A multi-storey building can either be constructed using steel or reinforced concrete. In Kenya, the latter is used more often. The columns and beams of multi-storey buildings are often built of concrete that has been cast with strengthening bars within it. Steel is not commonplace as a material in multi-storey buildings. In the United States, for example, though steel is still a minority, you are more likely to run into a high-rise building made of steel frames.
A steel multi-storey building would ordinarily consist of an assemblage of I-beams that are welded and bolted to form a framed structure. Cladding and walling would then be provided with a suitable material like aluminium or light brick, or the fronts could be fully glazed. Sifa Towers, a towering development under construction along Lenana Road in Nairobi is an example of a steel structure with fully glazed fronts. The steel sections for this project were imported from India.
Though a few builders are embracing steel for low-rise buildings, the material is more common with warehouses and go-downs, because of the ease of erection and dismantling, if need be. But you are not likely to see many high-rise buildings in Kenya having been erected in steel.
However, steel frames are ideal for commercial office developments due to the improved speed of installation. For example, there is a higher likelihood for columns to be introduced in steel frame structures than in the reinforced concrete option. Construction of upper floors can proceed unlike in the reinforced concrete frames where concrete in slabs, beams and columns have to be cured before work in the higher slabs can continue.
How does this then save money? The faster pace at which steel structures are erected leads to savings. There are costs associated with site activities which are dependent on time. The shorter the time of construction, the greater the savings. In addition, in case you have used a loan to finance the construction, the shorter time will save you a lot of money on interest. And since the steel members can be assembled away from the construction sites, it will lead to reduced site costs and also translate into minimum disruptions of activities on the construction site.
Dickson Ong’esa, a structural engineer at Steel Structures Kenya Limited, offers an explanation for this. “Steel buildings are not common because of the cost implications involved in the fabrication and erection of steel. Steel is conventionally used with metal sheets hence may not be appropriate in most areas in the country,” he says. “This is in addition to the belief that steel is for industrial construction and roofing only. Compared to reinforced concrete, more so for multi-storey buildings, steel is expensive.”
Samuel Njoroge, an engineer at HP Gauff, concurs. “Here in Kenya the cost of fabricating is too much – almost equal to the cost of material.”
What then would make an architect propose steel frames as the construction material for a building?
“The architect would go for steel because of reliability and predictability; to deliver the building fast for use and as a cost effective measure with regard to reducing labour requirements during construction,” says Ong’esa.
Steel has the benefit of requiring few labourers on site because much of the construction will consist of bolting and welding. Lifting is done mechanically by cranes. Reinforced concrete, on the other hand, requires a huge labour force of form carpenters, steel fixers and masons.
In case your development is adjacent to residential areas, steel frame structures would be ideal due to minimum noise produced and significantly lower amounts of dust emitted from the site. There is also significantly lower volume of waste produced from sites where steel frames are used.
That said, in a country like Kenya where it is easier to provide labour than to provide steel for construction, we are not likely to see steel multi-storey buildings taking over from reinforced concrete any time soon.
[Image Credit: youjenzi.com]