Comparison of measured and predicted response of manufactured circular steel tubular members under concentric and eccentric compressive and tensile loads

Tubular steel members are seeing increased usage both in building and bridge structures due to their efficient geometry and to aesthetic benefits that they offer over more traditional open, thin-walled cross sections. While the utilization of small (152 mm or less), stocky (wall thickness greater than 1.6 mm) diameter circular tubes has been increasing, experimental studies of these types of structural members have been rather limited, with most research focusing on large diameter, thin-walled tubes prevalent in offshore structures. Therefore, this manuscript discusses a series of tests of manufactured steel circular tubes under concentric and eccentric axial loads. These tests were performed to (1) examine their behavior, (2) develop instrumentation schemes and (3) ascertain the capacity of round tubular members used in cross-frames of a prototype curved steel bridge tested by the Federal Highway Administration as part of their Curved Steel Bridge Research Project. Testing procedures are described and results are presented and discussed. In addition, data produced from the tests was utilized to perform comparisons between experimental results and predicted capacities from AASHTO and AISC design specifications, which utilize approximations coupled with interaction concepts to quantify behavior. Results from the comparisons indicated that measured ultimate loads were an average of 1.3 times higher than values from factored AASHTO and AISC ultimate load predictions. However, when reduction factors were removed from the AASHTO or AISC prediction equations, actual ultimate loads were an average of 5% higher than predicted values, with certain predictions being slightly nonconservative. While the nonconservative predictions were attributed to member imperfections and slight specimen misalignment, they do demonstrate the sensitivity that can exist when attempting to predict stockier circular tube ultimate loads using approximate, design-based criteria.