Adherence to building code prevents structural failure, says Fadayomi
The quest to sustain high-rise buildings in Nigeria, especially, those that had been constructed since independence and the need to prevent collapse of buildings has been a subject of concern to stakeholders in the real estate sector. In this interview with The Guardian’s Tunde Alao, OreOluwa Fadayomi, a fellow of Nigerian Institution of Structural Engineers, NIStructE, who is also the Deputy President of the institution, spoke on how Nigeria can preserve these old buildings; how to deal with incidents of collapse building, especially, high rise ones, among others. Excerpt…
Buildings in Nigeria and in particular those in central Lagos built since independence are still there while some had suffered a kind of dereliction. How do you think those buildings are preserved?
Buildings in Nigeria and in particular those in central Lagos built since independence and thereafter fall into two major categories, namely; Class “A” and “B”. Those in A category are buildings designed and supervised by reputable professionals and constructed by seasoned building contractors.
Class B are other buildings that did not involve reputed building professionals and contractors.
Class A buildings usually undergo the standard processes of design, tender, evaluation, award and construction supervision. At any particular stage of the process, the best team usually emerges leading to a sound, safe and economical design and construction.
Such buildings are: High rise and medium rise building structures owned by either the private sector or the Federal or State Governments. Government owned schools, residential estates, hospitals and similar structures, while privately owned estates, institutions and establishments where the owners’ value input from relevant professionals.
On the other hand, Class B buildings belong to the set of people, individuals or organizations, including Government (when political considerations override the general interest and caution is thrown to the wind). Such projects are executed without sound professional input and construction is carried out shoddily and to no particular standard or specifications. Many of such buildings end up being unserviceable and ultimately collapsing.
The structural state of building structures depend on many factors: How good the structural design was; The compliance of the contractor to design specifications during the construction; The use to which the building has been put to through the years and the maintenance culture of the managers of the building.
Whether the building is located in flood prone areas and the regularity of such or other natural disasters are paramount on its sustainability.
The design life of buildings is usually 50 years, but most buildings, if well designed and constructed can last for longer years. The Western House in Lagos is about 55 years old and it possible can last twice as long if properly kept. The Union Buildings in Pretoria is about 102 years old. Many more ancient buildings abound around the world.
Class “A” buildings usually satisfy the five criteria listed above and since many of our consultants are very competent, structures designed and supervised by them usually meet the desired life span.
How will you assess those that were constructed in the 60’s?
In the years around 1960 when Nigeria became independent, most of the contractors capable of handling high-rise building structures were expatriates. Many of the consultants and allied firms were also expatriates. The codes of practice and construction standards were British based and many designs were constructed according to the specifications. As such, building structures built in that era were sound and many remain so till date except for cases of natural disasters and accidents like fire and so on. Examples are the NECOM House and the Independence building both in Lagos.
The generation of designers and contractors immediately after these were a mix of expatriates and indigenous firms. Even now, the design engineers are mainly local consultants and their structural designs are more tailored for the country than their foreign counterparts’ design especially with their knowledge of the local environment. Moreover, the construction of such buildings is limited to construction firms, both local and foreign, that have the expertise to construct such. Thus the design, construction and construction supervision of such structures are sound and safe. This explains why none of these structures are collapsing.
The state of buildings in Nigeria and central Lagos in particular can therefore be viewed from the perspective of CLASS B buildings. Most structures in this class belong to the do-it-yourself (DIY). Seasoned professionals are not usually involved. As such, all the preliminary investigations concerning location, planning regulations, soil information and design standards are jettisoned. Because of the limited knowledge of the owners and those they engaged to construct the structure, many critical parameters as listed above were ignored in the planning and the construction.
Consequently, buildings were constructed in flood plains like in Makoko, Maroko and Iganmu areas of Lagos, where no subsoil investigation was carried out to determine what the soil could possibly support. As such, the use to which the building would be put to during its lifetime was vague. The owners assumed they know it all and embark on the construction.
Additional floors were randomly built over the existing structures without consideration for its ability to support such. These are rampant in Isale Eko and central Lagos.
Residential buildings were converted to commercial blocks like spare parts stores and warehouses, as being witnessing in places like Ladipo and Ebutte Metta areas in Lagos Mainland.
Besides, buildings were closely packed especially within the high-density areas, to the extent that access for rescue operations was usually impossible during disasters.
These owners of this class of property usually have no access to mortgage and bank loans, proper title documents for their lands, regular incomes and so on. But, they appear to be in the majority although the data to back this up is not within easy reach. Their maintenance culture is virtually nonexistent. As a result, the building structures deteriorate without being attended to at a fast rate.
The ownership structure of some of the properties has not helped either. There are instances where a property would be divided amongst many family units – making it unclear as to where the responsibility for the maintenance lies.
The picture painted of these types of structures is awry and little wonder therefore why many of them collapse with age, abuse of use and fire incidents or other forms of accidents are rampant.
What should be done based on this assessment?
The Class A seems to have no major problems other than for them to be closely monitored to ensure that they abide by laid down rules.
For the Class B structures, the following are imperative: The slum areas and other very high density areas should first be identified; This can be done by Government involving the relevant professionals in these areas; A design fit for human habitation would then be carried out and the cost implications noted; Resettlement estates would be identified and constructed to accommodate those to be dislodged from the slum areas; Layouts with serviced infrastructure should be provided for would be house owners to build and live in; Government should facilitate access to soft bank mortgage loans for the construction of owner occupier structures and design and construction should be done according to established regulations using qualified professionals in the various fields.
Others are that Building Control Agency should be more pro-active and check construction works before they get to advanced stages; Schools for the training of technicians in the various fields should be established; Research grants for the development of local construction techniques should be provided for the Colleges of Technologies, Universities and other research centers and deliberate policy to develop the local contracts should be vigorously pursued. This should include access to loans for equipment and software development and purchase.
How can defects in building structures manifested before collapse occur?
Defects in building structures manifest in many ways depending on the nature of the defect.
The building as a whole may be observed to be sinking or slanting while its elements may crack, spall, crush, deflect or bounce as one walks over them. They can occur for some of the following reasons: Structures constructed in low lying and flood prone areas; Slanting or sinking of such a building may be observed. The slanting of a building may not be very obvious at the preliminary stage. A small ball at one end of the building could be observed to roll to the other end without any external force. Of course the slant becomes noticeable to the eye as the damage progresses. The building could slant and sink at the same time. The slanting nature will observe all the attributes already described above. The sinking will cause the building to be lower than the surrounding compound. One would therefore require steps to access the building – the number of steps will depend on the severity of the damage.
A sinking building is associated with severe dampness resulting from water ingress from the higher compound grounds. Sewage and water supply pipes could be damaged resulting in the effluent fouling the air and the flooding of the building. As a result of this, algae growth will be observed at the lower parts of the walls of the building thereby weakening them and at times resulting in cracks of the walls. Buildings of this type are common in Iwaya and Aguda areas of Lagos State.
A sinking building could result also in severe cracks of the walls and at times the beams and columns. Water is very unfriendly with reinforced concrete. Imagine what happens to the burglary bars of a kitchen window that is located near the kitchen sink; over the years the steel burglary would be torn to shreds as a result of the constant exposure to water. This is what happens when the beams, columns and floor slab of the building is perpetually exposed to water. Due to the poor concrete used in the building, the foundation, that was previously poorly designed, now fails.
However, in buildings that are properly designed and well constructed any of the elements of this type of structure can crack. This implies that the slab, beams or columns and the walls of the building could crack or crush. The slab of a building is like a tabletop on which everything is placed. Usually, the slab is supported on four sides – just like the tabletop is supported along its four edges by timber joists. The support of the slab is referred to as the beam. Consequently, the loads on the slab are transferred to the beams, which in turn transfer them through the columns to the foundation. The columns in this case are like the four wooden legs of the table that rests on the ground.
A crack at the bottom of the element especially near the mid span of any of these elements is indicative of that part being subjected to excessive tensile stress. This type of crack can also be observed at the top at the support of the elements. Diagonal cracks are sometimes observed near the supports of the beams.
Walls may be observed to crack. They can occur on one side or both sides of the walls. Cracks indicative of a structural defect usually open through to the other side.
What are the noticeable signs of buildings that are poorly designed and poorly constructed?
The following are the characteristics of these types of buildings: The concrete material is substandard; The building structural elements are out of alignment – either vertically, horizontally or both; The floor levels and heights are uneven; The timber forms during casting are warped and not well jointed. Consequently, the slab is of uneven thickness and the surfaces are uneven; the beams depths are not uniform and the beam could curve along its length; the cast concrete is not homogeneous. Honeycombs are noticed all over and the steel reinforcements are exposed in places.
The above characteristics are not exhaustive and the combination of these lead to the many or all of the defects listed previously for buildings.
How can the defects being tackled?
For new projects, the easiest way to tackle the defects is to prevent them from occurring. This is done by thinking through a building project before embarking on the design and construction.
A sound professional team must be assembled to advise on the various steps to be taken including the site location, statutory regulations, investigations, design and construction. All the professionals in the building industry are very relevant but the Structural engineer is very key as the function of others is dependent on a standing building structure. A visit to the website of the Nigerian Institution of Structural Engineers, The Nigeria Society of engineers and those of other professionals in the building industry will guide as to where competent professionals can be found.
For existing buildings that are yet to show these defects, it is advised that: All leakages should be promptly attended to; the building should not be converted for a use for which it was not designed. If it is for residential purposes then avoid letting it out to those that would use it as a bookshop or spare parts store; if a change of use were desirable, then consult a structural engineer and also obtain the necessary planning approval. However, regular maintenance of the building should be the watchword.
For buildings where these defects are already evident, they can be tackled first by inviting a competent structural engineer to assess the severity. This is often referred to as structural assessment or integrity. The engineer will carry out visual inspections and support it with tests that may be non destructive or partially destructive as the need arises. The result of his findings will invariably determine the next line of action. It is not advisable to just patch or repair any of these noticeable defects without a structural assessment.
How can one determine structural integrity of a building after a fire incident?
Building structures are normally expected to be designed to resist fire for a certain period. The period depends on the type of structure and the time anticipated for the fire-fighting agency to put out the fire.
Designing structurally for fire in multistory buildings is a standard process. In fact, fire fighting is usually part of the engineering services design. So, the hours assumed for structural design purposes are realistic and an economic design of the structure is assured.
In the other types of building structures, although fire is considered as a design condition, the exposure of the building in a real fire situation is often longer than the period allowed for in design. Practically, the building will become uneconomical to construct given the usual long time it takes to put out a fire due to environmental conditions.
However, where fire now has occurred, the structural integrity of the building should be ascertained and repairs effected before reuse.
For example, in a building like the FMBN (Mamman Kontagora House) recently gutted by fire, what determines the structural integrity of the building includes: The structural state of the building before the fire incident; The floor where the fire started from and the loads being supported by that floor and those above it if any; The cause or causes of the fire and its intensity; The number of floors gutted by the fire; The duration of the fire at each of the floor; The classification of the effect of the fire after a visual inspection; How long it takes to mop up the water and other chemicals used to put out the fire and prior to an integrity test being carried out; The report of the structural survey carried out on the building; How long it takes to implement the report of the survey; Integrity tests on high rise building structures especially in our environment depend on the maintenance culture of the building. Building structures need not be checked only when defects are noticed. They could be preventive and form part of the maintenance.
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