In need of support

CW India Staff , February 2nd, 2009

Formwork is a crucial element in construction. But contractors need to be careful as most accidents are reported at the time of installation of formwork

Did you know it was the Roman engineers who first began using slab formwork to complete constructions that used concrete? Most of the construction was built using arches and domes because concrete does not have a strong resistance to stress. Concrete only became a popular material with which to build once reinforced concrete was invented.

Formwork is a complex technique involved in construction which requires specialist contractors for proper use. It’s the term given to specific moulds or receptacles into which concrete is poured to make slabs for construction or actual components of buildings. Surprisingly, for a technique that has been used for thousands of years, it still has no substitute. Vinayak Bhosle, engineer at Larsen & Toubro says: “If there is a substitute for concrete, then maybe formwork will find a substitute.”

While concrete is quite strong in resisting compressive loads, it has relatively poor tensile or torsional strength. Little wonder why the early structures mainly consisted of arches, vaults and domes.

Of the most notable concrete structure from early times is the Pantheon in Rome. Moulding these structures meant constructing temporary scaffoldings and formwork or falsework in the shape of the structure. Such techniques were not isolated to pouring concrete, but were and are widely used in masonry. Because of the complexity and the limited production capacity of the building material, concrete’s rise as a favoured building material did not occur until the invention of Portland cement and reinforced concrete.

Vinod Deshani, vice-president (engineering department), Kanakia Spaces says: “Formwork has evolved over the years in terms of materials used. However, formwork is necessary to create strong structures.”

While wood is the most common fabric used, steel is gaining popularity considering that most developers are making maximum use of floor space index (FSI) and constructing high-rises. Because the system is easily dismantled into single parts, it is transportable.

The system is built in the same way as beam formwork, apart from these single parts. Joists and stringers are screwed, bolted or welded to become a deck. “Most of the construction techniques in India have mainly been borrowed from Europe.

In India, we prefer to use simple wood or plywood,” says Aniket Joshi, sales engineer, Peri India. “Bamboos are another material commonly used in India. The inherent strength of bamboos offers a tensility not seen in other materials. But this has a disadvantage – bamboos can tend to cave in, as once erected if can offer no access to the area underneath.”

The success of Billimoria’s Nagari Niwara Parishad at Goregaon in Mumbai proves that even unskilled workers could lift and erect a formwork if the material is right.

Billimoria opted to use lightweight aluminium formwork system of construction enabling in-situ casting of all the components of a dwelling unit including the walls, floor slabs, weather shades, lofts, parapets and staircase to form a monolithic structure which meet strict seismic requirements.

The resulting form finished concrete is highly durable and requires no further rendering. Especially when building low-cost mass houses, this system is the most cost-effective as a considerable repetition of floor layouts are required. Incidentally, system formwork is the checks that are carried out during designing or utilising a formwork.

However, there are certain issues with formwork that remains unsolved. Considering that the labour employed at the site is unskilled or semi-skilled, it becomes imperative that the engineering is in line level and the sizing of the formwork is uniform, says Deshani. The alignment is most important at the time of erection. Moreover, according to Bhosle of L&T, cost, successful repetition, weight, durability and adaptability are some of the common issues that linger with formwork. He should know. L&T and Peri are the two international brands that have created various types of formwork thus offering contractors a choice.

Construction uses many different types of formwork, for many different purposes. But the three main materials for creating formwork remain the same - timber formwork, engineered formwork (usually a metal frame) and stay-in-place formwork (usually pre-made concrete systems). These three alone can offer a variety of different ways to create slabs and structures.

Traditional slab formwork uses timber, masonry and carpentry to complete construction. The method works through tree trunks or other lumber supporting rows of stringers placed three to six feet or one to two meters apart with joints placed between the stringers. The only difference with the metal beam slab formwork is that steel is used instead of timber and metal props are used instead of supports.

This system is reusable and more methodical. The finish of the concrete is smoother and the formwork is easier to remove after the cement has cured. Modular slab formwork is created from pre-made timber modules or modules made from steel or aluminium.

These are usually produced in a factory offsite and added to construction once completed. In residential buildings, of up to seven storeys, contractors prefer to use wooden shuttering and wooden joists.

While formwork is an important aspect of construction, little attention is paid to it. Most construction companies consider it as a ‘form’ necessary before the concrete can be poured in.

Since the formwork also needs to be stripped or peeled off later, it is a temporary phase to the construction activity. However, according to Joshi of Peri India, a quantum shift in formwork was noticeable about 10 years ago. Formwork in casts is now available for up to 10 metres. Steel and aluminium, that can hold weight of 10 square metres, are also increasingly common.

This is a vast difference from the earlier formwork weights of 400-500 kgs. Compared to wood that requires large cross-sections and is not hollow, steel is available in tubes with a thinner framework and is lighter.

Safety is a crucial issue when building formworks. Since most formwork suppliers don’t have the supplier’s supervisor on site, the supervisor of the contractor needs to have the required mental bandwidth.

It is for this reason that Peri India ensures it provides a minimum of 30-days site supervisor to see the formwork through. Site safety is a most crucial aspect that contractors face. So what are contractors doing? Joshi of Peri India says that supervisors need to put in that extra effort to see that the formwork is being undertaken by a professional contractor who is experienced and certified in their knowledge and services.

Because formwork involves concrete which is heavily affected by a number of stresses, the incorrect use can be dangerous as the concrete may collapse. Formwork has, however, allowed people to build structures never before dreamed possible and paves the way for future construction.