Engineering Know-How: Lessons from Earthquakes and Rules for Seismic Design - Dynamic Behavior of Concrete and Seismic Engineering - page 339

circumstances (an earthquake, for instance). Such principles aim at ensuring
structure strength, usability and structure durability for an expected lifespan. They
are laid out in EN 90 regulations [COL 02], which also introduce the general
Eurocode philosophy.

The reliability of the approach used is demonstrated by calculating the
achievement of the goals targeted and is linked to the introduction of partial safety
coefficients for each of the materials, the actions and the calculation methods.
However, achieving these objectives is partly connected to the design methods used:
specific protection measures, the quality of the studies and of their execution, as
well as the follow-up of potential failures have contributed in an essential way to the
success of the objectives.

It is an acknowledged fact that the goals targeted have been reached by
verification of the boundary conditions of structures in project situations. These
situations are basic and are represented by combinations of actions in which the
seismic action is considered to have a higher occurrence probability higher than any
other accidental action.

The seismic situation is a specific one that gives rise to particular action
combinations that are expressed the following way:

¦ ¦

GPA \ Q [9.1]

kj , Ed 2, i ki ,

jl d il t

In the above expression, “+” means “combined with” instead of a mere algebraic
operation. G k,j refers to the characteristic values (in the probabilistic sense of the
word) of the permanent actions applied to the structure, P is the action representing
pre-stressing, A Ed the calculation seismic action equal to the J I A Ek product of the
coefficient of importance (see section 9.3.2) by the value characteristic of the
seismic action, Q k,i the values characteristic of the accompanying variable actions
(i.e. those that may be present during the seismic situation) and \ 2,i accompanying
coefficients expressing the intensity of the variable actions present when the
earthquake occurs. These coefficients are chosen as equal to their corresponding
values of the action quasi-permanent parts. Such combinations are used for
verifications in the considered limit states; they should not be used in a stand alone
manner to calculate the masses to be introduced into dynamic calculations (section
9.4.3.1).

Two structure-limited states classes are considered: ultimate limit states ( ULS )
which address the safety of people, structures and possessions, and service limit