17. Improved Earthquake-Resistant Design of Irregular Steel Buildings

In the past several years, the seismic behavior of eccentric buildings has been studied with detailed models of the plastic hinge type, first for reinforced concrete buildings and then for steel, braced frame type buildings, all of them designed in accordance with the appropriate new Eurocodes. In all cases, it was found that the distribution of ductility demands is not as uniform throughout the structure as one might have expected and desired for a well-designed structure. Such an uneven distribution indicates suboptimal material use and a potential for premature failure of certain members. In this chapter, a design modification that has been proposed earlier and improved substantially the inelastic earthquake behavior of buildings with biaxial eccentricity but with rectangular layouts is applied to eccentric, L-shaped buildings. Both a torsionally stiff and a torsionally flexible building are examined, and it is found that the modification gives also good results for such buildings, especially the torsionally stiff one. The improvement of the behavior of the torsionally flexible building may be considered marginal, but this is probably associated with characteristics of the specific building. In any case, modern codes suggest avoidance of torsionally flexible buildings whose seismic behavior is more difficult to control, and for this reason, stricter design requirements are specified.