Truss Design NS Negi
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![Page 1: Truss Design NS Negi](https://reader036.fdocuments.in/reader036/viewer/2022081803/55cf94f8550346f57ba5ab46/html5/thumbnails/1.jpg)
DESIGN OF STEEL TRUSS
Width of Bldg. = 8 m c/c
Length of Bldg.= 16.5 m
Height of eaves= 7.4 m
Number of bayes = 4
Angle of trust (Alfa) = 30 Deg.
Spacing of truss(assumption) = 4.05 m
Height of truss = 2.309 m
Incline length = 4.619 m
Each incline length = 1.540 m
Horizontal length = 1.333 m
Impose loads:Imposed load = 0.35 350.00
For purlin = 0.40 402.50
For truss members = 0.27 268.33
Wind loads:
Take basic wind speed(Vb) = 50 cum (Assume)
F =
Cpe & Cpi = Force coefficient for exterior & interrior of building. (Ref: Table B7 and Table B9 ;( " BOOK = Design of steel structure, second edition, LS Negi", pg:309 & 311)
A = Effective area of the structure.
Design wind pressure.= 0.6Vz^2
Where,
Design wind speed , Vz = Vb x K1 x K2 x K3
Accroading to the IS:875(part3);
Risk factor, K1 = 1.08 ref; Table B-11, Risk Coefficient K1;( " BOOK = Design of steel structure, second edition, LS Negi", pg:312)
Height and size factor, K2 = 0.91 ref; Table B-12, K2 factor;( " BOOK = Design of steel structure, second edition, LS Negi", pg:312)
Topography factor, K3 = 1 K3 = 1 for upward slope Ø < 3º; K3 = 1 to 1.36 for upwind slope Ø > 3º
Therefore, Vz = 49.14 m/sec.
1448.84 N/m2
Now,
Height of bldg., h = 9.709 m
Width of bldg., w = 8 m
Length of bldg., L = 16.5 m
h/w = 1.21
L/w = 2.06
Internal air pressure coefficient for normal permeability, Cpi = ± 0.2
Total pressure =(Cpe -Cpi) x Pd
Wind normal to ridge :Cpi = 0.2
Downward
Wind ward Cpe = -0.3 -724.422
Lee ward Cpe = -0.4 -869.306
Wind parallel to ridge
Wind ward Cpe = -0.8 -1448.844
Lee ward Cpe = -0.6 -1159.075
Max.wind load for design = 869.31 N/m2 (downward)
Max.wind load for design = -1448.84 N/m2 (Uplift)
Design of purlins
Spacing of purlins = 1.540 m c/c
Weigth of 20gauge CGI sheets = 112.7 N/m2 (Assume)
Size of CGI sheet= 1.8*0.9 m*m
Load on purlins per meter length :
Weight of sheeting = 173.513 N/m
Weight of purlin (Assuming) = 10 kgf/m
100 N/m
Total dead load = 273.513 N/m
KN/m2
KN/m2 (horizontal area)
KN/m2 (horizontal area)
(Cpe - Cpi) X A X Pz
Pz =
Design wind pressure (Pz) =
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Impose load = 536.667 N/m
Wind load = -2230.641 N/m
Dead load + impose load = 810.180 N/m
Dead load + wind load = -1957.128 N/m
When wind load is consider permissible stress is increased by 33.33%,
Therefore, dead load + wind load may be considered 33.33% less effective;
Design wind load = -1471.525 N/m; combination of dead & wind load is critical
Maximum bending moment in the purlin = 2413.668 Nm
250
Permissible bending stress = 165
Therefore, section modulus (Zx) =14628.294
14.63
Required tubular purlin (as per common steel sections):Zx = 14.4
Outside Diameter = 76.1 mm
Nominal Bore = 65 mm
Class = Medium
Thickness = 3.65 mm
Weight = 6.53 kg/m
Area of X-section = 8.31
Design Load for roof trussLoads:
1) Dead loads:Length along the sloping roof = 4.619 m
Self weight of the truss = 100 N/m2 (Assume @100 N/m2 horizontally)
Gauge of CGI sheet = 20
weight of roofing material = 112.7 N/m2
No. of purling = 8
Weight of purling = 65.3 N/m2
Therefore;
Load due to :
Self weight of truss = 3240.00 N
Roofing material (CGI sheet) = 4216.37 N
Purlins = 2115.72 N
Total = 9572.086 N
No. of panels = 6
Load acting on intermediate panel point = 1595.35 N
Dead load acting on node = 1595.35 N
Dead load acting on shoe = 797.67 N
2) Imposed loads:Miscellaneouse load (Live loads) = 0.2 N/m2 (Assume)
Total live load = 8724.48 N
Load acting on intermediat panel point = 1454.08 N
Live load acting 0n node = 1454.08 N
Live load acting on shoe = 727.04 N
3) Wind loads:Total wind load = 1448.84
Wind load acting on one intermediat panel = 9034.10 N
Wind load acting on shoe = 4517.05 N
Yield stress(fy) = N/mm2
N/mm2
mm3
Cm3
Cm3
Cm2
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Force coefficient for exterior & interrior of building. (Ref: Table B7 and Table B9 ;( " BOOK = Design of steel structure, second edition, LS Negi", pg:309 & 311)
ref; Table B-11, Risk Coefficient K1;( " BOOK = Design of steel structure, second edition, LS Negi", pg:312)
ref; Table B-12, K2 factor;( " BOOK = Design of steel structure, second edition, LS Negi", pg:312)
K3 = 1 for upward slope Ø < 3º; K3 = 1 to 1.36 for upwind slope Ø > 3º
Total pressure =(Cpe -Cpi) x Pd
Cpi = -0.2
Uplift
-144.884
-289.769
-869.306
-579.538
N/m2
N/m2
N/m2
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N/m; combination of dead & wind load is critical
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Load Combinations:
30 Deg.
49.11 Deg.
60.00 Deg.
1) Dead loads:Dead load acting on node = 1.595 kN
Dead load acting on shoe = 0.798 kN
2) Imposed loads: 1.45 kN
3) Wind loads:Wind load acting on one intermediat panel = 9.03 kN
Wind load acting on shoe = 4.52 kN
Sign convention (Compression -ve, tension +ve)
Member
Forece (KN) due to Load combination
Design load
Dead laod Imposed load Wind load Maximum Minimum
(a) (b) (c ) (a+b) (a+c) / 1.33 KN KN
Principal LoU1 -7.98 -7.27 39.12 -15.25 23.42
27.34 -15.25Rafter U1U2 -7.98 -7.27 44.33 -15.25 27.34
Rafter U2U3 -6.38 -5.82 39.12 -12.20 24.61
Main tie L0L1 6.91 6.30 -31.62 13.20 -18.58
13.20 -18.58Main tie L1L2 5.53 5.04 -22.59 10.56 -12.83
Main tie L2L3 4.14 3.78 -13.55 7.92 -7.07
Main sling U3L2 2.76 2.52 -18.07 5.28 -11.51 5.28 -11.51
Main strut U2L2 -2.39 -2.18 15.65 -4.57 9.97 9.97 -4.57
Minor sling U2L1 2.11 1.92 -13.80 4.03 -8.79 4.03 -8.79
Minor strut U1L1 -1.60 -1.45 10.43 -3.05 6.64 6.64 -3.05
Angle of trust, ө =
Angle of trust, α =
Angle of trust, β =
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Design of truss member1) Rafter (L0-U3 & U3-L5):
Design load =27.34 KN; Tension
15.25 KN; Compression
Effective length, l = 1077.72 mm; since rafter is continuous over panel points
Maximum bending moment = 3175.11 Nm
Therefore, section modulus (Zx) =19243.11
19.24
Section adopted for rolled steel beam Section type = Medium
Nominal bore, d = 160 mm
Outer diameter, D = 165.1 mm
Weight per meter, w1 = 19.2 kgf/m
Radius of gyration, r = 56.7 mm
Yield stress of steel, fy = 250 N/mm2
19.01
148.92 N/mm2
150 N/mm2
11.71 N/mm2; Safe in compression
20.99 N/mm2; Safe in tension
2) Main ties (Lo-L5):
Design load =13.20 KN; Tension
18.58 KN; Compression
Effective length, l = 933.33 mm
Maximum bending moment = 1618.52 Nm
Therefore, section modulus (Zx) =9809.19
9.81
Section adopted for rolled steel beam Section type = Medium
Nominal bore, d = 90 mm
Outer diameter, D = 101.6 mm
Weight per meter, w1 = 9.75 kgf/m
Radius of gyration, r = 34.5 mm
27.05
146.61 N/mm2
150 N/mm2
14.27 N/mm2; Safe in compression
10.14 N/mm2; Safe in tension
3) Main sling (U3L2 & U3L3):
Design load =5.28 KN; Tension
11.51 KN; Compression
Effective length, l = 2266.67 mm; since ends of copression section partially restrained for lateral bending
Maximum bending moment = 5912.30 Nm
Therefore, section modulus (Zx) =35832.09
35.83
Section adopted for rolled steel beam Section type = Medium
Nominal bore, d = 90 mm
Outer diameter, D = 101.6 mm
Weight per meter, w1 = 9.75 kgf/m
Radius of gyration, r = 34.5 mm
65.70
116.48 N/mm2
150 N/mm2
mm3
Cm3
Ratio, λ (l/r) =
Permissible stress in axial compression, σac =
Permissible direct stress in axial tension, σat =
Actual compression stress, σac,cal =
Actual compression stress, σac,cal =
mm3
Cm3
Ratio, λ (l/r) =
Permissible stress in axial compression, σac =
Permissible direct stress in axial tension, σat =
Actual compression stress, σac,cal =
Actual compression stress, σac,cal =
mm3
Cm3
Ratio, λ (l/r) =
Permissible stress in axial compression, σac =
Permissible direct stress in axial tension, σat =
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8.84 N/mm2; Safe in compression
4.06 N/mm2; Safe in tension
Actual compression stress, σac,cal =
Actual compression stress, σac,cal =
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mm; since ends of copression section partially restrained for lateral bending
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U3
Lo L1 L2 L3 L4 L5
fig: Truss components
ө= 30 α = 49 β = 60
1.333 m 1.333 m 1.333 m 1.333 m 1.333 m 1.333 m
fig: Truss
U1 U4
U1 U5
1.54 m 1.54 m
1.54 m 1.54 m
1.54 m 1.54 m
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1.595 KN
1.595 KN 1.595 KN
1.595 KN 1.595 KN
0.798 KN 0.798 KN
4.786 KN 4.786 KNfig: Dead load
23.471 KN 23.471 KNfig: Wind load
4.517 KN 4.517 KN
9.034 KN 9.034 KN
9.034 KN 9.034 KN
4.517 KN 4.517 KN
![Page 12: Truss Design NS Negi](https://reader036.fdocuments.in/reader036/viewer/2022081803/55cf94f8550346f57ba5ab46/html5/thumbnails/12.jpg)
7.824 KN
7.824 KN 7.824 KN
4.517 KN7.824 KN 7.824 KN
4.517 KN 4.517 KN3.912 KN 3.912 KN
4.517 KN 4.517 KN
2.259 KN 2.259 KN
fig: Wind load components