Advances in the Stability of Frame Structures

As far as structural engineering is concerned, scientific and technological advances are often fostered by the occurrence of collapses involving a more or less relevant amount of damage and, in the most unfortunate cases, also the loss of human lives. Indeed, it seems fair to say that every time a structural collapse takes place, designers and researchers will immediately start searching for a rational explanation; this boost of attention and interest invariably leads to the unveiling and investigation of new phenomena and also paves the way to the development of design tools intended to anticipate and prevent the detrimental effects of such phenomena. The above statements are especially true in the case of structural stability, as attested by the following illustrative examples: (1) The progress in the theory of laced column buckling due to the collapse of the Quebec Bridge in 1907; (2) the crucial role played by the Tacoma Narrows Bridge failure, in 1940, concerning the awareness and understanding of the aerodynamic torsional instability phenomenon; and (3) the development of Koiter’s general elastic postbuckling theory, essentially inspired by the sudden collapse of several thin-shell structures at surprisingly low applied load levels.

The very recent and unbearably tragic collapse of the World Trade Center twin towers, on September 11, 2001, highlighted the importance of devoting new attention and resources to a better understanding of behavioral, design, and safety issues related to the overall and member stability of framed structures—particularly when these structures are subjected to extreme loading conditions, such as the ones caused by impact, explosion, or fire. By publishing this Special Issue of the Journal of Engineering Mechanics, ASCE aims at making the above problems more visible, thus drawing the attention of the structural stability scientific and technological communities and encouraging them to devote new research to developing and disseminating more advanced methods for the efficient solution of these problems. At the same time, one has the opportunity of showing a representative sample of the activity currently under way in this field.

The recent exponential growth in computer capabilities, affordability, compatibility, and interconnectivity is responsible for a virtual “computational revolution” in many areas related to structural analysis and design. In particular, this situation will certainly lead, in the near future, to the routine incorporation of geometrically and materially nonlinear concepts and methodologies into the daily design practice. It will also enable designers to feel more comfortable and secure when faced with the ever-expanding tasks of coping with increasingly slender structures and more complex loading combinations, as they will have easy access to user-friendly tools that are able to handle advanced structural behaviors like the inelastic geometrically nonlinear behavior of initially imperfect members and framed structures, the global and local stability of nonprismatic thin-walled members, the influence of mode interaction effects on the stability and postbuckling behavior of curved members, the dynamic behavior of slender frames under earthquake loadings, or the inelastic stability behavior of members and framed structures subjected to high temperatures and/or to impulsive forces. This Special Issue includes a sample of papers that reflect recent advances in the field of the stability of thin-walled members and frames structures and cover a wide range of specific topics and research techniques/approaches. Nakashima and Liu report the results of an experimental (primarily) and numerical investigation on the instability and failure of steel columns under cyclic loading. The cyclic behavior of steel structures is also the focus of a second paper, authored by Castiglioni, addressing the influence of the loading history on the local buckling behavior and failure mode of welded beam-to-column joints in seismic resistant frames. Andrade and Camotim, on the other hand, develop and implement a variational formulation intended to analyze the lateral-torsional stability of singly symmetric tapered thin-walled open beams. A somewhat related topic is tackled by Teh, who presents a critical and clarifying review of various concepts dealing with spatial rotation kinematics, which are illustrated through their application to the flexural-torsional buckling behavior of 3D frame members.

The recent interest in the area of stability and nonlinear behavior under extreme loadings is attested by the paper co-authored by Chen and Liew, about the nonlinear response of steel frames under actions stemming from explosion and fire, and also by the technical note from Usmani, which provides a method that makes it possible to perform a simplified stability analysis of the WTC twin-tower frame subjected to a fire involving several floors. The three remaining papers are concerned with the stability, nonlinear behavior, and design of steel and composite plane building frames. Silvestre and Camotim propose an asymptotic-numerical method to analyze the frame elastic postbuckling behavior and imperfection-sensitivity, which is able to handle mode interaction effects. The paper by Chan, Huang, and Fang deals with the second-order plastic hinge analysis of portal frames with pinned or semirigid column bases, and looks mostly at the influence of the initial imperfections on the frame ultimate load. Finally, composite sway building frames are addressed in the paper co-authored by Demonceau, Jaspart, and Maquoi, who propose simplified design methods that can be viewed as straightforward extensions of the current European specifications for bare steel sway frames.

Before concluding this foreword, it must be made clear that, in spite of the enormous progress achieved in the past few years, the stability and advanced analysis of framed structures is still a highly challenging subject, with very clearly defined research needs. Without attempting to be complete and warning the reader against the limitations of our own personal views, it seems possible to identify the following three main lines: