Page 258 - Advanced Design Examples of Seismic Retrofit of Structures

Example of a Steel Frame Building With Masonry Infill Walls Chapter 4 251

(A) (B)
FIG. 4.16 Some steps in implementation of shotcrete. (A) Water-jetting the walls. (B) Using stan-
dardized pumps. (Permission from DRES.)

composites [19]. Because the infill walls in this example are made of masonry,
several retrofitting methods for URM buildings can also be applied to masonry
infill walls, albeit with some modifications. Among these methods, shotcreting
of the vulnerable infill walls is considered.
Based on ICERIFB [2], if the surface of the walls that are to be shotcreted
is smooth, the surface should be made rough by water-jet or sandblast (see
Fig. 4.16A). Before shotcrete, all the walls’ finishing should be removed and
the surface of the walls should be slightly wet to facilitate the bonding of con-
crete to the masonry. In addition, the cement grout should be poured on the
walls’ surface in order to fill the surface voids on the masonry walls. Shotcreting
should be carried out using standardized equipment (see Fig. 4.16B); shotcret-
ing by hand is not acceptable due to the low pressure of concrete on the walls.
The reinforcement should be at least 0.3% in each direction and should be
according to the related code requirements. Curing concrete which is based on
the related codes’ requirements should be particularly monitored, considering
the high surface-to-volume ratio of concrete.
If the shotcrete is applied on one side of the wall only, the dowel bars (shown
in Fig. 4.17) should be able to transfer total force acting on the wall in the out-of-
plane direction, which is determined in Section “Evaluation of the Walls in Out-
of-Plane Direction.” The minimum dowel bars ratio is 0.03% and the maximum
allowable distance in each direction is 50cm (see Fig. 4.17). The dowel bars
should be bent over the most external reinforcement layer to at least 10cm.
The shotcrete should be uniformly applied on the walls, and the thickness
related to a triangular area with the chord 1.5 times of the width of the equiv-
alent strut based on Eq. (4.12) should not be less than the thickness of the
rest. In the design procedure, the shotcrete with the least thickness should be
considered. The thickness of shotcrete usually ranges from 2.5cm to 5.0cm.