America’s Empire State building and the New York Times Tower at 102 and 52 floors respectively are some of the world’s tallest buildings.
In addition to being architectural wonders, the iconic buildings have another factor in common - they are steel-framed structures.
Construction of the New York Times Tower was completed in 2007, after four years, while the Empire State building was finished in 1931 after 13 months of onsite construction.
The New York Times Tower’s structural steel frame weighs 23,500 tonnes while the Empire State building’s frame has 60,000 tonnes of steel. Both buildings are covered with glass.
Closer home, the 12-storey Sifa Towers in Kilimani, and the Kithiki Towers in Mombasa, both erected by Zenith Steel Fabricators are some of the sturdiest office structures in the country.
The two buildings put up recently are symbols of the country’s changing architectural trends as developers are drawn to the appeal of steel-framed structures over brick and mortar, decades after the method was adopted by countries in the west.
Geoffrey Gikandi, a Steel Engineer from Zenith Steel, says steel-frame construction begins once an engineer comes up with a structural design.
The process of a multi-storey building starts by laying the foundation first. This serves as the grounds of the steel columns, which are erected vertically.
Once the columns are up, primary steel beams are placed horizontally. Another layer of beams is added to form a grid. The fifth step involves drilling of floor decking sheets to the grid to get the building’s first floor.
Decking sheets are made of steel and are strong enough to be used for flooring. They are strong and of high intensity making them resistant to cracking, warping or splitting. They are never affected by changes in temperature or humidity and can even withstand earthquakes.
After the decking sheet layer, concrete is spread on it.
The process of erecting columns and laying beams is repeated for the remaining floors to have a building's steel frame. Once the top most floor is complete, another contractor takes over the project to begin finishing of the building.
“Our main job as steel specialists is setting up the structural steelwork frame,” says Gikandi.
“Once we are done building the frame, the other contracted party comes in to do the finishing work, which includes building of walls and installing the lifts among other features.”
Why go the steel-structure way?
The steel-framed building style may not be popular in Kenya yet but the advantages, according to Gikandi, far outweigh those of brick and mortar. To start with, buildings made of steel frame are known to take a shorter construction period. This is because most of the materials used come ready for installation.
“Steel and the decking sheets are pre-manufactured and are assembled quickly leading to minimum onsite labour - eventually this accelerates project schedule,” says Gikandi.
“It took seven months for the structural steelwork frame of Sifa Towers and one-and half-years for the whole building; that is, including the civil works, interior design, plumbing, electricals.”
The minimum onsite labour and the short period taken by the project translate to lower costs of construction. Due to the strength of steel, fewer columns are erected when setting up the structure because steel spans for a long distance.
Gikandi, Zenith’s project engineer, says steel structures are 15 per cent cheaper to build. However, Stroutel Africa consulting engineer, Nathan Njenga differs.
“There was no major economic consideration and I am of the opinion that the structure did not save the client any money,” he said.
“In fact, I would consider it a very expensive building because of the structural steel members used,” he said.
Steel’s ability to bridge long distances, leaves large open spaces and allows developers to maximize the internal width of the building. Fitting thin walls, for instance those made of glass, on the structure ensures that minimum space is used.
“Steel allows large free space in the building making it architecture friendly,” says Gikandi.
“The concept is applied where the project is huge, for instance when building an airport where steel members spanning 20 to 30 metres are used for glass walls - to allow light inside,” explains Njenga.
The concept of steel-framed multi-storey building is not limited to high-rise commercial buildings. Steel-built homes are a workable reality and Zenith has explored the residential market.
The houses are made of steel support and the main varying feature between them and houses built using traditional materials, is the number of man-hours spent on construction. A two-bedroom house can be set-up in eight weeks using steel frames.
“A person is likely to spend the same amount of money to construct a steel-built home but it takes eight weeks compared to the many months that would be taken to build a brick and mortar house. The house saves on time,” says Gikandi.
Why it's not popular in Kenya
It cost Sh2.4 million to build a two-bedroom 50 square metre steel-built house. According to Samuel Kamau, a Quantity Surveyor, it would take four months to build a brick and mortar of similar size.
“If other factors (finance, materials and labour) are constant, it should take four months to build a brick and mortar house, the construction process is not continuous because you have to allow the building to cure first before proceeding for a desired outcome,” said Kamau.
The company builds the houses according to the pre-designed house frames the engineers have drawn. However, the interior finishing of each house is done according to an individual’s taste and preferences.
The lag in the adoption of steel-built buildings is mainly because of the lack of technical capacity in the country.
“People are not aware that steel is stronger than contemporary cement. This is mainly because we lack the technical capacity to begin with,” explained Gikandi.
The local companies constructing steel structures are only concentrating on building factories, warehouses and roofs yet ignoring the opportunities available in the real estate sector, he added.
“Steel with greater strength is what is needed in multi-storey frame construction but it is hard to find in the country. Which means that we are still lagging behind and this method of construction may never pick seriously,” said Njenga.
“The country also lacks the human resource capacity to keep up with such projects. The trend may take a long time to catch on if at all it survives other upcoming trends that are easier to implement and which save on time,” he added.
Currently, Zenith is the only major player when it comes to this architectural trend with other companies playing second fiddle yet to venture into building office and residential buildings.
Zenith is currently working on a 10-storey mixed-use building in Eldoret.