The composite effect of sealing concrete offers quake resistance
Internal force of bolt + internal force of supporting reinforcing bar
The number of bolts varies depending on bending moment
  (8 pcs ~ 16 pcs)
It prevents corrosion of bolt connection part
Welding is feasible and as strong as steel pipe pile

Qucik construction and easy quality management by using ready-
  made articles
Unnecessary to intall non slip device inside steel pipe pile
Unnecessary to install a seperate deck plate and to fill with sand
To concurrently lay spread foundation concrete and sealing