Page 100 - Advanced Design Examples of Seismic Retrofit of Structures

92 Advanced Design Examples of Seismic Retrofit of Structures

Ferrocement is ideal for low-cost housing since it is cheap and can be used
by unskilled workers. It improves both in-plane and out-of-plane behavior. The
mesh helps to confine the masonry units after cracking and thus improves
in-plane inelastic deformation capacity. In a static cyclic test [18], this retrofit-
ting technique increased the in-plane lateral resistance by a factor of 1.5 [23].

2.8.3.3 Repointing
In many cases, the surfaces of masonry walls are exposed; over the long term,
this results in weathering and erosion of masonry by freeze and thaw, sunlight,
wind, rain, and snow [24]. In cases where bricks are of good quality but the mor-
tar is poor, the mortar can be replaced to some extent with a higher-strength
bonding material. The advantages of this technique include minimal cost and
convenience of implementation. However, this method is not sustainable and
the success of this technique lies in the compatibility of the new mortar with
that of existing bricks [21].

2.8.3.4 Tying Paralleled Walls
One of the main causes of collapse of an arched roof is the unbalanced motions
of the support walls. If the walls move monolithically during seismic actions,
arched roofs can probably withstand earthquakes without experiencing serious
damage because they are among the most stable geometrical roof systems. In
order to enforce in-phase response of the support walls, they can be tied
together. This is usually done by steel rods passing through the parallel walls.
For more information, see Chapter 6, “Shaking Table Tests” section.

2.8.3.5 Adding Tie Columns
The confinement prevents disintegration and improves ductility and energy dis-
sipation of URM buildings, but has a limited effect on the ultimate load resis-
tance [25, 26]. For new constructions, according to EC 8, no contribution of
vertical confinement to lateral resistance should be taken into account in the
design [27]. However, the real confinement effect mainly depends on the rela-
tive rigidity between the masonry wall and the surrounding frame, and to a
lesser extent on material characteristics. Before cracking, the confinement
effect can be neglected [20, 26, 27]. At ultimate load, the confinement increased
the lateral resistance by a factor of 1.2 [25, 26]. However, for walls with a higher
aspect ratio, the confinement increased the lateral resistance by a factor of 1.5
[27]. In addition, the confinement improved the lateral deformations and energy
dissipation by >50% [25, 27, 28].

2.8.3.6 Grout and Epoxy Injection
Grout injection is a popular strengthening method especially for historic build-
ings, as it does not alter the esthetic and architectural features of the existing
buildings. The main purpose of injections is to restore the original integrity