Comparison of Seismic Design Requirements for Steel Moment Resisting Frames with Emphasis on Stability of Columns in North America, New Zealand, and Europe

The seismic design provisions and stability requirements for steel columns used at the first storey of MRFs as specified is Canadian steel design standard (CSA S16), U.S. design provisions for steel buildings (AISC 341 and AISC 360), the New Zealand steel structures standard (NZS 3404), and Eurocodes 3 and 8 (EC3 and EC8) are reviewed. The code provisions are applied to a deep, slender steel I-shaped column to identify possible failure modes. A finite element analysis of the column is performed under cyclic inelastic lateral drift history to validate code predictions. The column was found to fail by out-of-plane instability, after local buckling has developed in the base plastic hinge. This failure mode was not expected from the axial-bending interaction equations available in the design standards except the equation of Eurocode 3. Limits for out-of-plane slenderness in Canadian and European provisions indicate the observed failure mode.

Influence of embedded steel column base strength on earthquake-induced residual deformations

Hiroyuki Inamasu, Dimitrios Lignos

Recent experiments on steel columns under multi-axis cyclic loading suggest that a steel column may experience appreciable axial shortening due to local buckling. Reconnaissance reports from recent earthquakes indicate that a number of embedded column base (ECB) connections in steel frame buildings were found to be lightly damaged although they are expected to remain elastic. As a result, the amount of inelastic damage concentrated in the respective steel columns was much less than it was expected to be. This paper investigates the influence of the ECB strength on the residual deformations of first story interior steel columns in steel moment resisting frames (MRFs) under multi-axial cyclic loading. The evaluation is conducted with rigorous finite element (FE) simulations. The developed FE model is able to simulate the pinching hysteretic behavior of typical ECBs. The parametric study involves two main cases. In the first one the ECB remains in elastic. In the second case the inelastic behavior is spread to the ECB and the steel column itself. The simulation results suggest that the resultant plastic deformation within the steel column is much smaller in the latter. The onset of column local buckling is delayed; therefore, the residual column axial shortening becomes fairly minimal. In particular, it is reduced by 50% at lateral drift demands associated with low-probability of occurrence earthquakes.

2018

Analytical investigation of the cyclic behavior and plastic hinge formation in deep wide-flange steel beam-columns

Ahmed Mohamed Ahmed Elkady, Dimitrios Lignos

This paper investigates the cyclic behavior of deep wide-flange sections, used as columns in steel Special Moment Frames (SMFs), through detailed finite element (FE) analysis. A wide range of wide-flange sections is subjected to symmetric cyclic lateral loading combined with different levels of constant compressive axial load ratios representing the loading conditions of interior steel columns in SMFs. The FE simulations demonstrate that wide-flange beam-columns, with web and flange slenderness ratios near the current compactness limits of seismic design provisions (AISC 341-10), experience rapid cyclic deterioration in flexural strength under high axial load ratios. It is also found that deep wide-flange slender sections shorten axially to about 10 % of their length due to severe flange and web local buckling. Based on the FE simulations, for bottom story columns, where axial load ratios are in the range of 20–35 %, a reduction to about two thirds of the current compactness limit for highly ductile members would achieve a 4 % chord rotation while maintaining a flexural strength larger than 80 % of the expected plastic flexural strength of a steel column. The FE simulation results also suggest that the pre-capping rotation predicted by current modeling recommendations for steel components (PEER/ATC 72-1) is overestimated for sections with high web and flange slenderness ratios undergoing monotonic and/or cyclic lateral loading combined with high axial load levels. © 2014, Springer Science+Business Media Dordrecht.

Springer Verlag2015

Dynamic Stability of Deep and Slender Wide-Flange Steel Columns – Full Scale Experiments

Ahmed Mohamed Ahmed Elkady, Dimitrios Lignos

In North America, a common design practice for steel frame buildings with perimeter steel special moment frames (SMFs) is to employ deep and slender wide-flange steel columns (i.e., range of column depth, d > 16 inches). Till recently, very little was known regarding the hysteretic behavior of such members because of lack of available experimental data. This paper discusses selective findings from a full-scale testing program that was conducted at École Polytechnique Montréal with the use of a 6-degree-of-freedom experimental setup. The testing program investigated the cyclic behavior of 10 full-scale beam-columns. The specimens had a depth of 24 inches (i.e., W24x146 and W24x84 cross-sections) and were subjected under various lateral-loading protocols coupled with constant compressive axial load. The boundary conditions of the specimens simulated a fixed support at the column base and a flexible boundary at the column top end to mimic the flexibility of a beam-to-column connection at the floor level. The tested specimens represented typical interior first-story columns in mid-rise steel SMFs. This paper summarizes the main observations related to the effect of local and global slenderness ratios on the cyclic behavior of beam-columns. The effect of bidirectional lateral loading on the dynamic stability of beam-columns is also addressed. Observations related to the effect of the employed loading history as well as the lateral bracing force design requirements on steel wide- flange beam-columns are also provided based on the available experimental results.

Structural Stability Research Council2016