~ PROFESSIONAL
Welcome
IP51S0LUTIONS
Thank you and welcome to 'BS6399-2 Wind Loading - Practical Design, an IStructE seminar presented by Alasdair N Beal.
Alasdair N Beal BSc CEng MICE FIStructE is a Member of Thomasons LLP Consulting Civil & Structural Engineers, Leeds. He has over 30 years experience in practical engineering
design. He has written papers about various aspects of codes of practice and design including 'A Bit Windy? - BS6399-2 in practice' (The Structural Engineer 16th Nov 2004). He has also served on IStructE committees producing design guidance for reinforced concrete structures and retaining walls.
© Professional Solutions 2006
Thomasons Consulting Civil & Structural Engineers and Building Surveyors 12 United Business Park,
BS6399-2
DESIGN FOR
WIND LOADS
Low Fields Road. Leeds LS12600 tel. 0113 245 1282 fax. 0113 244 3557 leeds@ thomasons.co.uk
Afasd,.air N. Be-at BSc CEn"gl MICE FIStructE Thomasons LlP Consulting Civil & StructuraI Engineers, Leeds Tholll850nS
Engineers need to know wind pressures for designing buildings like these
The consequences of getting it wrong can be serious.
This roof came off 10 minutes after children's playtime.
2
CODE OF PRACTICE
. . _... . 'If:;rt>r ......~
[O~~ IID'1'ft1JlE11 1_
CP3:
V·2:
~JV
.~fMo.lqM
~ , A ';01iom.! .1\
(~odp.of
RS4J!99.2i 1997
BllmSRSTJ\NDAKD
1
1:,
~ J, h"'; 50
e..m..-J..... lI.Io.l CanwNd..."J
Loading for buildings
NPn~ h,..ftMt
These are different: a code for 'wind loads for design' should specify wind pressures which produce safe, reasonably economical building designs. It does not matter if it does not model wind behaviour perfectly.
!
Basic data for the
design of buildings -
I I
Part 2: Code of practice
fOT
wind loads
I
Chapter V: l.oading-
Part 2: Wind Loads
I
""'-_.61
.....,
•
COI'IUIU_"~.""".~U1If
CP3-V was a 'code of practice for wind loads for the design of buildings'; BS6399-2 is a 'code of practice for wind loads'
.a . "'Si· .
British'· Stlfld8rds
BS6399 is more like a collection of research data than a code of practice for design. The data are presented and it is up to the engineer to work out what to do with them. To make matters worse, the information is presented in a different order from the logical sequence for design, so engineers also need to find where the different pieces of information are and bring them together in the form they require.
3
shovr ~t~t te>OT 'fJeAS I \)J
,Ohet
~'n(J(e,;;;)s.
VJI"i£. ~~
6~.sfG)
'" 5pee..cL ~ s b~...se..dJ oh Q)
.-0•• _ _• • • '
5/'0'1':"[:6'0-,:1;
Input building height H, input building
- type factor Kb (table 1)
Stage 2: Checkllmlts of appIloeblllty Cr < 0.25. H < 300 m (U.2)
-r,c>'fh~
;;i..
f\') 5:J 7-~
h0> pp~~ VI
o~ &...~~
BulIding Is dynamic. This part does not apply (lI8ll references (1) 10 (4])
Yes
-------' Basic Wind speed map (figure 6)
le=-v ~~ d' --,
AIIItude factor 8•• d1rectlonal factor Sd' seasonal factor S,. probability _f~or_Sp_ _ _ _ . _
...
•.
_--- .. .._
_ !i
i
Directional and topographic effects
I ! ; 8~~~_, ~l' ~ .!1t. S/L _________0
I
~s-....·
Site len'aln type. level of upwind roottops H" • separatiOn of buildings X
....
'4-~~! f~ -·~c: ,;~ ; :~; : ~.; ~ efI~-z-=-~=~=;r=~=- ~=~d=-~=·- -=~=- - "'' ·-11
;-_n-l
.
I Dynamic pr~sure Cle. q, (3.1.3)
1
,__ _______L __ . DlrliCtiona, pressure coeffiCients Cp
1 3.4.2 1 ;,; (303)
P
_._.~L
~
~: }.'i
-"
Directional Wind Ioad6 P (3.1) ~;
Flpn 1 - Flo'lfchart iU'Ilstratto.I outlllle p~clul'.
4
3>
~e.c. :~nd (jJSt"
} 014 ~
ALI':TlJd~ ~L pas;~tthn
/iwl8S63!a fl-foUY~ ()h~
lf2e>T CD()h~ ~
heW et>Je,
eoJe,
~~
Calculating the Site Wind Speed 11
2.U Site wbul .peed 2.2.2.1 ~~,
Ht\!
JF
r" _..
",.,,(1 ~._.<+-----~-
"':<'-~~\~
.
~~
"iiL
:j.lf
j
f:':-~~1
'~;',\II
{liF, i:\~
\;Pi'/~
Tbtt site wind speed ~ for aDY particular direc:ti0ll
v. =lIi. )( Sa
S. )C
s. x S.
1
where
1\ S.
S. S.
oS,
is the basic wiDd. speei from 2.2.1; is an altitude £actor (see 2..2.2.%); is a ~ factor (He 2.2..2.3); la a HUOIDA1 factor
1U.%.2W11en toIIoIa'aDhv is ftOt amsiderea sicDifiaurt s.
S. = 1 + 0.00148
when ds
"I,
)C
Site wind speed is allculated from Clauses 2.2.1 and
2.2.2. NB CP3-V wind
speeds were based on
peak gust speeds. In
BS6399-2, the basic
site wind speed is
based on the hourly
mean wind speed
(which is much lower)
but this is then
factored up to give
peak gust speeds for
design.
If topography is
signiflClUlt (Le. near
summits of ridges or
escarpments), there are
6 pages of guidance to
be followed.
istlle ate altitude (iJ'l.blI!!trea ah:we meaa -level>
U2.2.3Whea ~ is ~cllipifieaDtSa shoa1cI be t,'
....
Sa = 1 + O.OOU\S
.48 is the site altitude OD metres a130ft meaJl sea le\.1); or S. =1 + O.OO~ + 1.2(11...
WMre
..............
~t..,...,
~u.
"'p,.l-
\\~lftmt.,
fd~§.~S \?h wind 5t~ Glh chDl\l-%e DYCJS\ lca \\ LA thfJ WI ~1c1 pv ess,u veJI.. ~~
10 F'°~rC) p
hf\:
ReLwcS> 'nt"
4T is t1w altitude ot tlae upwiad __ ot ~ t topopaphy .,. ia the efJecIift . . . otthe tlltJIOpap}tic _tuN; • is. ~Jocatioafactar.
5
~---
lJ\ --------------- ---------
z
_.~
~"t/50eth.'w''&- --.I}n~?n
b(Ysfo \.{) ?hcL s~ d:'~V~h
o
UK
Ih
Cl. 2.2.2.3 gives factors to be applied to the
1.2.2.3 mNetio,,·'_ctor 'J.1ae.4inmcm fact.or S. ~ he lIIICKl to aG;lJIt the huic wiDd apeed to prochce wiDd apeeda witll the same liB af__ aceedeiiD uqr wiDi dinc6oll. Va!u.es aTe Ii'NIl in Taw., 3 for aD. wiJul di.reetiaDa iD. 3Cf iatervaJs (where tlse1ViDd iirectiaD.ia tIefiaed·ia tM 0CJI'lWIlti0M11IUlJII*': aaeMt wiDd.is a wiJul clinctiou = go- IIJli bJowafromtheeuttothe aite). JfdleOl'ierJt8tioD ofthelnWdtncis 'tIDbowa or iporecl the val. of tile cIirection£actor should_ takeJl.. = 1.00 £or all ~
of.,
s,
widt~·r.t:adtUtUW a
NOTE W1t.D_ tiMahoafatw
iatftpD1a. . fotm. ...... ~
_ ....... Ol'tU
' urietJora...... fna.TaIU 3 M _ _ iau..napci1rilulGncda..,. ~
Table 3 - Values of dtrecdOll factor S.
Dtrfttl...
I.
iliA
M. . . ..,.:
Dinedoa t'acQr S.
basic wind speed depending on its direction NB Cl. 2.1.1.2 states that in design. all wind directions within 45 degrees of a design wind direction must be considered. The orange column in the table shows effect of this where differences in distance from sea etc. are not important. In theory, each side of a building could be designed for a different wind speed and different wind pressures but in practice this would complicate the design without any benefit in economy.
mq
2..Ll.2 For each ~ ~ the l'IIJlI'8
«wiml ~:!4V eitller..tIe of die directiaa.1'IOl'DJ81 to =er aJUl8:: l8C1 .-w.. omci. . . . aaci the mare
. .MWc1incface 80alci M ~ \VJsea ..,18rIletrY iI UHd to nd1acetbe JlUIDJt.. of~loacl
casea. both opJK:l8.iDcwirlll cIirectiaaa. e.... , diNllt'tWm usec:l
0Iler'0QS
45°e.>lch
'1f
However it can be useful sometimes - e.g. to reduce design wind pressures for a building near the east coast. It can also be useful for internal pressures from a dominant opening (see later).
6
• L. '0. : 1fWl1~O~CJ~ G-V~hdJ5r:;het f9 VCl show
DV
~~OYdY~ \x.IoY~'--1
Ten1 porary Structures
J..UA S.uoncd factor n. 8eII8OINd fae.tcao s•. ." ueecl to nduce the basic wiIul speecl for huildmcs w1Iich are expedeclto'be atothewiJulfOrlJ*lilc StlhnmvaJ ~ iD puQcularfor tempor.y ..... ..a1Mail6tp dm:iIc ~ Values whic1l maiataiD. th.risk(prohal:Jiliti)~ezceedecIof Q=0.02 iD the stated..periocI celiftD. iD Armex D. PorpenDlllle1lt lnDWinp IIDCllNilctinp eQCI.ecl to the wind for acontimaou period ofmore than 6mcmths • value of 1.0 .hoaW he 1Uecl for S.~
GPO.'
'IoIcIIatM JaIl
O.Be
F_
0.83 0.82
.Mu
•
1_
T...I. D.l- v.t... of ".10841 ~r . . . . . . .I)Mdoda
2 .....
,0.88
a.-to 0.11
d1U
0.62
10."11
AuK
0.71 0.82
0.85 0,95
JaIl
0.98
O.Wl
[FM
0.83 0.82
I~
Mal" .~
U~J6
Mv O.BS
,1. . 4hll
0 .86
1
Aa.
0.90 0.96
Sep 1.00
Del
New Dec
1.00 1.00
IU)Q
IJIUl
Felt
0.88 WUIrIl'
year.
Felt
0.83
0.13
0.89
0.83
0.88 OJJ4
IIbr
0.87
0.82
Oci\
The reason for the reference in this clause to Appendix D is tmelear, as this gives a factor of 1.0 for a probability of occurrence of0.02 per
.I_
0.98
0.6'1
New IDee
Cl. 2.2.2.4 gives reduction factors on basic wind speed for the design of temporary structures and buildings under construction.
• JI1IDIatIg
0.75
0. • O.te
hp
o.
10,W
J1la
Uq
JIoIlths
----,
•
........
fI&1' to
J'IMN
7
R-e.ssore- is eoh5ti,;t1iht'o~hout" LL. ~*T~ 1{he;
I
~
...
~
'-J-l ~ ." -I ~HL- ~h" t:lDII ~Set\Sibl£;
pYeSSV~ fV"l
bU\2dth~
feY'
~e.>
BS 63~
rYllvsT be-
~v I
wnt
.. I
~
--- --r----l--l I .
""
1t--
H. I-.---~
- - - - __
0.81(.
H
If
I
·""",r
·r,'"
-- -.----- "----
., 'F,
., X
.1_.1..,_.................,..
Hr
-
I l
I
I
--... 1
,/
',.or" '/
G.51
wh...
B.
bl
V"is the site wiBd speed
to
obtl.iMd hm: 2.2.1, for the ....... = W aroundt& notioaaIorthopna1 'IriJld dir«tions cW'iMd with'the
15
factor obtained from 2,2.3.3.
~Ohcl pr0SSU re C,L&ckJ~V\~
-r
Y
•
).:fIr; 1.18 1.86
to
1..90 1.96 1.06 2.12
100 1Nott2
INon,a 1NDtt.
..,.
1
I
I
I
I
2
3
..
5
:
1.36 1.67
1.7'
1.90
I .• 1. •
L98 2.04 2.12
2..04 1.12
Loa,
=t> -d..O -l;o-
-t
Ill"
-G,O
t
1.28
:(.2
1.18
1.41 1.62 1.11
5
UjO 1.73
10
1.95
15 20 30 50
2~O7
100
t.11 t~85
1,- Z \&/~~
'dYO()'ncL
8 ~----a.i
Ina
a
V. . . . . . . . . . . . . . . . . . . . . .=5 ... 1f. . . lOO . . . . . . . . . . . .l . . . . . ef. . . a.
.s
I
a-.. lti. ._ t........1. .
B.
le
LilO 1.12 1.78 1-85
.~JMl.
n....... d8.................IRantes-!5l.
e.s.TIVh~·rf 0 h
X h\~h 1~e1~
I..
1."
30 50
.a:
. . . ha ....., .......... : ....................
CIeM...................
li
pressnre coeflkiem data for eaclt form of buildi:nc'; Sf, .the terrain and building
o
_ . . . ......,..,.. . . 1 ...........
e2
z:I
"'f:1
11
0.1
DIlNd........
should be calculated from:
(12)
If'r I ..",' I
l'a.W. -& - Faetar s.. for .tamdard method
u.&1 The etHdiw wind
Vc = V. S"
101 1/
11.3
o
sptMMl Ve
Nr~DI·
....
0.2
tclis-ittaedft wbld speed
Cl. 2.3.3 Table 4
:~ I H,IHab2 ~:r ~I 1~~~~:~~~l(CI. 1.7.3) and distance
2J1.
hei~
.,
.1 ~
dispIacremlInI
s&'h.e;
The site wind speed including these factors is converted into the effective wind speed the gust speed, based on
1 Prolireof
~
6H.,
L
h1~'n yTs~
~id~ 1£.,~
h~~r.
aOO.J
Sl
jhr\?
\(Iv
le 1.15 1.46
u-
. 1. .
1.07 1.36 1.51 1.11 1.77
1.85 1.90
1112 1.89
1.96 JUN, 2.12
IJJG
1;,$5
1,04
1.95
2.12
2.07
I from the sea. For overall forces and roof pressures, H. is the overall height; for wall pressures, H. is height to top of wall. Shelter from other buildings can be taken into account but note surrounding buildings etc. may change in the life of a structure.
NB The same effective wind speed applies over whole building height. If the effective wind speed at the top of a skyscraper is 55m1s, then the same wind speed applies to shop windows at 'ground level. Cl. 2.2.3.2 permits 'division into parts' for overall forces on tall buildings but not for local pressures.
8
Wind Pressure 2.1.2 Dynamio preanre
2.1.2.1 "the value of the clvnamic pressure Qs of theltllJldardmethocl is liven 'by q,
=O.613Ve2
where 4'1. is tile dynamic PresRI'e (ill Pa'J); Ve is tJ1e effective wiDd apeecl from 2.2.3 (in mll).
2.1.2.2 Values of clvnamic presJnUe q. for various values of Ve are RiftA in Tote 2.
.. Ve
10 20 30 40 50 60
Once the effective wind speed has been calculated (Cl. 2.2.3), the wind dynamic press1D"e can be calculated (Cl. 2.1.2). A problem in BS6399 is that not only are its clauses often out of logical order in this way but clauses are often on different pages from the tables they refer to - Cl. 2.1.2 is on a different page from Table 2.
T.llle 2 - Dye.mle preaure 9s(ia Pal +0
61 245 552 981 1530 2210
+1.0
+1.0
14
88
210 1030
297 628 1080
1590
1860
2t80
2360
589
+3..0
+4..
+&.0
+1.0
104
120
138
157
824
353 709
383
414
751
194 1300 1920 2670
668
~~ ~~"
1130 ( _lUKf) \ 1240 1790 1850 1120 2510 2590 2430
+7.0
177 447 839 1550
1990 2750
+8.8
199 481 88S 1410 2080 2830
+9.0
221 516 932 1470 2130 2920
9
OLd 'eod~
.51l)~
if} I (!lackJ,,,,~o~
~Bu.~"~..:
~\a~~
Different types & sizes ofelements and buildings are allowed for by 'Ca' on wind pressW'e. (Cl. 2.1.3.4 (p. 14), Fig. 4 (p. 16), Fig.
5 (p. 17). Exposure categories are defined in Cl. 1.7.2 (p. 9).)
~e-Se
G..WBS ,)V)A)J f\~e
J~£0ire ~t, 'vJloh
e) ~1't.. 101k1 on
Jut_.
mdMdHI. .
pr tIlneer
'(e-SS v
~ =='
.~d_
0.55
oa
10
\01I?o he> 12 d~'O '" ~.-=~~I~~:::
.....
_..............
..
S\M la ecIiIUIt~tIMMt .
1000
'to-t'
a.
,tD.ct'
Ill"
l'to-'" le Ill_ c
A
IB
S
B
> to,
t.
B
B
C
c
le
;>1iD 10 > toto 11
A A
~
B 8 B
B
A-
le
B
A
C B
>.tJlto!O
A.
>~nollo
A A
A
A
~
:(;2
>IMHCli80 ::0150
A /l' A
• 4
A A
C
=10 X
~·voIume of 8tDrey
~edintc)J:'OOJUwith·intemal doors
(IlaI>
ltte'-t..
wh . or.t
- &1.% When l!l8eloMd bui1cliJw is
....ta.....cfMIIt ..........to...
~
'to""
umU
3 tim pum thaJl . . . . . . .win....
Dl.gonII ClImel'llton .. m
14
..
100
.
.fch ... nota lust.dB_ times more ·--.bJe tb;Qtth.~dOOl'S et:lllt
10 X ~intemal volume of room
IB
This appears simple but in practice it means a . different wind pressure for every element of the building. This is pointless: the variations in member sizes and comtections would be uneconomic. It is essential to rationalise a values. Usually curve 'B' applies. NB Ca. applies to pressW'e, not wind speed and is usually 0.8-1.0, so small differences are unimportant. Ca also used for internal
B
~
B
B B
111. 111.
A A
•
pressure (Cl. 2.6.1.1, 2.6.1.2, pp. 53, 54).
18
B
lA
A
B
Fig. 5 gives guidance on a values for overall forces on a wall or roof panels but no guidance on a values for supporting beams.
1'8
P1...... l-SI. . . . . , . - - c.ol....anl ~
~fUlU d /5 -tee- bI9~~~ ~o-z, It a '.fal..\le.. IS w,e. £~O'1'"IoQ.., Oel cWmelh/c)lOh7tl?Qt"
1.e.
~(!Mr~'?s_JW,~ ~I ~~~~~M~~~eJ ~ ~
fiaT _b~ ~;(f0rem C('/2l
10
•
I'tts
a.e a iVJJAA&.t't' ~ ~F"j~~
It is often said that a is
Size effects - a and Ca
Beam or coil...
..
r4C
the diagonal ofthe load tributary area for the beam (half ofthe area on each side).
Putl,•• or "iftber /filsts o
..
0'
.
trfbutsrya,rea
..
tribolary area
Loaded width
Loaded width
4
..
• I
•
For main rafters, beams or columns, it is reasonable to take a as the diagonal across the full panel area on both sides. For roofjoists, purlins or side rails it is reasonable to take a as the diagonal across two panels on each side of the member being designed.
Diagonal dimeMion 11
bean-. b
~
d~~
However influence lines show that the load on the beam actually comes from twice this area; for more flexible members with load sharing (e.g. joists, purlins) the relevant area is larger still.
PlJ~);h ~
6"2.J
d~~~ 11
Calculating total wind load on a building is complicated - see Cl. 2.1.3.6 (p. 15).
Ove ra 11 Wi nd Force s 2.1.3.8 Owrall loads Theoveral1loadPon a bUildirag is taken as the sum of the, loads onindividual surfaCN with allowances for non-simultaneous action between faces and for mildly dynamic response. The overall horizontal loads are given by P = O.85(tPfroat - l:Preu) (1 + <;>
(1)
where
tJ>froIlt is the horizontaloomponent of surface load summed over the windward-facing walls and roofs; t:Paar is the horizontal component of surface load summed over the leeward-facing walls and roofs; is the dynamic augmentation factor from 1.6.1; Cr T.hle5.
31D equation 7 (EPhat
r..> foreomribo:tiontofuwalls be taken as q.CpCoA. where"
Net preuure coemeienu for overaB load
ilID
DIH
sI
.2'4
~lf.5
1~
1.0 0.8
~4
1.2 1.2 1.1
is the net pressure coemd~1L 1 venin Tablets.. ~ 2
,p
0.8 0.8
-l-.-le,o/ Drn~
tableli· FrtdiomIl drqcoerftelents Dra9coeftident 0.01
'Q~02
I
r
~ppt~
~ ce~Q)'\ VI erred S .
Standard wall and roof pressure coefficients may be used (Cl. 2.4, pp. 30, 31 and Cl. 2.5 (pp. 36-53». Alternatively, Fig. Sa (p. 32) gives overall net pressures. NB the factor 0.85 in Cl. 2.1.3.6 applies to both. Then factors must be applied for dynamic effects and friction forces. Friction forces on walls are in Cl. 2.4.5, Fig. 6 (p. 35) but they only apply to parts of the side walls more than b downwind of the windward end, where b = the smaller of B or 2H. Friction forces on roofs are in Cl. 2.5.10.1 (p. 53) and apply to areas of roof more than b/2 downwind of the windward end.
0.04
12
0"
B r----.-.--
I·o.s.
1-'"
·t02~."
._--,
__
.
.
:t:
"--{' ....
:t:
• ..j,
lo.1~~----~--+--+~.,.L ~ ,
o.+-.....
L .._ ",".. --~
L.LL"!
1
.,._ .....1.
4 , I ..
10
t'
t!
,l:
cot pi ~
~
t ,
"', .. . .1IfWlll., IIdB
Ftpl'. S- !)YDamle . . . . .Jl'tGIoll laotOl' <;.
... .
~d''''''. ".......ei:fIIJCIc......
~ ~:.,.flhst."'anflBc:rhJ...
--.. ~. (uh1~K~l~~~ Hi'"201h'-)
~;=;?;~.
.• .....
If",. ", 2
o.
~MfJ
~
c.o~~Oh
l/p0
5
pressures on walls of building) Division into parts is permitted for
_~
l····..
l
'--"'-'-"'-J' i
.
""'--1.:".
:to I
I
""
tD~.. ~!~
I 1:: 2:1
~t :t:
11) . . . . . . .
""""11
!
1/~ °t bu 72dth%, Kb
t1e.f! of bU72J1~
:
"
-iDl il:t
:
ftpre tl-Divt.Hoa.,
1-+ ~oJ
..B
f)
,...f14 ..'. . . . . . .
~....,,..,.< fr.,mhtt·~·; .. (.~lMIt
a.,
precise calculations are Wlimportant. Usually the tota1 force is approx. 0.85 x 1.05 = approx. 0.9 x (sum of
force on tall buildings (Cl. 2.2.3.2 (p. 28), Fig. II (p. 29» but not for local wall pressures.
BUilding height, H Cm)
..#.':;t~:·~
9».
calculating total wiftd
,~---...l.,_, __,
100
The dynamic augmentation factor is from Ct. 1.6.1 (p. 9), Fig. 3 (p. 10), Table 1 However it is (p. usually 1.05 or less, so
! I
111
~ ...... tor Oftl'allloU.t
13
Overall Wind Forces
Usually total lateral force is approximately 0.85 x 1.05 = approx. 0.89 x (sum of pressures on walls of building).
Here is Table 5a with the coefficients multiplied in.
Ta},l. 6a -!'Jet pressure coefiieients for overall load , bIB
s 1 2 ~4
.l'.
't.
1-2' .,"~ ,~."", 12 ' 1,.1 , " ' "
14
-1Mli~ fYQbabil;~ 'to h~~ ar-~ ,I' Plan
"",D
J
~---~-~
1
,_J
Wlnd~ I
Wind pressures on walls are straightforward. and the figure and table are both on the same page for once (Cl. 2.4.1, p.
Plan
w.o , ........
:
Mv Bt'€J62e (BRE \A.)~VlcL'\ ~e116~ )
co!
I
W1nd~
,
30, Fig. 12, Table 5 p. 31)
ru
I
Note high pressure zone on inset top storeys (Cl. 2.4.4.2, Fig. 15, p. 34)..
This can be onerous for inset top floors on skyscrapers, although it is not clear that this was intentional.
III IA"'~ wind 0111,. ~utd wmd IJIl ~ f.",
D
~-"""-~~
Elevation of side face
,- -
D
.:oL~ll
1IAi
.
Wind
-
B
; C
..
-I ....9.2b '
-'' "' 1 AI
B
l~
J:
•
:t
Wmd •
c Butldlng with D S b
BUIlding with D > b
':1;....
b) K~ to.-m-e nIOIIfIIct!lU._ tlflsWilQlce
l'ipre 12 Key to wall pNUUft data
T.ble S- ExmlUll JJ.....ure cuemO~eDta c,.. for vwtioal wall•
............T ... _..... _-
M
-_.- ~)
Co,",,,,€/( oV'
.d~ ?os';T;onS
-................
3::>Vles
-
-
=t:r" •
DOL>b~ tl
rI'""\VI.--PN
Vi I'
'I
f~Y LAhS> ~ sid~
r'd its
1~~~,$ ~ G)cJJi~ P~)--'eJ'tS
Pc':>~-CS
£'F2J)J
~Tr&
0+ I-/I~~
15
"All• •
a-,.,..
Cl. 2.8.2 (pp. 56-59)
Freestanding Walls & Signboards
-.satrIIf... ..... "''''''415
----,1
4h
2h
lablell. Reduction hetors tor,frreestaDdlne
covers signboards and freestanding walls. Allowing for shelter in the calculations can malce a big difference.
lwaJl$·andparapets
0.3 h
c
B
D
"
Llb <3
RedudiClll factor
5 10 » 15
0.7 0.8 1.0
O~8
'\ COrner or free end
Tabl. 21- Net'preuuft coefficients Gp tortr.e-staDdiDg waDs aDd parapets
t
~h-,e;ablo fr~
SOJ'6
~\"
~-l ~ '=0.8
h~ W&>10
wan.
Soltlllty
Zoaea
IS
A
IWithout return comers
With return corners All U«lmay
I
~ClII'
8.4
Ih
2
_tuna CGnIIIlf'
2.1 1.2
\
J)
C
12.1
1.7
11.2
1.8
1.4
1.2
1.2
1.2 1.2
.--.ilL
"-:~2 StQrt~rd'
FOf"'gnboatds Hpatated tromtheWOUIrJl6J itf t· lftllelrMtght, Cp • tt tfiegap it ·nJ••, : lffiiVht~ot_;~ treat dl _,ll ]'heforcesh·ouJd be:apfJled::at the mfd·hefgM·Of,tI'Ie·boerd~
I~
tfu h~Slde(pof':-~;~h Iou f@1'I
dWrS
~h mn€J ~ (~~~~~;) -re..~ sheQTeal ~
~~y-~~~_~~~2.d1~~
6
Cl. 2.5.1, pp. 36-38)
'·;.&f~:Loadld,zOlf.
=
Roofs up to S degree pitch are considered as 'flat'.
=
iiJ;lgtength b B or b 2H, tidtever isthe smaller, ,fr~B:is:the crosswind . . . ."ofthe b\JitdihQand H 'height of wall, including -apet.
o
"",..."..,. ,...'"'."..."....",;-_•. """'~,.<~""" .._'''''''"',.,'"''''''''''''''''''''',.'''"....,-,~ ...",.......
~'__~'~._,
c
~;
o
S· .t~"
r
...,, A
,~~l!'IIt
' t
. 'if"'" WInd tII\tbltrool
Zone 'D' pressures for a 'flat' roofof 4.9 degrees pitch are much lower than those for a 5 degree 'monopitch' or 'duopitch'roof: as degree roofhas a suction of -0.7 when wind is at 90 degrees. yet a 4.9 degree 'flat' roofhas a pressure of +/-0.2.
,
A
~~4., ...
The B86399-2
Fi..... Ui- Key r.r Oat roof.
committee is happy that the figures are correct.
Table 8 - Enernal pres.urecoefBeienb Cpe for flat roofs of'buUdiDp Flat roof'type
I
Zoae
B
A
.-or-
c
eav••
.
pressure.
-La
This is all very dubious.
-1.0
-0.8 -0.55 eaves
. -1.8 -1.25
D
Therefore on low pitch roofs on low-rise sheds, reducing a roof pitch to slightly less than 5 degrees can greatly reduce design uplift
.
,-0.4
1-0.6
17
Cl. 2.5.2 pp. 39-41) Pressures for monopitch roofs
...
•
tl
.1
:1::'1
e",O"
--: ,.11./10 ' , Plan -lA i ~. Itwp.
~ 6=180"
Wlnd_
r
'
.. ~
[
c
]
I
~
.,
'
HlQbIlMM
lA
I
._,
C
D
~ '-I~j I L.- __ '~I2__
II t I
11./4t
'- - - - _.--..-.-c..--_.. . . . IJI.IIl
lit
coefficients for overall pressures, so the total load on the roof must be calculated by adding up all the pressures on
different areas.
. 4. :r~"CJ~
&2.2 Loaded mnes It19lilnglhs llt. '" smaller or L or 2H and bw '" sm&Iler of W or 2H
---,.------.-- 0;----:_.-'-
i
NB there are no
I
f-!oo
Is Yh
+~I
o'2..1
ecoto h-> ; e-od1 it&\-
't ,-~ 5 d~~
- I:a-l; tr1:; I:; i ;i~'j':~ is b1J t:; I ff1JOhO~lo~t-L12
-
\) (
Q..
ofloodWbop
e
YOo
1-+0.8
+0.8
1.1 1-0.1 +0,8 .
.... v·
1+0.8
1+0.8
+0.8
1+0.8
+0.45 .......-u...... ~ .... ~,~-,- ...............-.. <11-
18IJ-.:IiMIIW.. . - - . .. . . . . . . . . . . . . . . . . .. . . . . . , . . . . . .
P..."..
18
6
.
r-r~
6o\--rR.; IC1Cl""d
et-
d- \f"&d.S\
~
-=-r
Jr{(exeenlpr'ec;su'(e,s t.u~I'U)'$ iTi$rlI Sf be- Ye~\I~ ~~..:J ~_._-_.~-~---------_._------
For duopitch roofs, the total force must be worked out by adding up all the different
--------~
Pressures on Duopitch Roof 1.
no Plan
~f~
E
..
I
.
..
e
'------r--L-f..-.. I ..._._..,....
A
.
It 12',1,
I> J2 ~--
Considering all the pressure zones with a different a dimension
0 ~j
for every member,
,I
8 I
. ~t
\
!\--.
b
would result in dozem of different design pressures. It is essential to rationalise a values pressure and coefficients and use only a limited number
0
C
4'
I
12
. ..,... YL~ --f
TaWe.tl- ~ PI'UMIJlIt aoefBdellU e,. lordaophehMOfs o t ~
Rt,.. 8_0",
z-...... -r
JIhIlII.......
«>~ ~f
A
l-WO
-1...7 r-UJ -2••
-1.0 -1.0 '-:1.2
1-4,)·9 1-4,)·9 1-0.9 :-4,).8
-t.8
-1~
-0.•
+0.0
+0.0
+16'"
.-1•.1
[-0.8
+0.2
+0.9
+30"
-0.6 +O.S
i-(lo
+4~
-0.0
...,.
+0.8
-l.tr'
• :tf.~ J
~.'
!otV.1I
-to.6 1""',11
l+o.ll
,+o.s
-1.1
1-0.7 1'-'0-'1
.G i~~
A
-LO
.:
{
~%
rU
..
C
D
-LU
-0» 1-0.8 1-0-7
-V. A
-1.7
-o.~
~~
-o.i
-ZOO -2.2
-..• :-1.5
-1.0 -0.8 -0,7
-0.3 ~
-0."
40
-1.1
-0.'
-o.S
-1.~
:-0.9
-o.~
-l.e
-1,0
-O.IJ
1-0.4
+0.2
i-US
-0.9
-o.~
HU
1-«);9
-0.5
-0.5
-1.9
-1.1
1-0.6
1-0"5
-1.2
-1.2
-0.1
1-0.4 1-0.0
-<1;8
-0.7 -0.5
rob
+0.0
-0.9 -0.1
,:-0.4
i-La
-o.a r
p- dt'ffe,yemI
-0-4
-a6
+0.4
~.9
-0.6
-0.0 +0/7
1-0.4
-O~
-o.~
:-0:.
-0.3
11UI
-0.1' -0. .
I-U:i
-Cl! I-u.e
-.1.:4
1-1.2
-0:1
I-~UJ
!-eL!
-1.2
1-1.2
-1.16
. ,",.8 '
~,rdesign.
z..... ,·w
Al.: ........ .,' . ~"'''''''_.~,''''''_
t. . . . . . . .. . , . .. .t1Icr'....... tNMN• . , .. . . . . . .
r. .........m-...... ,.I
",.,.
+0.6 :-0.0
,
.B
C
r-o»
+6"
Wfnd . .
B -eL8
I-W
r-o'
13!
i
r
eT ~
_. __ WlndO.
•
II
l .'-r._..
i i
-..:::L:---...i.
Wid..
!
J .. .-.
A
I
_•
~!
C
•
.. soo, •
j
areas.
'-'
-"
v~~ues
I-CUt <'C'lc+D".
. . . . . . . .r. ................................_ _ IIip.:Bc-piala ..... +6.
_'""!Wt;r'z. . ._,.,..... . . . . . . . . .a.,. . . J.;f"l . . . . . . . . . . . . . . . . . . .
• DUVnP~h;\) rPn
ed .. .sp~~~L, srY~Ke$
~ 7;;2
~
0-(
c1~ml'"\~
1: ~ Ife?~ vJ~V"dJ 0QSc1
19
ct. 2.5.5, p. 47· multibay pitched roof.
rJlultibay Pitched Roofs
u.s M........,. roof.
..
~'"'* ClOIIftici...·. . dowu.W~o t ~qcldaopitehanalti.bay ..Fip:re 13.1U7 ~ _1IIbn. to1Ht tU. . . . . . . . ~%OI1i.
roan as debecl
lIotN.... ftldacea ...... ofaterM1JlNHurecoeftideata..,. he _ _ lrOBa TUle 90r Table 10, ..
~ ..fG1ItMt: It) J"oI'......._ nota... .mwaia llJure tIa}• ..,.JllQlifiwpr.....ClOf'ffWeDt ~ from. TaW. 9 ...-w._nplacM..OIl tlse·..-.4. . ...,.. ~.,.l»ye,.=-o.4. It) For•••aat•.) Iitch iuopit.dal'GC6. .ul'Olll cIowa clthe. .l'1dIalhou1.i.... ueaad_1Miac tavqW(Jaeptiw)iitdl-.le>. ...... vpwjIul rWpd . . . . . iIlHpre 231J).lOthat the1ocalcoeffieieats helBa&Ieac:!l rWce-eiwa."tkeDMlft _ _ A_Beavemnea far DePtift
1dIea.
pitch ......
.u.ro«......... ........,.eto....iriclaell·(poiiIiftpi_tIJIIJ.>. . t:NIIIW e)For..-l·pitch~IOOU..
wiIlll«.tM 1QIWUtl""mouLl\e awecl••
--pc8tiw
ja.fitut-.). . Jli.-.~• __ .JocalCl . . . . . E aaclFIictp pitch aacIes.
(aepti"
...............
BOTE ""'~m.iauafO)""",,""""'1ID_""""'"
)u .....
are aiWIl by1he les. --1r,r . . . . . . 10'.
6eplll:ll
lW ..... &om,=fr Dd' = UIlt. ill.nthe .... CMU,..~~iJt. . . . .""...,JyiBrthl. .lII!tiIIa
efT.tt..12 tetlJa. . . . . . 1IiItIe.-r TaW. 12faetol' for andti-ltay room
liillllllCtGla.
11.0
lOll ..... ~
ttp;t;i --
IbA.
".awiIul"'. iII&IlNa7a I
PftDiIft·1DII,)'
AD . . . . i
T. . _1fdged CIoWIMInd _....,.
Wtnd . .
~'''''" '-......,-."'.
~ ~ ,./ .,... ' / . '. \'. " . ·,;;;,~_··..'-.-'II \ , . . "I T...... o '
Wlhd,
blows
_net
,
"
"··,T. . . . 11IOUIJhId downWInd ,,/
Plgure ·23 cyCYoss
tt-,e '{oo~
f
~.
.1
...",_11I.,".11I"
CP3-V gave detailed recommendations for pressures on multibay pitched roofs. However BS6399·2 does not give pressures on multibay roofs explicitly - adjustment factors are applied to the figures for single bay roofs. This takes care to work out. BS6399 says nothing about multibay roofs with longitudinal wind (90°). Are internal roofslopes positive or negative? According to the BRE, outer slopes should be taken as positive pitch and internal valleys as negative pitch. This gives high suction over the whole area of a typical 5°-10° pitch multibay shed roof. If the mofis 'flat' (i.e. pitch slightly less than 5°), suction is much lower.
20
Table 13 (p. 50) gives pressures for freestanding canopy
Open-sided Canopies 'PlWIl UC'l.«
I..wt!l ....
f1'
all'
,all,
-1.3
1-1.4
2.2 .--0 -1.8 2.6 ( 2.1) +1.6 -2.1 1-2.,1 t 1.8) +1.8 -2.6 1-2.8( 1.6)
[+0.4
+0.8
~
-0,1 -1.4 (-1.2)
-1.1
~1.1
-1.4{:-1.~
-2.6
+0:5
de
+0.8
+1..2 -1.5 -1.4( 1.1) +1.4 -1.8 -1.5{-1.0) +1.7
M;!IIi. . . . C=O
-1.8
Minjmpm.( -1
Vjni>muDC - 1
all'
ID"
MjPrim-C=O · . C 1
de
ViJrimmnC =0
MinjmgmC=l 12fT
· ·
all'
(,=0 (=1
.ur
·
C=O MiaUnum.C =1 . ..,
-0.9 1.4(-1.1) +0.7 -1.1 -1.5 ~ 1.0)
C
+I:!
~1.8
1
Miai.aumC =0
INnTII"1
B
a
fH.B
-1.3
I)"
W
A
1+0·0
Hl,fS
..
Bo·
~.2
...... .........
-0.6 1.2
MiJrimumC = 0
15
0Mr.u
-.ftIideat.
roofs.
+2.4
'-2.0 -2.6 +S.7
-2."
2~9
+~t9
>+2.1
-1.2
-2.8
1..5 f-0.9) +1.0
-1.5(-0.1') +.2.0
-2.9
-2.9 -2.1 (-1.5)
+3.l
+2.3
-us
'-2.&
-3..2
-3.2
-1.4E 0.$ +1.3
-1.4(-0.8> +2.2
~2..5
~..!
....2 ..5(-1.4) +2.4
-1.8
-3.0
-1.4f-O~
-1.4(-0.8)
-3.8 -2.0
-2JS(-l.2)
.... _
.......
-3.6
.t ,. _ ".. ._~_.-
---r--'j" Cp > 0 downMIl'd8
~'1 i
1..
_~~10 i
,
•
""--1 !
....! 0'
..-, j , -~t+--,.··-·_·· '·r~--'
.
.
fk.~w_---J lii'gure.~ .' ·,,\11
goo((''''
~l .....................f=1..fim--il .. ~ . . . . . . . . . . .- -. . . . . . . . . . .
...............................W ......
21
"'.
I
~ E!CJ~~~eaea ~ c:ke.b ~8'>
~otw . .
~
qtrs o~1.tSJ1i) Cl. 2.6.1, 2.6.2: internal pressures are important for design but poorly covered by BS6399-2. Cl. 2.6.1 and Table 16.
-
- Wmd. DGrIDII1 to ~leface - W1.Ili 1IGI'JIlIl1 to i!DpezlDellhle face IFour wan. ~ JleII• •We; lOOliwlpeloleeWe
OCI~~~ publtcations recommend shed design as 'all sides equally
+0.2 -o~3
~::~I~~ claim
.3
2.... "'1ril1ft1111t tiJaea...
1.2 Where aJl eD£1oMd build. . la . .diYi.tled.iDtlO noma with iJItetMl doonwhidt aTe DOt at 1eut ~tlumtlle"""'~taeiDtez...lpre..... ma,y moms. Thia: ill n.wiDll OIl UlteIwJ walls. A 1IIIttlIoi1cR ~dte iJIlemalpnl ill
"'--I8J.lW ~ ...iJItetMl....' JlII.urecoefB c....Id· _.ei.tJJR-G..3 CIC' +0.2. w1dc:JM, ..' ......coetIicieIlt dIe ~11ae. .xi_Jlet---..ooet&ciIIftt C.
....,.....
JDIti.roo.aa.lMIiJ,mp,ia
the...... Mt.
i lwaDaahaald . . . . . . . 0.5•. '11ae releveat c1iatoJsa). . . . . . a_the iJItetMl...... 1MY'"' tlIkea as:
\tfndows _____/
l\n~ O~G)~
div
Also,aUbuildingshave doors and most have
• IhT~YhC3\ PV~SSLJVe., jJ
I •
Cp~
'\femT~ '_I ODeM\Y\a~ ~O~Vol\O~ I. ~-- cJ ') V b u\l., Lrt
Cpe
~);n~\'(o\r\ o+~ Two ~cT~
0\ 'vICJ\\S 1< Roof @ g,rn{)<;)bit~
~:s~~~vents.
~1~n;
...r-
RDamS . .on)e..ss
Inrevr\~L S\)~Oh shoulcL hot checK~~ t~€.J
However ifwaUs are impermeable, an internal pressure of -0.3 is impossible: it must be O. The B~6399-2 code co~mittee says the SCI J~ wrong: pressure IS -0.3/ +0.
r::".
Q\~e.. t)OlJ UC\)
r , ye.
0
t \-¥
an)..
\~hlJ
c.o\'\s·,de.Y
D00YS 1/ ••
be.., CDhsid~ve.£L when
Yoof fOY DpL,{t !!
the sides. Openings are
.~~=::refaces made. 'All sides
:t:=::~
Generally use coefficients -0.3/+0.2.
22
---f.--
--1-'"
".."....>'."1'• ••,.
·""'f"""r-···'.""''''''~>'--'''i_'
~'C_~~··~·~ . ~~:;~:'~~"" -:.~, ~:::::r:...-+-~.::r~'._~.. ..... _~~':T' ~=- .. ~:= ~=, ..... ............,.,.."l _
0.55
--~
T--"
--'-"'::: :::::,;"c;
__
•
,1.2 Wha",an'ac__ bo:ildinc is
-\'-,
~ Into_os witti iDtemaldoors
."."'==; ''',::
to
100
....
1000
OIIgor111J cstmenIlbn .. m
1fIit. . . . .
~
~1IIIfItlt
s..
"
~
:>s.' >lHo 10' >0 10 to 15 ::. 16,to!O >JOto30 :> "10 to 60 >DO
U."l.
I ... S
III
il;!
S1 ...1.
C C
A A
B
8 B B B
A A A
A
B
A
B
A
A A
B B
B
i\
A
A~
A
A
A
A
A
UlJocl.
C A
B
i\
A
...
•
a 3: 10 x
"intemal volome of room
Typical values of Ca:
houses: 0.78...().85;
low rise offICeS: 0.75
0.8;
high rise offices: 0.8
0.85;
single storey sheds: 0.7
0.75.
C
e
B B
B A
1r
A A
B 8
Flpr.4-St. . . . . . . . C.of. . . . . . . . . . . .
The. k'fiw-t ~ ih'fe \'h~l
'\fo1.um~
k\ \ " -ki" _.• ..,.--, '1I1'\e, lt~~~Y 'vr\t, 'YtleVh~~
pvessuve,
NOW6"f"ek', fn\eru"Y\ Q.\1 IN Ql\.15 ~ 0!l"Ol;\ be" bui'lt 1~etr' ld d\'\f~d~
Where intemal doors are usually open or are more permeable than external doors and windows. a may be based on storey volume rather than room volume. In practice the relevant volume is probably the volume enclosed between
internal ftre doors.
(1I:lI9
18... 1.. • lit C C
iJl B
ich .-0 not at 1Hs'.t:b!a times mON ,ob. than the aternal doors
....1a..... ~ ~ I I O _
C
JI
A A
B
For internal pressures the factor Ca is also applied. In theory. the a value is different for every room. In a large open shed a is large. giving a low Ca' However note that internal walls may be built later to divide it into smaller units.
It InTo 5m(;))\eY
Vh~ts .
Ca = 0.85 is sensible in most cases but Ca = 0.75 can be used for internal pressures in single storey sheds. 23
Dominant openings are covered in Cl. 2.6.2 p. 54. This has problems.
Tote 17- Iatemal........ ooefBeIeata GR for ltalldblp.... clcmD...Jlt GP. . . . .
......................
-.ot.._ .....
.lIdoof
3 1 ..1.3 W1Itn an estel'IIa1 opetrinc. nc:Il . . . door. wnhl ae dnmiDaat . . . . opea 1Nt .<:onaiclencl to De cla.aiatlMuItimate 'limitatatt. the ccm.f1it.iewit:h cIooropeaahola1cl),e ~ • • "'~.' .... (Affe.nd?.x .) ·door l.e.(t" opcath CJkWK U,fI ~%
........
wind... ~~e.sSl,)'(e")
l i D D ". t..
~1YJtJ?4 ':"~
at dim' • ..:A_.J th· fth· .1 __: . agon . . ensrona·.......:I'enus 011 e SlZe·Q C UUUJUliWt
I ..... di·
.lllc,teevanl
of.- _
.qperIi. relative to die itlfetnaI:vohunciand may be taken as the ,reater of: a
=diagonal dimension ofdominant opening; or
a = 0;2 x \flntemal volume
...
.
~
wberethe Internal volume IS the volume of the ....:.. ·tbe dommantopemng. . . storey or room COD:uumng'
T.lde 18-1JJterDa1 Dn:aure eoeIBcielde G- £or opea..eided IndldiIlp WWtlincti....
I
. Ill...
• v.-p1e \
tw
"l
6Ir'
0-........
I
Loatrw
nar~.l'Wtae
·. ...,
ITwe~
I
TJu.ee ...........
.........
Of7JV:>r:>ALOO,
-II&.
(~I?~€/z,A
wall penneabilities, so how do we know whether opening is 2x or 3x? Can only guess: 2x for small doors and 3x for big doors. Reference to 'serviceability limit state' in 2.6.1.3 is confused(serviceability cannot be OK unless ultimate is OK). Clause refers to Appendix D, which is illogical but gives sensible outcome - use 0.71 x normal design wind pressures. Internal pressure varies with a - larger opening gives smaller internal pressure but if a whole building side is open Table 18 applies, which gives higher pressures. Makes no sense. If dominant opening faces N or E, wind direction factor (Cl. 2.2.2.3) may reduce intemaI pressure. Cl. 2.2.3.3 (distance from sea) may also help.
1;,e, bf~ 1f.e ~(ho-n-r o~ ~ 0F':ed-> ~P.l srvno.OO.euc. ~~ f~~~
No reliable data about
24
1 "\
~emal
pressures 'fur,a,DtmgumeasuDng 5Om{L) )( 50m (B) x tSm (H) 08,8
". • 41L. Sitelftwe,coooUy
"'iDe: I.5mx lm
AFea
0.2 x O.7S'(Ca) .
2mx lm 2m:x 1.Sm 3mx'4m 6m,x:8m lJJmix.l;,6m ':' . :t'~'m,.·.'. ;,,;1:1:I< 4·~. 'V '4: J.:~,
FJdI1sRfe,opeti
UlPea •
OMlJ'ltiiell't
',-,
'\
O~ 7"x 0.98 x O.7)K @:.7Y O~9xO::98'x 0.7 x 0.71 O£9\xO~98x,:O.7 x··0.71
O~9 x· O!95x'O. 7 x'O. 71 O~9tX;019'w,:Q. 7 x Et71 "0'0"",;.,;.1\ ,,0>6 ,,,,4"\ , '~.'C" :A;~'·:U'.lQc4f·'~A,~;V~.
\
/.
'\
d:f"'~':C&'lt~41
7 .':0 7+1. A - -'c. ,··L \
"'1' ) "
QitG~~~~-:~;:V-•.~:~.~/
= O~'t5 =0.37 =0.44 =0.44 =,0.42 ......... . -"0.4:0'" =10' 3'8.' . ,.
.
.
';'~'.
"
---"
.
,;-.'
'.
=}g.,•.u A.'I!
~tobD)
These are the pressures for dominant openings calculated to BS6399-2. The calculated internal
pressure from a 2m x 1m opening is the same as a40m x ISm opening. From a common sense point of view the figures seem completely wrong.
(0.$3)
According to Professor N J Cook's book Designer's Guide to Wind Loading of Building Structures, Part 2 Static structures, p. 322, 'The variations in internal pressure caused by dominant openings are greater than for buildings with open sides ...'.
<8~f6)
seen, BS6399-2 gives
(0.51) (0'.6'2) (0.62)
(0.60) (D.57)
However as can be the opposite result.
This anomaly has been referred to Code committee but no response has been received. For the present, must use roles for dominant openings as they are but hope that it gets sorted out.
25
8S6399·2 DESIGN FOR WIND LOADS A N Seal
Worked Example No. 1 SINGLE STOREY SHED
I~
1
3
40
:'1
Roof purlins and siderails at 2m clc, Dado wall 2m high.
A single storey shed on level site in open country near Warrington. Main doors face north.
Altitude 40m, distance from sea (west) 30km
Basic wind speed Vb = 22.2m/s (Cl. 2.2.1, Fig. 6)
Altitude factor Sa 1.04 (Cl. 2.2.2.2.2) => site wind speed Vs = 1.04 x 22.2 23.1 m/s
=
=
~
-=
--
=
Dynamic Pressure Qtt (Cl. 2.2.3.3, Table 4, Cl. 2.1.2) Ha (side walls) = Bm, Sb = 1.63, Eff. wind speed Ve 1.63x23.1 = 37.7m/s, !JJ1 He (roof, front wall & rear wall) = 9m, Sb = 1.67, Ve 1.67x23.1 38.6m/s, ga
=
=
=
=0.B7kN/m
2
=0.91 kN/m
2
\ \
8S6399-2 DESIGN FOR WIND LOADS A N Beal Worked Example No. 1 SINGLE STOREY SHED
2
Local pressures (rationalised C. values) Member wall panels & cladding purlins, siderails·& columns rafters gable wall a <9 9-18 18-35 >35 0.90 0.85 Ca 1 0.95 Internal pressure coefficients Main doors closed: cp;Ca = +0.15/ -0.23 SmallI door open (dominant) Cp; = 0.75x(+0.66/-0.5/-0.8) (N/SIW)(Table 5). a = 2.2 Ca = 1
Cpi X Ca = 0.75x1x(+0.66/-0.5/-0.8) +0.5/-0.38/- 0.6
Large door open (dom.) Cp; = 0.9x(+0.66/-0.5/-0.8) (N/SIW) (Table 5). a = 5.8 Ca = 0.99
Cp; X Ca = 0.9xO.99x(+0.66/-0.5/-0.8) = +0.59/-0.45/-0.71
Large door open is critical for dominant opening .
For dominant opening, for wind from W or S apply coefficient Sp = 0.71.
For wind from north, directional coefficient for wind +1- 45 deg. from N: Sd = 0.87, so
pressure X 0.872 = xO.76 => wind pressure x 0.71xO.76 = xO.54.
Design pressures (roof)
bL = 30m, b w = 40m, transverse wind bJ10 = 3m, bJ2 = 15m, longitudinal wind bvJ10 4m, bvJ2 =.20m. 1. Roof Cladding (a) Main roof areas (areas C, 0, F & G, Fig. 20, Table 10) worst case cpe = -0.711+0.02 (longitudinal wind in valley, Zones C, D), doors closed: combined pressure = -(0.71+0.15)xO.91 = -0.78kN/m2 or +(0.02+0.23)xO.91 = +0.23k~/m2 dominant opening: combined pressure -(0.71+0.59)xO.54xO.91 = -0.64kN/m2 max. pressure +0.23kN/m2/ -0. 78kN/m2 (b) 4m zone adjacent to gable, 3m adjacent to eaves and ridge - worst case Zone A Cp; = 1.96. Combined pressure = -(1.96+0.15)xO.91 = -1.92kN/m2 2. Wall cladding
D/H = 3.3; b = 2H 18m (Table 5)
(a) general windward cpe = +0.66, wind parallel cpe = -0.8 doors closed: pressure = +(0.66+0.15)xO.91 = +0.74kN/m 2 or -(0.8+0.23)xO.91 = -0.94kN/m2 dominant opening pressure (west Wind) = +(0.66+0.71)x O.71xO.91kN/m 2 = +0.89kN/m 2 or (north Wind) -(0.8+0.59)x 0.54xO.91 = -0.68kN/m2 Critical pressure +0.89kN/m 2 /-0.94kN/m 2 (b) Within 0.2b = 3.6m of corner cpe = -1.3 doors closed pressure = -(1.3+0.15)xO.91 = -1.32kN/m2 dominant opening, N wind, pressure = -(1.3+0.59)xO.54xO.91 = 0.93kN/m2
=
=
=
=
Critical pressure = -1.32kN/m2
1
.
BS6399-2 DESIGN FOR WIND LOADS A N Beal Worked Example No. 1 SINGLE STOREY SHED
3
3. Purlins (6 degree pitch roof) Main roof areas (areas C, D, F & G, Fig. 20, Table 10) worst case cpe = -0.71/+0.02 (longitudinal wind in valley, Zone C) 3m strip adjacent to eaves Zone A -1.73/0, 3m strip adjacent to ridge: Zone E -0.94/0 Main areas design pressure (doors closed) = (-0.71xO.95 - 0.15)xO.91kN/m 2 = -0.75kN/m 2 or (+0.02xO.95 + 0.23)xO.91kN/m2 = +0.23kN/m2 Main areas (door open), design pressure =(-0.71xO.95 - 0.59) x 0.54xO.91kNfm 2 = - 0.62kN/m2 or(+0.02xO.95 + 0.71) x 0.71 x 0.91kNfm2 = +0.47kN/m2 4. Rafters Pressure coefficients
Longitudinal wind (average = - 0.745
Design pressure = Ca>
=0.82Cp; + 0.91 C.Cp; (doors closed), O.54x( 0.82Cp; + 0.91 C.Cp;) (with dominant opening) -0.58xO.82
~0.48kN/m')
~
!(.().
-0.91xO.82 75kN/m')
-0.58xO.54xO.82 ~.().26kN/m')
~
!(
-O.91xO.54xO.82 .().40kN/m')
~!
+0.15xO.91 (+0. 14kNfm2 )
+O.59xO.54xO.91 (+0.29kN/m
doors closed
2
)
with dominant opening
5. Columns and siderails Pressure as wall cladding with external pressure x Ca = 0.95 doors closed: pressure = +«O.95xO.66)+O.15)xO.91 = +0.71 kN/m 2 or -(O.95xO.8+0.23)xO.91 = -0.90kN/m2 dominant opening pressure (west wind) +«0.95xO.66)+0.71)x 0.71 xO.91 kN/m 2 +0.86kN/m2 or (north wind) -«0.95xO.8)+0.59)x 0.54xO.91 = -0.66kN/m2 Critical pressure +0.89kN/m 2 / -0.90kN/m2
=
=
8S6399·2 DESIGN FOR WIND LOADS A N Beal Worked Example No. 1 SINGLE STOREY SHED
4
6. Pressure on gable (for wind bracing design) As column design pressures but external pressure x Ca = 0.85 doors closed: pressure =+«0.85xO.66)+0.15)xO.91 =+0.65kN/rn2 or -(0.85xO.8+0.23)xO.91 -0.83kN/m2 dominant opening pressure (8 wind) =+«0.85xO.66)+0.45)x 0.71xO.91kN/m2 =+0.65kN/rn 2 or (north wind) -«0.85xO.8)+0.59)x 0.54xO.91 =-0.62kN/m2 Critical pressure +0.65kN/rn 21 -0.83kN/m2
=
-0.9xO.8xO.51
-..
+0.95xO.6
-..
-O.95xO.5
Pressure coefficients (Cl x e,ga) Table 1: Kb =2, H = 9rn => Fig. 3 er = 0.04. Cl. 2.1.3.6: for overall forces mUltiply pressures xO.85x(1 + er) xO.89 roof: qd = 0.91 kN/m2, 0.89xqd = 0.81 kN/m 2 side walls: qd 0.87kN/m2, 0.89xqd-= 0.77kN/m2
=
=
+0.01 ~N/m2
~
-0.69kN/m~0.3 kN/mio.29~/m2 -0.55kN~~.;4kN/m2
~""""'"--~
~
-0. OkN/m....'
!
-..
-..
-0.36kN/m2
+0.44kN/m2
7.0
Pressures for calculating overall forces
7.0
~I
BS6399·2 DESIGN FOR WIND LOADS A N Beal Worked Example No. 2 TOWER BLOCK
M
8
ME
14
... 8...
5
15
o
N
l{) (\')
/
l{)
Tower block in Liverpool.
Altitude = 20m, distance from sea = 1km (NW), 30km 0N& SW), >100km (N, E, 5)
Basic wind speed Vb = 22.3m/s (Cl. 2.2.1, Fig. 6)
Altitude factor Sa = 1.02 (Cl. 2.2.2.2.2) => site wind speed Vs = 1.02 x 22.2 = 22.6m/s
Dynamic Pressure Ch Cl. 2.2.3.3, Table 4, Cl. 2.1.2 (~S\C \JyfnQ)Yn\ C \Xl,.. . Ha (plant room) = 65m, Sb = 2.06, Ve = 2.06x22.6 = 48.7m/s, ~ = 1.45kN/m2
He (higher walls) = 60m, Sb = 2.06, V. = 2.06x22.6 = 48.7m/s, gll = 1.45kN/m2 He (lower walls) = 40m, Sb = 2.00, V. = 2.00x22.6 = 45.2m/s, g" = 1.25kN/m2 1. Overall loads
Direction factor Sb = 0.98 (5), 1.00 (W), 0.87 (N), 0.77 (E). a = 68m => Ca = 0.84 (Fig. 4)
Table 1: Kb = 1, H= 65m => ':i9' 3 Cr..= O.O~ ~ is wo)-'th D/H < 1, 0.67<8/0<1.5 => netpress. coeff. = 1.2 (Table 5a) 1"&12 bu ~ 2.J1·v-.~ ,
Cl. 2.1.3.6: for overall forces multiply pressures xO.85xCax(1+Cr) = xO.74 C,...J 2 2 plant room & higher walls: qd = 1.45kN/m , 0.74x1.2x1.45 = 1.29kN/m lower walls: qd = 1.25kN/m2 , 0.74x1.2x1.25 = 1.11 kN/m 2 2 ENV wind up to H = 30m (ref. Fig. 11) Sb = 1.96, Ve = 44.3m/s, qd = 1.2kN/m2 => 1.07kN/m
cL P ~tJ re
Tt"
& cl
~
"\
BS6399·2 DESIGN FOR WIND LOADS A N Beal Worked Example No. 2 TOWER BLOCK
6
2. Internal pressure coefficients No dominant openings: ep;Ca = +0.17/-0.25 => internal press. = +0.25/-0.33kN/m 2 3. Wall cladding (a) General Ca = 1 S wind: D/H <1 => Cpa = +0.85 windward/-0.6Ieeward, side walls -1.3 (Zone A), -0.8 (Zone B). Fig. 12: lower parts B = 45rn, Zone A extends 9m from each corner, upper parts B = 30m, Zone A extends 6m from corners Wwind: D/H <1 => Cpa = +0.85 windward/-0.6Ieeward, side walls Cpa = -1.3 (Zone A), -0.8 (Zone B). Fig. 12: B = 30m (Zone A extends 6m from corners)
max. +ive pressure = +(0.85+0.33}x1.45 = +1.71kN/m2
max. -ve pressure = -(O.8+0.25}x1.45= -1.52kN/m2 (Zone B) A~ '2..~:t b20\.\lS max. -ve pressure = -(1.3+0.25}x1.45= -2.25kN/m2 (Zone A) --~ -~~nh~ >< /h'l ~ DU NB these design pressures also apply at ground levell!!!! ~~ @. Note +ve pressure & Zone B pressures will be standard for design to all faces. In theory, e.. ,- S(; ( directional coefficients could be used to reduce Zone A pressures at NE corner and some d . IOWeA'" of others but this would introduce variations in details and risk of error on site, so better to (JK use same Zone A pressures at all relevant locations. L (b) local Zone E on side wall at base of upper section (ref. Fig. 15)
Cpa = -2.0, qd= 1.25kN/m2, max. -ve pressure = -(2.0+0.25)x1.25 = -2.81kN/m2 I)
(c) Check effect of dominant opening-at ground floor level (main door open). Internal pressure 0.707x 0.9xO.85x1.45kN/m2 =.+0.78kN/m 2 External pressure (Zone B) =
-O.707xO.8x1.45kN/m2 = -O.82kN/m2 • Total pressure = -1.6kN/m2 > -1.52kN/m2 , so critical.
Check Zone A. Total pressure = -0.707(1.3+ O.9xO.85)x1.45kN/m2 = 2.12kN/m2 < 2.25, not
bLe
--.lol!O>')~I~
=
critical. 4. Internal partitions
~1.s
b~ed
oh
~
Q
D lr\
e S\r.B O\,
~~.
ref. Cl. 2.6.1.2 cp; = 0.5, CII = 0.85, design pressure = O.85xO.5x1.45 = O.62kN/m2
BS6399-2 DESIGN FOR WIND LOADS A N Beal Worked Examples No. 3 Display Sign, No. 4 Parapet wall
7
Example 3 Display sign 1300
Site in Halifax, Yorkshire Altitude = 140m in town> 100km from sea Nearest buildings 20m away, Ho = 6m ~ Vb = 23m/s (Fig. 6) Y:h" C) Sa = 1.14 (Cl. 2.2.2.2.2) -, I l.sb ~5ScJ~J7 fOh.J)
H,=40 ~. ~;~£: ao V\ vw...
= 4'.0.: (1.2x6 20) a.8m mm. Ha - 0.4x4.0 - 1.6m ( . . .3.3) / 0 g
Sb = 1.07 (Table 4) t.i I\-. • I\ => Ve = 1.14x1.07x23 = 28.1m/s
=> fq = 0.48kN/m2 (Table 2)
Cl. 2.8.1
Zone A extends 0.3x4 = 1.2m from edges (Fig. 26)
Cp = 3.4 (Table 21)
I( = 0.6 (Table 21 a)
=> design pressure = 0.6x3.4xO.48 = 0.98kN/m2
H~
~.2x
~~eI H
(or~eX'~~ CDLJ~ ~
~ ~~oil2,'l
Example 4 Parapet wall
q N
Same location as Example 3
Parapet 30m long, with return corners.
Vb = 23m/s (Fig. 6) S. = 1.14 (Cl. 2.2.2.2.2) H. = 22.0 - (1.2x6 - 0.2x 20) = 18.8m (Cl. 1.7.3.3)
Sb = 1.72 (Table 4)
=> Ve = 1.14x1.72x23 = 45.1 m/s
= 1.25kN/m2 (Table 2)
=> Cl. 2.8.1
Uh> 15 => K = 1.0 (Table 21a)
Main part of parapet is Zone 0 (Fig. 26)
C p = 1.2 (Table 21)
=> design pressure = 1.2x1.25 = 1.50kN/m2
Zone C (4-8m from ends: C p = 1.4 (Table 21) => design pressure = 1.4x1.25 = 1.75kN/m2 Zone B (0.6-4m from ends): C p = 1.8 (Table 21) => design pressure = 1.8x1.25 = 2.25kN/m2 Zone A (0-0.6m from ends): Gp = 2.1 (Table 21) => design pressure = 2.1 x1.25 = 2.63kN/m2
a,
o ci N
/
fO~
