The purpose of this report is to explore the effects of a proprietary socket connection on the behaviour of steel circular hollow sections. These sections, used as part of a screw pile foundation system for residential houses, consisted of 76.2x3.6 galvanized, cold-formed CHS joints, with a simple socket connection pressed into the steel tubes.
The research focused on testing these sections under various loading situations, comparing the strength of the joints both as part of a column system and independently.
Test results showed a dramatic reduction in axial capacity of jointed sections when compared to the same tests on standard tubes. Further testing on the moment capacity and axial crushing of jointed sections showed that the joint is of equivalent strength to the rest of the tube section. From this it followed that the joint had a negative effect on the axial capacity of columns, although failure was not due to failure within the joint itself.
Following this hypothesis, a series of analyses were undertaken on the test data, plotting the results of Southwell plots for each section and comparing the findings. The Perry-Robinson formula was then fitted to test results to estimate the degree of initial deflection.
Results from testing and analysis showed that jointed columns had a much larger initial deflection than standard tubes and that this was the most likely cause of a reduced failure load in jointed specimens.
Comparisons to basic design calculations presented in AS4100 showed that the capacity of jointed columns is not adequate and that a more stringent or conservative design is required for jointed columns.