Advances in Seismic Design Methodologies - Earthquake Engineering for Structural Design - page 395

Advances in Seismic Design Methodologies 395

Figure 9.3 Evolution of multi-level design approaches (Truta et al, 2003)

In function of taking different limit states for structure and non-structural elements,
some multi-level base approaches have been developed (Fig. 9.3):
One level design approach , in which only the ultimate limit state (ULS) is
considered, for the prevention of structure collapse. This approach was the official
design approach for a long time in many codes.
Two levels design approach , which is today a current code methodology and the
seismic design philosophy of Eurocode 8. These two levels are:
-Damage limit state (DLS), for which structures are designed to remain elastic,
or with minor plastic deformations and non-structural elements remain undamaged
or have minor damage.
-Ultimate limit state (ULS), for which structures exploit their capability to
deform beyond the elastic range, non-structural elements being partially or totally
damaged.
Three levels design approach , which can be considered as the objective
for the next generation of codes. Verification at the three levels has been
proposed by Mazzolani and Piluso (1993, 1996), Gioncu and Mazzolani,
(2002), being defined as the combination of the followings limit states:
-S erviceability limit state (SLS), for frequent earthquakes. This limit
state imposes that the structure, together with non-structural elements,
could suffer minimum damage and the discomfort for inhabitants should be