Are hoop irons necessary in walls?
Highlights
- Further still, if we are to worry about the tensile resistivity of the wall, it is grossly inapplicable in our case here
- These tensile stresses are generated by dynamic loads from earthquake, high speed wind
By Avini Jimmy
Visiting up-coming construction sites, one does not fail to have sight of rolls of hoop iron (payani) as an inclusion in the wall units. The strands are run horizontally over successive masonry unit courses.
And so, are the hoop irons necessary in walls? This is a million worth question in the minds of our local constructors, contractors and developers.
This article may come as annoyance factor to a number of builders, constructors, contractors and some clients, but the notion that “knowledge is power” shall not be in vain.
A number of arguments have been advanced for the indiscriminate use of hoop irons that it improves the tensile property of the wall. While this is largely true, because, aware that the common masonry units (wall units) such as clay bricks, concrete blocks, stone.
Only have good compressive properties and are poor in tensile resistance, hence the hoop iron is to improve the tensile resistance property of the wall.
Secondly, it mitigates vertical failures of the wall. This assumes that any failure, or a crack in the wall, that is in vertical orientation will stop at the hoop iron.
Why use Hoop Iron
It is used to reinforce masonry works to prevent development of cracks, due to repeated expansions and contractions. It is typically 25mm wide and 0.8mm deep with a Zinc coating—Editor
However, every stakeholder in the construction industry should draw a deliberate attention to the fact that there are only three (3) primary requirements of a wall.
Strength: this is determined by the weakest link. (Hence, the saying, “the wall is as strong as its weakest link”). And this weakest link is at the hoop iron. Please note that there is no proper bond between the surface of the hoop iron and the cement-sand mortar in which the hoop iron sits.
“Therefore, if there is anything that jeopardizes the strength of the wall, our friend “hoop iron” (payani) is culpable.”
Stability: this characteristic of the wall is immersed in the section property of the wall. This has more to do with the slenderness ratio of the wall. Clearly, our friend hoop iron is a no-body in this respect.
Durability: this is a measure of how much the wall can resist the adverse conditions as presented by the environment. This has more to do with the exposure conditions than the presence of hoop iron. In any case, if the hoop iron is exposed to the adverse weather conditions, it rusts, which is already the beginning of the trouble to the wall.
“The use of hoop iron in the construction of walls can be traced to the culture of “copy & paste” by the Ugandans from the European practices. Owing to the adverse and extreme and weather conditions in Europe, cavity walls are largely preferred to the strip walls, which is common in our case.”
Cavity walls provide perfect thermal properties, with the cavity acting as insulation against extreme temperatures, and sound. The presence of the cavity generates the requirement that the wall-leaves need to be tied with metal ties.
Since the cavity and the insulation materials used in these cavities are weak, the cavity has to be as thin as possible, this then prompted the use of hoop iron. It should dawn on us that the wall insulation technologies have greatly changed overtime.
Further still, if we are to worry about the tensile resistivity of the wall, it is grossly inapplicable in our case here. These tensile stresses are generated by dynamic loads from earthquake, high speed wind among others.
The effects of high-speed winds can only get significant on high-level structures, with the respective wind factors. Our dwarf structures here should not even worry about wind.
Despite, technology has helped develop advanced improvements such as provision of Tuned Mass Dampers (TMD) as seismic dampers, or better known as the harmonic absorbers, to mitigate the effects of sway.
Therefore, other than this, the inclusion of hoop iron is pointless in the Ugandan construction context. Its elimination would act as an economic rescue in the overall cost of putting up a moderate house.
The writer is a Civil Engineer, Avini Jimmy
+256 (0) 782 720 720
Post Comment