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Word document for skylight structure - pre-requisite
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DESIGN CALCULATION FOR SKYLIGHT STRUCTURE
DESIGN CALCULATIONS FOR THE SKYLIGHT STRUCTURE
I. General
1. Design Philosophy - PREAMBLEThe purpose of this calculation is to verify the supporting structure for its integrity, strength and stability verification. The result of this conclusion is that the structure considered adequate in meeting the required of design criteria.
2. Unit of MeasurementUnit of measurement in design shall be in Metric system.
II. Design Standards
1. Design Code and reference:BS 5950 1190: Structural use of steel work in buildingWind loads as per BS 6399 Part 2, 1997STAAD PRO – Structural Program for calculations.
2. Material PropertiesThe modulus of elasticity of Steel E = 210000 MPaUltimate Bending stress steel – Po - σ = 275 MPa = 275 N/mm2
Ultimate Tensile Stress steel – Pa = 435 MPa = 435 N/mm2
Ultimate Shear Stress steel – Pv = 0.6X Po = 0.6X275 = 165 MPa = 165 N/mm2
3. Materials UsedMain Frame Steel I Beams – JO 102X102Secondary Frame Support Aluminium Tubes – 50X50X3mm thickAll Weld thickness are maintained at 4mm thick
III. Loadings
a. Dead LoadsDead Load – Self weight is considered
Dead Load of glass is considered as 55 Kg/m2
Live Load is considered as 0.75 KN/m2
b. Wind loads calculations as per BS 6399 Part 2, 1997:
Wind loads (WL) calculated as per BS 6399 Part 2 – 1997:
Basic hourly mean wind speed assumed as 27 m/s.
Design wind speed Vs = Vb x Sa X Sd X Ss X Sp
Where,
Sa – Altitude factor = 1.0
Sd – Directional factor = 1.0
Ss – Seasonal factor = 1.0
Sp – Probability factor = 1.0
Design wind speed Vs = Vb x Sa X Sd X Ss X Sp
Design wind speed Vs = 27 X 1 X 1 X 1 X 1
Design wind speed Vs = 27 m/s
Wind pressure q = k Ve2
K – Constant = 0.613
Effective Wind Speed Ve = Vs X Sb
Sb – Terrain and Building factor from Table 4 as Site in town exceeding > 2 KM upwind from the site and 10 KM closest distance from sea at height of 30m,
By interpolation, Sb = 1.96
Ve = 27 X 1.96 = 52.92 m/s
Ve = 52.92 m/s
Wind pressure q = 0.613 x (52.92)2
Wind pressure q = 1717 N/m2 or 1.717 KN/m2
From the above mentioned table,
Cp = 0.7,
Net wind Pressure = Cp X q
Net windward (front face) wind pressure q = 0.70 X 1.717 =1.202 KN/m2
c. Load Combinations
Design & Ultimate factors are considered.
as per BS standard,
UL = 1.4 DL + 1.6 LL
UL = 1.4 DL + 1.4 WL
And for deflection,UL = 0.9 DL + 0.8 WL
IV. Design Method
1 Basic data
The skylight structure will be loaded considering the overall lengths and widths are 6.260m and 6.840m respectively with a height of 0.50m above level. The glass is placed on the skylight structure with a maximum size of 1560mm X 850mm distributed along the line loads, whereas the steel sections is placed below the glass to support the glass and structure is checked and verified separately below.
Loads are calculated on the spacing between the supporting beams i.e. 1.275m which are as follows:
Dead Loads:
a) Self Weight to be checked from the programb) loading is calculated as 0.550 X 1.275 = 0.701 KN/m
Live Load – 0.75 X 1.275 = 0.956 KN/m
Wind Loads:
a) Uplift wind load = 1.202 X 1.275 = 1.533 KN/mb) Downward wind load = 1.202 X 1.275 = 1.533 KN/m
To check the maximum length of the skylight structure against all the above loading combination and to be on factor of safety (see attached calculations made by the structural program STAADPRO).
Conclusion:
All sections used and connections provided are structurally sufficient and meet its intended purpose.