Page 458 - Advanced Design Examples of Seismic Retrofit of Structures

404 Advanced Design Examples of Seismic Retrofit of Structures

(E) 4
Good precondition, unretrofitted d
t
t
e
Poor precondition
Retrofitted
EERI damage level (C) 2 motion of cracked block
3
(D)
Severe damage- Large
Moderate
1
collapse
(B)
damage- Cracks
open section and potentioal
Slight damage-
Crack initiation
(A) 0
0 0.1 0.2 0.3 0.4 0.5 0.6
PGA, g
FIG. 6.9 Damage level versus estimated horizontal peak ground acceleration for historic adobe
buildings after the 1994 Northridge earthquake (for damage states, refer to Table 6.2).
improvement of such buildings, the results of 10years of research in the form of
shaking table tests on nine small-scale (1:5) adobe specimens are presented in
this section. This research was conducted by GSAP with the help of an inter-
national group of specialists and earthquake engineers, which was performed
first on small-scale models at Stanford University [5].

Specimens’ Description
The description of the small-scale model buildings are shown in Table 6.3. List-
ings of the 10 simulated earthquake motions based on the 1952 Taft earthquake
in Kern County, California are presented in Table 6.4. The estimated peak
ground acceleration (EPGA) is similar to the actual peak ground acceleration
(PGA), except that the EPGA is determined from the response spectrum
between 0.125 and 0.5s. All models were shaken in a uniaxial east-west
direction.
The concept of Model 8 was to add further retrofit measures to minimize the
extent of damage during very strong ground motions. That is because in some
cases it is necessary to reduce intermediate levels of damage and to ensure that a
building remains reparable. The tests on Models 4, 5, and 6 were performed to
determine the effects of wall thickness on seismic behavior. As shown by the
results of this study which are presented in the following, the specific retrofit
system used was the dominant factor in the performance of these models and
walls slenderness ratio was of secondary importance. The retrofit system used
on Model 8 was similar to that of Model 7, except fiberglass center-core rods
were installed in two adjacent walls. In general, the retrofit systems used in
models 7 and 8 were extremely effective and greatly improved the overall seis-
mic response. Further information about the specimens may be found
elsewhere [5].