POV Ganguly

7/30/2019 POV Ganguly

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41JANUARY 2008 The IndIan ConCreTe Journal

Point of View

K.K. Ganguly

Applications of structural engineering

in projects and other associated issues

A brief review

An attempt has been made to review the type of designand construction that are being done in some specicareas other than major industrial applications. Thiscovers different forms of construction with various typesof materials. Structural applications are also includedto some limited extent. Some photographs have beenincluded to explain innovative structural applications.

Special use with respect to structural morphologyare highlighted briefly and the important issues inengineering buildings in the built environment arediscussed apart from re engineering and connecteditems. Facade engineering and hybrid construction is alsoreferred. Repair and restoration of structures especiallyheritage structures is an important responsibility ofstructural engineers. Some comments on restoration ofstructures have been made. Finally, specic commentsare given about future trends highlighting structuralsafety, ready mix concrete, high strength concrete, selfcompacting concrete, decorative concrete, admixtures,recycling of wastes, etc. It is commented that both

architects and engineers will have to work together toproduce purposeful and innovative design for modernbuildings. The education and training of engineers isalso touched upon. The review of different structuralengineering applications and associated issues aspresented here is limited and restricted to a few specicareas only as per the liking of the author and hencecannot be treated as complete by any standard.

It is interesting to mention that the structural design inall the cases have been carried out with close interactionwith the architects and engineers of other services. Itmay be noted that structural morphology was given toppriority for all the applications mentioned here

A few photographs (Figures 1 - 31) of different projects

are also presented. These are chosen from non-industrialprojects (i.e. not from industrial projects like powerplants). It will be interesting to note the structuralmorphology as demonstrated by the architects in thedifferent projects. Structural forms and shapes aregenerally different in each project in order to meetthe requirements and to produce innovative design.

These columns of ICJ offer an opportunity to the engineering

fraternity to express their views on the current practices in

design, construction and management being followed in the

industry.

To share your opinion with our readers, you may send in your

inputs in about 1500 words via e-mail to [email protected]


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The IndIan ConCreTe Journal JANUARY 200842

Point of View

The photographs have been selected carefully topresent various structures from different parts of thecountry. These structures have been built by differentcontractors.

Isti t pjctsA brief review of different structural engineering

applications in industrial projects has been made inthe past.1 The basic layout of a power plant is normallydeveloped by mechanical/electrical engineers usingequipment manufacturers guidelines/requirementsand with the help of architects/planners who areresponsible for the development of the total masterplan of the project. The basic dimensions of the plant,therefore, are related to the layout of major equipment,the operational requirements and maintenance. Thearchitects have limited freedom regarding the layout ofthe plant buildings of such projects. After carrying out1 or 2 such projects, the job may become repetitive in

most cases and the challenges to a structural engineermay also be restricted. Furthermore, references from thepast and similar projects may be used by the consultinghouses wherever possible to cut down the design time.Incidentally, the cost of civil and structural items is lessas compared to equipment cost. Hence, the attemptsfor innovative design to reduce civil/structural cost arenot there and not important.Therefore, opportunitiesfor renement of structural analysis and design maybe limited. In some cases, however, bigger structuraldimensions may have to be provided when the loadingdata including other details are not properly availableat the time of designing the structure. Hence, structural

design work may not be very challenging as the structuraldesign may have to be carried out using higher loadsintentionally. The question of economy on structuralitems may be missing in industrial projects due tovarious reasons and the emphasis is on the completionof the structural design quickly. This situation may not

be encouraging to the structural designer which maydemotivate him/her.

In non-industrial projects such as university complexes,hotels/resorts, hospitals, housing projects, commercialcomplexes, etc. the architects normally play a majorrole in the development of the layout, building form,aesthetics, etc. The cost of architectural nishes alongwith services may also be very high in such projects.The challenges are more here for the structuraldesigner and there will be pressure to cut down thedimensions of structural elements for visual and otherrequirements and to produce economical design fordifferent structural schemes. The services of structuralengineers are more demanding and more appreciated inthis case as compared to industrial projects. Engineersand architects are dependent on each other to designand construct innovative modern buildings. Structuralengineers must learn to work with the architects inharmony for creative and innovative design. Each

profession has different skills and carries differentresponsibilities. Structural engineers would have to learnto work in multi-disciplinary teams having differentprofessionals and understand how others think andwork. Architectural creativity must be supported byengineering skill to produce innovative design. Theclients should be convinced that the innovation willbe worthwhile and cost effective. The engineering


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argument should not come in the way of architectural

solutions. Mutual respect and appreciation betweenarchitects and structural engineers will be requiredas there will always be an engineering solution to agood architecture. Best buildings can be designed andconstructed from a symbiotic relationship betweenarchitects and engineers. Structural engineers have toshoulder a bigger responsibility of the work both indesign and construction to produce a safe and durablestructure at the end.

egiig biigs i t bit

vimt

It is very important to assess carefully the presentsituation that is developing on our planet earth

before deciding on the design of buildings in the builtenvironment. The following points are relevant

Continuous supply of irreplaceable constructionmaterials and the use of cheap non-renewableenergy is going on. This condition cannot continueforever.

Population growth is very high and it is now over6 billion and likely to be 9 billion by 2050. Someresearchers have estimated the above gure tobe more2. The rate of increase is about 80 million.extra persons per year worldwide. This is the mostserious problem on our hands.

Carbon dioxide loading is an indicator ofpollutant potential. As per current estimate it isabout 5.5 t of CO2 per person per year for USA,2.7 t for Europe and 0.8 t for China.2

Building activities would have to take intoaccount the geographical imbalance of wealthand population.

It is reported that 70% of our forest has alreadybeen destroyed and going by the current rate,100% destruction might take place by the year2027.

Global warming is already taking place andaccording to some estimates, the temperature risein next 100 years may be in the region of 5.8oC.It is also suggested that after 2020, (i) winters

will be reduced in length (ii) summers will havemore hotter spells with periods of drought (iii)

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tidal heights will increase (iv) wind speeds willbe variable and may be stronger.3

We cannot pass on our planet in this condition to ourchildren and grandchildren. We must save the planetfor our future generations.

The challenges before the engineers/architects are (a)better whole life performance (b) to use less primarymaterials (c) to use less non-renewable energy (d)wasting less (e) causing less disturbance to naturalenvironment (f) to reduce the burden on the planet and

working out solutions that full social, environmentaland economic criteria. Hence, it is important for theengineering and management team to work together onall issues covering conception, planning, modelling andcalibration, construction, operation and use.

Fi giig f stctsFollowing recent res in various parts of the world, theperformance of structures during re has become a veryimportant design issue for engineers. The real structure,however, will behave differently from a simple beamcommonly tested in a furnace for obtaining data for re

design. The actual structures will have in-built secondaryload paths which are often mobilised during re whenstructural deections are larger4. Fire engineering is amulti-disciplinary activity but the structural engineershave to play a major role. It is important to adoptperformance based design approach against re loadsfor the structures. Previous designs were primarily basedon the control of the structure for non-combustibility and

separation to provide the required time. The design of thestructures must consider re load cases also along withnormal working loads for obtaining the best solution.This may vary from a simpler prescription identifyingrequired thickness of applied re protection to steel orcover to reinforcing bars in concrete to more complicatedanalytical calculations using whole frame action with

real re loads for design. The degree of complexity willincrease depending upon the particular circumstanceand objectives of the particular design. The structuralperformance under re may not be the direct measureof protection of life or protection of property. The otherconsiderations such as provision of sprinklers to reducethe spread of re, increased ventilation to lower retemperature, corner columns and beams cooler thaninternal columns and beams, providing safe means ofescape, etc., also will have inuence on re design.

Simpler prescribed rules will be easy to operate andguidance may be obtained from national building

standards and manufacturers literature. Alternatively,designing for less stress level for normal workingload condition and keeping provision for higher reperformance against re loads is also a good option.The other option will be complex and the engineers willneed additional knowledge of ventilation condition, reloads and knowledge of high temperature performanceof the structural material including lining if any withadequate analytical skill. To study the provisions ofboth passive and active fire protection systems inbuildings becomes important. The post re assessmentshould cover possible cause and duration of re, overallstability, strength and robustness of the structure, defects

and damage to the building, re safety provisions afterre, serviceability and durability aspect. Proposals forstrengthening and repair work, etc, also will have to beconsidered. It seems that re engineering for structureswill be more detailed in the future at least for importantbuildings.


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hybi cstctiHybrid construction utilising different materialsespecially precast and in situ concrete has been inuse for some time. The structural engineers generallywill need more experience in such technique speciallyfor the performance of joints and their detailing. Afew aspects such as aesthetics, function, speed, safetyintegration, buildability, etc. will need very specialcare. Hybrid concrete construction may in some cases

be more expensive than conventional in situ concreteor structural steel frames with concrete decks.5 Highstandard of nish is possible with precast concreteelements and the same may be accommodated to thestructural forms. Composite action should be consideredfor economy.

F giigFaade is the envelope of the building and it is generallycomposed of all exposed walls, roofs and oors. Theengineering relates to various aspects and parts of theenvelope design and creating an innovative look atthe end. Faade engineering presents more challengesto the structural engineer to maintain the aestheticlook of the building and the safety of cladding systemadopted. The cladding and main structure interactionis very important and it is primarily related to, a) Loadtransfer Apart from vertical loads, horizontal loadsfrom wind and seismic forces will also be applicable b)

Accommodation of oor movement c) Accommodationof other movements.

The use of stones and glass curtain walls with differenttypes of xing arrangement are quite common. Thecomplexity of faade design has to be understoodespecially when glass and stone panels are adopted.In recent years, the use of coloured aluminium sheetsin faade design is gaining popularity. Other materialsinclude metals, plastics, timber, ceramics, polymers and

fabrics. The external envelope takes most of the wear, thecladding or roof will be subjected to risk from prematurefailure well before the service life of the structure. Onehas to be careful about leakage problems through the


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joints especially in the case of glass and stone panels6.The provision of cleaning and maintenance of thefaade materials should be given due importance inthe design.

T s f cmpts f giig

cctisNowadays, software packages are used for all structural

engineering design activities. It is observed that a shiftin emphasis from design calculations to structuralmodelling has taken place7. This may lead to, in some

cases, inappropriate modelling and wrong results at theend. The use of computers have denitely cut down thetime consumed for design computation which was amajor time consuming factor for the structural designerin the past. The engineering calculations may be treatedas a series of modelling exercises and may be brokendown to, (a) an engineering model representing thephysical existence (b) a conceptual model that allows formaterial and structural behaviour (c) a computational

model (a description of the structural arrangement in aform suitable for computer analysis).7


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Each stage should be checked against acceptance criteriaand nal outcome should be assessed against overallmodelling review. The guidelines published by theInstitution of Structural Engineers, London related to

use of computers for engineering calculations may bereferred.7

The responsibility of checking the modelling exerciseshould not fall on the analyst. This review shouldbe done in-house by a senior engineer. In large andimportant projects such responsibility may be given toan independent consultant also. The engineering modelwill consider the overall geometry of the structure, allload bearing components with dimensions, supports,materials used and loads including lateral loads. Non-structural components are not considered but theireffects are assessed and considered in the calculations.

The detailed analysis of the model is carried out usingthe theory of analysis, material behaviour, boundarycondition, loads and the geometry of the structure.3D modelling for analysis and design and the use ofsoftware packages have led to a tremendous increase inthe productivity in the design ofce which until recentlywas unimaginable8. This, in turn, has given engineersthe opportunity to provide better services and a betternal product to the clients.

Cstcti mtisDifferent materials for construction have been tried byengineers and architects over the years. Out of theseconcrete and structural steel have been mostly used.Other materials include brick, stone, timber, glass anddifferent composites. Figure 21 shows a combination

of load bearing rammed earth construction with


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timber roofing. This application has been done bythe architect in the north-eastern part of the country.Timber trusses were preferred to suit local conditions.Fly ash and lime-sand bricks have also been tried in

many projects in recent years. Figures 24, 25, 27 and28 show the use of compressed earth blocks (CEB) inplace of conventional burnt bricks. The compressedearth blocks have been produced with the help of handoperated machines. Different types of arches, domes etc.have been constructed using compressed earth blocks asshown in Figures 16, 17, 25, 27 and 28. Applications offerrocement roong units have been shown in Figures16, 24, 25 and 27.

Stct tiigSimple and practical detailing should always be aimedfor during design. Aesthetically, detailing should bepresentable and must avoid clumsy joints. Specialemphasis has to be put on seismic detailing in orderto provide ductile behaviour. Column-beam junctionswill need additional care to ensure ow of concretebetween bars especially when ductile detailing hasbeen done for connement of concrete. Often the detailsfor joints are not shown fully in the drawings to cut

down time. Proper seismic detailing will be essentialto control damages to the structure. Providing correctcover to reinforcement during construction is veryimportant for structural performance especially withreference to strength, durability and re. Some concretestructures may not achieve their intended design livesdue to deciencies of cover actually provided during

construction. Due to inadequate cover, structures mayhave to be demolished prematurely or may have toundergo expensive repair and protection work. It isreported that for an external concrete wall sheltered fromrain and having 30 mm cover will provide 135 years ofprotection to reinforcement but 10 mm of cover will onlygive 10 years of life for the same wall.9

Spacers and chair as per BS:7973 may be considered forconstruction.10 Plastic and cementitious spacers andwire chairs are recommended for use. It is importantto specify the use of the same in the specication andto show the correct type of spacers and chairs in the

drawings, i.e., at least the standard details for easyunderstanding and use in construction.

The major comments made after Chi-Chi (Taiwan)earthquake in 1999 are improper lap splices of rebar,column tie hooks without 135o bend and poor concretequality control at job site.11 These are the typicalcomments after examining the earthquake damages ofstructures and are applicable in our country also. Careshould be taken by the site engineers to ensure that theconstruction is done correctly as per the drawings.

rpi stti wkStructural engineers have to play an important rolein restoration work. Using nondestructive test (NDT)methods, the causes for damage are studied initially. Theengineers then develop a suitable technical specicationand methodology for carrying out restoration/


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retrotting work. Injection grouting, replacement oranticorrosive treatment to rebars, use of bonding aids,

jacketing to structural members, patch repair, applyingspecial coating/treatment to protect structures againstharmful exposure/environment, water proong, etc.are often adopted.

Various materials are available and the engineershave to be careful to select the right one after detailedinvestigations and as per the requirements. More carewill be necessary for underwater repair work andrepairing of large oors. For repairing/restoring heritagestructures, clients and government authorities may insistupon the use of original materials for the repair work.Materials like polyurea has been used in pharmaceuticaland other industries to seal ne cracks and to maintaindust free environment. FRP composite systems are alsobeing used in our country for strengthening structuralelements. Brief comments are made below on externallybonded FRP systems.

exty b FrP systms f

stgtig cct stcts

Composite materials made of bres in a polymeric resin,are known as bre reinforced polymers (FRP) and thismaterial may be used to strengthen concrete members.12The method is an alternative to traditional strengtheningsystems like steel plate bonding, section enlargement,external post tension, etc. The advantages of adoptingFRP system over traditional methods are (a) lightweight (b) relatively easy to install (c) non corrosive.

The constituent materials include resin primer, putty,adhesives and bres. The long term performance ofFRP systems is not yet available. ACI committee : 440suggested reduction factors for various environmentsto take care of the effects of long term degradation

and durability12. Carbon, glass and aramid bres aregenerally used in the composite materials. Proper

detailing and installation of FRP systems is important toprevent debonding failure modes. It is not recommendedto use this system for compressive reinforcement.Mechanical and other forms of anchoring systems maypresent problems due to the brittle and isotropic natureof composite materials. FRP systems are expected to bedamaged in re. This system should not be applied onconcrete members containing corroded reinforcing barsor deteriorated concrete unless the substrate is repairedproperly.

While using FRP systems for repair/retrotting work,care should be taken to verify the following :

Existing dimensions of structural members

Location, size and cause of cracks and spalls

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Location and extent of corrosion of reinforcementsteel

Quantity and location of existing reinforcementsteel

Compressive strength of concrete

Soundness of concrete at all areas where FRPsystem is to be bonded to the concrete andespecially concrete cover.

Sit spvisiGenerally, as per contract, consulting engineers arerequested to do only periodic supervision and notconstant monitoring to cut down costs by saving thefees paid to him/her. The structural engineer from theconsulting house may visit the site as per the contractand site requirements. Hence, continuous supervisionmay be missing if the structural engineer is from thedesign ofce of a consulting house. However, propersupervision and project management is required fromthe consulting house in case of large industrial orpower projects. It is vitally important for the structuraldesigner to supervise continuously the constructionof different structural elements that he has designed.This will provide valuable experience to the structuralengineer and help him to become a better designer.Further, the structural engineer is made aware of thecost aspect, variation of quantities (due to incompletedetails in some cases), non-scheduled items (due tochanges done later), etc., thus giving him/her insights

into the practical aspects of construction and design. Thestructural designer is not supposed to just carry out ananalysis mechanically by using a software or providereinforcement details as per the computer output. The

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art of economical structural design has to be learned anddeveloped in stages through experience.

ecti tiig f gisWe have to initiate rigorous training programmes forthe young and fresh engineers in order to make themfully prepared to cope with the requirements of design,

construction and project management. This is not beingdone seriously at present. A lot more will be requiredto train our engineers.

Employers are always looking for experienced engineers.With our university education it has been noted thatengineers are not fully prepared and they have toactually learn from senior persons, the different aspectsof analysis, design and detailing of structures. There isa tendency among young structural engineers to learnstructural engineering software packages with a lot ofinterest but there is not much interest to understand thebehaviour of structures and to check the acceptability ofthe results generated by the software. It is very importantto check the computer output before acceptance ofthe design. Fresh engineers should be exposed to thepractical aspects of design and detailing. To carry outthe analysis of an idealised structure using a softwarepackage is only a small (but very important) part of thetotal work. The structural engineer has to visualise andunderstand the complete behaviour of the structure.He/she should largely and will be able to check somesalient parts of the computer output with some simplecalculations or by some other software packages toeliminated design errors.

We have to reexamine the nature of education andtraining that is being offered to our students so thatthey are given proper knowledge ad skills to copewith the challenges of the modern times. The potentialemployers including consulting houses must spendtime and money to formulate training procedures for


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our young engineers. They must be encouraged to stayin the profession and carry out their work efciently ina competitive market.

Ft tSome of the future trends are briefly highlightedbelow:

dsig f scity13

In recent years design for security has taken a prominentplace especially for buildings. Architects and engineershave to understand the different aspects with respect tothe safety of the building components. Some basic issuesassociated with building design are briey mentionedblow.

Blast

Blast pressures decrease signicantly with distance. Ablast within 5-10 m can cause damage to modern framed

buildings and major damage to load bearing masonrybuilding. A canopy at the entrance can trap and enhance

blast pressure.

Bomb threats

This can cause signicant local damage. Car and lorrybombs can damage nearby structures also. The use of

chemicals is also dangerous as it may be more harmfulto people as compared to buildings. Much will dependon the size of the bomb, type of explosive and how itis detonated.

Blast on buildings

The ideal shape of a building against blast is the circular

shape.13

Balconies are desirable as a clean and smoothfacade amplifies the blast forces. The provision ofa central core may provide space for shelter duringemergency. Stone claddings in buildings may notperform satisfactorily in a blast. Replacement of stone orglass after damage especially in a multistoreyed buildingis not an easy task. If glass can be replaced from insideit will save money.

Blast on glass

Glass is often used in the facade of a building. Thisis a high risk material and can cause a lot of damagewhen exposed to a bomb blast. Flying glass pieces areresponsible for most injuries. The type of glass usedin the building is important. A blast can destroy allthe windows in a building while leaving the structureundamaged. Hence, care should be taken to ensurethat glass and the frame remain intact and withstandthe blast. Unprotected annealed plain glass will breakfrom a blast at a distance of 100 m away and causepotential injury upto 50 m from the place of explosion.


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Toughened glass on the contrary will offer twice the

protection of plain glass. Laminated glass can also offergood performance with proper frame design.

Stct sfty

Periodic inspection of the structure covering salient loadbearing elements is crucial in identifying weak areas andthus would help avoid catastrophic collapse that maytake place later. Based on the inspection it is necessaryto provide warning to engineers to carry out preventivemeasures quickly. Inadequacy in the structure may oftenmanifest initially as serviceability losses and may nallylead to collapse from corrosion of reinforcement, spalling

of concrete and large deections. Errors in calculationsmay lead to safety values much less than intended.During construction, situations may arise where safetywill be in jeopardy. In such cases, detection by alertengineers in advance will help in averting catastrophic

failure and ensure safety.

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cstcti

Engineers have attempted to use waste materials forconstruction especially from the building industryby recycling the same. This approach is particularlyimportant as the raw material stock is dwindlingrapidly. Attempts have been made in Hong Kongto produce paving and partition blocks by recyclingconstruction waste and waste glass.14 A mechanisedmoulding method is used for producing the concretepaving and partition blocks. The method uses, recycledaggregates from construction and demolition waste,and waste glass as 50 - 100% replacement by weight

of material aggregates in the manufacture of concreteblocks. Crushed concrete rubble, after being separatedfrom other construction and demolition wastes andsieved, can be used as a substitute for natural coarse

aggregates in concrete. Generally, the ne fraction isnot commonly used due to its higher contamination andwater absorption levels. Recycled wastes have been usedin our country for the construction of roads. We haveto devise methods so that more recycled materials areavailable and used in projects with condence.

hig stgt cct

The use of high strength concrete will reduce structuraldimensions and lead to economical design.1 Thedenition of high strength concrete as per ACI codestates that the compressive strength of high strengthconcrete should be at least 42 Mpa. We should use high

strength concrete in our structural design. With theimprovement of cement quality now, it is not difcultto produce concrete of M 30 - M 40 strength quite easilyat most construction sites in our country. Concreteswith compressive strength around 140 Mpa have beenproduced in USA15. In such a scenario, there is no point


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while completely lling up the formwork of differentshapes and even around congested reinforcement. Theplacing of this type of concrete is noiseless as vibratorsare not required for compaction. Portland cement is oftenpartially replaced by GGBS or PFA for technical andeconomic reasons. Fillers must be carefully selected afterstudying their effects on water demand for determining

ow characteristics and workability retention. Modernsuperplasticiser such as poly carboxylated ethers (PCEs)are particularly relevant to SCC. At similar water-cement ratios, the characteristic strengths and strengthdevelopment will be similar to that of traditionalconcrete.16

Cct mixts

The use of admixtures in concrete design and constructionhas increased steadily over the years. The advantagesof using an admixture in a concrete mix has been wellunderstood by engineers. It is expected that admixtureswill be used more and more in concrete constructionin the future. In the UK, according to the currentstatistics, over 75% of ready mixed, site mixed andprecast concrete now contains an admixture.17 Thepercentage of admixture usage, in concrete constructionis comparatively low in our country. However, the use ofthe same is increasing slowly. With the changes in designrequirements, it seems admixtures would be a normal

in designing structural elements now for M 20 grade ofconcrete. For producing high strength concrete (above M- 40) with controlled water cement ratio, silica fume, PFA,GGBS, superplasticiser, etc., may be required dependingon the requirements. Ready mix concrete produced

using the local raw materials may be considered forconsistent supply and economy. Contractors must befamiliar with the techniques associated with placingthe material when ready mix concrete is used. Qualityassurance is a must and the quality control lab must beable to analyse it. Engineers are expected to be familiarwith the knowledge of production of high strengthconcrete consistently at site.

High strength concrete is often referred to as highperformance concrete (HPC) since it has been foundto be not only stronger but also more durable. HPC isa material with low water/binder ratio (0.3 - 0.4) andneeds to undergo sufcient water curing to control itsdimensional stability.

Sf cmpctig cct

Self compacting concrete (SCC) is getting popular inthe construction industry. SCC in its plastic state owsunder its own weight and maintains its homogeneity


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constituent of concrete in the future. The importantpoints for consideration are:

Economical - Mix design can be optimised

Placing - Helps to provide required consistency,compatibility, cohesion, setting and strength

development.

Customisation - Helps to produce concrete thatwill meet special needs with reference to placingor performance.

Durability - Ensures that intended design life willbe met as per requirement.

Environmental - Helps to reduce differentnegative aspects of health and safety normallyassociated with construction especially duringplacement. It also reduces the environmental

impact of concrete constructions.

One type of admixture may not meet all the aboverequirements and as per the requirements, more thanone admixture may be necessary. With the advancesin technology and especially the introduction ofpolycarboxylated ethers (PCEs) based plasticisers andsuperplasticisers has made a remarkable change inthe performance of admixtures. Previous generationsof cement dispersants were mainly based on lignosulphonates or sulphonated melamine or naphthaleneformaldehyde condensates.

BS:5075 has been withdrawn and replaced by EuropeanStandard BSEN:934-2. All admixture types are not coveredby BSEN:934-2. The cement and concrete associations inU.K. are working to cover the following:

underwater concrete admixtures

shrinkage reducing admixtures

corrosion inhibiting admixtures

pumping aids

segregation reducing admixtures

foaming admixtures

semi dry concrete admixtures

Admixtures are probably the least variable concreteconstituent. Components are either synthetic or highly

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rened and carefully controlled at each stage beforeand after delivery to the admixture manufacturer.The manufacturers should provide more technicalinformation and details to the engineers and alsoprovide specic assistance that may be required duringnalisation of the mix design.

ry mix cct

One of the main purpose of using ready mix concreteis to maintain the quality of construction. Its use indifferent construction sites is increasing fast. Readymix concrete ensures good quality concrete from all

contractors including the small ones who are unable toarrange concrete from batching plants in their project.Suitable use of admixtures helps in transporting concreteto a long distance. The advantages of using ready mixconcrete are18:

Economy - The cost/m3 would be economical aslocally available raw materials are likely to beused for production.

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Ensures strength requirement - The designrequirements will be met with condence. Highergrades of concrete can be used by the engineers inthe design for slender and stronger structures.

Easy and safe use - By using ready mix concreteit will be possible to ensure the speed of

constructions, workability and better hygienicconditions.

Versatility - It adopts the specific needs ofdifferent work sites.

Service - The service would be regular anduniform to maintain the schedule as worked outfor the construction. Pumps, conveyors, etc aidthe use of ready mix concrete at site.

Quality - Ready mix concrete guarantees quality.The constituent materials are subjected to quality

checks rst and rigorous quality control checksare carried out throughout the manufacturingand delivery process.

Delivery - The deliveries of ready mix concretecan be taken from ready mix plants or theconcrete can be delivered to worksites by concretemixer trucks. The speed of delivery is as per thecustomers needs. The use of ready mix concretekeeps the work place clean. Dirt, congestion andnoise would be at minimum level.

Ready mix concrete offers different varieties of mix

design. It can utilise different types of ller, cement andbinders to produce special concrete as per the customersrequirement. To optimise cost it will be necessary to haveuniform and high quality concrete for durable and betterstructures as per specication.

Use of bres

The use of bres in cement concrete and mortar has beenproved benecial. Steel, acrylic, polymer, glass, carbon,polypropylene and natural bres etc. are commonlyused. These fibres control /eliminate developmentof shrinkage cracks which may normally develop/

appear during concrete curing stage. If such cracks inthe concrete can be prevented, then entry of water/moisture through the cracks would also be controlled.Hence, the corrosion of primary reinforcing bars wouldbe reduced. It is also reported that exural strength ofconcrete increases with the addition of bres. The bresmay be 12 mm long for concrete and 6 mm long forplastering work. The manufacturers recommendations

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are to be followed for best results. Application of highperformance wire-drawn steel bres 60 mm long and0.9 mm. in diameter has been done in oor slabs ofmultistorey buildings.19 The use of at polymer bres40 mm. long has been done in composite steel deck oorconstruction in a multistorey residential complex.20 Ithas been observed that composite steel deck oors made

with concrete reinforced with synthetic macro bres canbe completed quickly and at a cheaper price than withthe more traditional methods.

dctiv cct

Coloured concrete has been covered in detail in variousliterature. It is possible to get coloured concrete fromready mix concrete plants also, with a wide range ofcolours that are consistent from batch to batch, permanentand durable.21 Pigments in powder and liquid form havebeen tried in the past and there were problems associatedwith uniformity in the colour of concrete, water demand,

strength and durability. The present colouring systemcontains particles that are granular and they easilydisperse into the mix. It often acts as a water reducingagent and hence less water is required for its production.The colourant is conveniently packed in water-solublebags, each of which will produce one cubic metre ofcoloured concrete for a given cement content. This wayit will be easy to produce consistent, uniformly colouredconcrete covering a wide range of colours.

It is expected that the use of coloured concrete willgive architects/planners enough opportunities to gofor decorative concrete that will blend and improve the

built environment.

CcsisA brief review associated with the applications ofstructural engineering in non-industrial projectshas been presented. A few relevant items on designcovering re engineering in buildings, faade design,hybrid construction, etc. are mentioned. Issues relatedto repair and restoration work and especially the roleof FRP systems in strengthening reinforced concretestructural elements are referred. Structural engineershave to produce safe and economical design with

proper structural detailing so that the structures can beconstructed with minimum difculties. It is commentedthat architects and structural engineers are required towork closely for creative/innovative designs associatedwith modern buildings. The structural engineers in aproject are responsible for design and construction ofsafe and serviceable structures through efcient projectmanagement. The services that a structural engineer


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Point of View

offers are challenging and commendable and he/she cansurely claim to be an important member of the projectteam. Education and training of our engineers wouldplay a very important role in meeting the demands ofthe future. Structural security and safety, bre reinforcedconcrete, ready mix concrete, use of re-cycled materials

and bres, and SCC would be key components in thedesign and construction of structures in the future.

ackwgmtThe author would like to thank the management ofDevelopment Architects Private Ltd. (DAPL) for theirencouragement. The author expresses his gratitude andappreciation for the opportunity of working with DAPLand the representatives of the clients and contractors ondifferent projects whose names have not been mentionedspecically.

rfcsGanguly, K.K., A brief review of different applications with reinforced

concrete, in industrial projects, with present and future trend, Proceedings

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construction without depletion, The Structural Engineer, February 2002,

Vol. 80, No. 3.

Stanseld, Kathy, Global Warming : Issues for Engineers, The Structural

Engineers, July 2001, Vol. 79. No. 14.

Chan, Berenice, Challenge for the future, The Structural Engineer, October

2001.

Downing, Mike, Hybrid construction : The way forward, The Structural

Engineers, June 2001.

Ledbetter, Stephen, Faade engineering : The challenge for structural

engineers, The Structural Engineer, June 2001. Vol. 79, No. 7.

Farmer, Ian, Using computers in engineering calculations, Reports, The

Structural Engineer, February 2002.

Miller, Andrew, Productivity in 3D modelling and structural design, The

Structural Engineer, February 2002.

Shaw, Cris, Cover to reinforcement Getting it right, The Structural Engineer,

February 2007.

______BS 7973, 2001, British Standard Institution, London.

Su, N., Lin, T.D. and Chai, H.W., Damage to structures and buildings from

Chi-Chi (Taiwan) earthquake, Proceedings of the Institution of Civil Engineers,

Structures & Buildings, February 2002.

______Guide for the design and construction of externally bonded FRP systems for

strengthening concrete structures, ACI Committee 440, American Concrete

Institute, USA.

Stanseld, Kathy, Report on designing for security, The Structural Engineer,

October 2001.

Recycling of wastes as aggregates for construction, IEI, News, July 2006.

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Daniel Jansen, and Herman Protze, Removing barriers to high strength

concrete in Boston, Concrete, July-August 2001.

Rob Gaimster, and John, Gibbs, Current practice sheet No. 123 Self

compacting concrete, Concrete, July-August 2001.

Dranseld, John, Admixture current practice - Part 1, Concrete, September

2006.

Report on ready mix Concrete, i-Structure, June-July, 2006

Robery, Peter, Construction of composite oor slabs using steel bres in

reinforced concrete, The Structural Engineer, December, 2002.

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construction, Concrete, September, 2006.

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Dr. K.K. Ganguly, PhD (London), is a directorat Development Architects Private Ltd, Kolkata.His areas of interest are design and constructionof industrial and non-industrial projects apartfrom teaching and research.

POV Ganguly

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