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Steel Structure Design
1.0 INTRODUCTION
Steel structures are famous all around the world nowadays. There are some reasons for this
and economical factors as well as easy construction with less time duration are the main
reason for it. Most members in the steel structure are pre fabricated and this is saves lots
of time when constructing a steel structure. Steel structures are used for many purposes
and warehouses, factories and workshops are very much popular among them
In this report steel design is carried out for auto workshop which is located at Southport,
Gold Coast in QLD.
The structure consist single story and length and the breath are 25.0m and 15.0m
respectively.
2.0 METHOD OF ANALYSIS AND DESIGN
Frame analysis is done by using computer application SPACE GASS as well as manual
calculations. SPACE GASS is a general purpose structural analysis and design program
for 2D and 3D frames, trusses, grillages and beams.
Further design part is completely done by manual calculations and for this analysis and
design, Australian standard for civil engineering student (HB 2.2- 2003) and the study
guide for steel design are used.
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Steel Structure Design
3.0 PRELIMINARY DESIGN
Fig No 01: Plan view of the building
Fig No 02: Front view of the building
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Steel Structure Design
Fig No 03: Side view of the building
4.0 LOAD CALCULATIONS
4.1 Dead and Live Loads
4.1.1 Load by Roof Sheeting
Sheeting type: CUSTOM ORB
Thickness: 0.42 mm
Weight: 4.3 kg/m2
Area load: 4.3 x 9.81/1000=0.042 kPa
4.1.2 Load on Purling
Assume purling size: Z10012
Spacing: 1.25 m
Weight: 2.07 kg/m
Lind load due to self weight: 2.07 x 9.81/1000= 0.02KN/m
Line load on Purling by dead load
g purling= 0.042 x 1.25+ 0.02 = 0.07kN/m
Load on Purling by live load
Apurling=1.25x5=6.25 m2
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Steel Structure Design
1.8/6.25+0.12=0.41 kPa > 0.25 kPa (HB 2.2-2003 Table 3.2)
Line load on purling by live load = 0.41 x 1.25= 0.51 KN/m
Design load on purling
F = 1.2x gpurling +1.5x qpurling = 1.2x 0.07 +1.5x 0.51 = 0.85 KN/m
4.1.3 Load on Rafter
Size of the rafter: 200UB25.4
Spacing: 5.0 m
Weight: 25.4 kg/m
Lind load due to self weight: 25.4x 9.81/1000=0.25 KN/m
Line load on Rafter by dead loads
grafter= 0.042 x 5+ 0.02x5/1.25+0.25 = 0.66 KN/m
Live line load on Rafter
Rafter, A=5x15=75 m2
1.8/75+0.12=0.14 kPa<0.25 kPa (HB 2.2-2003 Table 3.2)
Therefore, take live load for rafters as
qrafter=0.25 kPa
Live line load on rafter = 0.25 x 5= 1.25 KN/m
Design load on rafters
F=1.2x grafter +1.5x qrafter = 1.2x 0.66 +1.5x 1.25 = 2.67 KN/m
Design load on purling = 0.85 KN/m
Design load on rafters = 2.67 KN/m
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Steel Structure Design
4.2 Wind loads
Details for the wind calculations according to the AS 1170.2:2002,
Wind Region: (HB2.2-2003, p530) - B (Southport)
Important level: (Study Guide 2103ENG Part 01,p27) - Level 1 for presenting a low degree of hazard to life and other property in the case of failure
Return period: (Study Guide 2103ENG Part 01, p27) - 100 years wind gust return period for non-cyclonic wind design and importance level 1.
Regional wind speed (VR): (HB2.2-2003, p530, table 3.1) - V100 = 48 m/s
Wind Direction Multipliers (Md): = 01
Terrain category: (HB2.2-2003, p532) = 3 for normal built up area
Average roof height (Z) : (5+5+ 7.5 Tan 50)/2 = 5.33 m
Terrain and structure height multiplier (Mz,cat): (HB2.2-2003, p533, table 4.1A ) = 0.83
Ms=Mt=1
4.2.1 Design wind speed (Vdes,θ)
Vdes,θ = VR x Mz,cat =48x0.83=39.84 m/s
4.2.2 Dynamic wind pressure (p)
Assuming Cdyn = 1,
p = 0.6 x (Vdes,θ)2x Cfig =0.6x 39.842 = 952.33 Pa = 0.95 Cfig kPa
4.2.3 Calculation for Aerodynamic shape factor (Cfig)
For external pressures
Cfig = Cp,e x Ka x Kc x Kl x Kp
External pressure coefficients (Cp,e )
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Steel Structure Design
Wind direction θ=00
1. Cp,e for Windward Wall
h = 5.33m < 25m and Cp,e = 0.7 (HB2.2-2003, p545, Table 5.2.A)
2. Cp,e for Leeward Wall
d=15m, b=25m
d/b= 0.6 ≤ 1, and α =50 <100
Cp,e = - 0.5 (HB2.2-2003, p545, Table 5.2.B)
3. Cp,e for Side Walls (HB2.2-2003, p546, Table 5.2.C)
Horizontal distance from windward edge
Cp,e
0 to h -0.65
h to 2h -0.5
2h to 3h -0.3
>3h -0.2
3. Cp,e for Roof (HB2.2-2003, p546, Table 5.3.C)
Horizontal distance from windward edge of roof
Cp,e
h/d = 5.33/15 =0.35
0 to h -0.9, -0.4
h to 2h -0.5, -0
2h to 3h -0.3, 0.1
>3h -0.2, 0.2
External pressure coefficients (Cp,e )
Wind direction θ=900
1. Cp,e for Windward Wall
h = 5.33m < 25m and Cp,e = 0.7 (HB2.2-2003, p545, Table 5.2.A)
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Steel Structure Design
2. Cp,e for Leeward Wall
d=25m, b=15m
d/b= 1.66 ≥ 1, and α =50 <100
Cp,e = - 0.37 (HB2.2-2003, p545, Table 5.2.B)
3. Cp,e for Side Walls (HB2.2-2003, p546, Table 5.2.C)
Horizontal distance from windward edge
Cp,e
0 to h -0.65
h to 2h -0.5
2h to 3h -0.3
>3h -0.2
3. Cp,e for Roof (HB2.2-2003, p546, Table 5.3.C)
Horizontal distance from windward edge of roof
Cp,e
h/d = 5.33/25 =0.21
0 to h -0.9, -0.4
h to 2h -0.5, -0
2h to 3h -0.3, 0.1
>3h -0.2, 0.2
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Steel Structure Design
Fig No 04: External pressure coefficients (Cp,e )-Wind direction θ=00
Fig No 05: External pressure coefficients (Cp,e )-Wind direction θ=900
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Steel Structure Design
For Internal pressure
Internal pressure coefficients (Cp,i )
Dominant opening area (Roller Door) = 8x4= 32m2
Sum of other openings = 1.0x 1.0 x 3 + 2.1x 0.9 =4.89 m2
So, Table 5.1(B) HB2.2-2003, P543 can be used with (32/ 4.89) = 6.54
According to the table Cp,i = Cp,e for the dominant opening in windward, leeward and side
walls.
Dominant opening in sideward wall (Wind direction θ =0 0 )
Cp,i = Cp,e = - 0.65
Dominant opening in windward wall (Wind direction θ =90 0 )
Cp,i = Cp,e = + 0.7
Area reduction factor (Ka)
For rafters
Tributary area =15x5= 75m2
Ka =0.87 (Table 5.4 HB2.2-2003, p547)
Combination factor and porous reduction factor (Kc , Kp )
Assume, Kc= Kp= 1
4.2.4 Design wind load on rafters
Maximum downward wind load (θ=00):
Cfig = Cp,e x Ka x Kc x Kl x Kp = 0.1x0.87 x1.0 x 1.0x 1.0 = 0.087
pe= 0.6 Vdes,θ2 x Cfig = = 0.087x 0.95 = 0.083 kPa
Maximum internal uplift wind pressure
Cfig = Cp,i =-0.65 pi=0.6 Vdes,θ2x Cfig =0.95 x(-0.65)= -0.617kPa
p= pe - Pi =0.083-(-0.617)=0.700 kPa
Uplift wind line load on rafter = 0.700x5=3.50 kN/m
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Steel Structure Design
Maximum upward wind load (θ=900):
Cfig = Cp,e x Ka x Kc x Kl x Kp = - 0.9x0.87 x1.0 x 1.0x 1.0 = - 0.783
pe= 0.6 Vdes,θ2 x Cfig = = - 0.783x 0.95 = - 0.743 kPa
Maximum internal uplift wind pressure
Cfig = Cp,i = 0.70 pi=0.6 Vdes,θ2x Cfig =0.95 x0.70 = 0.665 kPa
p= pe - Pi = -0.743 -(0.665)= - 1.408 kPa
Uplift wind line load on rafter = - 1.408 x5 = - 7.04 kN/m
5.0 DESIGN FOR RAFTERS AND BRACINGS
5.1 Design for moments (Rafters)
Assuming rafter section as, 200 UB 25.4
Twist resistant factor (Kt) = 1.0 for FF condition (Table 5.6.3(1) HB2.2-2003, p186)
Load height factor (Kl) = 1.0 for FF condition (Table 5.6.3(2) HB2.2-2003, p186)
Lateral rotation resistant factor (Kr) = 1.0 for FF condition (Table 5.6.3(3) HB2.2-2003, p186)
Assume, bracing is located at node 3.
Consider segment 1-3 of rafter
Le= Kt Kl Kr L = 1x1x1x2.5 = 2.5 m
βm = 4.22/ 55.77 = 0.08 (Table 5.6.1 HB2.2-2003, P184)
Moment modification factor (αm) =1.75+1.05βm+0.3βm2 = 1.75+ 1.05*0.08+ 0.3* 0.082 = 1.84
(Table 5.6.1 HB2.2-2003, P184)
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Steel Structure Design
Moment design capacity (ΦMb) = 55 KN.m (AISC Table 2, Study Guide, P50)
ΦMb for actual αm on segment (kN.m) = 55* 1.84 = 101.20 kNm > (ΦMs = 75kNm)
So, ΦMb = 75kNm
Maximum design moment M* = 55.77 KN.m (By SPACE GASS software)
M*< ΦMb OK.
Consider segment 3-7 of rafter
Le= Kt Kl Kr L = 1x1x1x5.0 = 5.0 m
βm = 4.22/33.17 = 0.13 (Table 5.6.1 HB2.2-2003, P184)
Moment modification factor (αm) =1.75+1.05βm+0.3βm2 = 1.75+ 1.05*0.13+ 0.3* 0.132 = 1.89
(Table 5.6.1 HB2.2-2003, P184)
Moment design capacity (ΦMb) = 28 KN.m (AISC Table 2, Study Guide, P50)
ΦMb for actual αm on segment (kN.m) = 28* 1.89 = 52.96 kNm < (ΦMs = 75kNm)
So, ΦMb = 52.96kNm
Maximum design moment M* = 33.17 (By SPACE GASS software)
M*< ΦMb OK
5.2 Design for shear (Rafters)
Take rafter section as, 200 UB 25.4
Dp =
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Steel Structure Design
6.0 Column design
Assume column is pin joined to footing, fully fixed by rafter,
The critical column compression load case is: 1.2DL+ 1.5LL+ 1.0 WL (upward wind force)
N*=18.06 kN M*= 55.77 kNm (By Spacegass analysis)
Effective Length Factor (ke) =2.2 (Figure 4.6.3.2, HB2.2-2003, Page 168)
Column height L=5m
Le= ke L = 2.2x5 =11m
Choose 200UC46.4, Grade 300
ΦNc = 210 kN > (N*=22.86 kN) (Table 7, Study Guide 3, Page 55)
Therefore, section of the column is sufficint to take the loads.
Ag = 5900mm2, Zx= 451x103, fsy= 320 Mpa
σmax=M/Z+P/A
=55.77 x106/(451x 103)+ 18.06 x103/5900 = 123.66 + 3.06 = 126.72 Mpa
0.9fsy= 0.9x300 = 270 Mpa
270.0 Mpa < 126.72 Mpa
Safe
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Steel Structure Design
Fig No 06: Maximum Bending moment due to DL, LL and upward WL
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Steel Structure Design
Fig No 07: Maximum Bending moment due to DL, LL and downward WL
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Steel Structure Design
Fig No 08: Maximum Bending moment due to Upward WL
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Steel Structure Design
Fig No 09: Maximum shear forces due to Upward WL
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Steel Structure Design
Fig No 10: Maximum shear forces due to DL,LL and Upward WL
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