Page 99 - Advanced Design Examples of Seismic Retrofit of Structures

Example of a Two-Story Unreinforced Masonry Building Chapter 2 91

FIG. 2.45 An example of grout injection. (Permission from Desoi.)

A larger increase in this parameters of 6–25 was observed by Kahn when using
thicker shotcrete layers [19].
In order to transfer the shear stress across shotcrete-masonry interface, shear
dowels (6–13mm diameter @ 25–120mm) are fixed using epoxy or cement
grout into holes drilled into the masonry wall [18–20]. Nonetheless, the results
of a study by Kahn reveled that a bonding agent like epoxy is required to be
painted or sprayed on the brick so that adequate brick-shotcrete bond is devel-
oped [19]. However, there is no agreement on brick-to-shotcrete bonding and
the need for dowels. Diagonal tension tests of single and double wythe URM
panels retrofitted with shotcrete showed that dowels did not improve the com-
posite panels response or the brick-shotcrete bonding, and header bricks satis-
factorily joined the wythe of existing masonry panels. Furthermore, Kahn
recommended wetting the masonry surface prior to applying shotcrete. He
shows that such brick surface treatment does not significantly affect the crack-
ing or ultimate load, and extends the inelastic deformations in a limited fashion.
The negative points regarding the use lie in the facts that use of shotcrete is time-
consuming, creates disturbance in occupancy, and affects the esthetics [21].

2.8.3.2 Ferrocement Covering of the Walls
Ferrocement consists of closely spaced multiple layers of hardware mesh of fine
rods with reinforcement ratio of 3%–8% completely embedded in a high
strength (15–30MPa) cement mortar layer (10–50mm thickness) [22]. As men-
tioned by Abrams et al. [23], “ferrocement overlay” refers to coating of concrete
reinforced with steel hardware cloth. The steel hardware cloth was 19 gauge
wire 1mm diameter with 13mm grid spacing. The cement plaster coating
was made of a 1:3 volume ratio of Portland cement and sand with water added
until a workable consistency was achieved. The compressive strength of the
cement was approximately 6.9MPa.