Development in Concrete Building Design

8/10/2019 Development in Concrete Building Design

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DEVELOPMENT IN CONCRETE BUILDING DESIGN

By

ENGR. DR. VICTOR O. OYENUGA

(HND, BSc(Hons), MSc, DIC, PGD(Comp. Sc.), DSc (Honoris Causa), FNSE, FNIStructE, FNICE, MNIOB

Managing Director: Vasons Concept Consultants Ltd(Consulting Engineers and Town Planners)

Victor O. Oyenuga became a

Partner of M/S Vasons Concept

Group in 1991 and currently the

MD/CEO of the Firm (now,Vasons Concept Consultants Ltd).

He worked briefly, as a lecturer,

with Yaba College of Technology,

Yaba, Lagos and Lagos State

Polytechnic, Isolo, Lagos, where

he resigned his appointment in

1989 as a Senior Lecturer and

Acting Head of Department ofCivil Engineering. His design

works include: Teslim Balogun

Stadium, Surulere, Lagos;

Reconstruction of Petroleum

Products Jetties Apapa; Ikeja

Plaza and the various projects of

Babcock University, Ilishan

Remo, his town of birth; many

Road Projects for the FederalMinistry of Works and Federal

Capital Development Authority,

Abuja; some notable projects in

Ondo State and Federal

Polytechnics, Ado Ekiti. He is a

Fellow of the Nigerian Societyof Engineers (NSE), the

Nigerian Institution of

Structural Engineers

(NIStructE) and the Nigerian

Institution of Civil Engineers

(NICE).

Engr. Oyenuga is the author of

the following publications:

1). Todays Fortran 77

Programming 2). SimplifiedReinforced Concrete Design, 3).

Concise Reinforced Concrete

Design 4). RCD2000 -

Reinforced Concrete Design

Programs and 5) Design and

Construction of Foundations. He

was a member of the Pioneer

Executives of NICE (then Civil

Engineering Division of NSE)

and served the Institution for10years (1989 to 1999). He

joined NIStructE in 1998 and

became the Honorary Secretary

and Secretary to Council in 1999

till 2002. He was elected Vice

President, Deputy President andPresident of the Institution (2009

to 2011). He is currently a

member of NSE Board of

Fellows and member of

Regulation and Control

Committee of COREN Board.

Recently, he was appointed a

Member of the 5th

Board of

Council for Registered Builders

of Nigeria (CORBON).

Engr. Oyenuga is married with

children and they are members

of the Seventh-Day Adventist

Church in Nigeria.

1.0 INTRODUCTION

Design of buildings entails the following:

Architectural Drawings;

Structural Drawings;

Electrical/Mechanical Drawings or Services Drawings and in case of an Estate

Civil Engineering Drawings and External Works.

Each set ofdrawings is produced by the professional concerned. The objective of this discussion isto elucidate on the Structural Drawings and Specifications. Structural frame can be of any of the

following materials:

Concrete (reinforced or pre-stressed);

Steel and

Timber.Aluminum is also used for frames of light weight buildings and for partitioning.


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In this country over 90% of our buildings are of concrete frame while steel frames are restricted to

factories, warehouses, bridges and few residential or public buildings such as: The Sheraton Hotels

and Towers, Lagos and many large auditorium churches. Timber structures are relatively few in

Nigeria, unlike in overseas countries where the use of such, is rather rampant.

In view of limited strength of timber and for the fact that it is a homogeneous material, but un-

graded in terms of strength properties, the usage is limited. However, in previous years timber

stairs and suspended floors were common and some still exist. The major advantage of timber, isin maintainability, the removal of a weak member and replacing it with a new one in most cases is

all that is required to get the entire structure new again.

Steel has great strength and, can be put to immediate use; therefore, it is used for large spans

structures such as roofs to Churches, Factory Buildings, Bridges and Sporting Complexes. Since

steel can be welded together deep girders to carry heavy loads are easily fabricated and this allows

a lot of free space. This is one of the major advantages of using steel structures for large span

buildings.

Concrete Buildings are generally of two forms, the buildings on load bearing walls which are

limited to bungalows and two storey buildings (buildings with rooms on the ground floor and one

upper floor). These buildings depend on the strength of the walls to sustain the loads of the

suspended floor, the walls and the roof. The bearing capacity of the soil for such site, however,

must be of at least 100kN/m2, that is relatively good soil. Buildings of higher load capacity on

poorer soil must be framed. This is the second type of concrete buildings Framed Buildings. In

this category we have buildings in excess of two storey such as multi-storey office complex,

sporting complex buildings, large churches or churches with gallery, mosques etc. This paper

focuses more on Framed buildings or when reinforced concrete plays a dominant role.

2.0 REINFORCED CONCRETE

Concrete is a composite inert material comprising of a binder course (e.g. cement), mineral filler(body) or aggregates and water. Aggregates on the other hand are two categories of fine (sand) and

coarse (gravel or crushed stone) aggregates. The aggregates are usually graded from fine sand to

stones of say 20mm in diameter depending on the job to be executed. There are basically two types

of concrete, viz.

(i) Dense concrete and (ii) Light weight concrete

Lightweight concrete can be defined as those weighing less than 1920kg/m3 and are made in

densities down to about 160kg/m3. The group of lightweight concrete includes: aerated concrete,

lightweight aggregate concrete and no-fines concrete.

Dense concrete is the most common form of concrete for reinforced concrete work and the average

density is 2400kg/m3. For most usage, concrete is reinforced with reinforcing bars.

Concrete is reinforced to give it extra strength; without reinforcement, many concrete buildings

would not be possible. Reinforced concrete can encompass many types of structures and

components, including slabs, walls, beams, columns, mats, frames and more. There are multiple

ways of reinforcing concrete; the two main methods are conventional reinforcement (non-

prestressed) and pre-stressed.

Reinforced concrete consists of two materials group combined together in specific proportions and

form. The materials are plain concrete, which is characterized by having high compressive strengthbut low tensile strength, and steel reinforcing bars or strands embedded in concrete to provide the

needed strength in tension.


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In prestressed members, compressive stresses are introduced into the concrete to reduce tensile

stresses resulting from applied loads including the self weight of the member (dead load). Pre-

stressing steel, such as strands, bars or wires, is used to impart compressive stresses to the concrete.

Pre-tensioning is a method of pre-stressing in which the tendons are tensioned before concrete is

placed and the pre-stressing force is primarily transferred to the concrete through bond. Post-

tensioning is a method of pre-stressing in which the tendons are tensioned after the concrete has

hardened and the pre-stressing force is primarily transferred to the concrete through the end

anchorages.

3.0 CONCRETE MATERIALS

Concrete is a composite materials comprising of cement (the binder course), fine aggregates (inner

filler), coarse aggregates (strength giver) and water (to provide the medium of interaction, for the

completion of chemical reaction). These materials are briefly described. In some cases admixtures

are added to modify the properties of the mixed concrete. In most cases admixtures retard the

concrete strength.

3.1 CementPrior to year 2000, Cement properties, tests, and characteristics were being controlled by British

Standard 12 (BS 12). BS 12specifies some tests that govern the quality of cement. They include

fineness test, chemical composition test, setting time test, soundness test, strength test and heat of

hydration test. The details can be obtained from the BS 12. Cement for concrete work should

satisfy, at least, the minimum requirements of BS 12.

In the spirit of globalization, a new standard for cement was developed as EN 197-1:2000. The

Standard Organization of Nigeria adapted from this standard, NIS 444-1:2003 which replaces NIS

439:2000. The NIS 444 defines Cement as Cement is a hydraulic binder, that is, a finely ground

inorganic material which when mixed with water, forms a paste which sets and hardens by means

of hydration reactions and processes and which, after hardening retains its strength and stability

even under water. The Standard continuesCement conforming to this standard, termed CEM

cement, shall, when appropriately batched and mixed with aggregate and water, be capable of

producing concrete or mortar which retains its work ability for a sufficient time and shall after

defined periods attain specified strength levels and also posses long-term volume stability.

The Standard listed twenty-five types of cement broken down into five main groups identified as

CEM I (Portland cement), CEM II (Portland-composite cement), CEM III (Blastfurnace cement),

CEM IV (Pozzolanic cement) and CEM V (Composite cement). Over 90% of the cement used in

the country is the CEM II type. The cement that is commonly used is the general normal setting or

Ordinary Portland Cement (the colour resembles Portland stone, hence, the name). The principalchemical compounds of Portland cement are, tricalcium silicate (3CaOSiO2), dicalcium silicate

(2CaOSiO2), tricalcium aluminate (3CaOAl2O3), and tetracalcium alumino ferrite (4CaO

Al2O3Fe2O3). The most important of these are the dicalcium and tricalcium silicates.

Low Heat Portland Cement, Super-Sulphate Portland Cement and High Alumina Cement are not

covered by the Standard. Low heatcement is required when massive concreting is to be carried

out such as Dam construction. During the process of hydration of the cement, a large amount of

heat is generated as a result of the chemical reaction. In case of massive concreting, the large heat

can lead to disintegration of the structure, hence, the need for low heat cement. To circumvent this,

the concrete designer specifies the heat of hydration required and an agreement is made with the

cement manufacturer to produce the cement of required heat of hydration. In the same vein, sincethe use of sulphate resisting cement are not very common, a discussion can be held with the cementmanufacturer to produce, using appropriate additives, cement that can be used in such aggressive

soils. High Alumina Cement is useful where early strength is required, like in war time. However,


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the development in the cement industry has advanced to a level that a desired high strength cement

can be achieved from the normal cement once the manufacturer is properly briefed. This makes the

production of High Alumina Cement (which is not a Portland cement) more or less obsolete.

In terms of strength the classes are 32.5N, 32.5R, 42.5N, 42.5R, 52.5N and 52.5R. The 32.5

category must have strength between 32.5N/mm2 and 52.5N/mm2, while the 42.5 grade has its

range between 42.5N/mm2 and 62.5N/mm2. The minimum strength of the third category is

52.5N/mm2. These are strength after 28days. The appendage N refers to a class of cement withordinary early strength while R refers to those with high early strength.

3.2 AggregatesThese are inert filler in the concrete mixture consisting of between 70-75% by volume of the whole

mixture. Aggregates are categorized as fine aggregates and these include sand and very rarely

quarry dust; and coarse aggregate which are gravel and crushed stone. For effective performances

aggregates must be clean, hard, tough, strong, durable and of proper grading. Other types of

aggregates especially for lightweight concrete include: blast furnace slag, broken bricks, clinker,

pumice, foamed slag, expanded clay, shale and exfoliated vermiculite.

Like cement, aggregates must be tested for quality and the tests include:

(i) Test for durability using freezing-thawing test procedure or alternate soaking in Na2SO4

or Mg SO4solution and

(ii) Gradation test for purposes of controlling workability of the mixed concrete.

3.3 WaterThe quality of the water used in mixing the concrete must be such that the chemical reactions,

which take place during the setting of the concrete, are not impaired. In general, portable water is

suitable for concreting. Thus, the water should be free from impurities such as suspended solids,organic matters and salts, etc. which may affect the setting of the cement.

3.4 AdmixturesThese are substances used in cement mortars and concrete for the purposes of improving or

imparting particular properties. The purpose may be to improve on workability, reduce the

quantity of water required, improve durability, retard or accelerate hardening and improve

resistance to attack e.g. sulphate attacks or impart colour e.g. white cement for terrazzo work. In

general, admixtures reduce the concrete strength.

3.5 ReinforcementSection 7 ofBS 8110:Part 1: 1997, specifies that reinforcements should comply with BS 4449, BS

4461, BS 4462 or BS 4483 and that different types of reinforcement may be used in the same

structural member. Hence, for a beam, the main reinforcement might be high yield bars while mild

steel bars are used for the links. It may be mathematically cumbersome to use two types of

reinforcement as main bars since their strengths are not the same.

Reinforcement should be kept clean by stacking them off the ground. Prior to usage

reinforcements should be free from mud, oil, paint, loose rust, all which weakens the bond with the

concrete. Unless the bars are rigidly fixed in the correct position the reinforcement may be

displaced during concreting, particularly where the concrete is to be vibrated. Special care shouldbe taken in fixing top tension steel particularly in cantilevers. The correct amount of concrete

cover should be maintained. It is important to ensure the correct placing and fixing of all


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reinforcements before concreting. Should there be any discrepancies between the bending schedule

and the drawings, the design engineer should be contacted.

4.0 REINFORCED CONCRETE PRODUCTS IN BUILDING

The end product of a reinforced concrete in building is through two major processes of Design and

Construction. The Structural Engineer will carry out the structural analysis and design based on

the architectural drawings. The objective of the design is to determine the size of the members

required and the reinforcements needed for the strength and stability of the structure.

4.1 DesignThe design is based on a Code of Practice which specifies the methodology and the specification of

the materials to be used. In the area of reinforced concrete design, the concrete cube strength (at

28days) is specified based on the quality of performance desired in the structure. The quality is a

function of the type of structure and the following are typical example:

Residential Buildings - (Grade 25), 25N/mm2

High Rise Buildings - (Grade 30), 30N/mm2

Piles - (Grade 30), 30N/mm2

Bridges - (Grade 30), 30N/mm2

Some structure such as prestressed concrete may require very high strength and strength up to

50N/mm2 (Grade 50) is not uncommon. In this country when the quality of the contractor is not

known a lower strength of 20N/mm2 is used. It should be noted that Grade 25 concrete is

internationally the absolute minimum grade required in reinforced concrete works.

In view of the new cement strength requirements as discussed in Section 3.1, strengths that are

much better than those specified above can be achieved. The major advantages of this include

slimmer member sizes and ultimate reduction in cost.

Design of the structure starts from the estimation of the load which is based mainly on the usage of

the structure and the environment (for wind analysis). Several computer programs are now

available for the analysis and design of the structure and this include RCD2000 (developed by the

author and for analysis and design of concrete elements such as slab, beam, column, stair and

foundation), RCC, Strand, SAP and of recent ORION which will analyze, design, detail and

produce the bending schedule for the entire building structure. There are limitations to the use of

these design packages and the engineer must be in a position to design the structure himself so as to

be able to interpret the results. Results from the best suite of computer program is as good as the

data input (garbage in garbage out they say).

An example of a design and the resulting product for Babcock University Stadium completed over

5years ago is attached. Each of the frames is at 5m interval and the roof cantilever is 14m. The

design was fashioned out from Teslim Balogun Stadium for Lagos State Government (both stadia

designed by the author) which has 6.0m centre to centre frames and 23m cantilever roof. However,

because we do not believe in ourselves, the 23m cantilever was propped and today free view is

impossible in the Stadium. Only Nigerians can develop Nigeria, foreigners can only help.

The current trend now is to design structures to Eurocode 2. The need to revise the academic

curriculum of our universities and colleges of technology/polytechnics to reflect this new trend

cannot be over emphasized. Eurocode 2 requires very high strength steel and the fear is the abilityto be able to meet that standard in the country. The onus is, therefore, on the Standard

Organization of Nigeria (SON) to assist in ensuring that this is done. We need to give kudos to the


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Cement Manufacturers in the country that are up to the challenge in the areas of making cement for

concrete of high strength.

4.2 Design SoftwareQuantum development in software computer programs has made the work of the instructed and

experienced structural engineer very exciting in the sense that:

He is liberated from the drudgery of repeated manual and frustrating analysis.

He does not need to be the best mathematician to deal with complex analytical problems in

building design.

As a designer he is freed from the frustration of often incessant changes by the architect.

He can obtain instant references form other designers in any part of the world through the

internet.

He can allow the architect to dream his dream, produce interesting but intelligent buildable

designs.

Buildings in concrete can be built and tested on the engineers desk before the first work is

performed on the site.

Different schemes can be analyzed, designed and costed before the decision to execute the

project is taken.

The implication of the above listed gains is that the industry is programmed for men and women

who are consumed by the zeal to practice the profession. Fewer hands but highly qualified in

structural engineering principles are required to drive these innovations.

The new innovations can cause serious disruptions in the professional practice of any nation. It

means that it is possible to be colonized in your own country by foreign expertise because the

indigenous engineers and practitioners have refused to grow and the government has not put in

place effective and necessary legislation to protect her professionals. Therefore, in seeking the best

in terms of the practice, outsiders reduce the locals to spectators. This is a major issue that can be

addressed and should be addressed by all concerned. A total adherent to the Procurement Law of

2007 and paying economic rate for services delivered will go a long way to assist in the solution.

4.3 Codes of PracticeIn this Country, our concrete strength specification is based on the British Standard Code of

Practice BS 8110 Parts 1 and 2. Recently the Euro Code was introduced but most designersincluding the author are still using BS 8110. About two years ago, The Nigerian Institution of

Structural Engineers, under the leadership of the author set out to produce a new code for concrete

practice in the country titled The Structural Design and Construction of Reinforced Concrete

Structures The Scope of the Code is as stated below, quoting from the document.

This Code regulates design and construction in structural concrete in Nigeria, bearing in mind the presentstate of technological development in the country and in Africa generally.The Codes provisions were arrived at after a thorough evaluation of similar Codes of Practice eitherpresently or once operative elsewhere.

Although fundamentally based on the limit state method of design, suitably adapted to satisfy the exigenciesof the Nigerian environment, the Code nevertheless maintains the positive features of earlier Codeespecially as it concerns simplicity of use, ease of comprehension and conciseness of presentation of itsprovisions.


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The Code specifies guidelines and precepts for design, detailing and construction in reinforced, precast andcomposite concrete with the notable exception of prestressed concrete.

The Codes state clearly responsibilities of the various parties as follows:

1.4.0: RESPONSIBI LI TI ES OF VARIOUS PARTI ES1.4.1: The Client

The Client is the owner of a building project and shall, for the purpose of this code, becharged with the following responsibilities:

1.4.1.1 He shall obtain all necessary permit and building approvals required by the stateand/or local planning authority for effective execution of the project. This normally shallinclude fencing, piling, building (architectural, structural and services).

1.4.1.2 He shall ensure that qualified and registered professionals are appointed by him

to design and supervise the project in accordance with the provision of this Code.1.4.1.3 He shall permit access to the project site by the authorized

Representatives of Local Government such as Building Inspectors, Adept persons,etc. and ensure that all local Government approved documents are available onsite, at all times, during construction period.

1.4.1.4 Because the Client appoints accredited professional agent; under code, he shall besolely and severely liable for all the foregoing responsibilities

1.4.1.5 A Client must recognize the need for adequate and prompt remunerations of allmembers of the design and construction teams so as to assure that money is wellspent, using the prevailing and respective professional bodies Scale of Fees.

1.4.2: The Structural EngineerThe Engineers charged with the design of structural projects under this Code, shal l be

either a COREN registered structural Engineer or a COREN Ci vil Engineer who must be

a Corporate Member of N iger ian I nstitu tion of Structur al Engineers.

1.4.2.1 Submit to the Client structural engineering proposals drawn to minimum scales of 1:100

(general arrangements), 1:50, 1:25 (detail drawing), all elements must be appropriatelyand properly drawn and clearly annotated to permit easy setting out on site.

1.4.2.2 Submit structural calculations if demanded by the local government, for economy in design,all structural elements must be individually designed and generalization of designing onebeam, for example for use for others which are not similar in all respects would not be

acceptable by this Code.1.4.2.3 All structural calculations must be based on the provisions of this Code of Practice and

others adopted by it.1.4.2.4 A design Structural Engineer must hold himself ready to supervise his design during the

construction of the building project and issue a Structurally fit for Habitation

Certificate when the building is completed. Ref National Building Code 2006.1.4.2.5 No registered Structural Engineer, under the provisions of this Code shall accept to

supervise a building project designed by another Registered Structural Engineer, unless hehas obtained, in writing, the approval of the Engineer who designed the project.

The two quotations from the proposed Code give an idea of the content of the Code and relevant it

may be to the Practice of Reinforced Concrete design in the Country.

Also in the proposed Code we have the expected various concrete cube strength for the various

types of cement based on characteristic strength of 20N/m2.

In order to guide the concrete production manager as to the quantity of materials needed for a

specific concrete mix, Table 2.2 of the proposed Code gives an indication towards this. Thus, for

the local concrete producer the proposed Code has enough information to assist.

In a well coordinated construction the design should specify the required concrete strength and thisis achieved through design mix. That is, various trial mixes are carried out prior to the execution of

the work and the particular mix ratio that certifies the design strength is chosen and used for the

execution of the Works.


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It is instructive to note that this new proposed code may need to be massively revised to reflect the

global practice of Eurocode 2. This is a call on The Nigerian Institution of Structural Engineers to

do just this and liaise with the Cement Manufacturers Association of Nigeria (CMAN) for guidance

on the possible strength of concrete that can result from the various types of cement produced.

4.4 Contract DocumentsSpecifications.There are three major Documents to most Civil Engineering Contract apart from the drawings and

these are:

Volume I: The Standard Condition of Contract or the ICE Condition of Contract;

Volume II: The Specifications and

Volume III: Tender DocumentsInstruction to Tenderers, Form of Tender, Statements of

Qualification, Tender Security, Form of Agreement and Bill of Engineering Measurements and

Evaluation (BEME).

Volume I is expected to be a general document while Volume II is also a general document

emanating from the Federal Ministry of Works. Volume III is produced by the organizationconcerned through Consultants, as the case may be.

The Highway Manual was metricated in 1995 and reasonably updated that time. The author was

the technical secretary that edited and produced all the various curves in the metricated version.

The concrete aspect of this was based on BS 12 and BS 8110. In addition the various

Specifications from the Ministry of Works as regards cement and its products are based on BS 12

including the various tests to be carried out when the work is in progress. Definitely in the light of

the discussion above, these need to be revamped in line with global practice. The call is hereby

made to the Ministry to constitute a panel for the review of the various specifications in

conjunction with the Universities, The Nigerian Institution of Structural Engineers, The Nigerian

Institution of Civil Engineers and the various other professional bodies that are relevant including

the Geologists.

4.5 ConstructionConstruction of concrete products starts from the formwork (or falsework). There are two types,

sawn formwork and fair-face formwork.. Sawn formwork is used when the surface of the finished

product needs to be treated while fair-face for is employed when the product surfaces will not

receive further treatment such as rendering. In this case it is customary to use large surface

plywood or steel sheets properly oiled to avoid the concrete sticking to the surface. The concrete

during placement must be well vibrated and cured after placement to achieve the desired strength.

Quality control must be ensured during the production and this is generally done through

workability tests: Slump Test or Compacting Factor Test. Cube strength test must be carried out

to ensure that there is no deviation from the control design mix.

5.0 CONTEMPORARY ISSUES

The major issue facing the professional in the built environment is the influx of professionals from

other countries who in some cases will want things to be done according to their own Code of

Practice and experience In some cases, designs are done and drawings produced using these Codes

without proper interpretation. It is believed that such construction will be carried out by companiesfrom their country duly registered here. Unfortunately, most of these so called professionals fall

short of Professional Registration standards and as a result could not be registered according to law

establishing such bodies in Nigeria. The onus is on us to ensure that any engineer, architect,


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builder, surveyor etc coming from overseas is duly registered by the relevant professional body,

before such a person is allowed to practice. Drawings produced from their country should also be

duly checked and authenticated using the prevailing Code of Practice here and all necessary

corrections duly effected.

6.0 CONCLUSION

In conclusion I will like to quote from Man on the Job leaflet published several years ago by the

United Kingdom Cement and Concrete Association which states:

A good concrete job is only good, strong, long lasting, good-looking and economical to build, if

every man on the job shares in making it so.

A good concrete building or road or bridge does not only depend on a good designer or a clever

engineer: it depends on good materials, accurate batching, the right amount of water and thorough

mixing: it depends on well-placed reinforcement, well-made formwork, careful compacting: it

depends on good finish. No stage is unimportant.

One mans carelessness can let down the whole job: every mans care can make it a job to be proud

of.

SO IT REALLY DOES DEPEND ON YOU

Thank you for your attention.

References.

1.

NIS 444-1:2003. CementPart 1: Construction, Specification and Conformity criteria for

common cements. Standard Organization of Nigeria, Abuja.

2. Simplified Reinforced Concrete Design by Victor O. Oyenuga, 2nd Edition, Asros Ltd

Lagos.

3.

Eurocode 2: Design of Concrete Structures. European Committee for Standardization.

4. The Structural Design and Construction of Reinforced Concrete Structures; Proposed Code

of Practice, Not yet published.

Attachments:

Design Detail of Babcock University Stadium, Ilishan Remo, Ogun State.

Semi Finished and Finished Product of the Stadium

Development in Concrete Building Design

Documents

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