24-01-2013, 12:17 PM
WIND LOAD ASSESSMENT FOR STEEL LATTICE TOWER WITH DIFFERENT CODES
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ABSTRACT
The paper describes a comparison of wind load calculation on lattice tower with different
wind load standards in Asia pacific region. Steel lattice tower of height 80 m assume to locate
at rural area with open terrain. The design wind speed and other wind properties as per
different standards were calculated. The comparison of different coefficients and loads were
prescribed and comments on the difference are given.
INTRODUCTION
A practical outcome of this paper is a comparison of wind load on lattice tower from different
code of practice. Wind loading codes and standards of three different countries American
standard ASCE-7-05 , British standard BSI:CP3:chapter V:part2 and Indian standard IS 875
and IS 802(part1/sec1):1995 were used in comparison of wind load on lattice tower with
similar condition of topography , return period, basic wind speed on same lattice tower. In the
comparison reported in this paper design wind speed, chosen terrain, gust averaged over a
short time interval of about 3 seconds, and return period were all specified.
General consideration of steel lattice tower:
The lattice tower was 80 meter height with base dimension 10.790 x10.790 m and top
dimension 2.0 x2.0 m located in open terrain (figure 1) .The tower has 23 panels, 75.0 m
inclined and 5.0 m straight. The along wind base moment and shearing force were required to
be calculated for wind direction normal and diagonal.
Basic wind speed of 47 m/sec with open terrain with well scattered obstructions having
height generally 1.5 m to 10 m (this category includes normal country lines with very few
obstacles) and return period of design loads of 50 years was considered. The basic wind
speed is applicable at 10 m height above mean ground level and based on peak gust averaged
over a short time interval of about 3 seconds corresponding to mean height above ground
level in an open terrain
Wind load on lattice tower
Table 3 compares maximum loads on 80 m height tower under different panel at different
height with respect to various standards. Wind load is calculated with respect to Indian
standard, British standard and ASCE standard.
The wind load on tower at different panel height varies 3 percent to 23 percent between the
Indian and British standard. Similarly, 25 percent to 65 percent varies between Indian and
ASCE standard. Likewise, 71 percent to 86 percent varies between British and ASCE
standard for wind load.
CONCLUSIONS
It is noted that variation is more significant. The variation ranges from 29 percent to 48
percent for base shear and base moment calculation for wind loading cases. Because of
various factors consideration in different standard, wide variation in wind load, base shear
and base moment are found and well harmonization is required.