www.sefindia.org

[Econf_Moderator]

Dear All:



Greetings! Welcome to the second day of the E-conference on "IS 16700-
Criteria for Structural Safety of Tall Concrete Buildings".

We hope you had  a good session yesterday. If you need time to catch up
with that session, we suggest you first participate in today’s session
and go back to the previous day’s deliberations later.

We will be discussing Sections 7 and 8 today i.e. Structural Analysis
and Structural Design. You will have time to discuss Section 8 tomorrow
too. (You may continue to post queries and comments on Sections 1 to 6
too)


Section 7

Section 7 is on Structural Analysis. It talks briefly on type of
software that may be used for structural analysis and the considerations
to be included in the modeling. Most of it is familiar to a structural
designer. The new addition in the specification on cracked RC section
properties for unfactored (typically wind forces) and factored loads
(such as earthquake which have been factored down by means of ‘R’
factor) to be used for analysis. These factors also need to be used for
deformation estimation. The section also describes how to model the
floor slabs  rigid diaphragm or considering actual stiffness and when
to consider construction sequence in design.  A brief description about
foundation flexibility modelling considering upper and lower bounds of
soil stiffness is presented.  A general subsection drawing the
designer’s attention to building long term movements is also included.


Section 8

Section 8 deals with Structural Design.

Backstay Effect.

There is a sub-section on Buildings connected to a podium (which may be
part of superstructure and/or  substructure). It specifies the method of
conducting sensitivity analyses using upper and lower bound stiffness
coefficients for the diaphragms, tower core and perimeter walls and has
a long detailed discussion on the backstay effect of the podium outside
the tower and how it needs to be accounted for in the design. The
section discusses buildings with podium having basement(s) and without
basements as well a podium with multiple towers on it.

The section discusses the multiple conditions that the podium level slab
and flexural elements as well as vertical and elements need to be
designed for. It also specifies the amplification factor for design of
these elements when the structure has certain types of irregularities as
specified in the earthquake code IS 1893.

The section specifies prescriptive values of min thickness and
reinforcement in the backstay diaphragm floor slab.

Section 8 has separate subsections for General Design Requirements for
different Structural Systems  Moment Frame, Structural Wall,  Framed
Tubes and so on.

Here’s wishing a very productive discussion on the relevant Section(s)
of IS 16700!

best regards,

Econference Moderators

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