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Applications - Seismic

Megaframe Building in Osaka, Japan

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

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.

As the building exceeds 60m in height it was subject to a special approval procedure from the Tall Buildings Committee of the Ministry of Construction, requiring non-linear seismic analysis.

The conventional approach in Japan for such projects is firstly to perform a quasi-static non-linear lateral push-over analysis up to "failure" of the structure to determine the force-deflection characteristics of each storey of the building. Non-linear dynamic analysis for appropriate ground motion records is then performed on a simplified vertical cantilever model where the storey masses are connected by non-linear shear springs representing the inter-storey force deflection characteristics, as calculated from the earlier pushover analysis.

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.

Before Earthquake

During Earthquake