Page 471 - Advanced Design Examples of Seismic Retrofit of Structures

414 Advanced Design Examples of Seismic Retrofit of Structures

negligible effect on the initiation and early development of cracks in the walls.
However, strapping system controlled the relative displacement of cracked sec-
tions of walls with more significant displacements or offsets.
In-plane damage was much less affected by vertical straps. This is largely
because in-plane offsets are smaller and can benefit from the considerable resid-
ual strength in this direction. Similar to their effects on out-of-plane motion of
the walls, straps can only prevent large displacements and crack offsets, as well
as preventing piers from becoming unstable.
Moreover, vertical center-core rods were found to be very influential in
delaying and limiting the damage to walls under both in-plane and out-of-plane
directions. Contrary to straps which were ineffective in delaying the initiation of
cracks, the center-core rods were pretty effective in this regard. Epoxy grout
surrounding the rods which was soaked into the adobe unevenly provided effec-
tive shear transfer between the adobe and the steel rods. Some cracks in the
in-plane walls that started at the corners of the door and window openings prop-
agated to a center-core rod and then were arrested, thus indicating the rods acted
as dowel pins that minimized the relative motion of adobe blocks. The cracks
never became severe [5]. Also, the center-core rods acted as reinforcing ele-
ments in the out-of-plane walls.
Generally speaking, the effects of slenderness ratio were noticeable in out-
of-plane response of the walls, whereas this parameter had negligible effects on
the walls’ in-plane performance. The thin walls easily rocked about their bases
(Fig. 6.16a), and the principal lateral support was provided by the bond beam.
This behavior was not observed in the walls of moderate thickness with the
same bond beam because the thickness of the wall did not permit easy rocking
about the base (Fig. 6.16b). In addition, the out-of-plane motion at the top of the
walls was not amplified as it was in the thinner walls.
The effectiveness of the retrofit measures during test level VI is shown by
the performance of Models 8 and 9. The out of plane unretrofitted gable-end
walls collapsed during test level VI (Fig. 6.17A). The retrofitted gable-end walls

(A) (B)
FIG. 6.16 Comparison of damage in the East wall (out-of-plane direction) after test level VII.
(A) Model 6 (SL:11). (B) Model 2 (SL:7.5). (Adapted from E.L. Tolles, E.E. Kimbro, F.A.
Webster, W.S. Ginell, Seismic Stabilization of Historic Adobe Structures, The Getty Conservation
Institute, Los Angeles, 2000.)