Civil Engineering Reference
In-Depth Information
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Strain
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ATERIAL
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ECTIONS
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EMBERS
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ONNECTIONS
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YSTEM
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Figure 2.4
Hierarchical relationship between local and global structural response
in-series chain is inadequate to characterize the complex response of structures under earthquake loads.
Networks, e.g. road networks, provide a basis for conceptual and pictorial description of the seismic
behaviour of structures (Figure 2.5) and also prove that barriers between sub-disciplines are artifi cial.
The transportation network combines parallel and series failure modes that may take place in structural
systems. It also provides a visual description of other important aspects of seismic design, such as load
path (direction of traffi c fl ow), capacity (maximum fl ow capacity of a link) and plastic redistribution
(likelihood of alternative routes in the case of traffi c congestion).
In the network analogy, the demand on the network (earthquake actions) may be expressed by the
origin-destination pairs imposed on the network. The capacity of roads to carry traffi c symbolizes the
capacity of structural members.
2.2.4 Nature of Seismic Effects
Unlike most other types of dynamic actions, earthquake effects are not imposed on the structure but
generated by it. Therefore, two structures founded on the same soil a few metres apart may have to
