assessment of the quality of steel reinforcement bars available in nigerian market

8/13/2019 ASSESSMENT OF THE QUALITY OF STEEL REINFORCEMENT BARS AVAILABLE IN NIGERIAN MARKET.

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ASSESSMENT OF THE QUALITYOF STEEL REINFORCEMENT BARS

AVAILABLE IN NIGERIANMARKETy

Opeyemi Joshua, Kolapo Olusola and Calistus Ayegba.


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1. Motivation

2. Introduction

3. Methods

4. Results

5. Discussions and Conclusion6.Limitation.

7. Recommendations.

Contents:


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According to Ede (2010), the occurrence and casualtiesof building collapse from the year 2000-2010 wasalarming. Lagos state alone experienced over forty (40)

cases of building collapse and over one hundredseventy five (175) deaths within the years. Over 90% ofthe collapse occurred in over two (2) storey buildings.

Oni (2011) also used the predictive linear trend equationto show that an average of ninety-one (91) storey

buildings will collapse between the years 2007-2017 withan average of nine (9) collapse annually.

Something have to be done to prevent theseoccurrence .

Motivation.


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Pilot survey in Lagos metropolis and the Nigeria Institute of Building(NIOB) reveals that over ninety percent (90%) of storey buildings inNigeria are structures whose structural frame/elements are made ofreinforced concrete and in fact, bulk of her construction industryrevolve around the use of reinforced concrete, be it in dams, bridges,buildings and all other civil engineering works.

Buildings can never collapse until the structural component(s)/systemsfails or begin to fail and since over 90% of structuralcomponents/systems in Nigerian Buildings are made of concrete, it can

be deduced that the greatest percentage of collapse is as a result ofconcrete failure, though, triggered by several factors like the use ofquacks (incompetent professionals), corruption and other sharppractices to maximize profit that compromise the integrity of theBuilding process.

Introduction.


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Ogunsemi (2002) and Oke and Abiola-Falemu (2009) shows

that about 26% of building collapse in Nigeria occurred as aresult of the use of poor standard materials.

The primary materials that make up reinforced concreteinclude cements, steel reinforcements, aggregates andwater.

There arise a need to study the quality of these materials inan attempt to curb the rate at which buildings collapse inNigeria.

Introduction cont


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Steel reinforcement is one of such materials this study

will focus on.The role of steel in reinforced concrete include:

Improves the tensile and compressive strength of theconcrete, and

Improves the ductility of the concrete evidenced bylarger deflections before failures

Introduction cont


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The design of reinforcement in concrete to BS 8110:1997, the

yield strength of steel is taken to be 460N/mm2

and thecurrent EuroCode2 (EC2) now states that the yield strengthof steel be 500N/mm2.

The specification for steel reinforcement for concrete toBS4449:2005 states that the minimum steels yield strength

be 500N/mm2

.The Nigerian standard as specified by the Nigerian IndustrialStandard, NIS 117:2004 specify the yield strength of steelGrade 420 to be 500N/mm2.

Introduction cont


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If steel reinforcements in reinforced concrete are

designed based on these design values and the actualsteel available for constructions falls below thesestrength values, the failure of such structures is almostcertain. It is on this premise that the need arose to

study the quality of steel reinforcement in the Nigerianmarket to ensure its not one of the factors contributingto building failures/collapse in Nigeria.

Introduction cont


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Sampling and Testing

The method of sampling these rebars is by market survey toidentify the steel brands used in Lagos, purchased three cutsof 12mm diameter rebars for each identified steel brand fromthree different outlets. The cuts were labeled and sent to the

laboratory for tests. 12mm diameter bar size was chosenbecause it is the most used in structural design work inNigeria.

Nine (9) steel brands were identified denoted as Brands 1-9.

Methods


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Caliper was used to determine the actual diameters.

The tests conducted include tensile yield and ultimate

strengths and elongation.The actual market length was determined.

Prices per standard market length of the identifiedbrands were also surveyed. The results are as shown

in Fig. 1-3.

Methods Cont


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Figure 1:Steel Brandsyield and ultimate strengths.

Result

0

100

200

300

400

500

600

700

800

A B C D E F G H J

MPa

Steel Brands

Yield Strength (Mpa)

Ultimate Strength (Mpa)


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Figure 2: Ductility and Ultimate/Yield strength ratio ofdifferent steel brands.

Result Cont

0

0.5

1

1.5

2

2.5

3

3.5

A B C D E F G H J

Steel Brands

Steel Ductility.( X10)%

Utimate/Yield strength ratio.


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Figure 3: Cost of standard length (12m) of the differentsteel brands.

Result Cont

1400

1450

1500

1550

1600

1650

1700

1750

1800

1850

A B C D E F G H J

Naira()

Steel Brands


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All identified steel brands satisfy its specified diameters if12mm.

By local and foreign standards, only three (3) of the nine(9) identified steel brands meet the required yield strengthof between 460-500 MPa as design value in BS 8110:1997and minimum values in NIS 117:2004 and BS 4449:2005. SeeFig. 1.

All steel brands satisfy the required minimum percentageelongation of 7.5% as specified in BS4449:2005. As seen inFig.2, the least elongation is 20%. Prabir et al(2004) assertsthat the greater the elongation, the better.

Discussions and Conclusion


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Four (4) of all identified steel brands satisfy the ultimateto yield strength ratio of between 1.15-1.35 while the restof the brands are greater than 1.35 as seen in Fig. 2.

Almost all brands that meet this requirement also metthe yield strength requirement.

All steel brands that falls short of strength requirements

are relatively cheaper than the ones that met thestandard as seen in Fig. 3. They also didnt meet theultimate to yield strength ratio of 1.15-1.35 as specified inBS4449:2005.

Discussions and Conclusion Cont


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Conclusion No. five (5) above tend to agree withBS4449:2005 that a relationship exist between the

ultimate/yield strengths and their ratios that confirma good quality steel. Since the best steel brands thatsatisfy the ultimate to yield strength ratio range alsosatisfies the strength requirement.

The steel marketers admitted that though thestandard length is 12m (40ft), its usually less butalways greater than 38ft.

Discussions and Conclusion Cont


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Conclusion was only based on the physical andmechanical properties of the steel brands tested.

Other tests that would further qualify the qualitiesincludes the X-ray analysis to determine the percentageof the chemical composition and microstructuralanalysis.

Limitations


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It is highly recommended that all steel batches berandomly sampled and tested to ensure compliance beforebeing used in construction work.

Standard regulatory agencies within the country shouldundertake periodic market survey to identify substandardproduct and discipline erring brands.

In calculating accurately the number of reinforcementsneeded for a project by Quantity Surveyors (QS), it isrecommended on the interim that lengths be based on

market dimension of 38ft and not the usual 40ft pendingwhen regulatory authorities are able to enforcecompliance on the manufacturers to produce 40ftstandard bars for proper on-site steel scheduling.

Recommendations


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Nigerian Structural design Engineers should either basetheir designs on 340 MPa or use greater factors of safety

when designing for structures in rural areas that haverestricted access to laboratories to ameliorate the effectsof these margins from the standard strength.

Building contractors should be careful with cheap

reinforcements and other practices that seems to reducecost, these mostly results in the purchase of sub-standardsteel materials as shown in Fig.3 that the cheaper ones aresubstandard bars.

Recommendations Cont


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Thank you

assessment of the quality of steel reinforcement bars available in nigerian market

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