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

structure.

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

semi-rigid joints

 

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.