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ICCBT 2008 - F - (21) pp221-234
ICCBT2008
Development of Terrain Height Multiplier for Seberang Jaya,
Suburban Area
N. M. Husain*, Universiti Sains Malaysia,MALAYSIA
S. S. Zaini, Universiti Sains Malaysia,MALAYSIAT.A. Majid, Universiti Sains Malaysia,MALAYSIA
ABSTRACT
It is important to understand the behavior of wind acting towards structures in a particular
area to avoid wind characteristics that may contribute to catastrophic results to the
infrastructure. Hence, Malaysia has developed its own standard of practice in wind loading
which is fully adapted to the Australian Standard 1170.2 (AS 1170.2) and it is known as MS
1553:2002 Code of Practice on Wind Loading for Building Structure. A number of studies
have been carried out with the objectives of finding our own Malaysian values of parametersand modification factors that is needed in deriving the wind pressure upon structures. In this
study, terrain height multiplier, Mz,catfor terrain Type 3: Suburban area is to be defined. The
Seberang Jaya Telecommunication Tower is chosen to be the study area representing terrain
Type 3: Suburban area. A five year period of data are recorded at three different levels by
using the Ultrasonic Wind Sensor (USW). Power law equation has been used in deriving the
Mz,cat for terrain category 3. From the results obtained, the proposed results are much lower
than the current values in MS 1553:2002. It varies from 22% up to 28% difference in value.
This is due to the fact that different location may contribute to different wind speeds and other
wind characteristics. A reasonable good agreement and a consistent result can be noted from
the comparison of the proposed value to the other international codes and standards. The
current value of Mz,cat for MS 1553:2002 is similar to those in AS 1170.2. BS 6399 on theother hand has the highest value of Mz,cat. This is probably due to its high basic wind speed
collected in the area studied.
Keywords: Terrain Height Multiplier, Suburban Area,, MS1553, 2002.
*Correspondence Author: Ms. Nadiah Md Husain, Universiti Sains, Malaysia. Tel: +60122546955, Fax:
+6045996282. E-mail: [email protected]
http://www.uniten.edu.my/newhome/content_list.asp?contentid=4017 -
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1. INTRODUCTION
The development of modern materials and construction techniques has resulted in the
emergence of a new generation of structures that are often, to a degree unknown in the past,
remarkably flexible, low in damping, and light inweight. Such structures generally exhibit anincreased susceptibility to the action of wind [1]. Wind engineering is the discipline that has
evolved, primarily during the last few decades, from efforts aimed at developing such tools. It
is the task of the engineer to ensure that the performance of structures subjected to the action
of wind will be adequate during their anticipated lifespan from the standpoint of both
structural safety and serviceability. To achieve this end, the designer needs information
regarding the wind environment, the relation between the environment and the forces induced
on the structure and the behaviour of the structure under the action of these forces.
Due to the increasing demand of high rise building and other factor of safety to structures,
Malaysia has developed its own standard of practice in wind loading. It is fully adapted to the
Australian Standard 1170.2 (AS 1170.2) and it is known as MS 1553:2002 Code of Practise onWind Loading for Building Structure (MS 1553:2002). The development of this standard was
carried out by the Construction Industry Development Board Malaysia (CIDB) which is the
Standards-Writing Organisation (SWO) appointed by SIRIM Berhad to develop standards for
the construction industry [2].
The adaptation from AS 1170.2 is due to the similarity of wind climate between Malaysia and
Australia [3]. Unfortunately, all the parameters that have been adapted are not precisely
accurate due to different location that may contribute to different wind pressure.This practice
may lead to an uneconomic design. This is due to the fact that different countries may use
different approach to withstand building structure from their respective high wind speed.
Malaysia on the other hand may not have the same wind speed as the other countries, thus by
deriving our own modification factor may reduce the possibility of over designed structures.
In order to validate these parameters in MS 1553:2002, wind data collection must be based on
their exact location. This is due to the fact that different location may give different wind
characteristic. In 2002 under research grant of wind profile study, three ultrasonic wind
sensors were installed in Seberang Jaya Telecommunication Tower [4].The tower has three
levels of ultrasonic wind sensor to measure wind speed at 45.72 m, 75.28 m and 97.23 m.
Therefore vertical wind speed profile can be produced. Thus, it enables the objective of this
study to be achieved.
In this paper, the main focus will be on the production of terrain height multiplier, Mz,cat Type3: Suburban area. According to the previous researcher, terrain height multiplier, M z,cat is
defined as, the multiplier to obtain wind speed according to variation of height z in different
type of terrain category [4]. Seberang Jaya Telecommunication Tower has been chosen for
data collection in this study as it represents the closest location with wind characteristic of
terrain Type 3: Suburban area. Thus, terrain height multiplier may be derived from wind
vertical profile that is obtained from the data collected.
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2. MATERIALS AND METHOD
Seberang Jaya
Telecommunication Tower
Wind Speed Record Using
Ultrasonic Wind Sensor
Butterworth Meteorological
Station
Daily Mean Win Speed at
10m
5 Years
Raw Data
2002-2004
Data Extraction
Using Computer
Programming i.e.
Fortran 90
Monthly Average
Wind Speed for 3
LevelsFit All 4 Values Into
Model Equation
Power Equation: y = axb
Least Square Method
Microsoft Developer
Excel
Curve Expert
Determine The
Value of a and b
Determine Mz,Cat using
mathematic
calculation
Rearrange eq. x = cyd
Which x = V/Vrefy = Z/ZrefThus, V = Vref[c ( Z/Zref) ]
d
Mz,Cat = [c ( Z/Zref) ]d
Curve Expert
Proposed Mz,Cat
Comparison
with MS
1553:2002
and other
international
Conclusion
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3. RESULTS AND DISCUSSION
As explained in the preceding chapter, wind speed data have been recorded at two different
places i.e. Butterworth Meteorological Station and Seberang Jaya Telecommunication Tower
in Pulau Pinang. In Butterworth Meteorological Station, data are recorded at 10 m heightwhile in Seberang Jaya Telecommunication Tower, data are recorded at three different levels
i.e. 45.72m, 75.28m and 97.23m. These data are recorded and labelled as shown in Table 1.
Table 1: Data Recorded
Location Level Height (m)
Butterworth Meteorological
Station Reference 10
Seberang Jaya
Telecommunication Tower A 45.72
Seberang Jaya
Telecommunication Tower B 75.28Seberang Jaya
Telecommunication Tower C 97.23
Data recorded are called raw data where all the informations of wind characteristic such as its
humidity, direction, pressure, temperature, and wind speed are collected. These raw data were
then extracted to obtain the wind speed for every 10 minutes per day.
Mean wind speed for each month of each year is then calculated. Table 2 shows the monthly
mean wind speed for three different levels during the five years study period. Table 3 shows
the overall mean wind speed at three different level for five years that is to be used in the next
steps in determining the terrain height multiplier, Mz,cat.
Table 2: Monthly Mean Wind Speed
Level A Level B Level C
2002 Jan Not available Not available Not availableFeb Not available Not available Not availableMac 2.2106 2.5766 2.7021
Apr 2.2754 2.5766 2.9490
May 2.1286 2.4392 2.7411June 2.3999 2.7984 3.1322
July 2.1531 1.8924 2.7744
Aug 2.0104 Not available 2.4146
Sept 2.3843 Not available 2.9814
Oct 2.2598 Not available 2.9014
Nov 2.3275 2.7792 Not available
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Cont : Table 2
Monthly Mean
Wind Speed
Level A
m/s
Level B
m/s
Level C
m/s
Dec 2.0845 2.4610 Not available
2003 Jan 2.6621 3.1420 Not available
Feb 2.4133 2.7990 Not available
Mac 2.1997 2.5285 Not available
April 2.0994 2.4804 Not available
May 2.2911 2.6590 1.3265
June 2.1017 2.4804 1.2114
July 2.4420 2.7770 2.8488
Aug 2.2677 2.6577 2.3239
Sept 2.2515 2.6331 2.8097
Oct 2.3362 2.7721 2.9962
Nov 2.0544 2.4218 2.5956
Dec 2.6413 3.1206 3.4019
2004 Jan 2.4469 2.8954 3.1702
Feb 2.3508 2.7703 2.9986
Mar 2.4231 2.8164 3.0072
April 2.0701 Not available 2.6429
May 2.3206 Not available 2.9572
June 2.4114 Not available 3.0273
July 2.3310 Not available 2.9804
Aug 2.2065 Not available 2.8030
Sept 2.2091Not available
2.7593Oct 2.1525 16.5595 Not available
Nov 2.1643 Not available Not available
Dec 2.5384 Not available Not available
2005 Jan 2.7219 Not available Not available
Feb 2.4987 Not available Not available
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Cont : Table 2
Monthly Mean
Wind Speed
Level A
m/s
Level B
m/s
Level C
m/s
Mar 2.4720 Not available Not available
April 2.1438 Not available Not available
May 2.1015 Not available Not available
June 2.3236 Not available 2.199
July 2.0731 9.7105 Not available
Aug 2.3781 Not available Not available
Sept 2.4860 Not available 2.6074
Oct 2.5278 Not available 3.5545
Nov 2.2736 Not available 2.5915
Dec 2.2862 Not available 2.45
2006 Jan 2.6727 Not available 0.3889
Feb 2.4010 Not available 1.7887
Mac 2.4375 Not available 7.8
April 2.1671 Not available Not available
May 2.2273 Not available 3.9365
June 2.2607 Not available Not available
July 2.1451 Not available 2.7858
Aug 2.3696 Not available 2.7337
Sept 2.1285 Not available 0.4
Oct 2.2319 Not available 1.1
Nov 1.9626 Not available 1.75
Dec 1.8333Not available Not available
Table 3: Mean Wind Speed for Five Years
Level Reference A B C
Mean Wind
Speed of 5
years
2.3 2.2921 3.5312 2.6578
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3.1Fit into Model equationHeight is dependent on the mean wind speed. Thus, height is chosen to be in the y-axis while
mean wind speed of five years is to be in the x-axis. The power law equation is given by y =
axb
. The value of a and b is obtained by first dividing the mean wind speed and height ofeach level with its reference value respectively i.e. xrefand yref. The conversion will give the
value of X and Y as shown in Table 4.4. Using the method described in Chapter Three, values
of X and Y in Table 4 are fitted into the power law equation. These values were obtained from
the least square method and the analysis was carried out by using the Curve Expert 1.3
software.
Table 4: Reference and Levels of Mean Wind Speeds and Heights
x, Mean Wind
Speed of 5 Years
= v (m/s)
y, Height = Z (m) X = x/xref Y = y/yref
2.3 (Ref. Level) 10 (Ref. Level) 1 1
2.2921 (Level A) 45.72 (Level A) 0.9966 4.572
3.5312 (Level B) 75.23 (Level B) 1.5353 7.523
2.6578 (Level C) 97.28 (Level C) 1.1564 9.728
3.2 Determining Terrain Height Multiplier, Mz,Cat
Figure 1: Curve Expert curve: to define a and b value
From the graph and analysis done by the Curve Expert (Figure 1), the values obtained
are as follows:
a = 2.8209
b = 8.5105
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The curve obtained is closely accurate and it is proven by the correlation coefficient of
the power equation graph i.e. 0.9092. These values were then substituted in the power law
equation and can be expressed in the following equation:
Y = 2.8209X8.5105
(1)
As explained earlier, Y is the height above ground while X is the mean wind speed. Rearrange
equation 1 into equation 2 below so thatX is the function of Y.
X = 0.8853Y0.1175 (2)
As shown in Table 4, X is equal to x/xrefor V/Vrefand Y is equal to y/yrefor Z/Zref. By
substituting X is equal to V/Vrefand Y is equal to Z/Zref into equation 2, it can be expressed in
the following
equation 3:
V/Vref= 0.8853 (Z/Zref)0.1175 (3)
Given that Vrefand Zref is respectively equal to 2.3 m/s and 10 m substituting these values into
equation 3 and with some arrangements, it can thus be expressed into equation 4:
V (z) = Vrefb (z/zref)
V (z) = (2.3) [0.8853 (Z/10) 0.1175 ] (4)
Equation 4 is in fact the vertical wind speed profile for Seberang Perai Region which
was initially classified as terrain Type 3: Suburban area.
As discussed, terrain height multiplier, Mz,cat can be derived using the power law as follows :
Terrain height multiplier =b (z/zref) (5)
Thus, by making comparison to equation 4 with equation 5, it can be concluded that terrain
height multiplier for Seberang Perai Region is defined in equation 6 below:
Terrain height multiplier = [0.8853(Z/10) 0.1175 ] (6)
3.3 Comparison with MS 1553:2002
Table 5 elucidates the proposed terrain height multiplier and its percentage difference with the
current value in MS 1553:2002. It is found that the proposed value is much lower compared to
the current value from MS 1553:2002. Figure 2 shows a clearer view on the pattern of
proposed terrain height multiplier obtained.
The negative percentage obtained is due to the different wind characteristics for both collected
data. This is due to the fact that all the parameters used in the Malaysian Standard are fully
adapted from the Australian Standard AS 1170.2. It was undoubtedly caused by the difference
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in basic wind speed for both situations i.e. Australian and Malaysian climates. Thus, it is
important to accumulate basic wind speed based on an exact location for the simple reason
that different location may give different wind characteristics. Hence, it is recommended for
our country to have our own parameters according to specific locations.
Table 5: Comparisons of Proposed Mz,Cat and MS 1553:2002 Mz,Cat
Height (m) Proposed Mz,Cat MS 1553:2002
Mz,Cat
Percentage
Difference
0 0.000 0.000 0
5 0.865 1.116 -22.49
10 0.938 1.236 -24.11
15 0.984 1.325 -25.74
20 1.018 1.399 -27.23
30 1.068 1.489 -28.27
40 1.104 1.548 -28.68
50 1.134 1.593 -28.8175 1.189 1.667 -28.67
100 1.230 1.727 -28.79
Height (m) vs Terrain Height Multiplier
0
20
40
60
80
100
120
0.000 0.500 1.000 1.500 2.000
Terrain Height Multiplier
H
eight(m)
Proposed
MS 1553
Figure 2: Comparisons of Proposed Mz,cat and MS 1553:2002 Mz,cat Mean Hourly
3.4 Comparisons with Other International Standard
This section is to distinguish the significance of the proposed value when compared with other
major international standard [5-8].
The power law has been used to determine wind speed profile for Seberang Perai region. It
can be computed as below:
V (z) = Vrefb (z/zref)
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Terrain height multiplier, Mz,cat on the other hand can be derived using the power law equation
as follows :
Terrain height multiplier = b (z/zref)
Table 6 provides the constant value of and b for major international codes in deriving wind
speed profiles and terrain height multiplier. Some modification has been done to the value of
and b for AS 1170.2 and Euro code which was originally are using logarithmic description.
Hence for comparison purposes, some mathematical calculations were carried out on both
standard using power law [9]. Table 7 provides terrain height multiplier for all the
international codes, proposed value and also value from the previous study done by [4].
Table 6: Wind Speed Profiles in Codes and Standards [5]
ASCE 7-98 AS 1170.2 NBCC 1996 AIJ 1996 EuroCode 1995
b b b b b
1/7 0.84 0.1 0.91 0.25 0.67 0.27 0.58 0.21 0.77
Table 7: Mean Hourly Terrain Height Multiplier, Mz,Cat
Each of the standards explained above has its own basic wind speed averaging time. As
explained earlier, different country may use different averaging time. It is crucial to
understand the role of basic wind speed for the purpose of comparisons. Thus it is significantto standardize these values to mean hourly by using Durst (1980) ratio (Table 8) as reported
by [10]. This is obviously meant to avoid inconsistency during comparisons. By using Durst
(1980) ratio (Table 8), the value of terrain height multiplier from all international standards is
to be changed to mean hourly. Table 7 shows the value of terrain height multiplier for each
code that has been changed to mean hourly. These values are then plotted as shown in the
Figure 3.
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Table 8: Ratio of Probable Wind Speed for Time to Mean Hourly (Durst, 1980)
t 1hr 10 min 1 min 30 sec 5sec
Ratio 1 1.06 1.24 1.33 1.47
Height (m) vs Terrain Height Multiplier, Mz,Cat
0
20
40
60
80
100
120
0.0000 0.5000 1.0000 1.5000 2.0000 2.5000
Terrain Height Multiplier, Mz,Cat
H
ei
ht
m
)
Ramli (2005)
Proposed
MS 1553
AS 1170.2
Eurocode
ASCE 7-98
NBCC -1996
AIJ- 1996
BS 6399
Figure 3: Comparison of Terrain Height Multiplier Profile with Other International Codes and
Standards
A reasonably good agreement among these profiles can be noted in Figure 3. It can be
seen that the proposed value of terrain height multiplier is in the same group with the AIJ-
1996, NBCC-1996, EuroCode-1995 and also values by [4]. It shows that the proposed value
has a similar pattern with these standards plotted. The proposed profile results are also in
consistent with the other international standards. Generally, a reasonable good agreement canbe observed at relatively low heights. The current value of Mz,cat for MS 1553:2002 is similar
to those in AS 1170.2. BS 6399 on the other hand has the highest value of Mz,cat. This is
probably due to its high basic wind speed collected in the area studied. Figure 3 proves that
every standard has its own terrain height multiplier profile. These profiles are all based on
local basic wind speeds. The higher wind speed collected at a particular location, the higher
value of terrain height modification factor will be obtained. Therefore, accumulation of wind
speed data at location of interest is crucial in order to obtain its own wind characteristic and its
own parameters.
3.5 Percentage Different of Proposed Values to other International Codes
Table 9 shows clearly the percentage different of the proposed values to other international
codes and standards. The negative value indicates that the proposed value is much lower than
the compared value while the positive value signifies that the proposed value is higher than
the compared value. Table 9 also shows that the proposed values are much lower than AS
1170.2 with maximum negative percentage of 31.57%. Although the current values of Mz,catin MS 1553:2002 are fully adapted from AS 1170.2 due to similarity of wind climate, the
Authors results proved that Malaysians local wind speeds of terrain category Type 3:
Suburban area are much lower compared to the Australians local wind speeds.
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Table 9: Percentage Different with other International Codes and Standards
Percentage Different %
Height
(m)
AS 1170.2 &
MS 1553:2002EuroCode ASCE 7-98 NBCC -1996 AIJ- 1996 BS 6399
0 0.00 0.00 0.00 0.00 0.00 0.005 -31.57 22.52 -23.65 53.64 69.6 -36.40
10 -30.77 14.95 -24.96 40 52.52 -40.63
15 -30.26 10.69 -25.74 32.79 43.44 -41.08
20 -29.89 7.839 -26.28 27.73 37.38 -40.47
30 -29.37 3.89 -26.99 21.09 29.14 -39.66
40 -29.05 1.099 -27.56 16.46 23.49 -40.32
50 -28.72 -0.877 -27.95 13.17 19.49 -41.85
75 -29.24 -4.57 -28.67 7.21 12.28 -40.85
100 -27.86 -7.09 -29.20 3.27 7.424 -42.79
Thus, it is crucial to accumulate wind speeds at precise location in the purpose of wind study.This is again to the fact that, different location may give different wind characteristics. Figure
4.6 shows a clearer view on the percentage different of the proposed value to the international
codes and standards.
4. CONCLUSION
This paper has stressed on the importance of accumulating the exact wind speed data in
deriving terrain height multiplier, Mz,cat at any location interest. This is due to the fact that
different location may have different characteristics and thus would give different values of
the modification factors. This paper has derived the terrain height multiplier, Mz,catbased on
five years of continuous wind speed data for Seberang Perai Region and can be concluded as
follows:
The proposed terrain height multiplier for Seberang Perai Region is defined as follows:
Terrain height multiplier =
[0.8853(Z/10)0.1175
]
The result obtained is closely accurate with the value of correlation coefficient of 0.9092.
The proposed terrain height multiplier, Mz,cat for Seberang Perai Region obtained are
relatively lower compared to the values in MS 1553:2002, which was originally obtained from
the Australian Standard AS 1170.2.
The percentage difference of the proposed terrain height multiplier with other international
codes and standards varies for each country. This is due to the fact that, different country may
have different wind speeds for the same terrain category.
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A reasonably good agreement among these profiles can be noted. It can be seen that the
proposed value of terrain height multiplier is in the same group with the AIJ-1996, NBCC-
1996, EuroCode-1995 and also values found in the previous study. It also showed that the
proposed value has a similar pattern with these standards plotted.
Acknowledgements
The authors would like to thanks the School of Civil Engineering, Universiti Sains Malaysia
(USM).
REFERENCES
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Aplication to Design, 3rd Edition,John Wiley and Sons.[2]. Malaysia Standard (2002), Code of Practice On Wind Loading For Building
Structure, MS 1553:2002Department of Standards Malaysia.
[3]. Sundaraj G. (2002), Wind Data Validation and Determination of Basic Wind
Speed for Building in Malaysia, A Master of Science thesis, Universiti Sains
Malaysia.
[4]. Ramli N.Irwan (2005), Determination and Validation of Terrain Height
Multiplier for Type 3: Suburban Area for MS 1553:2002
[5]. American Society of Civil Engineers (1998), Minimum Design Loads for building and
others structures.ASCE 7-98.
[6]. British Standard Institution. Loadings for building (1995), Code of practice for wind
loads, BS 6399 Part 2.[7]. Architectural Institute of Japan (1996), Recommendation for Loads on Buildings,
AIJ.
[8]. National Research Council of Canada (NRCC) (1996), Users Guide -
Structural Commentaries NBCC 1995 Part 4.
[9]. Zhou Y. and Kareem A. (2002), Definition of Wind Profile in ASCE 7,
Journal of Structural Engineering ASCE, Vol 128, No 8, pp, 1082 1086.
[10]. Davenport A.G (1995), How we can Simplify and Generalize Wind Loads?Journal of
Wind Engineering and Industrial Aerodynamics vol 54/55, pp 657-669