Civil Engineering Reference
In-Depth Information
Ductile Link
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Brittle Links
Brittle Links
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Large Inelastic Deformations
Figure 2.5
Capacity design analogy: chain (
top
) versus network system (
bottom
)
accommodate vastly different action and deformation demands, depending on their own mass, stiffness,
strength and ductility. It is argued herein that the fundamental quantities are not period and damping,
since period is a function of mass and stiffness (as well as strength in the inelastic range) and the main
source of damping in earthquake engineering is energy absorption by inelastic deformation. Setting the
'mass' term aside, earthquake response is affected in a complex manner by stiffness, strength (or capac-
ity) and ductility. In a simple version of this complex problem, stiffness dictates vibration periods, hence
amplifi cation. Changes in stiffness cause detuning of the structure and the input motion hence also
affects amplifi cation. Figure 2.6 provides an example of two single- degree - of - freedom (SDOF) systems,
one stiffer than the other, but the dynamic amplifi cation is such that the less stiff structure (taller pier)
displaces less than the stiffer structure.
