uniten iccbt 08 development of terrain height multiplier for seberang jaya,

8/2/2019 UNITEN ICCBT 08 Development of Terrain Height Multiplier for Seberang Jaya,

1/13

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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Development of Terrain Height Multiplier for Seberang Jaya, Suburban Area

ICCBT 2008 - F - (21) pp221-234222

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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N. M. Husain et. al.

ICCBT 2008 - F - (21) pp221-234 223

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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ICCBT 2008 - F - (21) pp221-234224

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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ICCBT 2008 - F - (21) pp221-234 225

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


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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ICCBT 2008 - F - (21) pp221-234226

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



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




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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ICCBT 2008 - F - (21) pp221-234 227

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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ICCBT 2008 - F - (21) pp221-234228

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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ICCBT 2008 - F - (21) pp221-234 229

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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ICCBT 2008 - F - (21) pp221-234230

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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ICCBT 2008 - F - (21) pp221-234 231

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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ICCBT 2008 - F - (21) pp221-234232

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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ICCBT 2008 - F - (21) pp221-234 233

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

[1]. Simiu E. and Scanlan R.H. (1996), Wind Effect On Structures, Fundamental and

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

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