Page 104 - Advanced Design Examples of Seismic Retrofit of Structures

96 Advanced Design Examples of Seismic Retrofit of Structures

FIG. 2.49 Schematic representation of the retrofitted walls (shown with inclined stripes).

the roof from collapsing on the residents during an earthquake. The weight of
each frame is about 500kg. In other words, with an affordable budget for the
people, each house or school will be equipped with a “safe room” [45].
A schematic view of the safe room is presented in Fig. 2.49.

2.8.3.11 Placement of Steel, Polymer, or Plastic Grids
Two types of polymer mesh that have been used to retrofit URM structures are
an industrial geo-grid and a weaker mesh that is usually used as a “soft” fence on
construction sites. The mesh is wrapped around the wall and then coated with a
mud plaster finish. Three variations of the geo-grid (100%, 75%, and 50% area
coverage) and one soft mesh system (80% area coverage) were tested by Blon-
det et al. [46]. The results proved satisfactory responses of retrofitted specimens
compared to those in the control specimens.
Another method of reinforcement uses PP packaging strips that can be found
in many packaged items. Testing under static loading had been carried out by
Macabuag [47], in which two scaled wall sections were constructed and tested
under diagonal compression. It was found that the horizontal strips prevent sep-
arationofbricksonthesamerow.Verticalbandsincreasethefrictionalresistance
between rows and consequently prevent sliding. In conclusion, this method
effectively improves the shear resistance of test specimens under static loading,
but there was a recurring problem of the mesh snapping at points of stress
concentration such as the wall corners. A similar test was carried out at Tokyo
University by Meguro et al. [48] under dynamic loading conditions. The testing
showed how the retrofit improved the specimen seismic performance signifi-
cantly, displaying increased load resistance and ductility before failure.
Macabuag et al. [49] studied the effect of retrofitting of URM buildings in
Nepal using PP meshing, being subjected to artificially generated strong shocks.
The study concluded that use of PP mesh prevents spoiling out the masonry
blocks, and thus enables the system to accommodate more deformation without
collapse.