Engineering Know-How: Lessons from Earthquakes and Rules for Seismic Design - Dynamic Behavior of Concrete and Seismic Engineering - page 364

test series ([BIS 98] and [BIS 02b]). It was first codified in the PS 92 rules ([COL
95a], section 11.4, paragraph 11.8.2). Although Eurocode 8 verification rules differ
from those in the PS 92 rules, the basic principles of behavior and strength modes
are the same, except the diagonal cracking failure mode is not considered in the PS
92 rules.
Another difference concerns the behavior coefficient: in Eurocode 8 this type of
wall is only considered in M ductility, therefore its value is limited to 3, yet it does
not require any specific justification. Moreover, this maximum value decreases for
walls that are not very thin. In these cases, the shear load does influence the dynamic
behavior, and the behavior coefficient is therefore lower.
Data obtained in the last series of CAMUS tests disclosed important factors.
These are outlined below, but have not yet been incorporated into the standards:
- because of the highly non-linear behavior of concrete due to cracking, linear
calculations do not allow all the phenomena that appear during the motion to be
taken into account. For instance, a stress in one direction can generate displacements
in the perpendicular direction, owing to the different extensions of the medium lines
of the walls caused by different cracking directions (whatever the cause);
- floor torsion stiffness plays an important part in the redistribution of stresses
and the ultimate strength of a building, but this stiffness varies with time because of
variable cracking conditions;
- the dynamic normal force does not influence bending, yet it modifies the strain
of concrete and the reinforcements, though uniformly.
The calculation method developed in the PS 92 rules gives satisfactory results
for the ultimate strength. However, it does not allow accounting for the
displacements that it widely underestimates. The very accurate models developed
during the experiments have given satisfactory results, but they are not yet within
designers' reach, mainly because they do not allow the representation of a whole
construction work. In this respect, advances are expected as far as modeling and
calculation practical methods are concerned.
9.6.5. Detail designing
9.6.5.1. Anchoring and overlapping
The anchoring of reinforcements within the concrete matrix implies the stress to
which the reinforcement is subject will be transferred towards the concrete, whether
it is compression or traction. This transfer is carried out by several different
mechanisms: