16|The Structural Engineer – 2 December 2003

viewpoint: wilson

One of the most difficult ques-tions we have to ask ourselvesat the start of our careers

must be ‘Am I ready for the Part 3Examination? Here are some hints forself-assessment.

1. Have I had experience in realis-ing the client’s requirements for anew building?This experience is usually obtainedwhen you go with your senior engi-neer to a meeting with the client andarchitect at the very start of a job. Thearchitect lays out plans for a buildingshowing all the spaces and functionsof the new building. The ‘team’ nowexpects you to advise on the alterna-tive structural framing systems.

Where will the columns be? Can wehave a clear span here? The structuralfloor zone can only be of a certainthickness – no more. There will beservice cores at defined points. Thearchitectural (sculptural) qualities ofthe building require certain roof formsor cladding, or even a curved frontage.What materials will be used? Whatare the benefits of one scheme overanother?

At the meeting you take notes aboutall these and many other features ofthe proposed building. You add yourown impromptu ideas. Details aresketched and discussed. Later, in thequiet of the office, you put the alterna-tive schemes together. There aresizing calculations to make, cata-logues to consult, outline generalarrangement drawings and sections todraw, and another important responsi-bility is to anticipate how the buildingwill be constructed.

2. Have I had experience inappraising the pros and cons ofeach of the proposed alternativeschemes and can I make a recom-mendation on the most appropri-ate scheme?After a second meeting, where theclient has rigorously examined your

alternative schemes, you will be askedto recommend a scheme. You musthave done your ‘homework’ and beable to present your reasons. At theend of the meeting you will departwith instructions to develop a particu-lar scheme.

3. Have I had experience in sortingout a late request by the client oradjusting the chosen scheme to anew situation, say an extra flooror two?It can be quite difficult for a client tospecify all the requirements of a newjob at the very beginning. It is notuncommon for additional features ornew ideas to ‘bubble up’ during theconcept stages. These changes maycome about because more up-to-dateequipment becomes available, becausemore (or less!) money is available, orbecause of a change of the client’ssenior director! The changes are not‘optional’ – they should be regarded asinstructions to comply.

Before any letter can be written tothe client there is a lot of backgroundwork to do in a hurry. The proposalhas to be visualised with drawingsand sketches. These must be exten-sions of the earlier concept drawingsas the new proposals modify the origi-nal scheme. What was a roof mustnow become a floor, service cores haveto be extended; new loads have to beincluded and carried to the founda-tions, etc.

Further sizing calculations need tobe made. It is often convenient tochange the material for top-of-the-building extensions, and a correspon-ding change of cladding may beappropriate. The extra structural costcan be estimated using the method ofPrincipal Rates for the mainelements. The steelwork, concrete andcladding quantities can be quicklyestimated and multiplied by aPrincipal Rate (e.g. £ per tonne).These elements constitute, say, 85% ofthe extra structural cost. Avoid usingpercentage ‘guesstimates’, as thesecan often be confusing (15% of what?The cost of the structure or the cost ofthe building?). Decisions have to be

made about how the extension will bebuilt and any special constructiontechniques that will need to be identi-fied.

You are now in a position to advisethe client about the new proposals.Drawings, schedules and programmesaccompany the letter. You may be ableto make helpful suggestions thatimprove the new proposals, e.g. thatthe former rooftop plantroom could berelocated to a basement or part of theground floor.

4. Have I had experience in devel-oping a scheme so that a budgetestimate can be prepared by thequantity surveyor?The initial scheme will have beenproportioned on the basis of somesizing calculations. These are oftenspan/depth ratios, simple soilsinformation, a quick estimate oflateral loads and a general ‘looks good’approach where columns fit intoenclosure walls, etc. The sizing calcu-lations err on the side of caution,preferring to be trimmed down ratherthan having to ask for more structurewhen everybody else has fitted intothe scheme.

At the development stage the prin-cipal elements, slabs, beams andcolumns can be checked out so thatthey conform to an appropriate stan-dard. Experience often allows theroutine structure to be confirmed withlittle detailed calculation, even toselecting from supplier’s cataloguesand safe-load tables.

Every scheme where a structuralengineer is employed will includespecial elements that are specific tothat scheme. These elements needmore detailed calculations than theroutine structure and are designed atthis development stage. They becomecritical to the scheme. Examples are:transfer and long-span structures andtheir supports or bearings; shearwalls to resist lateral loading fromwind, earthquake and moving loads;and main columns and cornercolumns with bi-axial bending.

These critical elements require agreater design experience because of

Bob Wilson uses his experience as an examiner to suggestsome guidelines for candidates to conduct self-assessmentprior to sitting the part 3 exams, and to help pre-examinterviewers to focus on the real issues

Do’s and don’ts of thePart 3 examination

Bob Wilson: make your answersvibrant, alive and full of enthusiasm

2 December 2003 – The Structural Engineer|17

viewpoint: wilson

their unique behaviour. A portal frameis a hyperstatic structure because ofthe moment-capacity of the joints. AVierendeel girder is another fixed-joint structure and is often used totransfer close-spaced column loadingto wider column spacing. Shear wallsare located within the building plan,but not always in a symmetrical way.The resulting torsion of the buildinghull needs to be considered. Again, thetransverse loads need to be broughtback to the shear walls, and this isdone through the slabs acting as hori-zontal girders (often referred to as‘diaphragm action’). Beams that arecurved in plan have to resist torsion.Cantilevers need to be ‘balanced’ bystructure within the main buildingframe or designed to resist thebending moment at the root of thecantilever. A site joint may be critical,so also the position of a bearing, or thetying together of separate units toprovide a robust structure.

If any of these special structuralelements are part of a scheme theyneed to be carefully designed. It maybe sufficient to design only themoment connection, the shearstrength or to check the deflection tobe reassured at this stage that theelement will be fit for the purpose.The detailed ‘number crunching’ canbe deferred to another time when suit-able software can be used.

5. Have I had experience inpreparing scheme drawings,general arrangements andbuilders’-work details?In the days before computer-aideddrawing most people in the office hadlearnt to use a tee-square and pencilto draw out their ideas. As yourresponsibilities grew you sketchedyour ideas freehand (in good propor-tion), and passed these to anotherperson who drew them out to scale.This system exists today in a modifiedform in that the engineer’s ideas,sketched with a pencil (in a meeting,say), are drawn out by a CAD techni-cian in the office. The need to developdrawing skills still remains.

Early on we need to communicateour ideas to the other members of the‘team’. Sketches and drawings do thismost effectively; besides, we also needthem in order to visualise our design.We need them in order to tease-outthe snags in a building’s detail. Weneed them in order to take-off quanti-ties. A bold and confident drawingstyle is a great way to inspire andcreate confidence in others.

Some of the key features of thisbold and confident drawing style are:a good, clear line; different line thick-ness for different functions such asoutline and dimension; a clear group-ing of the components shown on thedrawing; neat lettering and titles;good proportions or use of an appro-

priate scale; and, above all, the pres-entation of useful information.

Sketches and drawings cannot beproduced unless the correspondingbuilding construction is known. Thereare a number of architect’s andbuilder’s size books and other buildingconstruction references available, butin all cases the reference detail mustbe adapted to the particular circum-stances of the job in hand.

6. Have I had experience inpreparing a method statementthat explains to the QS andtendering contractors the limita-tions imposed by the designassumptions, and identifies thecritical aspects of the design anddetail?

Every design makes assumptionsabout loading, quality of the materi-als, the structural behaviour underload and the way that the building isput together. There used to be a well-known advertisement where a verylarge block of concrete was cast andthen hollowed out by several menusing hammers and chisels. Well, it isone way of constructing an in situconcrete house! But probably not theone you recommend.

‘Buildability’ is often the term usedto describe what we mean by efficientconstruction. Some designs need a lotof craftsmanship in their realisation,and are correspondingly time-consum-ing and expensive. An efficient designwill have identified these parts andseparated them from work that can bedone more cheaply or more quickly. Insome situations speed of erection iscritical and a suitable design has to bechosen. The design needs to be build-able within the time frame. Thisbuildability needs to be explained tothe client and the rest of the ‘team’.

In former times, when we reliedupon traditional crafts; the craftsmanwas allowed to choose his method ofworking. He could go from job to jobknowing that his tools and skills wereappropriate to the work. Today we usea very wide range of materials. Someof them are traditional like brickwork,but most have been modified byadvancing technology. The range oftools and techniques has widenedbeyond the capacity of any one person.The number of specialisms hasexploded and is reflected in thenumber of different questions in the

IStructE’s Part 3 Examination paper.The engineer is responsible (in the

UK) for the design, safe construction,maintenance and unbuilding of thestructure when it is no longer wanted.‘Safety’ is used in its widest sense andincludes: stability (temporary andpermanent), non-poisonous materials,consequences of damp or ageing,replacement of worn out equipment,and the eventual demolition sequenceor unbuilding of the frame.

A few examples can be given:In the UK, modern mortars are pre-mixed under close quality control, anddelivered to site. The designer mayassume the strength of the mix, andthis will be incorporated into the load-bearing masonry design. Site-mixedmortar may not have as high a qualitycontrol, and so the on-site masonrymay not have the required strength.The design has been compromised.

The supply of concrete in the UK issimilarly ready-mixed. If the design isfor a building to be erected outside theUK then the assumptions associatedwith ready-mixed concrete in the UKcannot be applied and the design maybe compromised.

Several traditional materials havebeen found to be carcinogenic –asbestos is the well-known example.These can no longer be used. Otherscan taint water supplies. In the waterindustry only approved and listedmaterials may be used. On bridges,only materials that are approved andlisted by the Department forTransport (DfT) can be used forwaterproofing, etc. The buildingdesign should not be compromised byspecifying inappropriate or harmfulmaterials. Some materials areallowed, but have volatile solvents orhigh flashpoints. These materials canonly be used under controlled condi-tions that need to be identified inadvance of construction, in the bill ofquantities or specification.

Construction beside existing build-ings can damage the adjacent prop-erty. The method of underpinning,shoring and weatherproofing all needto be specified in advance in the engi-neer’s method statement (EMS). De-watering the new site can affectadjacent water supplies and causesettlement of adjacent buildings. TheEMS must anticipate this happeningand instruct on the method of re-charging the ground water reservoir.

Driven piling and dynamiccompaction (DC) may be inappropri-ate where vibrations can causedamage. The EMS should specify anappropriate method of working.Tolerances for pile positions need tobe specified. This may be done in theEMS.

The theoretical design of precastconcrete units and balcony cantileverswill only call for reinforcement in thetension face. Handling and placing the

‘If you are lacking ineven one of these classes

of experience you willshorten your chances of

passing the exam’

18|The Structural Engineer – 2 December 2003

viewpoint: wilson

units will impose additional stressesand will need additional reinforce-ment. If the unit is accidentally placedupside-down there will be a weakplace in the floor, which will collapse.For balconies the risk is too great andthese units are reinforced for the fullloading on both sides of the unit. Thishas to be detailed in the office and theinformation passed on to the QS, thesupplier and the contractor.

Composite floors are common. Theslab provides the lateral stability forthe top flange (compression flange) ofthe supporting beam. However, thebeam is designed as a slender memberand depends upon the support fromthe slab before it can carry any load.If the slab is cast in situ the weight ofthe fresh concrete must be supportedon formwork and propping. It cannotbe transferred to the steel beam.Later, when the concrete has hard-ened the two elements act compos-itely. The contractor needs to bewarned that he cannot hang the form-work off the steelwork!

Many connections, in both steelworkand precast concrete, require specialprocedures, for example, high strengthfriction grip bolting. The special boltsneed to be tightened to a specifiedtorque. Regular bolts will not do.

Tolerances on plumb and level canbe critical. The engineer needs toconsider the buildability of the frame-

work and the consequences of ‘lack-of-fit’ and temperature.

We all have our own experiencesand examples. Hopefully these havecome about by forward planningrather than an unhappy experience onsite. The EMS is the setting down ofthe plan of construction from thedesigner’s point of view. At a laterstage the contractor prepares anothermethod statement, setting out theactivities, materials and their quanti-ties, plant to be used and the workforce needed. From these can be calcu-lated the duration of that activity. Theduration is used in the programming(CPM) and will identify the criticalactivities (no float), and the activitieswith ‘float’. The examination questionis not specific about which methodstatement is wanted. The expectationis that it will be the engineer’s methodstatement, but if you have contractingexperience the contractor’s methodstatement will be equally acceptable.Do not try and give both because youwill not have enough time!

Your self-assessment has to behonest! If you are lacking in even oneof these classes of experience you willshorten your chances of passing theexamination. If I am honest with you,the candidates that fail nearly alwayslack experience in sorting out the laterequest (number 3 in the list above);preparing builder’s work details

(number 5 in the list above); and themethod statement (number 6 above).So many marks are lost over thesesections of the question that even agood answer in the rest cannot makeup the bare pass mark! I suppose thatthis raises another question – do youwant a ‘bare’ pass or a ‘competent’pass?

P.S. I nearly forgot an important‘Don’t’! Each question starts life as areal building, though it is modified forthe examination question. It is impor-tant that you answer the question in a‘real life’ way as though you weremeeting the problems for the firsttime. Don’t try to reduce the answerto a ‘universal answer’. The universalanswer has all the components of theproper answer in a very general way –functional framing, load transfer andstability; fire resistance, cladding anda note about the foundations. Theuniversal answer never addresses thespecific problems of the question! Itreduces all the problems to a bland‘nothingness’ that would frustrate afirst-year undergraduate! The head-ings in the universal answer may wellserve as a good aide memoir and acheck that all these aspects have beencovered in your answer. Your answermust be vibrant, alive and full ofenthusiasm! Not a dull repetition ofsome classroom notes that has little incommon with the question. se

Maitland Lecture 2004Wednesday 25 February at 6.15pmRoyal Institution of Great Britain,Albemarle Street, London W1

Professor Robert Winstonpresentsthe human

embryo: thoughtson structuralengineering

Telephone: 020 7235 4535 • Website: www.istructe.org.uk/maitland