Experimental Evaluation and Numerical Modeling of Wide-Flange Steel Columns Subjected to Constant and Variable Axial Load Coupled with Lateral Drift Demands

Abstract

This paper presents results from an experimental evaluation on the pre-and postbuckling behavior of 12 steel wide-flange cantilever columns under axial load and lateral drift demands. The influence of several loading and geometric parameters, including the cross-sectional local web and flange slenderness ratios, applied axial load, and lateral and axial loading history on the performance of these columns is thoroughly examined. The test data indicate that crosssectional local buckling is highly asymmetric in steel columns under variable axial load. A relatively high compressive axial load can significantly compromise the steel column seismic stability and ductility but this also depends on the imposed lateral loading history. The AISC axial load-bending moment interaction equation provides accurate estimates of a steel column's yield resistance. However, the same equation underestimates by at least 30% the column's peak resistance regardless of the loading scenario. Measurements of column flange deformation, axial shortening, flexural resistance and lateral drift are combined in a single graphical format aiding the process of assessing steel column repairability after earthquakes. The test data suggest that current practice-oriented nonlinear component modeling guidelines (PEER/ATC 2010) may not provide sufficient accuracy in establishing both the monotonic and first-cycle envelope curves of steel columns. It is also shown that high-fidelity continuum finite element models shall consider geometric imperfections of proper magnitude in addition to the steel material inelasticity to properly simulate the inelastic buckling of wide-flange steel columns and generalize the findings of physical tests. Issues arising due to similitude are also discussed to properly limit steel column instability modes in future studies.

Steel column stability and implications in the seismic assessment of steel structures according to Eurocode 8 Part 3

“…Kommentare been conducted to address this pressing concern [14]- [19]. It is also worth stating that concurrent continuum finite element (CFE) analyses [20], [21] have been carried out to complement the experimental data and to expand the behavioural insights for a broad range of steel column geometries.…”

“…(see Figure 1a) and column axial shortening, ! "#!$ , versus (see Lignos [15], [18] and Cravero et al [19] Depending on the member slenderness ratio, % & ⁄ ( % is the unbraced length of the column; & is the radius of gyration with respect to the weak axis of the steel cross-section), the local buckling progression may be coupled with inelastic lateral torsional buckling [16], [18] at storey drift demands representative of significant damage (SD) limit states (see Figure 1e). Evidently, column axial shortening is a common instability mode observed in fixed-end columns due to the progression of nonlinear local and member geometric instabilities under lateral loading.…”

Proposed methodology for building‐specific earthquake loss assessment including column residual axial shortening

“…The surveyed individuals were provided with "repairability curves" that combine in a single plot the column axialshortening and flange distortion deformation amplitudes along with the column's residual flexural capacity as a function of story-drift demands. 1 The statistics from the collected survey responses are summarized in Figure 4.…”

“…Experimental evidence [1][2][3][4][5] and field observations from past earthquakes 6,7 suggest that first-story steel columns in capacity-designed moment-resisting frame (MRF) buildings may experience nonlinear geometric instabilities at modest lateral drift demands. In turn, these may cause column axial-shortening (Δ axial ) and flange distortion (δ f ) as illustrated in Figure 1A for a wide-flange steel column.…”

“…This issue has raised concerns regarding the steel MRF column repairability in the aftermath of earthquakes. 1 For instance, Figure 1C shows that at a story-drift of 3%, a W14x61 column subjected to cyclic lateral loading experiences column axial shortening of 30 mm and a flange distortion of 40 mm. At the same lateral drift demand, the column's flexural strength is reduced to 30% of its maximum strength, M max .…”