Engineering Know-How: Lessons from Earthquakes and Rules for Seismic Design - Dynamic Behavior of Concrete and Seismic Engineering - page 366

normal. A concrete cover that is not confined by transverse reinforcements cannot
stop this buckling, as it is ejected as soon as the shrinkage exceeds 0.35%. As a
consequence, buckling can only be averted by leaning longitudinal reinforcements
on transverse reinforcements that are correctly anchored into the concrete. The
spacing of the reinforcements determines the buckling length of the longitudinal
reinforcements, whilst their diameter determines their ability to counterbalance
reinforcement strain due to compression stress work.
That is the reason why both the French standards and Eurocode 8 impose both a
maximum spacing and a minimum diameter for transverse reinforcements. It is
worth bearing in mind that this spacing is equal to at least eight times the diameter
of the longitudinal reinforcement, and therefore imposes a maximum slenderness on
the latter reinforcement.
9.7. Conclusions
Design methods for reinforced concrete structures are based on experimental
results and analysis of structures subject to strains in the post-elastic field. Within
these contexts, the rotational ductility of plasticized critical areas appears to play a
particularly important role. Capacity design allows control over the location of
plasticized areas, as well as over the failure modes, which ensures good reliability in
predicted structure behavior despite the random nature of seismic stresses. The
design of both horizontal and vertical bracing structures emerges as the most
important point for ensuring acceptable building behaviors during an earthquake. It
is also determined by construction layouts and the choice of materials used.
Calculation plays a minor quantitative role in designing well-behaved buildings,
because at present, different stages in some calculations are based on unrealistic
approximations, but qualitatively, it remains an indispensable tool for identifying
relevant parameters, and understanding their collective behaviors in greater depth.
9.8. Bibliography
[BET 91] BETBEDER-MATIBET J., “Constructions parasismiques”, Traité Construction,
Techniques de l'Ingénieur , C 3290 and C 3291, 1991.
[BET 97] BETBEDER-MATIBET J., DOURY J.L., “Constructions parasismiques”, Traité
Construction, Techniques de l'Ingénieur , 3290, Paper C, 1997.
[BIS 02a] BISCH P., “Constructions parasismiques. Eurocode 8”, Traité Construction,
Techniques de l'Ingénieur , C 3292, 2002.