Structural Design of Tall NDCT Based on Boundary Layer Wind Tunnel Experimental Studies on Group of Towers

Abstract

Wind loading is extremely important in cooling tower design for several reasons. First of all, the amount of reinforcement, beyond a prescribed minimum level, is often controlled by the net difference between the tension due to wind loading and compression due to dead load. Second, the quasistatic velocity pressure on the shell wall is sensitive to the vertical variation of the wind and circumferential variation of the wind around the tower. There are also additional wind effects such as internal suction, dynamic amplification, and group configuration. The wind load variation along height and around circumference is specified in the codes like IS 11504 and BS 4485 with a restriction on height of the tower not greater than 120m. Nuclear Power Corporation of India Limited has proposed to set up NPP at Kakrapar, where sill diameter of NDCT is expected to be as large as 120 m and the height is expected of the order of 165m. It is proposed to setup two numbers of NDCT for each 700 MWe capacity. As the tower forms part of tower group and its height is greater than 120 m, aero-elastic model testing in an atmospheric boundary layer wind tunnel studies has been carried out. It is found from the experimental studies that there is change in the wind load distribution compared to given the codes. The paper discusses the structural analysis and design of tall NDCT based on the boundary layer wind tunnel experimental studies. The paper also discusses the difference in the outcome of structural analysis and design based on the aero-elastic model testing and approach given in BS 4485 part-IV.