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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.


3.0 PRELIMINARY DESIGN

Fig No 01: Plan view of the building

Fig No 02: Front view of the building


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


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


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 )


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)


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


Fig No 04: External pressure coefficients (Cp,e )-Wind direction θ=00

Fig No 05: External pressure coefficients (Cp,e )-Wind direction θ=900


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


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)


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 =


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


Fig No 06: Maximum Bending moment due to DL, LL and upward WL


Fig No 07: Maximum Bending moment due to DL, LL and downward WL


Fig No 08: Maximum Bending moment due to Upward WL


Fig No 09: Maximum shear forces due to Upward WL


Fig No 10: Maximum shear forces due to DL,LL and Upward WL

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