Journal of Wind Engineering and Industrial Aerodynamics, 29 (1988) 315-326
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
CONFERENCE ON WIND ENGINEERING
DISCUSSION OF SESSION
WIND LOADING AND FLOW FIELD
CSIRO Division of Building Research, PO Box 56, Hlghett,
T h i s S e s s i o n c o v e r e d a wide r a n g e o f p r o b l e m s o f l o w - and m e d i u m - r i s e buildings
w i n d . The p a p e r s
wind damage and p l a s t i c and smoke e x t r a c t i o n wind p r e s s u r e exception
in the structure,
and v e n t i l a t i o n
p r o b l e m s . However, a common t h r e a d was t h e u s e o f
b o t h s t e a d y and u n s t e a d y .
With t h e
o f t h e n u m e r i c a l c o m p u t a t i o n s o f Mathews and Meyer ( s u r e l y
method o f i n c r e a s i n g
importance in the future),
of s c a l e
included such disparate
Discussions and ' d i s t o r t e d '
these distributions Sessions,
of the e f f e c t s
m o d e l l i n g i n wind t u n n e l s
316 DISCUSSION ON PAPER BY P.J. S A A T H O F F A N D W.H. MELBOURNE
COMMENT BY H. TIELEMAN I have similar data to that shown in Figures turbulent boundary two experiments
layer. The only significant
is that I had a value of Lx/D of 7.0 instead of 2.6.
the pressure coefficients
do not change if Lx/D is changed between 2.6
and 7.0, the problem of integral-scale rise buildings
i, 2 and 3, obtained
for modelling of low-
REPLY BY AUTHORS It is possibJe that the effect of scale decreases, beyond 2. However the results shown by Nakamura, Conference
once values of Lx/D
Ohya and Ozono at this
show an effect of scale up to Lx/D equal to 10.
BY C. K R A M E R
have shown that when the leading edge is yawed relative
to the flow, the peak suction coefficient
and the mean
suction increases to very high values.
REPLY BY AUTHORS Our study was limited to the effects of turbulence of 2-dimensional investigate pressures.
models normal to the flow.
intensity and scale
In the future we intend to
the effect of flow angle on the generation
of negative peak
317 DISCUSSION ON PAPER BY R.N.
COMMENT BY A. LANEVILLE P a p e r s and d i s c u s s i o n the effect
of the scale
I n some t e s t s , in o t hers
on f l o w a b o u t b l u f f
b o d i e s was
a p p e a r s t o he s m a l l o r
seems t o be r e l a t i v e l y
REPLY BY R.N. MERONEY A general placing
c o n s e n s u s seems t o be e m e r g i n g t h a t
t o o l a r g e a model i n an o t h e r w i s e
due t o a d e c r e a s e
Whether t h i s
(~ 5~) o r l a r g e
intensity is also
i n low p e a k and mean p r e s s u r e s .
changes is not always clear. are small
not yet clear
is solely scale
whether the errors
CONNENT BY H. TIELENAN The r a t i o
of i n t e gral
L, t o m i c r o s c a l e ,
as (~-~)~. u
i n t h e wind t u n n e l .
wind t u n n e l
However, t h i s As a r e s u l t ,
i s 150 ( a t a g e o m e t r i c s c a l i n g
the atmosphere it
i s 25 000.
on t h e model r e l a t i v e
in t h e a t m o s p h e r i c
R e y n o l d s Number c a n n o t be
a typical ratio
I n t h e wind t u n n e l ,
o f t h e same o r d e r a s t h e l e n g t h s c a l e ,
L/1 i n t h e
~, a s s o c i a t e d and c o n s e q u e n t l y
c o u l d he
with separated alter
REPLY BY R.N. NERONEY I agree that the lack of turbulent scales below the dimensions of the
from m o d e l s i n w i n d t u n n e l s
to the confusion
on p e a k a n d mean p r e s s u r e s
may i n d e e d of t u r b u l e n t
on m o d e l s .
DISCUSSION ON PAPER BY E.H. /~ATHEWS AND J.P. NEYER
QUESTIONS BY S. ~JRAKAMI
Why was it regarded necessary to carry out an analysis of Reynolds Number dependency and how was it carried out wlth the k-s model?
REPLY BY AUTHORS:
We were not sure of the Reynolds Number at which the full scale measurements were done. We therefore studied the influence of Reynolds Number on the pressure distribution.
The turbulence properties and hence the turbulent viscosity change with wind speed.
BY A.P. ROBERTSON
I am a co-worker of the authors of the full-scale study referred to. The measurements were made with wind speeds between about 5 and 15 m/s (4 minutes mean at eaves height) over open country terrain.
The turbulence intensity of 0.14 in the numerical study is a little low. How sensitive are the numerical results to mean velocity profile and turbulence intensity?
of wind speed in the full-scale
s t u d y was t h e c h a n g e o f
geometry caused by the lifting of the film plastic cladding as the wind
REPLY BY AUTHORS The effect of mean wind speed profile is expected to be small, as also shown in the paper by Toy and Tahouri. If the turbulence intensity is increased, the effective viscosity will increase. This will decrease the effective Reynolds Number and decrease the pressure coefficients. This should improve the agreement between the predictions and the full scale mesurements.
The e f f e c t
of p r o f ile
d e f o r m a t i o n was n o t t a k e n
i n t o a c c o u n t in the
T h i s i s p r o b a b l y why o u r p r e d i c t i o n
point did not correspond with the full-scale
COMMENT BY R.J. KIND The k-s model has had considerable difficulty in predicting different types of flow without adjustment of the empirical ~constants'.
REPLY BY AUTHORS We have used the empirical constants suggested for atmospheric turbulence by Dr Yeung and Professor Kot of the University of Hong Kong.
COMMENT AND QUESTION BY D. SURRY We h a v e r e c e n t l y that
an t h e a u t h o r s pressures
made wind t u n n e l m e a s u r e m e n t s on s i m i l a r by t h e a u t h o r s .
Our e x p e r i m e n t a l
comment o r t h e p o s s i b i l i t i e s
d a t a show a much
o f R e y n o l d s Number t h a n do t h e a u t h o r ' s also
of p r e d i c t i n g
320 REPLY BY AUTHORS Transition Reynolds Number phenomena are difficult to simulate. However the measurements of Toy and Tahouri appear to confirm our low Reynolds Number predictions.
Computations for unsteady flows can be carried out
using the large eddy simulation method shown by Murakami et al in Session 3.
COMMENTS BY H. SOCKEL In real flows you will have a separation bubble with a re-attachment point downstream.
I think your boundary conditions do not allow this
effect to occur. At the freestream boundary you impose the condition that the flow is prohibited from crossing it. Figure 3 then indicates a very high blockage ratio of about 25~.
REPLY BY AUTHORS The flow separation from the greenhouse,
as well as the separation
bubble and re-attachment point were predicted.
It is not true that the
zero gradient boundary conditions at outflow will not allow these effects
The caption for Figure 3 states that only the grid in the vicinity of the greenhouse
is shown. The actual flow domain that was simulated was
60 metres by 64 metres in dimensions. domain is less than 5~.
The blockage ratio for this flow
321 DISCUSSION OF PAPER BY P.N. GEORGIOU,
B.J. VICKERY AND D. SURRYY
QESTION BY C. DYRBYE The response of elasto-plastlc structures to wind loading shows a strong resemblance to the response to seismic actions. Could the concept of ductility used in earthquake engineering be applied in wind engineering.
REPLY BY AUTHORS The role of ductility in wind (drag) response is somewhat different to that in earthquake action. The post-yield deformation due to wind accumulates
slowly due to the many small excursions which are all in the
due to the mean deformation.
there are large reversing excursions
In earthquake response
into the plastic range with large
COMMENT BY R. CIESIELSKI In the philosophy of limit states design, serviceability and strength limit states are considered separately.
In the former case,
structure should operate in the elastic range. limit states,
However for strength
the energy approach and ductility properties of the
material should be used, in my opinion.
REPLY BY AUTHORS Our a p p r o a c h c e r t a i n l y but the role earthquake
upon t h e a s s u m p t i o n t h a t
i s somewhat d i f f e r e n t
in the reply
ductility than for
t o C. D y r b y e .
DISCUSSION OF PAPER BY P.R. SPARKS,
J.A. MURDEN AND
QUESTION BY G. REARDON I am concerned about the reliance on static load values for hurricane anchors. Our research has shown that such straps are likely to fail by fatigue from the gustiness of a hurricane. quality hurricane anchors'
Could it be that the
that failed during Hurricane Elena tore as a
result of fatigue cracking?
REPLY BY AUTHORS Most of the failures of hurricane anchors in H u r r i c a n e
Elena appeared to
be due to insufficient nailing in situations where one would have expected the load to exceed the capacity of the anchor. American manufacturers do not provide fatigue data on their anchors. However they use a factor of safety of 3 which should provide sufficient fatigue capacity if the anchors are sized by engineering calculations.
COMMENT BY G.R. WALKER The paper needs qualifying by stating that it only applies to traditlonal-type construction lacking detailed structural engineering input, and only up to wind speeds for which damage observations were made. With engineered construction,
roof slope, exposure,
are automatically accounted for, and hence no longer variables, possible modes of failure are accounted for.
It is also important that
statements on probability of failure be consistent with known performance.
323 REPLY BY AUTHORS One of the purposes of the paper was to point out the dangers of using observed damage to estimate wind speeds, We attempted to cover in our paper all types of construction,
including those meeting the
requirements of a modern wind loading code.
The roofing systems In the US are covered with asphaltic or fiberglass shingles. At present these do not have to resist the design suctions on low-pitched or gable-ended roofs in hurricane-prone areas. The shape of the roof therefore has an important bearing on the performance of these structures even when engineered. With regard to probability of failure, the main purpose, different
in the paper, was to show the relative risk for
DISCUSSION OF PAPER BY Y. ~ATAKI t Y. IWASA~ Y. FUKAO AND A. OKADA
QUESTIONS BY R.J. KIND How was the large experimental air dome pressurised7 there substantial
leakage or ventilation flow rate as in an actual
structure? This can have a large effect on pneumatic damping.
REPLY BY AUTHORS The f i e l d However, larger
m o d e l was p r e s s u r i s e d the
o f an a c t u a l
i n t h e same way a s an a c t u a l
dome, b e c a u s e
of the field there
m o d e l was
w e r e many e x t r a
32,i DISCUSSION OF PAPER BY R.J. ROY AND J.D. HOLMES
COMMENT AND QUESTION BY D. SURRY The paper reminds us that maintaining similarity wherever possible is important.
I do not find it surprising that significant effects were
found for overall unsteady loads, but I would expect smaller effects for smaller tributary areas. Were any local pressure measurements made by the authors?
REPLY BY AUTHORS We agree that smaller effects should be observed for pressures and 3oads on smaller areas. However, we expect these would still be quite significant for bay or frame loads for which the ratio Luy/W is low.
Some further measurements of s c a l e
distortion on area-averaged panel
pressures and frame structural loads have been made at CSIRO. These have not yet been analysed or reported.
CONNENT AND QUESTION BY T. STATHOPOULOS I was very interested in this paper as it was a continuation of work presented by myself and Surry at the 6th International Conference. Concerning the errors in peak force coefficients
in Table 3, do these
include random variability inherent in peak values from single individual records?
REPLY BY AUTHORS All
was based and peak
on a s t a t i s t i c a l coefficients.
40 r u n s .
325 QUESTION BY A. ROBINS Detailed and careful studies of this type, giving some indication of the variability
loads on buildings,
findings affect procedures
are very useful.
for wind tunnel work?
REPLY BY AUTHORS We h o p e t h a t
and h a n d b o o k s f o r wind t u n n e l
testing will take account of the results in the paper when preparing their material. experimenters
it is necessary that individual wind tunnel consider the errors,
that may be caused when measuring wind loads with distorted model and turbulence
DISCUSSION OF PAPER BY TANAKA AND LEE
BY J. TEMPLIN
In Figure 2, a deviation of measured results from A.S.H.R.A.E. predictions
Is shown. Are the conditions
of expected and real conditions?
imply the A.S.H.R.A.E. ii)
How do you predict buildings
If so, this would
needs to be revised.
leakage areas in real
input to the analytical
REPLY BY AUTHORS i)
The A . S . H . R . A . E . real
d o e s n o t g i v e a good r e p r e s e n t a t i o n
e m p l o y s o n l y AH/Ao a s a p a r a m e t e r
This is shown by Figure 2 in the paper,
in which our
326 analysis gives good agreement with measurement, A.S.H.R.A.E. ii)
using AH/A o = 2.0, does not agree well.
We used a recommended value for typical opening per unit length of window frame to compute the leakage area.
QUESTIONS BY A. LANEVILLE How d o e s t h e m i x i n g p r o c e s s that
in the flow in the test
in the A.S.H.R.A.E.
b a s e d on a s i m i l i t u d e
Code? A r e t h e d i m e n s i o n s
REPLY BY AUTHORS The m i x i n g p r o c e s s
in the test
However t h e s i z e
o f t h e m o d e l was f o u n d n o t
on t h e r e s u l t s ,
of the analysis
showed t h a t
to have a
in the paper.
of the physical
o f t h e m o d e l on t h e
of the neutral
when t h e d i a m e t e r
t h a n 2 mm.