In engineering rules, roof tanks are not advisable to install on top of building which height exceeded 75m. May I know why ? Thanks
I not sure what country. But there is such regulation.
If it's water in the tank at 75 m then the water pressure in a communicating pipe at the ground is 735 kPa (107 psi), which is within the typical range of 35 - 150 psi at the supply to most buildings. So, that's probably got nothing to do with it.
Maybe it has to do with preventing the presence of a large free surface at the top of a tall building swaying in the wind. If the natural frequency of the sloshing liquid synchs up with the natural frequency of the building, that would be pretty bad.
There are buildings that use this effect to their advantage to minimize swaying due to wind loads. I think it's the Taipei tower that uses a movable mass to do this.