How to weaken the beam in the middle of the corridor and the ceiling can be referred to
How to weaken the beam in the middle of the corridor and the ceiling can be referred to 
How to weaken the beam in the middle of the corridor and the ceiling can be referred to How to weaken the beam in the middle of the corridor and the ceiling can be referred to How to weaken the beam in the middle of the corridor and the ceiling can be referred to How to weaken the beam in the middle of the corridor and the ceiling can be referred to 
