Seismic Zoning of India Questions and Answers

Answer: C

Correct answer: False, because the two demands differ in magnitude, direction and required ductility

Wind is a sustained external pressure on the exposed face, proportional to area, and it acts in one direction at a time. Earthquake force is inertial, proportional to mass, reverses rapidly through many cycles, and acts in whichever direction the ground moves.

The consequences differ accordingly. A wind design need not be ductile, because the load does not cycle into the inelastic range; an earthquake design must be, because it is expected to. Detailing, not merely force, is what the earthquake case adds.

Answer: D

Correct answer: the earthquake case, because force follows mass

Earthquake force is inertial and scales with the seismic weight, so a heavy building attracts a large demand however low it is. Wind force scales with exposed area and increases with height, so a low building presents little of it.

A low-rise heavy structure - a masonry warehouse, a squat concrete building - therefore has small wind loads and large seismic ones, and in Zone V the earthquake case governs comfortably. The reasoning reverses for a tall light building, where wind can control.

Answer: A

Correct answer: Estimating the exact acceleration a particular plot will experience

The map divides the country into four broad bands and gives one factor for each. It cannot supply the acceleration a specific plot will see, which depends on the source of the next earthquake, the path, and the local soil column - none of which a zone number carries.

The other three are exactly what it is for: selecting the zone factor, triggering the code's requirements such as mandatory ductile detailing, and setting a uniform minimum standard across a district. Where a project needs a site-specific figure, a site-specific hazard study is commissioned instead.

Answer: B

Correct answer: the zone in which the district falls on the IS 1893 map

IS 1893 tabulates the country by district against zone, and the zone gives the factor - 0.10, 0.16, 0.24 or 0.36 for Zones II to V.

Nothing else about the district enters it. Rainfall, population density and existing building heights have no bearing on how strongly the ground will shake; the classification comes from tectonic setting and the historical record of earthquakes. Districts are used as the unit simply because they give an unambiguous administrative boundary a designer can look a site up in.

Answer: C

Correct answer: Zone III

The four zone factors are distinct, so the mapping is one to one: 0.10 is Zone II, 0.16 is Zone III, 0.24 is Zone IV and 0.36 is Zone V.

A value of 0.16 therefore identifies Zone III without ambiguity. The set is worth carrying in memory as a whole, since questions in both directions - zone to factor and factor to zone - reduce to reading it off, and the intervals between the values are uneven enough that interpolation would be meaningless.