Structural Modelling using Etabs 2018

Aim - Model in etabs and analyse the according to given architectural plan and add shear walls

Procedure -

Open a new model in etabs

Give units as metric SI

Steel as indian

Design code as IS 800 : 2002

Concrete design IS 456 : 2000

Then give grids and story data

Give spacing in X and Y direction for the grids

Then gove story data

From base to plinth give height as 1.5m and remaining all floors as 3m

Give story 1 as master story

Then give remaining all as similar to 1st story

Give material properties

In the define tab go to material properties

Add new material India concrete and grade as M30

Again add new material

Material type as rebar , indian standard and grade as FE415 and HYSD500

Give beams,coloumns and slab

In the define tab select sectional properties and framed sections for beam and coloumns

Add new propert and rectangular concrete

Give property name as B250x450

Give depth as450 and width as 250 as given

In the same process add new propert as coloumn and name it as C400x600 and

Give depth as 400 and width as 600

Because we are modelling the lateral forces also

Give moment of inertia in 2dir and 3dir beams-0.35 and coloumns - 0.7 in the modifiers

Then draw beams at the grid lines

Secondary beams

Add the secondary beams at the places where wall present in the architectural plan

And add the beams at the balconies according to architectural plan

Use replicate and edit frames to draw the secondary beams

For slab

In the define tab select sectional properties and select salb sections

Add a new property

Then rename as S150 and give modelling type as membrane and give thickness as 150 and OK

Add the stair case slab also

But give thicknes of 175 and give one way

Shear wall

In the define tab sectional properties and wall sections

Give material as shell thin and thickness as 300

Then start modelling

Go to any plan view and select all stories

Select quick draw coloumns and select C400x600 and draw at the grid points

Then select quick draw beams and select B250x450Then draw beams at the grid lines

Secondary beams

You can also replicate the beams and coloumns by giving offset and no of times

Add slab

First select similar stories

Go to any plan view and select quick draw floors and select S150

Select the space where slab to be laid

In the same way add the stair case slab

Add shear walls also

There is a tool under the salb

Draw in the way that it should be 1.5% of area

Where you drawn the shear walls you can delete the coloumns in the elevation view

There is also option wall stacks i the draw tab and you can select the desired shape

This is useful in the lifts and staircases

Then assign the loads

In the define tab select load patterns

Select dead load with multiple of 1

Add live load of multiple 0

Wall load as super dead load and multilpe 0

Eq in X directiion of seismic load and code of IS 1893 2016

Eq in Y directiion of seismic load and code of IS 1893 2016

Then select Eqx and modify and select zone as 2 and I factof as .16

Earthquake loads

Time period

From the formula from code 0.09h/`sqrtd`

We get 0.5 sec this is time period in the Eq in all directions because it is symmetrical

Respose factor R

In the shear wall system - 4 and dual system - 5

Importance factor - 1 (Residential building ) IS1893

In the earthquke forces

Then OK

Assign live loads

Select all the slabs

Then assign shell loads and uniform loads and as live and give value of 3KN/M at balconies and lobbys

In the rooms add 2Kn/M

Then assign wall loads

Select all beams

Then assign and frame loads

Then UDl and give value as 3.5

Reduction in live loads by floor to floor

As the floors increases the live loads decreases

After the second floor the live load decreases to 10% till 6th floor as 40% and same for all the above floors

You can edit in desing tab live load reduction factor

Keep user defined and change as defined

Mass source

For earthquake load we have to assign mass source

Define and mass source

Select specefied load pattern and Ok

Now generate load combinations

Define tab and load combinations and select default design combinations

Then select concrete frame design and edit table and OK

Diaphragm

Select all the floors

In the assign tab and shell tool and select diaphragm

You can see the eccentricity of the structure which is useful in lateral loading

We can check the model cases in define

Then analyse the structure by clicking run analysis key

Check the base reactions

We got the base reaction of - 3226 in both sides (Eqx and Eqy)

Check the scale factor in Rsx and Rsy

We got Rsx - 1015 and Rsy - 829

3 times of X axis and 3.8 times Y axis

So add to the Scale factor in Rsx and Rsy to 9806 which is default

Re run the analysis and check the Response base shear which we got the nearly value to 3000

Modal participation ratio

In the tables and structural output we have modal participation ratios enter to display table

In the sum of X and Y axis check where 90% is achieved

It is achieved at mode 12

But Rx and Ry achieved at 16 so 13 modes are eneough

Story reeponse plots

In the story response plots inerstory srift

In the Eqx and Eqy both are less than 4 OK

Mode 1 and Mode 2 are differed by less than 10%

1.54 and 1.42

1.54,1.42 and 1.18

And the first three contribute more than 65% Achieved

Reactions in shear wall

Reactions in the X directions and Y directions at all the shear walls

-4+14-24+289+288-23-4+13 = 549

288-28-69+195-30+55 = 411

960 x 2

2000 approximately

But the base shear is 3226 means shear wall is taking 61% of total load

Then it is classified as dual type building

Axial load ratio

2000x1000/400x600

Thrn divide by the grade of concrete as 25

We get 33% which is less than 40% achieved