the hollow core of the vertical support member 4101 please be noted that other shapes of inner structure may also be applied as mentioned in previous examples there are several horizontal support members forming a surrounding top frames in some design the horizontal support members may have an external elliptical cross section shape in other design the horizontal support members may have a circular elliptical cross section shape a number of t shaped connectors as illustrated above may be used for coupling the horizontal support members and the vertical support members together besides the surrounding top frame may have a ladder positioning structure to mount a ladder for users to go inside the above pool from outside usually such pool may have a diameter larger than 2 meters and a ladder is usually necessary to help people to get in and out of the pool with a positioning structure like a hook a block or other detachable connecting structure a ladder may be more reliable and stable preventing unnecessary accident besides one of the end parts of the vertical support member may have a different peripheral shape from the middle part of the vertical support member for connecting to the surrounding top frame in other words the vertical support member may be adjusted to have a more narrow or wider width or have a corresponding shape to be clicked or.