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AN INVESTIGATION INTO STABILITY OF TUBE AND COUPLER SCAFFOLDS SUBJECT TO SEISMIC LOADS
Title
AN INVESTIGATION INTO STABILITY OF TUBE AND COUPLER SCAFFOLDS SUBJECT TO SEISMIC LOADS
Creator
Najafabadi, Aram Zare
Date
2012-11-23, 2012-12
Description
Temporary structures are structures that are set up for applications in relatively short time periods, most notably category of which are...
Show moreTemporary structures are structures that are set up for applications in relatively short time periods, most notably category of which are scaffolds that are built in two types: supported and suspended. Tube and coupler scaffolding systems are supported types and are commonly used in nuclear industry’s applications. This study evaluates the behavior of this type of scaffolding system due to the effect of dead, live, i.e. weight of workers and equipment, and lateral earthquake loads applied on the structure. Consistent with OSHA dimensional requirements, six different configurations ranging from 1 to 3 stories and 1 to 2 bay scaffoldings have been selected for this study. Using a finite element analysis, the significance of all gravity loads, as well as potential seismic loads on the safety and stability of aforementioned scaffold types was studied. The seismic acceleration level at which the failure occurs was determined for four failure criteria. These criteria are: (1) the structural member yield failure; (2) the structural member buckling failure; (3) the system sliding failure; and (4) the system overturning (tip-over) failure. The analysis results show that the most critical failure mode for all configurations of tube and coupler scaffolds studied in this thesis occurred due to instability and as result of sliding. No overstress or buckling failure was observed to occur prior or concurrent to this failure. This finding reaffirms that this type of scaffolds has considerable sufficient capacity to resist their intended loads yet are vulnerable to instability because of sliding. With regards to the effect of number of bays and stories on the critical earthquake level, it was observed that as the number of scaffold stories increases, the critical earthquake level becomes smaller except for the case of the 1-bay scaffold for the 2- and xii 3-story configurations. Addition of an extra bay to a simple 1-bay scaffold configuration does not considerably improve the earthquake level at which the sliding failure occurs. With regards to time of failure, addition of stories to a scaffold configuration delays the failure occurrence in all cases except for the case of the 2-bay scaffold and addition of a bay does significantly delay the occurrence of failure for 1- and 2-story scaffolds, about 6 second for 1-story scaffolds, and 8 seconds for 2-story scaffolds. However, this improvement is negligible for 3-story scaffolds. In general, addition of a bay postpones the failure time. The evaluation of stress levels in all various scaffolding elements suggests that increasing the number of bays and/or stories does not generally affect the induced stresses in beams. In addition, the study shows that buckling and overturning (uplift) effects have very minimal effect on the failure of tube and coupler scaffolds.
M.S. in Civil Engineering, December 2012
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