Design of Columns and Beams for a Multi-Storey Building
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This paper focuses on the design of columns and beams for a multi-storey building. It covers topics such as loading, slab design, moments, bending design, and shear reinforcement. Detailed calculations and recommendations are provided for each step of the design process.
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CONCRETE STRUCTURES By Name Course Instructor Institution Location Date
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Introduction The project aimed at the design of a building which was to be eight storeys in height.The building was to be used as an office at every level and one of its level being used as the car par just below the level of the street(Khatib 2016).The construction of the building had been identified to be at the Central Business District of Sydney.This particular paper however has focussed on the design of the columns that were to be located below the ground floor including the beams and the columns as had been shared below
Figure 1: The section to be considered for the design purposes DESIGN Layout plan
Loading Super imposed= 1.0kpa Live Load= 3.0kpa ρw=24+0.6vassume v=0.5% ¿24×0.6×05=24.3 gk=(24.3×0.2)+1=5.86kpa qk=¿3.0kpa
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Load combination ULS=1.2gk+1.5qk 1.2×5.86+1.5×3=11.532 Slab Panel 1 (corner slab) 2 adjacent continuous Ly Lx=5000 5000=1<2 Force design for every meter of the width noted as Fd: Fd=1.2G+1.5Q Fd=1.2×5.86+1.5×3=11.532kN/m Minimum effective Depth for the deflection check Lef d≤K3K4[(∆ Lef)Ec Fd.ef]1/3 Allowable deflection,∆ Lef =1 250 Lef=LesserofLorLn+Ds
¿Lesserof5000∨4700 ∴Lef=4700mm kcs=2−1.2Asc Ast ≥0.8say2.0Cl.8.5.3.2 ψs=0.7,ψ1=0.4(Building type-Office)From AS 1170.0:2002 Cl.4.2.2 – Effective design service Load,F¿=(1.0+kcs)g+(ψs+kcsψ1)qCl.8.5.3.2 (1.0+2.0)×5.86+(0.7+2.0×0.4)×3=22.08kN/m2 k3=1.0For two way slab k4=2.95 Ec=30100caseoff'c=32MPa d≥Lef k3k4 3 √Ec(∆ Lef) F¿ =4700 1.0×2.95 3 √30100×1 250 22.08×10−3 =90.5mm Effective depth,d=D−cover−0.5main¯diameter d=200−20−0.5×12where cover (A1) = 20mm, main bar=12mm ∴dx=200−20−6=174mm dy=174−12=152mm ∴dx,dy<90.5mmAcceptable
Moments Ly/Lx=1.0 M*x =β1FdLx2Cl.6.10.3.2 M*y =β1FdLx2 Coefficientβx=0.035 βy=0.035 Positive moment Mx ¿=0.035×11.532×52=10.09kNm My ¿=0.035×11.532×52=10.09kNm Negative moment (supports )Cl.6.10.3.2 (B & C) Interior supportMx=1.33×10.09=−13.42kNm Exterior supportMx=0.5×10.09=−5.045kNm Bending design ξ=α2f'c fsy α2=1.0−0.003f' c 1.0−0.003×32=0.904say0.85
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γ=1.05−0.007f' c 1.05−0.007×32=0.91say0.85 assuming∅=0.8 ξ=α2f'c fsy =0.85×32 500=0.0544 pt=ξ−√ξ2−2ξM ϕbd2fsy Bottom In the x- directiondx=174mm pt=0.0544−√0.05442−2×0.0544×10.09×106 0.85×1000×1742×500=0.00078 In the y-direction d=152mm pt=0.0544−√0.05442−2×0.0544×10.09×106 0.85×1000×1522×500=0.0001 Top In the x-direction pt=0.0544−√0.05442−2×0.0544×13.42×106 0.85×1000×1742×500=0.001 In the y-direction pt=0.0544−√0.05442−2×0.0544×5.045×106 0.85×1000×1522×500=0.0005
ptmin=0.2(D d)2f'cs fsy ptmin=0.2(200 174) 20.6×√32 500=1.793×10−3 pt<ptmin∴useptmin In the x-direction Ast=ptmin×bd1.793×10−3×1000×174=312mm2/m ∴provideN12@340mmspacing340mm2/m Checking spacingCl.9.4.1b Spacing¿Lesserof[2D;300]mm ¿Lesserof[400;300] Therefore use minimum spacing of300mm ∴provideN12@300mmspacing367mm2/m ∴ThereforethespacingisokCheck the transverse steel for cracking control In the y-direction Ast=ptmin×bd1.793×10−3×1000×152=273mm2/m ∴provideN12@400mmspacing275mm2/m
Checking spacingCl.9.4.1b Spacing¿Lesserof[2D;300]mm ¿Lesserof[400;300] Therefore, use minimum spacing of300mm ∴provideN12@300mmspacing367mm2/m ∴ThereforethespacingisokCheck the transverse steel for cracking control LocationdirectionptAstN12@ sAstactualposition SupportsX1.793×10−3312300367top Mid- region X1.793×10−3312300367bottom supportsY1.793×10−3273300367top Mid- region Y1.793×10−3273300367bottom Check shear V* =LyFd 2=5(11.532) 2=28.83KN Vuc=β1β2β3bvd0fcv(Ast bvdo) 1/3 Cl.8.2.7 β2=β3=1
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Coefficientβx=0.035Table 6.10.3.2(A) βy=0.035 Positive moment Mx=My=0.034×11.532×52=9.8kNm Negative moment Interior supportMx=1.33×9.8=−13.04kNm Exterior supportMx=0.5×9.8=−4.9kNm Bending design pt=ξ−√ξ2−2ξM ϕbd2fsy α2=1.0−0.003f' c 1.0−0.003×32=0.904say0.85 γ=1.05−0.007f' c 1.05−0.007×32=0.91say0.85 assuming∅=0.8 ξ=α2f'c fsy =0.85×32 500=0.0544
pt=ξ−√ξ2−2ξM ϕbd2fsy Bottom In the x- directiondx=174mm pt=0.0544−√0.05442−2×0.0544×9.8×106 0.85×1000×1742×500=0.00078 In the y-direction d=152mm pt=0.0544−√0.05442−2×0.0544×9.8×106 0.85×1000×1522×500=0.0001 Top In the x-direction pt=0.0544−√0.05442−2×0.0544×13.04×106 0.85×1000×1742×500=0.001 In the y-direction pt=0.0544−√0.05442−2×0.0544×5.4×106 0.85×1000×1522×500=0.0005 ptmin=0.2(D d) 2f'cs fsy ptmin=0.2(200 174)20.6×√32 500=1.793×10−3
pt<ptmin∴useptmin In the x-direction Ast=ptmin×bd1.793×10−3×1000×174=312mm2/m ∴provideN12@340mmspacing340mm2/m Checking spacingCl.9.4.1b Spacing¿Lesserof[2D;300]mm ¿Lesserof[400;300] Therefore, use minimum spacing of300mm ∴provideN12@300mmspacing367mm2/m In the y-direction Ast=ptmin×bd1.793×10−3×1000×152=273mm2/m ∴provideN12@400mmspacing275mm2/m Checking spacingCl.9.4.1b Spacing¿Lesserof[2D;300]mm ¿Lesserof[400;300] Therefore, use minimum spacing of300mm ∴provideN12@300mmspacing367mm2/m
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Dead Load,G=5×0.2×24 4+(0.5×0.3×24)+1×1 4=10kPa Live Load,Q=3.0kPa The load conditions that are considered: w=1.2G+1.5Q W=(1.2×10)+(1.5×3) ∴W=16.5kN/m External Beam (continuous Beam)/Secondary
Continuous beam with 3 equal spans Moment,M¿=αFl2wherelis the clear length, 4500 Figure showing Factors of moment Supports (A, B) Mid-span (C, D) Shear Force,V¿=βFl Figure showing Factors of shear force
αM¿=αFl2 (kNm) βV¿=βFl kN A-1/16-20.88½37.13 C+1/11+30.381/710.61 B1-1/10-33.411.15/242.70 B2-1/10-33.41½37.13 D+1/1620.881/89.28 Checking for the deflections: By applying the deemed to comply ratio, according toAS3600, Cl.8.5.4 Lef d≤[K1(Δ Lef)befEc K2Fd,ef]1 3 Lef=LesserofLorLn+Ds Where:ln=L−2×(500 2)=5000−500=4500mm Lef=Lesserof[5000;4500+200] ¿Lesserof[5000;4700]
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Check Ductility: Ku=dn d=21.1 440=0.047<0.4 Ductility is ok Lever Arm,z=d−(γdn 2)=440−(0.826×21.1 2)=431.3mm Capacity,Mu=TZ Mu=(402×103)×431.3 ¿173.38kNm ΦMu=0.8×173.38=139kNm ∴ΦMu=139kNm>M¿=30.38kNm Design for shear W=1.2G+1.5Q W=(1.2×10)+(1.5×3)=16.5kN/m V∗max=WL 2=16.5×5 2=41.3kN do=d=440mm ∴V∗¿ 3000−440=V∗max 3000¿ V∗¿41.3×2560 3000=35.24kN
Crushing checkCl.8.2.6 ΦVumax=Φ0.2f'cbvdo ΦVumax=0.7×0.2×32×500×440=985.6kN ∴ΦVumax=985.6kN>V∗¿57.3kN Adequate shear Dimensions The crushing of Web is not that much critical Checking of Shear Strength. Concrete shear capacity,Vuc=β1β2β3bd3 √f'c 3 √Ast bd×10−3 β1=1.1(1.6−440 1000)=1.14use1.1 β2=1 β3=2×do av =2×0.56 2.5=0.45say1 3 √f'c=3 √32=3.17<4MPaacceptable Vuc=1.1×1×1×250×440×3.17×3 √804 500×440×10−3=137.5kN Φ0.5Vuc=0.5×0.7×137.5=48.125kN SinceV∗¿57.3kN>Φ0.5Vuc=48.125kN
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Kcs=2>0.8AS 1170.0:2002 Cl.4.2.2 – Table 4.1 Ψs=0.7Floor for an office building ΨL=0.4 ∴Fd,ef=(1+2)20.9+¿ In order to get the value of K1: P=0.005fromAS3600 β=bef bw Where: bw=500mm bef=bw+0.2aCl.8.8a a=L(forsimplysupportedbeam)=5000mm So,bef=500+(0.2×5000)=1500mm ∴β=1500 500=3 So, p=0.005>0.001(f'c) 1 3 (β) 2 3 =0.001×(32) 1 3 (3) 2 3 =0.0015 Therefore:K1=(5−0.04f'c)p+0.002≤0.1 (β) 2 3
ΦVumax=Φ0.2f'cbvdo ΦVumax=0.7×0.2×32×500×440=985.6kN ∴ΦVumax=985.6kN>V∗¿63.104kN Section Dimension adequate for the shear Web Crushing is NOT Critical Shear Strength of Concrete:Cl.8.2.7.1 Concrete shear capacity,Vuc=β1β2β3bd3 √f'c 3 √Ast bd×10−3 β1=1.1(1.6−440 1000)=1.276>1.1use1.1 β2=1 β3=2×do av =2×0.56 2.5=0.45say1 3 √f'c=3 √32=3.17<4MPaacceptable Vuc=1.1×1×1×250×560×3.17×3 √804 500×440×10−3=137.5kN Φ0.5Vuc=0.5×0.7×137.5=48.125kN SinceV∗¿88.3kN>Φ0.5Vuc=48.125kN Shear Reinforcement is required. Minimum Strength of a beam with minimum reinforcement:Cl.8.2.9
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LiveLoad,Q=3.0×5×1.0=15kN N¿=2(60+20.4+24+15)=241.2kN W=1.2G+1.5Q W=(1.2×22.8)+(1.5×3.0)=31.86kN/m Nuo=N∗¿ 0.8=1074.6 0.8=302kN¿ Muo=M∗¿ 0.8=40.9 0.8=51.125kNm¿ Given Details: Beam concrete compressive strength,f'c=32MPa fsy=500MPa 4N16 been used Ast=Asc=804mm2 500×500mm, Tied columns is symmetrically reinforced Column on 7thlevel
In situ concrete is taken as 90% of cylinder strength (f’c) and is included in the coefficientα1: α1=1−0.003f'cCl.10.6.2.2 ¿1−(0.003×32)=0.904Within the limits0.72≤α1≤0.85 ∴α1=0.85
Ultimate strength in compression without bending, Nuo:
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Nuo=(α1f'c)bD+Ascfsy+Astfsy Nuo=(0.85×32×500×500)+2(804×500) ∴Nuo=7600kN Strength reduction factor (Φ¿in compression: Φ=0.6From Table 2.2.2(AS3600:2002) ΦNuo=0.6×7600=4560kN ∴POINT A: (7600 kN, 0 kNm) In terms of Strength reduction factor:(Fernández et al 2012) ∴POINT A: (4560 kN, 0 kNm) Zero Stress in Tension Bars
The parameters in stress blockCl.10.6.2.5 α1=1−0.003f'cCl.10.6.2.5.1 ¿1−(0.003×32)=0.904limits0.67≤α1≤0.85 ∴α1=0.85 γ=1.05−0.007f'cCl.10.6.2.5.2 ¿1.05−(0.007×32)=0.826Within the limits0.67≤α1≤0.85 ∴γ=0.826
The zero value for tension implies that the axis which is neutral actually passes via the bars with the tension. dn=Kud ∴Ku=1 εst=fst=0 dn=D−dst=d=500−60=440mm From Strain Diagram: εsc d−dsc=εu dn εsc=εu dn(d−dsc)=0.003 440(440−60)=0.0026 The yield strain for N bars:εsy=fsy E=500 200×103=0.0025 ∴εsc=0.0026>εsy=0.0025fsc=fsy=500MPa Ultimate Strength of eccentrically loaded Column, Nu: Nu=Cc+Cs Nu=(α2f'c)(γKudn)b+Ascfsy ¿(0.85×32×0.826×1.0×440×500)+(804×500) ∴Nu=5345kN ∴ΦNu=0.6×5345=3207kN
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To determine eccentricity (e), taking moments about the level of tensile steel: Nuh=Cc(d−γkud 2)+Cs(d−dsc) 5345h=4943(440−0.826×1.0×440 2)+402(440−60) →h=267.43mm ∴e=h−(D 2−dst) ¿267.43−(500 2−60) ∴e=77.43mm Mu=Nue=5345×0.07743=413.86kNm Strength reduction factor (Φ¿in compression: WhenNu≥Nub:Φ=0.6From Table 2.2.2(AS3600:2002) ΦMu=0.6×413.86=248.32kN ∴POINT B: (5345 kN, 413.86 kNm) In terms of Strength reduction factor: POINT B: (3207 kN, 248.32 kNm) Balanced Failure
Balance Failure occurs when reinforcing steel reaches the specified yield strain at the same time as the concrete strain reaches the limiting value of 0.003. εu=εcuεst=εsy→fst¿fsy kub=0.003 0.003+εsy ;εsy=0.0025forgradeNsteel kub=0.6 kubd=0.6×440=264mm εsc kubd−dsc=εu kubd →εsc=εu kubd(kubd−dsc) ¿0.003 264(264−60)=0.00231 The yield strain for N bars: εsc=0.00231<εsy=0.0025 σsc=Es×εsc σsc=200,000×0.00231=462MPa
Strength reduction factor (Φ¿in compression: WhenNu≥Nub:Φ=0.6From Table 2.2.2(AS3600:2002) ΦMu=0.6×565=339kN ∴POINT C: (2935 kN, 565 kNm) In terms of Strength reduction factor: ∴POINT C: (1761 kN, 339 kNm) Pure Moment Capacity,Muo(Nu=0)
Approximate Method is used for this section. The assumption made by this particular method is that it is possible to completely ignore the compressive contribution of the steel hence,Cs=0 From Equilibrium: Cc=Ts α2fc '(γdn)b=Astfsy dn=804×500 0.85×32×0.826×500=35.8mm Muo=Astfsy(d−γdn 2)=804×500(440−0.826×35.8 2) ∴Muo=171kNm Strength reduction factor (Φ¿related with the bending action in the absence of compression or axial tension Φ=0.8From Table 2.2.2(AS3600:2002) ΦMuo=0.6×171=102.56kN ∴POINT D: (0 kN, 171 kNm) When considering the reduction factor of the strength: ∴POINT D: (0 kN, 102.56 kNm) Interaction Diagram The interaction diagram is based on the following: Pure Axial compression, Nuo whenM=0(Squash Load Point) Zero Stress in Tension Bars
Balanced Failure State (Balanced Point)(Doran and Cather 2013) Pure Moment CapacityMuowhenN=0(PureBendingPoint) Construction of Interaction Diagram POINTMu(kNm)Nu(kN)Comments A07600The Axial compression is pure, Mu=0 B413.865345There is Zero Stress in Tension Bars C5652935This is Balanced Failure Condition D1710There is Pure Moment Capacity, Nu=0 Strength Interaction Diagram
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0100200300400500600 0 1000 2000 3000 4000 5000 6000 7000 8000 7600 5345 2935 0 STRENGTH INTERACTION DIAGRAM Moment capacity()𝑴𝒖 𝒌𝑵𝒎 Axial Force Capacity()𝑵𝒖 𝒌𝑵 Conclusion The design took into consideration all the required standards. Although there was slight variation of the actual figures from the expected digits, it is important to note that such differences were very insignificant. Step by step calculation produced reliable values that were adoptable for the construction process.
REFERENCES Doran, D. and Cather, B. eds., 2013.Constructionmaterialsreferencebook. Routledge. Fernández Carrasco, L., Torrens Martín, D., Morales, L.M. and Martínez Ramírez, S., 2012.Infraredspectroscopyintheanalysisofbuildingandconstructionmaterials(pp. 357-372). InTech. Hegger, M., Auch-Schwelk, V., Fuchs, M. and Rosenkranz, T., 2013.Constructionmaterials manual. Walter de Gruyter. Khatib, J. ed., 2016.Sustainabilityofconstructionmaterials. Woodhead Publishing.