JNIOSH

Abstract of SD-No.18

National Institute of Occupational Safety and Health, Japan

Strength of Wedge Joint Scaffolds

SD-No.18
Katsutoshi OHDO, Seiji TAKANASHI and Yasumichi HINO

: In recent years, various patterns of the wedge joint scaffolds based on the assembling of the wedge part of the horizontal member and the guide for the wedge of the vertical support member have been invented and used in many construction sites. However, there are very few data on this type of scaffolds and their performances are still not clearly known. Consequently, the standard of the general type of pipe scaffolds is applied for this wedge joint scaffolds in construction.
    Since the connection joint of the wedge scaffolds is different from the clamp used in the pipe scaffolds, the strength of the wedge joint scaffolds that are erected based on the standard of the pipe scaffolds is not known. Moreover, a problem on the wedge fitting at the connection joint of the wedge scaffolds that can possibly get loose during construction, which decreases the strength of the scaffolds, also needs to be clarified.
    The purpose of this document is to obtain the data that can be used as a standard for considering safety on using of the wedge joint scaffolds by experiments and analyses. The experiments on 4 patterns of the wedge joint scaffolds erected based on the standard of the pipe scaffolds were conducted and the effects of the loose-fitting wedge joint on the strength of the scaffolds were studied by using the Finite Element Method (FEM) analysis. The results were compared between the cases of the wedge joint scaffolds and the pipe scaffolds, in which the main conclusions can be listed as follows:
  1. Based on the results of the bending tests of the wedge joint, rotational rigidity of the wedge joint which affects the buckling strength of the scaffolds is lower than that of the clamp of the pipe scaffolds in some cases.
  2. Based on the same experiment condition of applying vertical loads on all vertical supports of the 6 story-3 bay scaffold, the strength of the wedge joint scaffolds is higher than that of the pipe scaffolds.
  3. From the results of the horizontal load tests to prevent failure from buckling of the wedge joint scaffolds, it is found that the cross bracing should be used in the same way as the pipe scaffolds.
  4. The FEM analysis on the buckling strength is found to be very effective and gives very close results to those obtained from the experiments.
  5. From the FEM analysis, depends on the location of the connection joint that the wedge fitting got loose, the buckling strength of the scaffolds can decrease a lot, even there is only one place of a loose-fitting wedge.
    Especially, if the location of the loose-fitting wedge of the horizontal member is near the location of ties, the buckling strength can considerably decrease.

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