RECOMMENDATIONS FOR THE EARTHQUAKE RESISTANT DESIGN OF BRACED STEEL FRAMES.

In this paper, the Eurocode 8 design approaches for concentrically braced steel frames are assessed with respect to observations and findings from shake table tests on full-scale concentrically braced single storey frames. The stiffness, resistance and ductility of the frames tested are assessed, and recommendations for estimating key response parameters are outlined. In particular, measured frame stiffnesses and natural frequencies are compared with estimates based on tension and compression brace stiffness. Several sources of member and frame overstrength, which play an important role in seismic performance and design, are identified. The tension-based design approach largely adopted in design is examined together with the member slenderness limits imposed on the bracing members. It is shown that the overstrength factor specified in Eurocode 8 for the design of connected non-dissipating elements of the structure may underestimate the actual behaviour. It is also observed that the bracing members with slenderness exceeding the codified limits demonstrated generally satisfactory performance. Despite lower energy dissipation, a higher fracture resistance, coupled with other practical and design advantages points towards a need to reassess the codified slenderness limits. Global ductility demands and capacities are used to assess the behaviour factors recommended for this type of structure.