Effect of boundary condition on the cyclic response of I‐shaped steel columns: Two‐story subassemblage versus isolated column tests

Exposed column base (ECB) connections are widely used in low‐ and mid‐rise steel moment‐resisting frames (MRFs). In this study, we investigated the impact of ECB damage on the overall seismic properties of low‐rise MRFs. A novel method was proposed to evaluate the post‐earthquake conditions of steel frame structures based on the coupling coefficient (CC). Using only the strain gauge data of the columns in the bottom storey, a method using a modified CC was adopted to classify the degree of damage by estimating the residual capacity of the MRF and predicting the future seismic response under specific intensity levels of hypothetical earthquakes, considering both the structural and non‐structural components. The limit values of CC were obtained by solving the deduced equations. Finite element analyses were conducted to validate the proposed method. The method was applied for calculating the test data of a four‐storey MRF tested at the E‐Defense shaking table facility. Four loading cases comprising six groups of monitored data in the X‐ and Y‐directions were used in this study. A comprehensive and systematic evaluation result was eventually obtained, and the accuracy of the method was validated.

Section: Expressions Of the Modified CCmentioning

confidence: 99%

“…y 0, j is the relative height of the inflection point of the column on the j th storey. The seismic performance of a column can also be influenced by its boundary conditions 20 . For instance, different stiffnesses of the beams and columns connected to this column result in different rotational stiffnesses of the beam‐to‐column joints.…”

Section: Conceptmentioning

confidence: 99%

A novel damage evaluation method for exposed column bases (ECBs) affecting the seismic properties of low‐rise steel moment‐resisting frames (MRF)

Shen,

Kurata

2023

“…However, in full-scale tests of steel building columns to collapse it has been seen that the seismic performance of steel columns is affected by the boundary conditions of the frame because of the flexibility of the beam-to-column connections intersecting the column. [2][3][4][5] Moreover, the internal force redistribution caused by the earlier yielding and local buckling evolution of beams due to the strong-column/weak-beam concept, further affects the boundary conditions at column ends. Such effects gradually become more severe at high inelastic levels of the structural response (near collapse) and can significantly alter loads and boundary conditions in columns.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, the location of the inflection point is constant throughout the loading. However, in full‐scale tests of steel building columns to collapse it has been seen that the seismic performance of steel columns is affected by the boundary conditions of the frame because of the flexibility of the beam‐to‐column connections intersecting the column 2–5 . Moreover, the internal force redistribution caused by the earlier yielding and local buckling evolution of beams due to the strong‐column/weak‐beam concept, further affects the boundary conditions at column ends.…”

Section: Introductionmentioning

confidence: 99%

Collapse hybrid simulation for testing steel building columns subject to boundary condition changes

Skalomenos,

Kurata

2024

This paper develops a hybrid simulation to experimentally evaluate the ultimate behavior of steel columns subject to boundary condition changes and bending moment redistribution due to the progressive seismic collapse of building structures. The proposed experimental method combines sub‐structuring test techniques and refined finite element (FE) analysis methods in a hybrid scheme. The inelastic behavior of steel moment‐resisting‐frames (MRF) is computationally simulated while ground‐floor columns are physically tested online with the FE frame analysis. Boundary conditions at the interface node between the column test and the frame analysis are reproduced with the aid of three actuators that impose axial loads and bending deformations to the column test. Two square tubular steel columns are tested as part of a five‐storey five‐bay steel MRF designed to employ two different heights of the ground floor (i.e., 4.6 and 5.1 m, respectively). The hybrid simulation revealed that individual failures of the peripherical frame members significantly alter the distribution of the bending moment along the height of the column test, thus changing the boundary conditions at its top end. The imposed moment distribution was further influenced by local buckling initiated at the base of the column test and ground‐floor beams and could cause the top end of the upper‐storey columns of the frame to buckle. In the MRF with 4.6 m‐height ground‐floor, this resulted in a global collapse mechanism that involved the ground floor and the second storey. In the MRF with 5.1 m‐height ground‐floor, a weak‐storey collapse mechanism was formed within the ground floor. Compared to a corresponding isolated column tested as cantilever using conventional methods, the columns tested with the proposed hybrid simulation exhibited a more favorable inelastic behavior primarily due to the more realistic loads and changes of boundary conditions which are ignored in conventional test methods.

“…The subassemblage is part of a seven‐story steel dual system including a special moment frame (SMF) in one bay and a buckling‐restrained braced frame (BRBF) in the other bay designed and evaluated as part of a previous study 9 . Considering that the seismic performance of steel first‐story columns are highly sensitive to the boundary condition at both ends, 10 ─ 13 the subassemblage specimen is extended to the mid height of the second story with an assumed inflection point at the top end. In addition, two steel beams at the second floor extend their respective mid‐spans to an assumed inflection point.…”

Section: Introductionmentioning

confidence: 99%

Hybrid simulation of a steel dual system with buckling‐induced first‐story column shortening: A mixed control mode approach

Wang

Chou

Huang

et al. 2023

Self Cite

This paper presents a hybrid simulation (HS) with a proposed substructuring technique that captures the effect of first‐story column local buckling and axial shortening on the frame behavior. The HS is applied to examine the seismic response of a two‐dimensional seven‐story, two‐bay steel dual system. The experimental substructure consists of a full‐scale interior column and beam cruciform subassemblage, including a moderately ductile first‐story built‐up box column and two I‐shaped beams. Under combined axial and lateral loads, local buckling can occur near the column base, resulting in column shortening. The specimen is loaded through a four‐degree‐of‐freedom (DOF) mixed‐mode control (three displacement‐ and one force‐control) actuation system that simplifies the actual complex boundary conditions of the frame structure. To account for column shortening in the HS, a new approach consisting of a set of fictitious equivalent forces applied to columns in the numerical model to achieve compatible displacements with the experiment is implemented. Shortening of the two exterior columns in the model is simulated through finite element analysis using the computer program ABAQUS in an attempt to capture the redistribution of axial loads with column shortening. The test results confirm that the proposed modeling and control methods successfully integrate the experimental substructure and ABAQUS simulation into the HS, resulting in a more realistic frame response that captures the effect of column shortening in the analysis. The moderately ductile built‐up box column is verified to perform well in near‐fault earthquake loadings.