Why buildings collapse

Getting a competent workmanship and using the right material measurements are some of the things to consider for a strong building.

What you need to know:

Before you occupy the building you are either to work from, or live in, it is important to beware of some engineering mishaps that could cost you your dear life or someone you know. Racheal Irene Nalubega explores why buildings may collapse.

About three weeks ago, Kyaseka Towers, a five storied building next to Ham Towers in Makerere collapsed, burying scores of occupants underneath its rubble. Kyaseka Towers was just one of the several buildings, both commercial and residential which have collapsed over years.
There are several reasons which have been advanced to explain why buildings collapse.

STRUCTURAL FAILURE
Most buildings collapse mainly because of structural failure. This is when a building is designed to carry a specified load. However with time, the building’s owner decides to increase the load by say, increasing the number of occupants from those earlier planned for in the structural or architectural designs. Also, when structural designs are done poorly, then the building is bound to collapse, Mr Bashir Ahmada Ssebunya, an architect says.
“When considering over loading, it is important for people to know that it is in three different types; dead load, live loads and wind loads which should be looked out for during construction lest the building collapses,” he says.

The dead or permanent load is load of the building elements themselves like the weight of the walls, roofs and permanent partition floors. The live or imposed load is the people and furniture that can be moved from one area to another.
Mr Ssebunya says once these loads are in excess, then a building will surely collapse due to the pressure exerted on the slabs and cannot hold the weight anymore.
The wind loads, though uncommon for building in Uganda to collapse because of this load, should also be considered. This particular load considers the direction in which the wind blows and here sufficient specifications are always catered for so that the building can withstand the wind pressure.

Design inadequacies
This requires for the builder to follow the structural designs to the neck. Once any of the instructions are not followed, for example loading more floors than the ones designed for, then a building will be weakened.
According to Mathias Omona, a civil engineer with specialty in structural engineering and graduate member with Uganda institution of professional engineers, change of earlier planned for building structural design to a more complex design that was not accounted for, will increase on the weight hence putting tension on the columns leading to collapsing.

Incompetence in engineering practices
Improper concrete mixing is the main incompetence done by engineers yet concrete determines how long the building will last for. The mixes give the building its durability.
Concrete before being approved is supposed to have passed through three different stages which are batching, testing and curing.
Ssebunya explains that concrete has up to four other sub materials which are sand, cement, aggregate or stones and water and if not mixed appropriately then the strength will not be achieved.

He adds, “different batching ratios lead to different concrete grades, for example, grade 20, 25, 30 and all these are applied on different parts of the building to achieve total strength.”
The curing process is the next stage of proper concrete verification.
It is the drying process of concrete and this enables concrete to reach its strength but it is advisable to carry out this process under moist conditions.
Thereafter, the concrete should be taken to the structure laboratories where it is tested with cube tests to confirm whether the structure has reached the designed strength. But most engineers are reluctant to take such measures as required.

Counterfeit material
Most building materials in Uganda are counterfeit, ranging from the cement to steel bars. If the engineer is not cautious then a building will end up collapsing because surely counterfeit cement can never guarantee a building’s strength.
Omona says it is up to the engineer to control quality where they look out for all these counterfeit products and not just leave the work to the Uganda Bureau of Statistics.
He adds, “It is not wise to just assume that the products are genuine.
Instead test them to find out if they are of the best quality you want.”

Poor workmanship
This is usually about poor role allocation. In this case, if the building owner or engineer does not supervise the builders, they may mix the material poorly.
There are also incidences when instructions of how to go about work on site are influenced by the owner even he has little knowledge, says Omona.
Such inconveniences lead to inefficiency and quack work on site since all specified measures and materials are not followed.
“Even the institutional regulatory bodies are partly blamed for not doing their work efficiently. So, bodies such as the Uganda Bureau of Statistics and other concerned local bodies are obligated to play their role.

Wrong building use
Most building owners in Uganda, once they realise that the business or use of the building they had earlier planned for does not earn them much or suit them, they switch to another. This switching could pose a threat to the building.
When a building is changed from its planned intentions, then used for something heavier, for example an apartment block being turned into a club - then there is an overload beyond the building’s design capabilities.

Building settlement
Another vital issue often neglected by engineers is the soil strength test which is done to ascertain how hard the ground is.
Omona says that different soils have different characteristics and in instances where the building will contain more than four floors, then a geotechnical report is required for submission after a geotopical investigation is done to determine how hard the ground is which will in turn decide the foundation strength.
Buildings are limited to 25 millimetres from foundation level and if they sink in then the buildings are bound to collapse, this goes to show that the soil is weakening and the building strength is pushing it down.
That is why when considering building a high raised building, bores are dug up to 20 meters to determine the soil quality and know what quantity and quality of materials that need to be used to prevent the building from collapsing.

Natural calamities
Natural calamities though has led to a number of building collapsing in most foreign countries, this is rarely the case in Uganda or even Africa at that.
The strong earthquakes, strong tsunamis and cyclones are some of the well-known calamities that destroy building which Africa has not experienced yet.

CORRECTING MISTAKES
Mr Omona says that modifications can always be made to correct the excess weight faults by considering adding additional columns for backing up so as to support the excess weight.

Outliving it’s age
Building materials have a time frame at which they can hold up after use. That is why buildings are given an expire time frame, say 100 years.
Once these years elapse then this particular building should be brought down.
This is not always the case in Uganda where bringing down a building is never a consideration until it collapses. That is when it is deemed to expire.