Masonry Magazine April 1986 Page. 41
Conclusions
The following general conclusions are related to the behavior of various types of structural systems in Mexico City:
1) Severity of structural response was directly related to the degree of resonant response. Investigators at UNAM have suggested a correlation between the geographical distribution of structural damage, and the depths of the soil strata underlying Mexico City. In general, such a correlation is significant on design of buildings in seismic zones and in particular in Mexico City.
2) As has been observed in many other earthquakes, and as has been noted in other reports on the Mexico City earthquake, many of the buildings which behaved poorly appeared to have the following structural characteristics:
a) lack of a consistent structural concept for resisting lateral loads:
b) abrupt changes in structural stiffness or strength from one level to another, or from one part of a floor to another;
c) unnecessarily heavy floors:
d) lack of structural redundancy and multiple mechanisms of lateral force resistance;
e) lack of ductile design characterized by inadequate detailing of beam column and beam slab connections:
f) inadequate separation between adjacent structures, often resulting in hammering damage; and
g) short column conditions created by partial-height infills.
Those characteristics, plus location, determined the performance of buildings in the Mexico City earthquake. The following conclusions relate specifically to the performance of masonry buildings in Mexico City, and to the influence of masonry on the performance of all types of buildings there:
3) Older, low-rise masonry construction generally performed well. Such structures were stiff enough so that they were not subjected to significant inertial forces generated by the long period ground motion.
4) Modern medium and high-rise framed structures with masonry infills generally performed better than otherwise similar structures without infills. This was due to the reduced inertial forces consistent with the shorter periods of vibration of the stiffer, infilled buildings, and was a consequence of the peculiar soil conditions of Mexico City. Masonry infills generally appeared not to have been designed as structural elements. They were usually unreinforced, were not tied into the surrounding frames, and sometimes suffered severe damage. However, they absorbed large amounts of dynamic energy and it appears that in many cases prevented structural collapse. Careful study is required to determine the applicability of this conclusion to areas other than Mexico City.
Recommendations for Further Research
1) Investigators at UNAM have suggested a correlation between the geographical distribution of structural damage, and the depth to the first hard layer. This should be investigated further.
2) In many areas of the city, some buildings collapsed while similar adjacent buildings remained standing. This study had concentrated primarily on buildings which failed.
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MASONRY-MARCH/APRIL, 1986 41