Four dial gauges were symmetrically arranged with starting gage length 20 mm in the middle of each steel plate (in Fig. 3(c)), for measuring displacement increment prior to local buckling.
Vertical and transverse strain gauges were also employed on the tubes for monitoring the strain and stress development of non-stiffened specimens and stiffened specimens.
To assureuniform compression, preliminary tests within the elastic range were conducted by carefully adjusting the position of the specimen, based on the data of the dial gauges and strain gauges.
The dial gauges and strain gauges were used for displacement and strain measurement, and for physical centering adjustment before actual loading.
A load increment of less than one tenth of the estimated peak resistance was employed in the loading scheme.
Each load interval was maintained for about 2 min.