The dynamic behavior of high rise structures like towers is more sensitive to the effects of wind than those of an earthquake. Vibration caused by wind is an important factor in structural design and serviceability. Therefore, wind load must be taken into account when determining structural plan and design of high rise structures. In this study, a comparison of wind loads in a tower structure was made utilizing different design standards from various countries. Moreover a comparative study between design codes and wind tunnel tests were made for the 120m high Busan Tower at Yongdusan Park in Busan, Korea.
To conduct the comparative analysis, wind load criteria from KBC-2009 in Korea, ASCE7-10 in USA, EUROCODE-2010 in European Union and AIJ-2004 in Japan were chosen. The definition and application of wind load related coefficients utilized by different codes was investigated, and a comparison of wind loads of the same tower structure extracted by different coefficients was made. Each code criteria are set to adapt to their country or region concerns, which leads to differences in form and methods.
In order to investigate the wind load acting on Busan Tower, a field measurement of acceleration at top of the tower had been performed. The natural frequencies and damping ratio for lowest three modes were extracted from the measured signal by applying the FDD(Frequency Domain Decomposition) Method. The aerodynamic forces acting on the rigid tower model were measured at wind tunnel test, and then the displacements due to wind loads were measured from the aeroelastic tower model which was tuned to the measured natural frequencies and damping of actual tower.
The base shear forces, overturning moments and dynamic displacements of the tower were compared at the basic wind speed of 40m/s. The KBC-2009 showed the highest design wind speed at reference height among four design codes because of its importance factor. Consequently the KBC-2009 provided 1.45 times larger base moment compared with ASCE7-10 and 1.23 times larger than EUROCODE-2010 and AIJ-2004. Maximum displacement at top of the tower evaluated from the KBC-2009 also revealed 1.66 times larger than that of ASCE7 and 1.3 times larger than EUROCODE and AU. Among the four design codes, the KBC provided conservative results on evaluation of wind loads.
When we compared the results evaluated from the design codes and measured from wind tunnel test, the ratio between code and experiment ranged around 0.84~ 1.01 in base shear forces and 1.23~1.49 in overturning moment. However the ratio between code and experiment were relatively low and ranged around 1.04~1.17 in displacement. These differences between design codes and experiment in evaluation of wind forces need to improve the design codes.