VERTICAL FORCES :
Eurocode8 requires vertical seismic loading to be considered in areas of high seismicityin the design of the following types of structural element
(a)beams exceeding 20m span
(b)cantilevers beams exceeding 5m
(c)prestressed concrete beams
(d) beams supporting columns
(e)base-isolated structures.
Rulesare given for the vertical response spectrum, which is independent of the soiltype. Vertical and horizontal seismic effects can be combined either using an SRSSrule or a 100%þ30%þ30%rule, similar to that discussed above for the horizontaldirections.
IBCrequires that a vertical seismic load should be considered in all structures.
This is calculated simply as a proportion of the dead load, the proportion increasingwith the seismicity of the site.
A few words from a good EQ book is:
The need to learn from earthquake damage studies and to apply good engineering sense and judgement based on this learning cannot be emphasised too strongly. It is far more important than any amount of computation and analysis.
The common sense lessons from damage studies are as follows.
(a) All frame elements must be detailed so that they can respond to strong earthquakes in a ductile fashion. Elements that are incapable of ductile behaviour
must be designed to remain elastic at ultimate load conditions.
(b) Non-ductile modes such as shear and bond failures must be avoided. This
implies that the anchorage and splicing of bars should not be done in
areas of high concrete stress, and a high resistance to shear should be
provided.
(c) Rigid elements should be attached to the structure with ductile or flexible
fixings.
(d ) A high degree of structural redundancy should be provided so that as many
zones of energy-absorbing ductility as possible are developed before a failure
mechanism is created.
(e) Joints should be provided at discontinuities, with adequate provision for
movement so that pounding of the two faces against each other is avoided.
Author: T.RangaRajan.
