Page 98 - Advanced Design Examples of Seismic Retrofit of Structures

90 Advanced Design Examples of Seismic Retrofit of Structures

(A) (B)
FIG. 2.44 Examples of retrofit of masonry walls by shotcrete. (A) Internal walls. (B) External
walls. (Permission from DRES.)

40years. Clearly, the largest benefit derives from a single-stage rehabilitation
done now, and it is designated as 100%. The benefits of single-stage rehabili-
tation done in the future must be discounted and expressed as some percentage
lower than 100%, as represented by the decreased arrows. The stepped portion
of the diagram represents incremental rehabilitation starting soon, and com-
pleted in four increments over 20years. The benefits of the future increments
must also be discounted, and the benefit of the completed incremental rehabil-
itation is therefore expressed as a percentage lower than 100%, but higher than
the single-stage rehabilitation in year 20. Reducing the overall duration of the
incremental rehabilitation will increase its benefit, and extending the duration
will decrease it [1].

2.8.3 Common Methods
2.8.3.1 Shotcrete
In the retrofit of masonry buildings, shotcrete refers to the method in which rein-
forcing mesh (usually steel) is installed on one side or both side of existing
masonry walls; then, under a specified pressure, fine-aggregate concrete or
mortar is poured to the surfaces of the walls. In order to improve the bonding
between the added layer of concrete to the walls, it is usually necessary to
remove the walls’ finishing before installation of the reinforcing mesh.
Fig. 2.45 shows examples of retrofit of masonry walls by shotcrete.
Shotcreting one or both sides of masonry walls have proved to be a very
effective method in reducing seismic vulnerability of masonry buildings. Shot-
creted masonry walls not only have larger strength capacities, but also show
larger ductility capacity. ElGawady et al. [17] performed static cyclic testing
on unretrofitted and shotcreted specimens. The ultimate lateral load resistance
of the walls was increased by a factor of approximately 3.6. An increase in the
maximum force capacity of about 3 was reported by Abrams and Lynch [18].