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In all the codes in one way or the other the following parameters are involved. • elastic seismic coefficient (base shear); • design force reduction; • lateral force distribution; • overturning moments.

**Comparison of codes **

In all the codes in one way or the other the following
parameters are involved.

• elastic
seismic coefficient (base shear);

• design
force reduction;

• lateral
force distribution;

• overturning
moments.

1 Base shear

NEHRP provisions, the source document of the IBC, gives the
period formula identical to the *Rayleigh method* in which static
deflection due to a set of lateral forces *F _{i}* is

By taking *R* = *Q*′ = *q*′
= 1 *C _{e}* in the building code corresponds to

2 Design force
reduction

Most codes specify that the
design base shear to be smaller than the elastic base shear (determined from
using elastic seismic coefficient *C _{e}*). For most of the codes
discussed the reduction factors are

3 Lateral force
distribution

According to structural dynamics force at any floor level *i*

If *φ** _{jn}* is
proportional to

but stipulates dynamic analysis for regular buildings *h*
> 40 m in Zones IV and V and *h* > 90 m in Zones II and III. In such
cases

and storey shears for all modes must be done using SRSS and
CQC rules.

4 Overturning
moments

Certain building codes such as
NBC, IBC, and MFDC allow reduction of overturning moment relative to the values
computed by lateral force *F _{j}* by statics because the response
contribution of higher modes are more significant for storey shear than the
overturning moments. The reduction factor in IBC at the base of the building
varies between 1 (no reduction) and 0.8, depending on the number of stories.
The EC-8 permits no reduction of overturning moments relative to the values
computed from lateral forces by statics.

In the following, we will calculate
shear in various buildings based on IS1893 2002, Part 1. The method used in the
other codes will be similar except for some variations. The reader can adapt
the following problems according to their country’s seismic code or
international building code.

Tags : Civil - Structural dynamics of earthquake engineering

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