TESTING ADVANCEMENT FROM ISOLATED TO SUBASSEMBLAGE STEEL COLUMNS UNDER AXIAL AND LATERAL LOADINGS
Journal
World Conference on Earthquake Engineering proceedings
Journal Volume
2024
ISSN
30065933
Date Issued
2024
Author(s)
Lai Y.C.
Xiong H.C.
Lin T.H.
Kumar A.
Uang C.M.
Mosqueda G.
Ozkula G.
El-Tawil S.
McCormick J.P.
Abstract
Recent studies on isolated steel columns under combined axial load and cyclic lateral drift showed that the column response is affected by the axial loading and boundary condition. To consider more realistic boundary conditions of first-story columns in a steel special moment frame, two-and-a-half story beam-column subassemblages were developed to investigate the column behavior under reversed cyclic loading. Each subassemblage had a two-and-a-half story single column with steel beams expanding to the midspan at two floor levels. An axial compression force corresponding to 20-40% of the yield force was applied to the column via a loading beam, hydraulic jacks, and post-tensioned bars. The subassemblages were statically tested by using one horizontal actuator at the column top end to simulate seismic loading and two vertical actuators at the beam ends to move with the column shortening from a feedback information at the column panel zone. Typical isolated fixed-fixed columns were tested to facilitate a direct comparison with the subassemblage testing. Steel I-shaped or built-up square box columns, which meet the requirements of AISC 341 (2016) for highly ductile or moderately ductile members, were tested in this proposed setup. Test results showed that the compactness requirement for highly ductile built-up box columns in AISC 341-16 (2016) is too stringent compared to the seismic response of highly ductile I-shaped columns in cyclic loading. The realistic boundary condition at the top end of first-story columns significantly alters the column plastic hinging, moment distribution, and out-of-plane deformation reported based on isolated column testing. Plastic hinging of the adjoining beams and column buckling near the base cause the inflection point of the first-story column to move in opposite directions. Re-distributing more percentage of the unbalanced moment from the second-floor beams to the bottom end of the second-story column may cause “unexpected” plastic hinging there. A closed-form solution that calculates the column stiffness for any boundary condition of steel columns was developed and verified from test results. Finite element analysis was conduct to verifiy the column response in the subassemblage frame and isolated column tests to determine a suitable compactness ratio range for the built-up box column.
Subjects
Boundary Condition
Cyclic test
Highly Ductile Member Requirement
Two-Story Subassemblage
Publisher
International Association for Earthquake Engineering
Type
conference paper