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[SKSNL at ltecd.ltindia...]

This is with reference to section 12 (Design and detailing for
earthquake loads) of the draft IS: 800, its correlation with IS: 2062
and availability of steel products.

Aseismic design heavily relies upon post-yield inelastic response of
结构,特别是SMF evident from the response
reduction factor (R). It implies that if the design criteria for SMF are
followed, then steel sections would be able to undergo plastic
deformation at specific locations to form a predicted mechanism.
Therefore, such frames are capable of collapse prevention and life
safety performance, even if they are designed for relatively less
seismic load.

As per IS: 2062, Fe 410W Grade-A steel is to be adopted only for
non-critical applications (Refer to Foreword), where there is no risk of
brittle failure. Otherwise, Grade-B steel should be used, wherever the
structure is subjected to severe fluctuation of stresses.

The risk of brittle failure cannot be accepted by any means in aseismic
design. This warrants usage of Grade-B steel strictly. But in reality, I
understand, manufacturers (irrespective of what their catalogue shows)
are producing Grade-A steel in general and Grade-B steel is not readily
available. As a result, we find only Grade-A steel is used to build
structures in India, except for plates having thickness > 20mm. All the
structural components (except large crane girders) are of Grade-A steel,
including the lateral load resisting system of the structure. So also
the connections adopting plate thickness lower than 20mm. For
illustration, this applies for large span trusses, columns, bracing
etc.

I was just pondering over .......

1) Does not this go against the criteria of earthquake resistant design
by enhancing the risk of brittle failure? Here also, the structure is
subjected to severe fluctuation of stresses in the inelastic range.

2) If the above understanding is incorrect, than how the usage of
Grade-A steel is justified in lateral load resisting system and the
connections, in view of earthquake resistance?

My concern is, if the material of construction (as available) does not
support or not compliant with design philosophy prescribed by the code,
then adhering to the codal provisions will not yield the desired result.



I shall be grateful for the advice / view of learned Moderators and
Participants, in this regard.


Respectfully,

Subhamoy Kar

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