in this lecture I will discuss about the
model analysis, for dynamic analysis
the first thing which we have to define
is a model analysis case that is present
here in the define, in the define model
cases here the default model case is
defined that is model icon model case
time so what is model analysis here is
the official website of computer and
structure in cooperation whose software
is e-tabs sap2000 our safe here is a CSI
knowledgebase okay that is option
official website wicked or CSI America
so what is the model analysis modern
analysis or the mod superposition method
that is second name of the modern
analysis okay is a linear dynamic
response procedure which evaluates and
superimposes free vibration modes mode
shapes to collect rise displacement
pattern for example there is a straight
rod for example for example this is the
building okay
and we apply a apply the letter load at
the top of the building and left it left
the building the building start
vibrating and after some time it comes
to its original position these vibration
modes that are the part of the modern
analysis so here for example when we
vibrate that is the first mode second
mode third mode each building have its
own it's a natural natural thing so mode
shape described the configuration into
which structure will naturally displace
okay and then the the response of each
mode is combined to get the the this
displacement pattern for the whole
bearing
okay so how to consider in the etabs
here in the define that is a predefined
model eigen case type okay here I'll
click modify
here is the properties model case
subtype eigen there are two eigen and
grids vector okay here is a mass source
as we have defined in the previous
lectures if in your building model
p-delta analysis is need to be
considered then automatically here
option will enable if P Delta is not
required then no need okay here is a
maximum number of mods okay so all these
types of things okay by default the
maximum number of towards a 12 okay in
this I will show you the better option
that is a routes vector okay
so parts the what happen with the number
of modes so here I will define three
load pattern set acceleration okay and
you by using okay and here target
dynamic mass participation ratio here
you will put 90 90 okay and what happen
with the number of modes for example
this is a 11-story building for example
for this building I am selecting five
number of modes okay okay then I am
running the analysis while running the
analysis I want to share with you with
you some points and for example if there
is no lateral force so definitely there
will be no displacements in the lateral
direction so gravity analysis will be
enough but in the more in the real be
the lateral forces definitely come and
if the magnitude is high so it's
analysis is compulsory means dynamic
analysis is compulsory so for that the
mode for every dynamic analysis model
this modern analysis is is mandatory so
here I am running the analysis I will
show you what happened with the number
of modes
you
okay now analysis is complete I will go
in the table analysis results then in
the model results then click model mass
participation ratio okay here I have
selected 5 mod okay here is the model
mass participation ratio some okay here
at the fifth mod first mod the mass
participation issue is 22 percent that
is divided by 100 so that's why it's in
the point zero point two two so maximum
that is 0.63 but our target is it should
be more than 90 percent up to 15 a fifth
mode for that I will go again
I will go again back in the define model
case is modified here I will put the how
many number of mods I'll be enough it's
two times your number of storey height
of number of storeys of your building
okay two times 11 okay that is a 22 okay
now I will run again then elseís
okay as the analysis is going on here I
want to also discuss what is the
difference between eigen and reads here
basically in the left side you can read
them in more detail when you picked
modern analysis there is rates and
verses eigen vectors eigen vectors
analysis determine and AM free vibration
mode shapes and frequency of the system
the natural modes provide an excellent
insight into the behavior of the
structure or what is the benefit of
reads vector analysis seeks to find
models mods that are excited by a
particle loading rates vector can
provide a better basics because in the
spawn spectrum a better basis that then
do eigen vectors when used for spawn
spectrum or time history analysis that
are based on model superposition when we
perform the model analysis then the read
specter will be wet okay
now I will again go in the results model
results then model participation
participating mass ratios okay so here
you can see now there are 22 mod ok here
is mod whole number there this modal
case okay more number here you can see
we are saving up to hundred percent mean
one okay
there is 96 percent okay even in de the
upper mods that is too good but the
requirement is complete now we are
considering the whole behavior
if in the first mode you got the 99% or
more than 90% model mass participation
ratio then the first mode will be enough
but now in this case higher mods must
need to be considered okay so we can
also see the time period for example the
first more time period is 1 point 6 6 3
the time period will not change either
you will use the rates vector or eigen
vectors here the first mode time period
second mode third mode up to 22 20
second mode ok we can also see the shape
of each mode I am closing all the tables
now I will go in the display show
deformed shape okay here is a mod so
here is all the mods up to 22 ok for
example we are saying the first mode
whose time period is 1 point 6 6 3
second apply ok it is a time period ok
you can also see the animation now on
for example if I want to see the mode
shape fifth mode ok here is a fifth mode
ok similarly you can check anymore for
example 7th mode apply you can check up
to 20 second mode ok
so that's all for model analysis have a
nice day
