New Advances in Seismic Design and Assessment of Steel Structures

In recent years, rapid advances have taken place in earth-quake engineering as applied to steel structures with major emphasis given to (1) development of advanced procedures for seismic performance assessment, (2) development of advanced design procedures for plastic mechanism control, (3) improvements in structural design detailing, (4) better modeling of members and connections for dynamic non-linear analyses, (5) development of new damping devices for supplementary energy dissipation, (6) development of self-centering structural systems, (7) development and testing of new design strategies for reducing structural damage under severe ground motions. Even though such advances have reached in some cases a refinement level justifying their in-troduction in seismic codes, the updating of Eurocode 8 with design criteria and new design strategies reflecting newly developed knowledge is still in delay. In the actual version of Eurocode 8, some advances, such as new structural ty-pologies like braced frames equipped with buckling re-strained braces and dissipative truss moment frames, are still not codified even if they have already gained space in American codes.

Because of these rapid advances, weaknesses of Euro-code 8 and new structural typologies to be codified have been recognized and a document focusing on such weak-nesses and new research needs has been published [1]. In particular, the sharing of knowledge obtained has been rec-ognized to be critical to improve the seismic design of steel structures. Therefore, a Thematic Issue on “New Advances in Seismic Design and Assessment of Steel Structures” can be considered timely.

Many researchers, all joined by the common interest in design, testing, analysis and assessment of steel structures in seismic areas, have accepted to contribute to this special is-sue. As a result, this thematic issue is composed by eleven contribution covering important design topics for seismic resistant steel structures.

Two works [2, 3] are devoted to the seismic design of Concentrically Braced Frames (CBFs), pointing out the drawbacks of the design provisions suggested by Eurocode 8 and also reported in the Italian Technical Code for Construc-tions. In particular, the need to revise the design procedure suggested for columns of CBFs is discussed showing that both the stability and resistance indexes of columns are often exceeded. The results obtained are in agreement with those presented by other researchers [4-8] who recommended de-sign procedures based on a rigorous application of capacity design principles. Also the third manuscript of the thematic issue is devoted to CBFs, but aiming to the development of a new buckling restrained system which can be easily dis-mounted [9]. As it is well known, buckling restrained braces (BRBs) are basically constituted by two parts: an internal slender steel member, known as the “core” and a restraining member, known as the “casing”. The core component has the key role of dissipating energy, while the casing component restrains the brace core from overall buckling in compres-sion. The buckling restraining mechanism can be obtained by enclosing the core (rectangular or cruciform plates, circu-lar rods, etc.) either in a continuous concrete/mortar filled tube or within a “all-steel” casing. Despite of the use of such braces allows to obtain wide and stable hysteresis loops, thus overcoming the main drawbacks of traditional braces due to the poor cyclic response resulting from overall buckling, and their design is already codified in ANSI/AISC 341-10 [10], their use is still not codified in Europe testifying an impor-tant weakness of Eurocode 8.

Two papers of the present thematic issue are devoted to beam-to-column connections [11, 12]. The first one [11] presents the results of a wide experimental program recently carried out at Salerno University dealing with extended end plate connections, with and without Reduced Beam Section (RBS), connections with bolted T-stubs and, finally, innova-tive connections equipped with friction dampers. The second work [12] is mainly devoted to the theoretical development of the analysis of the influence of gravity loads on the seis-mic design of RBS connections. In particular, it deserves to be underlined that such influence is commonly neglected in codified rules, such as ANSI/AISC 358-10 [13], because experimental tests constituting the base of the recommended design procedures are typically based on cantilever schemes where gravity loads are not applied.

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