Geoscience Reference
In-Depth Information
7
8
9
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1
2
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D
f
= 1m
5 bays of 7.5 m
Fig. 10.14. Three-storey structure elevation, plan and footing numbering
(ductility 3) structural models were designed using the loads and dimensions described
above. The fixed base period of the structuredetailed inFigure 10.14 is close to0.9s.
Footings 3.1m square, with the underside 1m beneath the ground surface, were adopted
forall24columnfoundations(thereasonforthisconstantfootingsizewillbecomeappar-
entlater).UsingtheloadfactorsgiveninNZS1170.5(1.2forpermanentloadand1.5for
imposedload),bearingcapacitycalculationsrevealedthatthesefoundationshadadequate
to generous bearing strength for the applied staticvertical loads.
5.2. RUAUMOKO MODELLING OFTHE STRUCTURE-FOUNDATION SYSTEM
Ruaumoko models of the three-dimensional three-storey reinforced concrete moment
resistingframestructuresweredevelopedtoundertakedetailednonlinearmodelling.The
numerical models could be run with an elastic or a ductile structure on fixed base or
compliant foundations.
For ductile behaviour under seismic loading a sway mechanism develops with column
hinging at foundation level and beam hinging within 1.5 beam depths from the column
faces. All of the calculations in this paper were for an elastic structure. Columns were
modelledusingconcretebeam-columnframemembers,andbeamsweremodelledusing
Gibersonbeamframemembers.TheGibersonframemembersconsistedofanelasticcen-
tral section with potential plastic spring hinges located at the ends. The concrete beam-
column members were of similar form, but the central section was defined by a beam
column yield surface.
Each floor was modelled as a lumped mass and a rigid diaphragm which restrained the
floor such that all points moved the same distance horizontally. All the footings were
connected with tie-beams. These were assumed to act under axial load but provide no
momentrestraintwhereconnectedtothefootings.FortheRuaumokomodellingRayleigh
tangentialstiffnessviscousdampingwasappliedtogive5%dampingtothefundamental
mode and at least 3% damping toevery other mode.
