: Recently, steel tubular scaffolding panels or frames have produced in multitude of design and sizes, and have been used for supporting concrete bridge mold. However, it is not clear completely that the load carrying capacity of those panels or frames when they are part or towers having more than three lifts or tiers. It has been widely believed that the rupture of those structures may be caused by the buckling phenomena of the leg members.
    To provide precise data to safety control in the use of those panels or frames, we have planned and carried out a series of load tests which are on single towers of 1, 2, 3 and 5 lifts in height, about several types of frames. The results of these tests have yielded the data which should be of interest to engineer and contractors who use scaffolding for supporting or shoring.
    The main results of this experimental study on the steel tubular scaffolding panels or frames may be summarized as follows :
  (1) It is interesting to note that in testing these structures the failures created the typical "S" bending, which has the nodes in the connecting joints of frames, that is a local buckling phenomena. And it is a important fact that the stiffening members affect the fractural buckling strength.
    The basic ultimate load each frame in the built structure will be experimentally expressed by
    P₀ = π² EI / h₀ ²
    I = 2 I₀ + n I₁·h₁ / h₀ ......... (1)
where, π is the circular constant, E is Young's modules of material, I₀ is moment of inertia for the section of a leg member, I₁ is moment of inertia for the section of a stiffening member, n is number of stiffening members, h₀ is height of a frame and h₁ is projecting length of stiffening members to the leg member.
  (2) Stiffness of cross brace may be required following condition in order to give availability of the frame strength,
    [ I_b / I ]·[ h₀ / l _b ] > 0.03 .......... (2)
where, I_b is moment of inertia for the section of a cross brace, l _b is buckling length of a cross brace, both h₀ and I are above mentioned.
  (3) Usually, these steel scaffolding frames are used with base-plates which are fitted at the top and the base of them, therefore, the ultimate strength of these structures which are one or two lifts in height may be larger than the strength calculated by Eq-1. This fact is caused by the restrictional effect of the top and the base, but this effect never appear when scaffolding frames are more than three lifts in height. When those structures are one or two lifts the ultimate load may be estimated as follow, the ultimate load for One lifts in height is 1.25 times as large as the basic ultimate load, similarly, the former load for two lifts in height is 1.1 times as large as the latter load.