Modelling of 25 storey building with the specified properties using ETABS
Modelling of 25 storey building with the specified properties using ETABS
Challenge 6 – ETABS modelling of a 25 storey building
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= 4.4 second Ty1= 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
AIM:
To 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.
Procedure :
- Open the ETABS software and the user interface will open
- Now click on the file tab and select the new model
- The model initialization window will pop up and secet the use built option
- After that chnage the units codes then click on ok
- Then the templates file will popup the emter the grid dimentions ans spacing number of storys as mentions in the quation
- Click on custom grid spacing then click on Edit grid data option then the grid system data window will popu
- In the qus we have 5grids in x direction spacting 4m ans 4grids in y direction 4m spacing
- Add grids and after providing data click on ok
- Now in the story dimention click on the custom story data the window will popup then enter the details as per question
- first we have to change the dimention of plinth as 1.5m
- And rename all and select master story as story1
- Now add story by clicking the right click
- The add story window will popup and provide data and click on ok
- Now the system provide the 25 storys and chnage the master story that story1
- Now click on ok the model will be prepared
- Now go for define tab then select the metarial property then the window will popup and add meterial we use.
- first we have change the region to india and material and its standerds and grades
- we will use M30 concrete and fe415 and 500 steel we should provide the data as given below
- This is for concrete
- This for rebars odf steel metarials
- after that click on ok
- Now in the define tab select the the section property then select the frame section and provide data
- Now click on the new property and the window will popup proivide data
- Beam data below
- Reinforcement data
- Coloumn data:
- Coloumn reinforcement
- In the same the go the tha slab sections
- Slab data:
- Now go to the load patterns
- Now define loads
- MOdify the Lateral loads
- In the define tab select the mass source..
- Now click on the add copy of mass source..
- Now select the specified load patterns then change the load multiplier then click on ok
- Now go to the load cases and check once
- NOw click on the load combination... the window will popup
- select the add default option then select the concrete frame option
- The default combinations will be loaded
- Then click on ok
- Now the material defining stage completed
- It is modeling stage now click on the quick draw coloumn tool
- change the settings one story to all storys and draw the coloumns
- The columns will be drawn below
- Now select the quick draw beam tool
- draw beams by selecting beam locations
- Now select the draw slab tool and draw the slab by using cusor
- if we dont need slab at plinth level so we have to change that to similar story and then draw the slabs
- Now we have to assign the supports
- The base supports are pinned at base
- Now by using select option select the beam elements
- now go to assign tab select the frame loads and the select the udl
- The frame load window will popup
- NOw select the wall load and give the wall load as 10
- Then click on ok
- Now by using the select option select the properties of slab the go to assign tab
- Click on apply then the load will be applied
- Again select the slab property then go to the assign tab then select the shell option then diaphragms option the window wioll popup
- NOw go to the analze tab click on Run analysis option
- The analysis is complted
Result:
Checking the translational fundamental natural period of vibration in both the x and y direction is approximately:
Tx1= 4.4 second Ty1= 4.2 second
for this information go to the tables and analysis results then structure output then model information then go to model periods and frequencues
Tx1 = 3.5
Tx2 = 3.3
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
That is 2.6
Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied
When we add the three mode mass ratios we get 0.9044 which menas first three modes of seismic oscillation contribute more than 65% of building weight as per ETABS anaysis.
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
- Go to display then Storey response plot
- Keeping load case to EQY and switching to max story drift the maximum drift value noted is 0.0020.
