Civil Engineering Reference
In-Depth Information
FIGURE 4.8
Damage caused by a soft story due to a parking garage on the first floor. The damage occurred
during the Loma Prieta earthquake in California on October 17, 1989. (
Photograph from the Loma Prieta
Collection, EERC, University of California, Berkeley.
)
beams, and beam-column joints to sustain deformation demands depended on how well the
seismic design and detailing requirements were followed both in design and in construction.
A large number of residential and commercial buildings were built with soft stories at the
first-floor level. First stories are often used as stores and commercial areas, especially in the
central part of cities. These areas are enclosed with glass windows, and sometimes with a sin-
gle masonry infill at the back. Heavy masonry infills start immediately above the commercial
floor. During the earthquake, the presence of a soft story increased deformation demands very
significantly, and put the burden of energy dissipation on the first-story columns. Many fail-
ures and collapses can be attributed to the increased deformation demands caused by soft sto-
ries, coupled with lack of deformability of poorly designed columns. This was particularly
evident on a commercial street where nearly all buildings collapsed towards the street.
Examples of this soft story condition are shown in Figs. 4.9 and 4.10.
5.
El Asnam earthquake in Algeria on October 10, 1980:
An interesting example of
damage due to a soft story is shown in Fig. 4.11 and described below (National Information
Service for Earthquake Engineering 2000):
Although most of the buildings in this new housing development [see Fig. 4.11] remained
standing after the earthquake, some of them were inclined as much as 20 degrees and dropped
up to 1 meter, producing significant damage in the structural and non-structural elements of the
first story. The reason for this type of failure was the use of the “Vide Sanitaire,” a crawl space
about 1 meter above the ground level. This provides space for plumbing and ventilation under
the first floor slab and serves as a barrier against transmission of humidity from the ground to
the first floor. Unfortunately, the way that the vide sanitaires were constructed created a soft
story with inadequate shear resistance. Hence the stubby columns in this crawl space were
sheared off by the inertia forces induced by the earthquake ground motion.
Although the above five examples show damage due to a soft story located on the first
floor or lowest level of the building, collapse at other stories can also occur depending on
