Earthquake Engineering

Courtesy of Ove Arup -

Megaframe Building in Osaka, Japan Arup

Arup have completed the structural design for the Osaka International Conference Centre, which is currently under construction.

Before Earthquake

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The building comprises a large steel braced megaframe structure of 100 m height above ground and four levels of basement. Extensive use is made of special damping devices in the superstructure called Unbonded Braces (by Nippon Steel Corporation). These components consist of ductile steel wad - carrying plate restrained from buckling in compression by means of an outer tube filled with concrete and debonded from the load carrying central plate. These elements have equal resistance in tension and compression and able to undergo many cycles of inelastic demand with very stable force deflection hysteresis. They can thereby limit the seismic forces in the remainder of the building, and absorb much of the input energy of the earthquake

After Earthquake
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Oasys CEAP was used for the pushover analysis and a non-linear time history analyses on the simplified models. However, in addition it was feasible to perform full 3-D non-linear seismic response analysis on a detailed model of the building as a whole in which every beam, column, brace and floor panel was modelled explicitly. This technique facilitated a more precise checking of the seismic response of the structure. The Figure shows the 3D structural analysis model, in which every beam, column and brace had the ability to yield when the combination of bending moment and axial force reached the appropriate "yield surface" for the element. The effectiveness of the unbonded braces in absorbing the energy of the earthquake is also shown in the lower figure