Design, analysis and application of Moving scaffold to the structural Maintenance
Liquid storage tanks are often used for industrial and social purposes. In case of an oil storage tank, it
is a huge structure and shows 100m diameter and 30m height thin steel cylinder. Also, in case of a gas
holder, it shows 30m diameter spherical steel shell. These are the important structure for industrial
and social infrastructures. These structures have been constructed on the ground and have been prone
to corrode. Therefore, the periodical maintenance is required to these structures. To maintain these
structures, the appropriate scaffolds are also required to do these works safely and completely.
However, in using the usual scaffold system, it will be a quite laborious work to cover such a huge
In this paper, to overcome these problems, the moving scaffold, which is composed of several
types of steel section and is movable on the tank surface, is proposed. The moving scaffold can be
carried easily and is assembled at the construction site. Also, it is easy to deconstruct after completion
of the maintenance.
These structures mainly consist of knee brace frames, pipes and
braces as well as spigots to connect them.
The moving scaffold is hanged on the
wind girder of a cylindrical tank and some touch rollers are placed between a cylindrical tank and the
scaffold to avoid the collision of them. The scaffold has eleven working stages. The height and the
width of this scaffold on the cylindrical tank of 26000mm are 20000mm and 1855mm, respectively.
To analyze the behavior of the scaffold, the dead load, the moving and the working loads as well as
the wind load are taken into account.
The scaffold has the driving system installed on the second wind girder from the
top of the storage tank and moves along an oil tank surface.
To represent the behaviour of the moving scaffold co
mposed of several pipes, 3D bar elements with
To support the maintenance work safely and efficiently, the moving scaffold is designed and is
numerically analyzed. From the numerical analyses under several loading conditions, following
conclusions are obtained
(1)In usual working conditions, all the elements show the elastic status and the stresses do not exceed
the allowable stress. Therefore, the safety of these structures is confirmed.
(2)Under the strong wind, the bottom of the moving
scaffold should be fixed because of keeping the
stability and reducing the internal stresses.
(3)In case of wind loading, several element stresse
s exceed their allowable stress. However, in this
analysis, the allowable stress relief is not considered and the element stresses do not exceed the
elastic limit. Therefore, it is possible to apply to all the loading conditions.
After analysing the safety of the structure, the scaffold system is assembled at the constructional site.
Then, the maintenance of the tank surface is actually performed safely and completely.