WIND LOAD DESIGN OF STEEL STRUCTURE ON ROOF TOP UNDER QCS 2014 CASE STUDY : OFFICE TOWER IN DOHA
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Transcript of WIND LOAD DESIGN OF STEEL STRUCTURE ON ROOF TOP UNDER QCS 2014 CASE STUDY : OFFICE TOWER IN DOHA
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WIND LOAD DESIGN OF STEEL STRUCTURE ON ROOF TOP UNDER QCS 2014 CASE STUDY : OFFICE TOWER IN DOHA
Introduction
This steel structure will be constructed on the roof top of high rise building in Doha, Qatar. Cladding material will be
used to cover this frame as façade or artificial structure to add architectural value of this building. Wind load design
is highly prioritized to be put into engineering calculation as top elevation of this structure is about 160 mtr above
Qatar datum.
Basic Engineering Design
In this article, we are going to modelling this structure into Staad Pro v8 SS6 as Finite Element Analysis Software and
apply wind load as dynamic pressure following QCS 2014.
According to QCS2014 in General Chapter under Introduction sub‐chapter, Wind speed is designed for 50 year return
period in three circumstances:
1. Nominal wind speed for 3 sec gust = 38 m/s (ASCE 7‐05 / IBC 2012)
2. Mean hourly wind speed = 25 m/s (BS 6399‐2)
3. Mean 10 minutes wind speed = 27 m/s (BS EN 1991‐1‐4)
This wind load is designed in extreme condition as the arch will be erected on the roof top. There are two design
procedure we are comparing to find accurate solution to be used for this Tower.
3D PERSPECTIVE OF ARCH STRUCTURE
3D figures above are rendered using Sketchup and Vray software
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Revised Steel Frame Structure including Cladding frame
3D figure above is taken from Staad Pro software
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Wind Load (WL) Design
First code is British Standard (BS) 6399‐1997 where we can conclude in such chart below:
According to wind speed map of Qatar, Doha city has minimum basic wind speed 25 m/s.
The site wind speed (Vs) for any particular direction should be calculated as below
Sa = 1 + 0.001∆s ; ∆s = Site altitude above sea level, tower top elevation is 160 mtr from sea level. Sa
= 1 + 0.001*160 = 1.16
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Sd is usually used to adjust the basic wind speed to produce wind speeds with the same risk of being
exceeded in any wind direction. If the orientation of building is unknown or ignored, the value of the
direction factor should be taken as Sd = 1.0 for all direction.
Ss is used to reduce the basic wind speed for buildings which are expected to be exposed to the wind for
spesific subannual periods. For Permanent buildings, value of Ss is 1.0.
Sp is used to change the risk of the basic wind speed. For all normal design, Ss value is 1.0
Vs = 25 x 1.16 x 1 x 1 x 1 = 29 m/s
Effective wind speed calculation in accordance with BS 6399‐2 is taken from table 4 as below
According to table above, effective wind speed (Sb) is 2.12.
Ve = Vs * Sb = 29 x 2.12 = 61.4861 m/s
ExternalpressurecoefficientsTable5iscoefficientofexternalpressureforverticalbuilding,dependentontheproportion/ratioofthebuildingaspicturebelow
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Ht=He=160mtra1=Diagonaldimension=162,67m(RedLine)a2=Diagonaldimension=162,22m(Blueline)
L/He=0.183Longitudinal coefficient
Cpe windward = 0.8
Cpe Leeward = ‐0.3
W/He=0.167Transversal coefficient
Cpe windward = 0.8
Cpe Leeward = ‐0.3
W = 26.780 m
L = 29.389 m
He
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Ca_longitudinal = 0.79
Ca_transversal = 0.81
Dynamic pressure according to BS 6399‐2 2.1.2 is
qs = 0.613*(61.48)^2 = 2317,01 Pa = 2,31 kPa
Pe_windward_Longitudinal = 2,31 * 0.8 * 0.79 = 1.46 kPa = 146 kg/m2
Pe_leeward_Longitudinal = 2,31 *(‐0.3) 0.79 = ‐0.55 kPa = ‐55 kg/m2
Pe_windward_Transv = 2,31 * 0.8 * 0.81 = 1,5 kPa = 150 kg/m2
Pe_leeward_Transv = 2,31 *(‐0.3) 0.81 = ‐0.56 kPa = ‐56 kg/m2
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Second code we are considering to calculate wind load using Staad Pro software is ASCE‐7 as described following
picture below
As a conclusion from both wind code, ASCE‐7 code is more extreme than BS 6399‐2 code. In this design, we are using
wind load generated from ASCE‐7.
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Wind Load X+ Direction (Windward face)
Wind Load X+ Direction (Leeward face)
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Wind Load X‐ Direction (Windward face)
Wind Load X‐ Direction (Leeward face)
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Wind Load Z+ Direction (Windward face)
Wind Load Z+ Direction (Leeward face)
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Wind Load Z‐ Direction (Windward face)
Wind Load Z‐ Direction (Leeward face)