Page 26 - Advanced Design Examples of Seismic Retrofit of Structures

18 Advanced Design Examples of Seismic Retrofit of Structures

- Limitations of structural walls
l Maximum free length of 5m;
l Maximum free height of 4m;
l Height to thickness ratio in regions with high seismic activity <10 and in
other regions <15;
- Limitations of openings in the walls
l Distance to ends of walls
l Area
l Length
l Dimensions
- Relative wall.

2.3.3 Existence of Seismic Rehabilitation Elements
Experiences from past earthquakes have shown that if there are simple elements
which provide a secure connection between perpendicular walls and also
between walls and roofs, considerable performance improvement can be
achieved from providing the buildings with integrity. However, installation
of these elements in inappropriate locations can result in their ineffectiveness
and in some cases, may cause stress concentration and local collapse of the
building. These elements may be in the form of horizontal or vertical ties,
braces, mesh on interior or exterior faces on the walls, or steel strips to provide
roofs with uniformity. Examples of these undertakings are shown in Fig. 2.5.

2.3.4 Condition of Building During Earthquake
A building may have experienced some other earthquakes before; consequently,
some damage may have occurred in its walls as the main load-bearing structural

(A) (B)
FIG. 2.5 Examples of the effects of preexisting retrofit elements on seismic performance of URM
buildings. (A) Effectiveness of horizontal tie in preventing collapse. (B) Effectiveness of vertical tie
in preventing collapse. (Permission from DRES.)