Introduction into seismic design of buildings.

This article was written based on Indian building codes.

Response reduction factor R for buildings in seismic design.

In the seismic design (earthquake) of masonry structures, design forces can be reduced by an R factor for seismic design. This factor is called response reduction factor. The R factor depends on the type of structure. Generally the R values are lower for unreinforced masonry structures and higher for reinforced masonry structures. For R factor related to the type of structure you are designing, consult the building code. In seismic zones or zones prone to earthquakes, the building code will specify the general requirements and type of building to be built.

Seismic weight.

 Seismic weight is the weight of the building that will participate in developing inertial forces during an earthquake. That is the calculated weight based on dead and live loads that will participate in the event of an earthquake.

Importance factor (I) in seismic design

Similar to the response reduction factor, importance factor is also used to adjust the design forces used in seismic design. The I factor increases based on how important the building is. The I  factor is based on whether the building is public or private. For the same kind of building the I factor is increased for public buildings. This is because there is tendency for much more people to be on this type building at the same time.

Design seismic coefficient (Ah)

The design seismic coefficient is calculated based on several factors. These factors are; seismic zone factor, response reduction factor, importance factor and spectral ratio.

As per the Indian building code, Seismic coefficient ;

Ah =(Z/2)(Sa/g)/(R/I) .

Z is seismic zone factor, Sa/g is spectral ratio, R is response reduction factor and I is importance factor.

General requirement for buildings to resist seismic vibrations.

  • Slenderness of the building should be limited as much as possible. This should reduce the possibility of bulking under vertical loads.
  • Building should provide adequate stability against overturning from horizontal forces.

The above points can be achieved if the building is properly designed and adequately  braced using beams, columns, cross walls and buttresses where appropriate.

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