Modelling of 25 storey building with the specified properties using ETABS
Challenge on:
Modelling of 25 storey building with the specified properties using ETABS
Model a 25 storey building on ETABS with structural properties as specified below. Ground floor or plinth floor level can be taken at a height of 1.5 metres from the base. Each of the successive 25 storeys has a storey height of 3 metres.
Structural Element Sizes
- Beams : 300 × 400 mm
- Columns : 800 × 800 mm
- Slab : 150 mm thick
Material Properties
- Grade of Concrete : M30
- Grade of Steel Reinforcement Bars : Fe 415
Loading
- Dead Load on beams from infill wall : 10 kN/m (Let us assume the same for roof floor in view of parapet)
- Live load on floor : 3 kN/m2 (Let us assume the same for roof floor)
a) Buildings are assumed to be pinned at the base
b) All columns in all storey are of the same size
c) All beams in all storeys are of the same size
d) Building is located on Soil type-II and in Zone-III. Assume other factors if required.
Carry out the following exercises:
- Check if the translational fundamental natural period of vibration in both the x and y direction is approximately: Tx1">Tx1Tx1= 4.4 second Ty1">Ty1Ty1= 4.2 second
This check will help confirm if modelling is done correctly. Some deviations from the above values is possible (± 2%). But any major deviation will suggest an error in modelling.
- Check if the following provision in Table 5 of IS 1893 (part 1) – 2016, on torsional irregularity satisfied:
The natural period corresponding to the torsional mode of oscillation must be less than the two fundamental translational modes of oscillation along each principal plan directions.
- Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied
- Check if provision on inter-storey drift limitations in clause 7.11.1.1 satisfied. Please note that this check is for Serviceability Limit State and hence is for situation when stucture is subjected to unfactored seismic base shear
Stepwise procedure :-
Step 1-
- Open ETAB software
- Click > New model
- One dialogue box will open
- Select all appropriate data and click OK
- Again one dialogue box will open
- Click >custom grid spacing > Edit grid data
- set the x and y ordinates as below
- click > Ok
- click > custom story data > Edit story data
- one dialogue box will open
- give all appropriate data (create 25 stories for the model as given in question and make the 24 stories as similar to story 1 excluding story 1)as shown below
- click > OK
Step 2-
- Go to Define tab
- Click > Material
- One dialogue box will open
- Click > Add new material
- Fill all necessary details as below
- Click > OK
- again dialogue box will open , fill the details
- click >ok
- Again click > Add new material
- Fill all necessary details as below
- Click > OK
- again one dialogue box will open , fill the details as below
- Click > OK
- Click > OK
Step 3-
- Go to define tab
- Click > section properties
- Click > Frame sections
- One dialogue box will open
- click>add new property
- again dialogue box will open
- Select > Rectangular section
- Again dialogue box will open
- Give property name : B300X400
- Material : M30 as shown below
- Click > Modify/show rebar
- Dialogue box will open
- Click >OK
- Again click > Add new property
- Dialogue box will open
- Give property name : C800X800 and all necessary data as shown below
- Click > Modify/show rebar
- Again dialogue box will open
- Fill all properties as shown below
- Click >ok
- Click > ok
- Click > ok
Step 4-
- Go to define tab >Section properties>Slab sections
- Dialogue box will open
- Click > Add new property
- Again Dialogue box will open
- Click >ok
- Click >ok
- Click >ok
Step 5-
- Go to define tab > load pattern
- Dialogue box will open
- Give required details as below
- Click > EQX
- Click > Modify lateral load
- Dialogue box will open
- Fill all details
- Click ok
- Do it same for EQY
- Click >ok
Step 6-
- Go to define tab > Mass source
- Dialogue box will open
- Click> modify/show mass source
- again Dialogue box will open
- fill all details as below
- click > ok
- click > ok
Step 7-
- Go to define tab>load cases
- Dialogue box will open
- Click >ok
Step 8-
- Go to define tab> load combination
- One dialogue box will open
- click > add default design combination
- Click > ok
- Click > ok
- Click > ok
Step 9-
- Click>quick draw columns symbols
- In the properties of object, select as C800X800mm
- ( ensure the all story option is ON )
- Click to draw the column on the intersecting grids/by the selecting all the grids
- Draw all the columns on required positions
- Click > Quick draw beams
- Select property as B300X300mm
- Create the beams by clicking once on each of the lines/ (or use the replicate option )
Step 10-
- Go to plan option (dialogue box will open)
- Select story 1
- Click >apply>OK
- Change the type as similar story instead of all story option
- Click . quick draw floors
- Change property as : S150 and all required data as shown below
- Create the by clicking once on each of the floor
- The floors is get created.
Step 11-
- Go to select >properties>frame sections
- One dialogue box will open
- Select B300X400mm
- Click > select>close
Step 12-
- Go to assign > frame load.> distributed
- One dialogue box will open
- Take all the details as shown below
- Click > apply > ok
- Go to select > select > properties> slab section
- Dialogue box will open
- Select S150
- Click > select > close
- Go to assign > shell loads > uniform
- Dialogue box will open
- Give the load pattern name and all the details as below
- Click > apply >ok
- Go to select > select > properties> slab section
- One dialogue box will open
- Select S 150
- Click > select > close
- Go to the assign tab > shell > diaphragm
- One dialogue box will open
- Select the D1
- Click >apply > ok
Step 13-
- Click on Run Analysis
- Choose the appropriate folder
- Click > save (it will take some time to analyse the model, once completed analysis the deformed shape of model is visible)
- For the result of model periods of different modes
- Go to the display tab
- click on Show responce plot
- box will open (change the details as below and see the results for the maximum story drift )
Result shown in tables for the different criteria:-
|
criteria |
|
Desirable solution |
Exercise result |
|
Fundamental translational natural period |
X-direction Y-direction |
4.4 second 4.2 second |
5.48 5.48 |
|
Torsional irregularity |
IS 1893-2016 (part-1) Table-5 |
Torsional mode time period should be lesser than X and Y direction time period |
YES |
|
Vertical irregularity |
IS 1893-2016 (part-1) Table-6 clause-7 |
First three modes together should contributes at least 60% in mass participation factor in each principal direction. Fundamental lateral natural periods in two principal plane directions are always from each other by at least 10% |
YES
NO |
|
Inter-story drift |
IS 1893-2016(part-1) clause7.11.1.1 |
Storey drift shall not exceeds 0.004 times the storey height for base shear with no load factors (4X10 -3 i.e. 0.004) |
YES |