WHY BUILDINGS COLLAPSE IN NIGERIA....A MUST READ FOR THE PROSPECTIVE AND EXISTING PROPERTY OWNER Buildings, like all structures, are designed to support certain loads without deforming excessively. The loads are the weights of people and objects, the weight of rain and the pressure of wind--called live loads--and the dead load of the building itself. Any type of building can collapse but multi storey buildings are more prone to catastrophic collapse. Recently in Benin City, Edo State, a section of the multi-billion naira ultramodern Central Hospital building where construction work was still ongoing collapsed. According to The Nigerian Tribune, the collapsed portion was a section of the third floor of a three-storey wing of the building. It was reported that a pail carrying materials snapped from the rope connecting it to the hook of a crane and crashed into a freshly constructed beam linking the pillars of the top of the third floor of the building, resulting in the collapse of the affected portion. The state Commissioner for Works, Mr Francis Evboumwan, said seven persons were trapped but six were pulled to safety sadly the project manager, was pulled out dead from the rubble at about 2.00 a.m on Tuesday. He added that the government would invite structural experts to determine the integrity of the three-storey structure and to establish if there was any collateral damage to the building because part of the building is still standing. THE REASONS /FACTORS WHY BUILDINGS COLLAPSE IN NIGERIA The causes of structural failure in Nigeria are numerous and can be complex depending on the type and complexity of the structure. According to Folagbade (1997), the inability of the engineer to carry out proper site investigations, inability to calculate design loads accurately, inability to prevent the use of substandard building materials, inability of the engineers/planning authority to have good design layout and inability of the engineers to understand structural analysis and design principles lead to structural failures. The possible causes of building collapse in Nigeria are listed below: • the absence of soil test report; • structural designs and details handled by quacks; • absence of co-ordination between the professional bodies and the local town planning authority; • lack of adherence to specifications by the unqualified and unskilled personnel; • poor and bad construction practices; • the use of substandard building materials; • lack of proper supervision by professionals; • inadequate enforcement of the existing enabling building regulations; • illegal conversion of buildings which often lead to structural deficiencies; • flagrant disobedience of town planning regulations by developers/landlords; • the compromising attitude of some workers of the town planning authority; • lack of sanctions against erring professionals and landlords. Report of soil test of any site is very useful to the architect and the structural engineer. This will enable them to specify what type of foundation is to be used. And also they will know what precaution to take in order to avoid collapse of the structure because of settlement and other foundation problems. In some cases, buildings that are above the ground floor level do not have structural designs and details, and often times lead to failure of the structure. On the whole, the professional bodies such as Nigerian Institute of Architects, the Nigerian Society of Engineers, the NIOB and the Planning Authorities, who represent the government share in the blame (as stated in the possible causes of building collapse above) that cause collapse of buildings in Nigeria. PROPOSED PREVENTIVE MEASURES Having considered the remote causes of collapse building structures in Nigeria, remedial actions such as those listed below could be used as preventive measures. Preventive actions are those that are taken when design and construction standards are appropriately stated, adhered to and tailored by the professionals and the planning authority officials. In order to reduce the problems of collapsed buildings to a manageable proportion, the following preventive measures are proposed: • Stringent penalties should be applied for those responsible for collapse of buildings, particularly when loss of lives is involved. • Town Planning Authorities should be adequately staffed and equipped with professionals in the construction industry. For effective monitoring of projects during and after construction. • Continuing professional development should be emphasized by both the professional bodies and the government on modern trends in the building industry. To keep members of the building industry abreast with new trends in construction. • Government should provide an enabling law for the training, and effective control of artisans and craftsmen in the building industry. • Government should screen those getting involved in housing projects. For any structure more than a bungalow, a structural engineer must be involved. • Construction work should only be carried out by registered contractors and supervised by registered architects, engineers and builders rather than engaging unskilled contractors. • Clients should obtain approvals before they begin construction. At the same time, they should work with the approved drawings and specifications. Any alterations should be approved before their implementations. • To promote the safety of buildings therefore, a holistic approach is required whereby all relevant outfits and organizations must be involved apart from the recognised professional bodies. • A regular audit of defective structures must be carried out and such structures marked for demolition should be demolished before it causes havoc on lives and properties. • Government at all levels should intensify public enlightenment, placing emphasis on how building disasters could be prevented rather than managing situations which might be costlier. HEAR THE PROFESSIONALS Victor Oyenuga , a one time Past President of The Nigerian Institution of Structural Engineers said that the central objective of a designer of a building structure is safety and economy. What then makes a shelter or structure to stand that is, withstand all the forces of nature that are willing to pull it down? Three major components can be identified as follows: a) The professional behind the structure; b) The materials used for the structure and c) The techniques or construction methodology adopted for the structure. The first component leads to the question - who are the professionals? The only set of professionals that makes or mars a structure in terms of safety is the Structural Engineers. No other, not even their closest counterparts- the civil engineers. Prof. D.N. Nwokoye, an erudite Professor emeritus of Structural Engineering, University of Benin, Benin City, Nigeria, and former President, The Nigerian Institution of Structural Engineers (NIStructE) defined a Structural Engineer, in his book titled The Philosophical Bases in Education and Practice of Structural Engineering as: “An Engineer who having attained the prescribed academic standard in the field of Structural Engineering or cognate fields and who having reached professional maturity in the practice of Structural Engineering is recognized as such by the Regulating Professional Body or bodies”. In practical terms, a structural engineer, in this country, is a) a COREN registered Structural Engineer OR b) a COREN registered Civil Engineer who MUST OF NECESSITY be a Corporate Member of the Nigerian Institution of Structural Engineers (NIStructE). Thus, a civil engineer who is not a Corporate Member of NIStructE should not be entrusted with the structural safety of any structure - buildings, culverts, bridges, dams, etc. In other words, to ensure safe building, the designer must be someone who is certified to carry out the design. The best design by the best and most qualified designer does not guarantee safe structure except the materials for construction is of the correct quality. The materials mostly used for building structure in the country are cement, sand, coarse aggregates (gravel and granite) and iron rods. The most common type of cement used is Portland Cement (Ordinary Portland Cement: is one of the most commonly used types of cement. OPC, as Ordinary Portland Cement is normally referred as, is made by heating a mixture of limestone and clay or other materials of similar bulk composition and reactivity, to a temperature of 1450 degrees centigrade. These results in partial fusion and formation of nodules called clinker. This clinker when ground with a certain percentage of gypsum results in cement. Different countries have different standards to test the cement ) Ordinary Port Land Cement is suitable for all modern types of construction, including all kinds of masonry, concrete works, pre-stressed concrete, repair works etc. and more often than not meet the required quality requirements in terms of setting time, soundness and strength. Sharp sand are obtainable from shallow rivers, hence salt contents are relatively low and permissible. Sharp sand from lagoons and oceans (if possible) should be tested for salt concentration. Gravels are perhaps the best coarse aggregates because of their natural roundish nature. The major problem is the dirtiness of the material. A properly washed gravel is better than crushed stone or granite. The flaky nature of crushed stone is a major set back in terms of strength. The issue of iron rods is the major problem that is facing concrete designers in the country today. The rods are undersized (11.5mm instead of 12.5mm) and characteristic yield strength less than 410N/mm2 when the new code (Eurocode) is putting the minimum to be 460N/mm2. Thus, in terms of materials much is required to be done in the areas of iron rods properties. In addition to good design and good materials, good workmanship with adequate quality control is desired. The methodology of construction must be strictly followed. For example, the quality of water (water cement ratio) in a concrete mix goes a long way to determine the strength of such concrete. It is not therefore, enough to judge concrete mix by workability alone. PRECAUTIONS NECESSARY There are many precautionary methods that can be adopted to prevent building collapse and some are alien to the client. SOIL TEST The first precaution against structural collapse is the carrying out of soil test. Soils vary from one place to another and the cost of carrying out such test is generally in order of 0.1% of the building project. That is, N100,000 for a building worth N100m and for a multi-storey building of over N1bn, one probably needs about N600,000 or 0.06%. Thus, the bigger the cost of construction, the less significant the cost of soil investigation. The essence of soil investigation includes but not limited to: Confirmation of soil bearing Strata; Confirmation of soil bearing capacity, Confirmation of soil settlement rate and Confirmation of soil general properties. Depending on the soil type and load to be carried (that is, structure type) soil investigations can be limited to simple penetro meter tests or extended to deep bore holes especially for high rise buildings. DESIGN AND USAGE. The live loads (user loads) of any building is a factor of the usage, for example a library is 5.0kN/m2 while a residential building is designed to a maximum of 2.0kN/m2, usually, 1.5kN/m2. Thus, a building for residential purposes should not be converted to places of assembly like a church or library, except such activities are limited to the ground floor. Thus, a major precaution is that the usage of the structure as envisaged during the design should not significantly change during the real occupation. The factor of safety embedded in the design procedure may not be strong enough to withstand such change. CONSTRUCTION METHODOLOGY. The method of construction is important and the rules must be followed. The quality control to achieve the desired result is very important. In project where a lot of concreting is involved, design mix must be carried out to achieve the concrete grade specified by the designer. FAILURE MODES A building can fail as a result of many defects and such failure modes include: Punching Failure, Bearing failure, Flexure Failure. The first two are due primarily to poor design and failure to carry out proper soil investigation. Each of this will be discussed briefly. Punching Failure :This occurs in a framed building (a building made up of columns, beams and slabs). Due to inadequate thickness of the pad base the column punches through the base and causes disruption in the entire loading system and finally a collapse occur. To avoid punching failure, the designer must provide enough base thickness that satisfies punching shear. This calls for a professional structural engineer. Bearing Failure: Bearing failure can occur in both framed buildings and load bearing wall buildings. It is the failure due to inadequate bearing area. That is, the load imposed on the soil is more than what the soil can bear. This calls for sound soil investigation and expert design. In most cases inexperienced designers assume a bearing pressure which in excess of the soil bearing capacity and failure occurs. The good news is that it can easily be remedied if detected on time before it leads to massive failure. The bad news is that it calls for additional column and column bases which may affect the usability of the building, in some cases. Bearing failure manifests through cracks of the natural ground after the base is cast, loaded and the foundation filled back . Flexure Failure : Flexure failure is the most common fatal failure that may not give any warning and may occur suddenly. It is due to the failure in most cases of the columns. When a column fails, it transfer its loads to other columns which are ill prepared to receive such and hence those columns fail too leading to massive collapse of the structure. This is the most prevalent in our country. The reason is simple, such columns were designed by inexperienced designer, they are under-designed and may not be robust enough to withstand the load imposed on them. Poor detailing can also lead to flexural failure especially in cantilever slabs. A Cantilever is a projecting structure, such as a beam, that is supported at one end and carries a load at the other end or along its length, A member, such as a beam, that projects beyond a fulcrum and is supported by a balancing member or a downward force behind the fulcrum or A bracket or block supporting a balcony or cornice. A cantilevered design house A cantilevered stone A Cantilevered Slab Poor materials and poor construction will lead to under design and cause flexure failure too. The strength required will not be achieved due to poor quality or poor content of the materials. For example a concrete member designed to grade 25 concrete will fail if the actual concrete strength is less than 20N/mm2. In the areas of iron rods, most designers would assume the British Standard value of 410N/mm2 for high yield high tensile bars. In actual practice some rods are as low as 380N/mm2. Thus members so designed will be undersized and can lead to flexure failure. 3.4 Falsework Failure More often than not collapses that occur during concrete casting were due primarily to collapse of the formwork. When casting at a very high level is involved steel props are recommended rather than bamboos and 2x3 planks. For normal heights, bamboos should be used as props rather than 2x3 planks. Their strength is better and possibility of buckling is minimal. The natural lateral supports at intervals braced the bamboo tree and makes it a stronger material for vertical false work. SOME The Nigerian Institution of Structural Engineers is saddened by the continuous collapses experienced in the country. We also had some specific questions ...... Finest Construction Nigeria Limited: What do you think is the reason we have so many failed buildings in Nigeria? Philip Nwokoye (a Civil/Structural Engineer ) : lack of proper Engineering services, use of substandard and fake building materials, quacks and untrained builders, and grass root corruption where safety is sacrificed for maximum profit. We need dedicated good Engineering practice regulatory bodies to endorse or reject buildings under construction. Finest Construction Nigeria Limited: In a good building design, should the weight of the building (the dead weight) be supported by pillars? (building project provider) : Sure in every building, the respective loads on the structure is transferred via beams and columns (pillars) to the foundation and finally spread across the soil. Finest Construction Nigeria Limited: So what is the role of the depth of the foundation in preventing buildings from collapsing In recent times the rate at which building collapse in Nigeria has become alarming, killing people and destroying properties in the ATE PROF. D.N. NWOKOYE a professor of civil/ structural engineering ,during his innaugural lecture , titled ENGINEERING DESIGN, A SOCIAL RESPONSIBILITY, 1983 ( the 17th INNAUGURAL lecture series in UNIBEN) said Medical doctors bury their mistakes in the grave but CIVIL ENGINEERS ARE FOREVER DAMNED BY THEIR MISTAKES.. Hence we at Finest Construction Nigeria Limited decided to do a little research from a novists point of view on why buildings collapse in Nigeria and also we spoke some professionals to get their most a (building project provider) : The depth of a building foundation is a direct function of the kind of structure that it will carry. Finest Construction Nigeria Limited : So the DEEPER THE BETTER? (building project provider) : The depth depends on the structure..the more the load, the more the depth of the foundation
Posted on: Wed, 19 Feb 2014 06:18:42 +0000
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