Earthquake risk management of civil infrastructure: integrating soft and hard risks - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 228

One of the most common methods for achieving desirable ductility is
through capacity design where strong columns are used with weaker ductile
beams. The columns need to have suffi cient ductility but could buckle in a
brittle manner - capacity design is used to ensure that the possibly brittle
elements are strong enough to withstand the full capacity of the ductile
elements. Suitable detailing is important to ensure that a structure designed
to yield can achieve the large strains required.

9.2.3 Stiffness

Although a structure needs to be ductile, the defl ections must be limited to
reduce damage to non-structural elements, such as false ceilings, wall parti-
tions, cladding and internal furniture (heavy book cases can cause injury).
This means that the structure must be adequately stiff with due consider-
ation given to the possibility of P - Δ effects in which large defl ections induce

extra bending in columns.

9.2.4 Foundations

General rules for foundations are diffi cult because local circumstances vary.
A major issue is to ensure that foundations can take different forces that
may be imposed during an earthquake. For example, some structures may
induce uplift forces, piles may need to take lateral forces, piles may be
unsupported over a long length and may buckle if soil liquefaction happens
(Bhattacharya and Madabhushi, 2008). Raking piles add to the lateral stiff-
ness of pile groups but have been found, by experience, to be prone to
failure in an earthquake.

9.2.5 Materials
Steel has a high strength-to-mass ratio and is ductile. However, buckling
behaviour is not ductile and connections can be problematic. Timber is
strong and light. Concrete beams and columns can be brittle so proper
design and detailing are required using capacity design and adequate con-
fi nement reinforcement. Masonry is not ductile and so must be designed
for large reserves of strength. An early report on the damage due to the
2011 Christchurch earthquake (Ingham et al. , 2011) showed that many of
the damaged buildings were of unreinforced masonry.

9.3 Reliability theory for the analysis of

uncertainty and risk

Managing the practical risks has to be contrasted with theoretical approaches.
Reliability theory is a mathematical framework for the analysis of uncer-