Choosing the right steel for your construction project

The primary purpose of iron bars during construction, Muhawe says, is reinforcement because concrete cannot act or stand alone. There are properties where it (concrete) is not strong enough.

“For example, under tension, concrete is not strong and you have to incorporate iron bars to give it the extra strength to counteract tensional forces. And under compression, you may have to incorporate iron bars of different sizes on structures that are not strong enough to make them stronger,” says Muhawe.

There are many types of steel on the market but the most common are thermo mechanically treated (TMT) bars and high tensile bars.

Peter Musomba, the sales and marketing manager at Hardware World Ltd, says iron bars come in varying sizes such as 4.5mm, 6mm, 7mm, 8mm, 10mm, 12mm, 16mm, 20mm, 25mm,32mm and 40mm. There are iron bars that should be used as ring bars but this is dependent on the nature of the building you intend to construct.

Iron bars of sizes such as 4.5mm, 6mm, 7mm, 8mm and 10mm are usually used as ring bars that are folded to hold other stronger bars and fixed with binding wires in square or circular shapes. 

Other sizes such as 10mm and 12mm bars are used at ring beam level for relatively smaller houses. Some constructors normally use 16mm and 20mm iron bars depending on the size of the building to be constructed. They are applied to reinforce and bind the wall together to prevent cracks from developing in walls.

“If you use poor quality steel, it means the strength and durability of all the structural members is compromised. Structural members include ring beams, foundation, columns and sheer walls where iron bars are used. They (iron bars) are the reinforcing factor of the combination of reinforced concrete. If it is not good enough, it means the loading can collapse during or after construction because some of the effects of using poor quality steel are realised in the short term and some in the long term,” Muhawe explains.

Muhawe advises against judging the functionality of the size of iron bars by merely looking at them. After you have acquired an architectural plan, you have to engage an engineer to design a structural plan in reference to the architectural plan.  Many factors that contribute to the integrity and longevity of a building are contained within the structural plan because it is where the loading is designed. The structural report is where the sizing of the beams and reinforcement bars are indicated.

“It is your structural engineer’s responsibility to give the right size of steel needed to support the structure.  They are aware what to incorporate in the beams, slabs and columns. It is the load design and not the artistic design and how to transfer loads from the highest point (the roof) to the foundation of the structure that is key,” Muhawe explains.

Determining size of steel to use

It is risky to rely on past scene technology or experience to determine the type and size of iron bars to use on new projects. According to Amon Atuhaire, a construction engineer, this is because, different buildings behave differently and require different expertise.

“The moment you change architectural design of a structure, the loading also changes. You could have a tower or a high point on one side of the building and you do not have it on another. It means there is massive loading on one side of the building and none or minimal loading on the other. This is why one should never use previous project structural designs for new projects. Each design should be handled differently because they are unique,” Atuhaire advises. 

Structural loading

According to Atuhaire, construction is about combining loads from the roof, through the slabs, beams and columns, to the ground. Everything is designed looking at the last component because construction is loading.

“When you are at slab or foundation level, you are loading the soil. When you cast slabs and construct on it, it means you are loading the slab and loading the columns below the slab and the load has to go to the ground. It is this path that is designed from top to bottom. Once you mess it up in the middle, there is a high likelihood that a building will collapse,” Atuhaire cautions.

Muhawe notes that structural design alone is not enough. If you are putting up big structures, you also have to look at the geotechnical survey that is more of soil investigation.

“Before you start construction where you load the ground, you have to be sure of the soil properties. You have to do soil tests before you put up a structure that has more than two floors because it is considered massive loading. If you do not do that, even if you have the best structural design, the structure can collapse. You may find that you are loading very weak soil without your knowledge,” he advises.

“Do not judge with your eyes. Engage laboratories to carry out technical survey on your plot to determine whether the soil can actually hold the weight you areintroducing on it. You have to submit a geotechnical survey and structural reports to construction authorities if your plans are to be approved. It helps to be sure that where you are investing your money is firm enough to hold it together,” Muhawe adds.

Holding capacity looks at aspects such as the number of floors the building will have and how much weight it is designed to have.  For tall structures, it is advisable to use bars of bigger sizes such as 20mm and 25mm or even bigger depending on how high and complex the structure will be.  If it is a small bungalow with columns, you could use 12mm iron bars or as recommended by your engineer depending on their capacity.

Identifying fake iron bars

Like many other building materials, it is physically hard to determine the strength of iron bars. The appearance does not mean it is strong or weak. It is usually advised that a laboratory test be done to determine the actual strength of the iron bar before use.

However, from a layman’s point of view, the bendability may also be used to determine the quality of the bar. You could bend the iron bar and if it does not break, it is deemed to be of good quality. An iron bar that is fake will not bend. If you try to bend, it will break.

There are many effects of using poor quality bars, such as walls appearing uneven, bending of the building and eventually the total collapse of the building.

Other factors

Other than quality of iron bar strength, there is an aspect of standardisation. According to Musomba, a standard iron bar is supposed to be 40 feet.

Engineers tend to calculate how many bars will be enough for the building depending on the actual size of the bar. You may, for instance, buy 100 bars that are 30 feet long. This means they will not be enough for the building and will not do the work. It will end into collapsing buildings because you are using bars that are not enough for the building.

Musomba advises that if an iron bar does not bear the name of the manufacturer and its size, do not buy it. For instance, if an iron bar is manufactured from Roofings Limited, it will bear the word Roofings and if it is from Steel and Tube Industries Limited, it will have the acronym STIL, among other companies.  

Cons

With all its advantages, there are a few problems with using steel in construction. In very humid areas or even in rooms such as the bathroom that get very moist, steel will corrode unless builders use extra coatings of anti-corrosives to protect it. Also, since steel conducts heat and cold well, it is not ideal from an insulation standpoint. To make a steel building energy efficient requires additional insulation.