companies have safety built into their processes and these seem to be rapidly becoming an industry norm also in India,” says Rajala, who has visited many Indian construction sites over the past years.
Finnmap Consulting Oy is a parent company of FMC Group, which is an engineering group specializing globally in structural engineering, building services, industrial and energy technology, environmental and civil engineering technology, and expert services.