PreCast Concrete in Earthquake Regions
How do concrete precast behave in earthquakes?
Based on experience in past earthquakes in Eastern European and in Central Asian countries where these systems have been widely used, it can be concluded that their seismic performance has been fairly satisfactory. when it comes to earthquake performance, the fact is that "bad news" is more widely publicized than "good news."
For example, the poor performance of precast frame systems of Seria 111 in the 1988 Spitak (Armenia) (M7.5) earthquake is well known. However, few engineers are aware of the good seismic performance (no damage) of several large-panel buildings under construction at the same site; these large-panel buildings were of a similar serial as the large-panel buildings.
The precast prestressed slab-column system has undergone extensive laboratory testing that predicted excellent resistance under simulated seismic loading. These building have been subjected to several moderate earthquakes without experiencing significant damage.
Due to their large wall density and box-like structure, large-panel(precast concrete panels) buildings are very stiff and are characterized with a rather small fundamental period. For example, a 9-story building in Kazakhstan has a fundamental period of 0.35 to 0.4 sec. In general, large-panel buildings performed very well in the past earthquakes in the former Soviet Union, including the 1988 Armenia earthquake and the 1976 Gazly earthquakes.
It should be noted, however, that large-panel buildings in the area affected by the 1976 Gazly earthquakes were not designed with seismic provisions. Most such buildings performed well in the first earthquake (M 7.0), but more damage was observed in the second earthquake that occurred the same year (M 7.3), as some buildings had been already weakened by the first earthquake.
Large-panel buildings performed well in the 1977 Vrancea (Romania) earthquake (M 7.2) and in subsequent earthquakes in 1986 and 1990
According to WHE reports, no major efforts have been reported regarding seismic strengthening of precast concrete buildings. However, seismic strengthening of precast frame buildings was done in Uzbekistan (WHE Report 66). The techniques used include the installation of steel straps at the column locations and reinforcing the joints with steel plates to provide additional lateral confinement of the columns.
By safe construction, 80% to 90% of loss can be reduced.
Design span of buildings
Dhajji: Timber frames and bracing. To make earthquake resistant mortar take 1 bag of cement + 3 wheel barrows of sand. The mortar should be used within 1 hr.
Provide beam at plinth + lentil level.