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I agree with NIA that quacks who parade themselves as qualified professionals are inexorably contributing to the upsurge in the incidence of structure failures in Nigeria; however, the problem goes deeper than that....


Sunday, December 16, 2001
Alfred Obiora Uzokwe
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NIGERIAWORLD COLUMNIST
RISING INCIDENCE OF BUILDING COLLAPSE IN NIGERIA;
Any remedy?



reader directed my attention to a news report on NigeriaWorld of November 14, 2001. In the article titled- Architects decry spate of collapsed buildings- the Nigerian Institute of Architects, Oyo State chapter, was reported as calling on the State Government to "consult architects on all building projects in a bid to provide safe building and hospitable environment"

The immediate past chairman of the Institute noted the collapse of 13 structures in Oyo State and said "it was caused by quacks parading themselves as professionals"

The reader hoped that as an architect, I would shed some light on why buildings are collapsing at an alarming rate in Nigeria. He cited more examples of building failures and consequent abandonment in some areas of Lagos and wondered if this was becoming a trend in the building construction industry in Nigeria?

I chose to respond through this medium because this is a subject of interest to most Nigerians in the Diaspora who at one time or the other, have residential construction projects going on in Nigeria.

I agree with NIA that quacks who parade themselves as qualified professionals are inexorably contributing to the upsurge in the incidence of structure failures in Nigeria; however, the problem goes deeper than that and I will elaborate later.

In response to the reader's question about the cause of structure failures, I wish to point out that engineers utilize a process called forensic engineering analysis to determine with some certainty, the cause of structure failures. Forensic analysis entails a methodical review of the original building plans to ensure that they were designed in accordance with established building codes. The construction method used by the contractor is also reviewed for any deviations from approved plans while the material used is tested (in the lab) to ensure that they are not of inferior quality.

In view of the fact that the cause of a building failure is almost always unique to the particular building in question, and cognizant of the fact that I was not involved in the investigation of those buildings that collapsed in Oyo state, I cannot give exact reason for the failures. However, from my vantage point as an architect who has designed several buildings constructed in Nigeria, I can advance some general reasons why buildings may be susceptible to collapse and then proffer some proactive steps that could help avert the problems in the first place:

THE QUALITY OF THE BLOCKS USED:

The quality of material used is a factor in building failure. Take for instance the 9-inch hollow blocks used for the construction of external walls of residential buildings; these blocks support the weight of the "decking" and other floors above it in conjunction with "pillars". Since the strength of the blocks depend on the ratio of cement to sand used for molding them, the right proportions must be used for molding the blocks to ensure that they are strong and durable.

The so-called "ready-made" blocks sold by some block industries do not measure up to expectation. Some of these block industries mass-produce the blocks and in a greedy bid to get the most number of blocks per bag of cement, they use more sand than necessary resulting in very weak blocks. This writer witnessed cases of 9-inch blocks bought from block industries crumble while bricklayers were trying to pick them up! Now tell me, if a 9 inch block crumbles as it is being picked up, how would that block carry the weight of the "decking"? The only reason we do not have even more cases of buildings crumbling as a result of weak blocks, is because of the presence of columns "pillars" which are the primary load bearing components in buildings.

THE QUALITY OF CONCRETE USED:

The other building material component that is sometimes bastardized at the peril of the building itself, is concrete. Concrete is used for construction of foundation footings, lintels, "decking", "German floor", beams and columns. Concrete is made up of sand, cement and stone and when iron bars (rods) are added, it is called reinforced concrete.

The strength of reinforced concrete depends on the proportion of cement, sand, stone and iron rod in it. After the design of a building by an architect, the structural designer calculates the amount of weight the building will carry - this is called structural analysis. The engineer then determines the size of beams and pillars that will help carry that weight. He also determines the number and sizes of rods that will be put into the beams and pillars to strengthen them for carrying the weight. What I have just described is the ideal situation, which is not always what happens resulting in structure failures.

Problem arises when proper structural analyses is not performed or better yet, when no analysis is performed. The result is that the contractor resorts to trial and error method of construction: he may not use the needed number and sizes of iron rods or may fail to construct adequate numbers and sizes of pillars. Some contractors even fail to use the correct mix design for the concrete, the list goes on. All these errors aggregate to make a building susceptible to failure.

POOR COMPACTION AND CONSOLIDATION OF FOUNDATION SOIL

The other important reason a building could collapse is lack of adequate compaction of the soil inside the foundation before placing hard-core and pouring the "German floor". If the soil is not properly compacted before the German floor is cast, as construction progresses, settlement occurs causing cracks on the walls and German floor that invariably lead to structural failure.

WEAK SOIL:

Also, because of their geologic make up, some layers of soil are just not strong enough to carry the weight of a building. This is mainly applicable to the top layer of the soil on most parcels of land. If this factor is neglected and the building is constructed on the soil anyway, differential settlement of the building starts and leads to cracking of the walls and decking. In some cases, the building just continues to sink and this can be seen in many parts of Lagos. If a soil investigation reveals the presence of weak soil on the upper layers of a parcel of land, the structural designer rectifies this by calling for a deeper than normal foundation. This means digging until strong soil is encountered before laying the building foundation.

There are other reasons why a building would be susceptible to failure but I think the reader gets the gist. So what can one do to guard against it? Below are some of the proactive steps that could help:

Always insist on structural analysis after the architect has designed your building before construction starts. Structural analysis and design determine the weight that would be exerted on the building and specify the correct number and sizes of columns and beams needed to help carry that weight. The correct location of the columns and beams and the sizes and quantity of iron rods needed, are also specified.

Make sure that the blocks you use come from reputable sources that use the correct mixture of cement and sand for molding them. Blocks with too much sand have the tendency to crumble at the slightest movement and could never support the weight of a building for long.

Insist that the building foundation is properly back-filled and consolidated before the German floor is cast. This will prevent secondary settlement and cracking of walls.

Your representative must keep an eye on the mixing of the concrete to ensure that the correct proportions of materials are used. For example, if the plans specify a concrete mixture of 1:2:4, it means that 1 part of cement to 2 parts of sand to 4 parts of stones should be used in the mixture. Make sure that the contractor sticks to it otherwise you would end up with concrete not strong enough to do the job. Also, ensure that the specified sizes and numbers of iron bars are used.

Finally, your construction representative must be knowledgeable, independent and assertive otherwise the contractor will have a field day in taking you for a ride. If you have more questions about this topic, email me.

MERRY XMAS EVERYONE