This paper discusses the design and analysis of Air Traffic Control Tower planned for one of the major metropolitan city of India. An Air Traffic Control Tower comprises of 2 main parts – The Core (that goes from the ground level to the top level) and the Visual Control Cabin (the topmost levels above the Core) from where the Air Traffic is managed. The visual Control Cabin is designed to have frameless glazing using laminated chemically toughened heated glazing panels, specifically designed for the topography, height and size of the glazing to reduce the visual distortion during night time operation and to reduce the effect of condensation during humid conditions. The tower offers 360degree unobstructed visibility not only to the air space but also at the Aircraft movements at Apron level.
This paper explains the changes made in the initial design proposed by the Architect in order to control both static and dynamic effects of wind on Human Discomfort and distortion of images to Traffic Controllers, while doing their work at control room. The intent includes design for serviceable behaviour during frequent winds and limit the acceleration at the Visual Control Cabin Level to acceptable levels. For the design of ATC with 50 year return period, the intent is to resist wind loads with no excessive deflection of structure. The tower has been designed for Earthquake Zone-IV Seismic loads (IS 1893 – 2002 Part -1) with importance factor of 1.5 and for a basic wind pressure of 50m / second as per I.S. 875 Pt – III.
The Tower has been modelled using two different softwares commonly used all over the country to compare and verify the analysis results in terms of the Base Shear, Deflection, Bending Moments and Shear Forces in various members. This paper also discusses the results of dynamic analysis for wind conditions subjected to ATC as per I.S. Codes.
ATC tower has core structure with staircase as well as floors at every 3rd floor level. These are in R.C.C. Top four floors are with structural steel.
The shaft is elliptical in shape having maximum base dimension of 12 meter in one direction and 14 meter in other direction. At visual control room level the dimension becomes 28 and 30 meter thus there is cantilever of about 8 meters all around.
The original design concept comprised of smooth semi-circular cores all around. This design was revised based on the preliminary analysis to avoid the discomfort for persons at the top of the tower (Visual Control Room) due to vibrations on a Windy day. The structure was modified such that the wind path is broken and the deflection at the top is reduced. Stiffeners were added all around the core with varying length.
RCC structure with typical core upto height of 86m above which is structural Steel upto 105.6m
Basic wind pressure of 50m / second as per I.S. 875 Pt – III.
Importance Factor 1.5
Earthquake Zone III, Z = 0.16
Time Period of the structure calculated as per IS 1893: 7.6.2 = 0.09h/vd
Time Period of Structure in X direction: 2.86 sec
Time Period of Structure in Y direction: 2.32 sec
SoIl type 1 (hard)
Response Reduction Factor 4
Modal Combination Method: CQC
Analysis has been carried out using Two Softwares to verify and compare the results in terms of Base Shear, Deflections, bending Moments and Shear Forces.
A brief summary of the Analysis results from Software 1 is given below:
The in plane horizontal direction is X Axis and in plane vertical direction is Y axis.
1. Base Shear in X direction EQx : 2475 kN
2. Base Shear in Y direction EQy : 2840 kN
3. Base Shear Wind X : 15972 kN
4. Base Shear Wind Y : 14840 kN
5. Deflection at Top due to WIND in X direction : 130mm
6. Deflection at Top due to WIND in Y direction : 200mm
7. Story Drift due to EQX 0.0005475 ( Well within the limit of 0.003)
8. Story Drift due to EQY : 0.00146 (Well within the limit of 0.003)
9. Modal participation achieved greater than 90% in first 30 modes.
10. Torsion is under control
The analysis results from both the Softwares are studied and the output results are reasonably matching. The analysis results show that the Torsion, Inter-storey Drift, Deflection at top are within allowable limits.