CHUNG-CHE CHOUChen, Guan-WeiGuan-WeiChen2026-03-122026-03-122021https://www.scopus.com/record/display.uri?eid=2-s2.0-105027865157&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/736238This paper presents testing and backbone curve development of steel high-strength, built-up hollow box columns (HBCs) under combined axial load and cyclic lateral load. Recent studies showed that the seismic performance of steel box columns is strongly influenced by the member compactness, the amount of axial load, and the material yield strength, not concrete infill. Moreover, the width-to-thickness (b/t) limit of a highly ductile box column per AISC 341 (2016) is much stringent compared to AIJ (2010) or Taiwan Code (2010). Both the ASCE 41 (2014) and NIST (2017) may also significantly under-estimate the cyclic lateral strength of steel box columns under high axial loads. Therefore, six full-scale, built-up hollow box column specimens, made of high-strength SM 570M steel with the actual yield strength between 460 and 530 MPa, were planned for the experimental program. Three parameters that affect the seismic performance of HBCs were investigated, which includes the b/t ratio of the section, the magnitude of axial load, and the lateral loading history (i.e., symmetric versus near-fault cyclic displacement histories). The column specimens, which were 290-400 mm in width and 4000 mm in height, were tested with both ends fixed, constant axial loads between 2591 to 7935 kN, and cyclic lateral drifts. The HBC specimens that satisfied the b/t requirement of a highly ductile member, as per AISC 341 (2016), under a high axial load (40%Py) performed satisfactorily at 4% lateral drift and experienced flange and web fractures at 5% lateral drift. However, the HBC specimens that satisfied the most compactness requirement per AIJ (2010) or Taiwan Code (2010), not AISC 341 (2016), did not perform well at 4% drift, losing the axial load carrying capacity due to significant column local buckling and column shortening. Therefore, a less stringent b/t requirement leads to poor seismic performance of HBCs under a medium-to-high axial load at 4% drift. The gathered test data, supported by test data of this work, was analyzed by using multiple regression analysis. Empirical relations were derived between the maximum column moment, column plastic rotation and post-yield hardening parameters. The proposed formulation reasonably predicts the first-cycle envelope curves of steel box columns under combined axial load and lateral load, and provides significant improvement of the current ASCE 41 (2014) and NIST (2017) models for steel built-up hollow box columns.falseBackbone Curve DevelopmentBuilt-Up Hollow Box ColumnCyclic TestingFractureLocal Bucklingconference paper2-s2.0-105027865157