Concrete Today May 2010 - the Irish Concrete Federation

concrete today - designing for earthquake - precast concrete
L’Aquila earthquake central Italy 2009
and the mass should be closely
symmetrical in plan with respect to two
orthogonal axes
• In this respect, if necessary, uniformity
may be realised by subdividing the entire
building by means of seismic joints into
dynamic independent units, provided
that these joints are designed against
pounding of the individual units
• Uniformity in the development of
the structure along the height of the
building is also important and can be
achieved when:
• Almost all lateral resisting systems
such as cores, structural walls or
columns in frame systems, run without
interruption from their foundations to
the top of the building
• Both the lateral stiffness and the mass of
the individual storeys remain constant
or reduce gradually and
• A natural flow of forces is ensured by
avoiding staggered beams or (worse)
staggered columns
• Other basic principles to be satisfied
by a sound conceptual design are
the bi-directional resistance, torsion
resistance and stiffness
Horizontal actions
The structure must be made to resist
horizontal actions in any direction. This
can be achieved by arranging all structural
elements (columns and/or walls) in an
orthogonal in-plan structural pattern
e.g. by distributing those close to the
periphery of the building, ensuring similar
resistance and stiffness characteristics in
both main directions and limiting possible
torsional motions which tend to stress the
different structural elements in a nonuniform
way. In all cases, special attention
must be paid to the position of the
elevators and staircases into the structural
system.
Soil, structure interaction
In seismic areas, the interaction of the soil
with the superstructure must be carefully
studied. In general, the configuration of the
foundation relative to the superstructure
should be such as to ensure that the whole
building is subjected to a uniform seismic
excitation.
L’Aquila earthquake central Italy 2009
Secondary structural elements and
cladding panels
Moreover, when designing precast
structures where secondary elements such
as infills/partition walls/claddings etc.
are envisaged, special attention must be
given to arranging them symmetrically in
plan, to avoid all possible irregularities in
a strong seismic event. Generally, all of the
aforementioned secondary elements must
be connected with the structural elements
in a way that they will not disturb the
predicted seismic response of the structure
and that they will not partially or totally
collapse. Based on experience from past
earthquakes (e.g. earthquake at L’aquilla,
Italy 2009) it has become obvious once
again that inadequate connection details
between cladding panels and the structural
panels can lead to out-of-plane collapse
of these cladding panels during a seismic
event, with considerable risk to human life.
The Development of Codes
Experience from the past has shown
repeatedly that construction techniques
of every type preceded any theoretical
and experimental scientific progress and
relevant codes, since complete code-bodies
governing the design and construction
of structures and especially of Precast
structures under seismic conditions, did
not exist in their current organised form. In
cases where basic code-bodies had formed,
they did not reflect the more recent aspects
of Earthquake Resistant Design Philosophy
such as ductility demand, capacity design
rules and other such factors. Also, in some
concrete today
6