THE ENGINEER’S TOOLBOX - Expedition Workshed

1 THE ENGINEER S TOOLBOXM aterialsDensities1 t/m3 = 10 kN/m3 Water 1 t/m3 normal t/m3 light t/m3 Carbon t/m3 to t/m3 Sand/gravelAbout t/m3 moistRockAbout t/m3 Strength and stress limitsConcrete (ult)Work at about 30% fcuSlabs/beams use fccu = 40 N/mm2 Columns use fcu = 40 to 60 N/mm2 Shear stress: v = say N/mm2 for beamsv = say N/mm2 for slabs and wallsStructural steel Grade 50 (working)Compressive stress: about 150 N/mm2 unless slenderness governsShear: about 100 N/mm2 Tension: about 225 N/mm2 Steel cables (working)Use 500 N/mm2 for concept designAluminium (working)Use 80 N/mm2 Timber (working)8 to 10 N/mm2 compression or tension (along the grain)Glulam timber (working)About 12 N/mm2 Carbon fibre (working)Use about 200 N/mm2 (but brittle!!)Masonry (working)215 brick wall: about 200 kN/m runBolts for steelwork (working)Grade 16 mm bolt will carry about 4 tonnes (working) in single shearWelds for steelwork (working)6 mm fillet weld will carry kN per mm Bolts for timber (working)12 mm diameter in 50 mm timber about 1 kN (100kg)StiffnessConcrete28 kN/mm2 (short term)14 kN/mm2 (long term)Steel205 kN/mm2 Timber6 kN/mm2 Aluminium70 kN/mm2 Carbon fibre120 kN/mm2 Sands and gravels25 mm settlement at normal bearing capacityDouble the depthAt least quadruple the stiffnessTHE ENGINEER S TOOLBOXL oadsLoads (characteristic)Average building1 t/m2 of floor area (10kN/m2)Imposed loadsResidential: to kN/m2 Offices: to kN/m2 Partitions: (light) to (heavy) kN/m2 Plant rooms: kN/m2 Car parking: kN/m2 Factories/warehouses: to kN/m2 Stadia.

2 KN/m2 Museums: to kN/m2 Wind (UK) kN/m2, 100 kg/m2 (smooth building, low drag) kN/m2, 180 kg/m2 (rough)Wind (typhoon) kN/m2, 400 kg/m2 (medium)EarthquakeUp to 25% g horizontallyUltimate Load factorsRough first shot for x working loadsDead (imposed) or resistanceResidential 2 storey30 minutesRoofsNoneOffice more than 30m2 hours sprinkleredBasements2 or 4 hoursRough sizing Steel and concrete limiting proportionsSimply supported beamsAbout 18:1 Continuous beamsAbout 22:1 CantileversAbout 7:1 TrussesAbout 30% deeper than beamsArchesAbout 6:1 CablesAbout 9:1 Heavily loaded columnsAbout 12:1 Lightly loaded columnsAbout 40:1 TimberJoistsAbout 15:1 TrussesAbout 8:1 THE ENGINEER S TOOLBOXT ypical spansTimber floorboards400 mmConcrete composite beam deck3 m between secondary steel beamsTimber joistsUp to 5 mRolled steel beamsUp to 18 mSteel trussesUp to 90 mSteel archesUp to 300 mCable stayed roofsUp to 300 mConcrete flat slabsUp to 12 mConcrete beamsUp to 18 mTypical gridsOffices6 m by 6 m up to 18 m by 12 m m to 11 m (to suit units)CarparksStalls.

3 M by mAisles m wideFactories/warehouse roofs24 m by 24 mAirports/station roofs36 m to 150 m by 24 m to 36 mStadium roofs48 m cantileversStandard reinforcement sizes6, 8, 10, 12, 16, 20, 25, 32, 40 mm diameterTypical storey heightsResidential3 mOffices4 m ( m clear)Carparks3 m ( m clear)Factories/warehouse roofs8 m to 16 m clearAirports/station roofsAbout 18 m highStadium roofsMustn t obstruct sightlinesUseful AnalysisForceNewtonF = maBending momentsSimply supported beam at midspanwl2/8 (udl)Pl/4 Cantilever at rootwl2/2 (udl)Concrete beamsDesign so that Mu applied is about 40% of its ultimate capacity Mr = moment of area for a rectangle b wide and d deep I = or tensionStress = P/A (also pressure)BendingStress = = M/zShear Stress = (b = web thickness, d = effective depth) Concrete column sizingFor short columns with minimum dimension = clear height/15: Area (mm2) = Load in newtons/18 For slender columns: Area (mm2) = Load in newtons/12 Elastic modulusz= bd2/6 (rectangular)THE ENGINEER S TOOLBOXD ynamicsEarthquakeNormally in the range to 2 secondsFloor vibrationTypically, Frequency f = 18/ deflection If less than 5 Hz, watch out!

4 Second per storey heightDeflection limits under working loadsBeams and trusses1/360th of span under live load, 1/250th under dead load Cantilevers1/180th under live loadStability systems under wind load1/500th of height (whole building) 1/400th (worst storey) Between foundationsAbout 1/300th totalFoundations and retaining wallsBearing capacityRock2000 + kN/m2 Dense sand/gravel200 to 500 kN/m2 (10 x SPT N blows)Loose sand/gravel50 to 100 kN/m2 Clays 25 (soft) to 400 kN/m2 (very stiff)PilesMinimum spacing3 diametersPiles in London Clay( cu av x shaft perimeter)/3+(9 cu base x base area)/3 Slope stabilityLong term angle of reposePhi , for sands and gravels use 25 to 30 Short term safe(ish) stability Sands and gravelsClaysRock1 vertical to 3 horizontal1:1 Vertical but watch out for bedding planesPressures on retaining wallsHydrostatic pressure= wghActive pressure coefficientka = 1 - sin 1+ sin Passive pressure coefficientKp = 1 + sin 1 - sin At rest pressure coefficientAbout pressure (active, passive, at rest)= k.

5 SghEnvironmental and Climatic Wind directionPrevailing wind in UKFrom South WestWinter stormsFrom North EastSun pathOver head at midday in summer, low 20 Rises in the east, sets in the westThermal massAs night time storeNeed about 75 mm of concreteEnvironmental and Climatic FactorsTHE ENGINEER S TOOLBOXW ater engineering Six most useful equations in practical hydraulics according to Ed- ContinuityQ = vA- ArchimedesImmersed body experiences an up thrust equal to the water displaced - BernoulliE = v2/2g + y + (p/ g)- Manningsv = 1/n (Rh) s - weir flow q = critical depthyc = (q2/g) Watery rules of thumbFlow velocities in UK rivers are typically between and 3 m/sNine out of 10 errors in flood estimation are a result of not measuring the catchment area correctlyFlows in pressurised pipe systems normally have velocities between and m/sPressures in normal distribution systems are typically between 1 and 6 bar (10-60 m).

6 Gravity drainage systems typically have velocities between and m/sTypical slopes in gravity drains are 1:100 1:300 Typical slopes on lowland UK rivers are between 1:1000 and 1 / m2 / m heightPower generationQ gh (watts)CostsApprox costs Residential buildings 1500/m2 50 storey 1000/m2 3 storeyOffices 1800/m2 50 storey 1100/m2 3 storeyFactories 400/m2 single storeyStructural steel 1000 per tonne (simple frames)Reinforced concrete 150/m3 (simple) 250/m3 (complex)Timber 1000/m3 Structural earth fill 15 to 20/m3 12/m3 to dig and re-use clean fill from site 40/m3 to dig and dump clean fill from site 50 to 100/m3 to remove contaminated material from siteFacades 150/m2 (brick) to 1000/m2 curtain wall triple glazedTHE ENGINEER S TOOLBOXB ored piles600 mm diameter, 20 per metre plus 5000 mobilisationSheet piles 80/m2 for 150kg/m2 piles plus 5000 mobilisationDiaphragm walls 250/m2 for 900 thick plus 30,000 mobilisationReinforcement estimatesPile caps150 kg/m3(amount of reinforcement per cubic metre of concrete)Rafts80 kg/m3 Beams250 kg/m3 Slabs200 kg/m3 Columns300 kg/m3 Walls100 kg/m3 Other things to ponderWhen you are looking at options spend 90% of your effort on your favourite scheme and 10% on the restIf it looks right, it probably is.

7 If it looks wrong lose it!Form follows functionGod is in the detailsThe Devil is in the detailNine out of 10 errors in flood estimation are a result of not measuring the catchment area correctlyThe best design is 10% inspiration 90% perspirationThe whole is greater than the sum of the parts (the worst third year projects are produced by groups acting as individuals)Work expands to fill the time availableThe law of diminishing returns (don t gild the Lily)KISS keep it simple stupidIf someone doesn t do what you asked them to, ask yourself whether you explained yourself clearly.