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">Tx1= 4.4 second Ty1">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

Answers:-

Aim:-

1.To model a 25 storey building with specified structural properties structural properties.

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.

2. To carry out the following checks.

• Check if the translational fundamental natural period of vibration in both the x and y direction is approximately: Tx1">Tx1= 4.4 second Ty1">Ty1= 4.2 second
• Check if the following provision in Table 5 of IS 1893 (part 1) – 2016, on torsional irregularity satisfied:
• Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied.

PROCEDURE:-

Step 1

• Open the ETABS software.
• Click > New Model
• One dialogue box will open

• Select model initializasation option as > use Build-in setting with
• Select Display unit > Metric Sl
• Steel section database > Indian
• Steel design code > IS 800:2007
• Concrete design code > IS 456:2000.

• A new window opens-NEW MODE QUICK TEMPLATES.
• Make the settings as follows.

• Now click on edit grid lines.
• One dialogue box will open
• Select > Display grid data as ordinates
• Fill the data in X-Grid data and in Y-Grid data as per shown below.
• Finally click ok.

• Now Select Custom story data in the window NEW MODE QUICK TEMPLATES.
• Click > Edit storey data
• one dialogue box will open
• Enter the datas as follows.
• Click ok

\

• A new window opens.
• Double click > Story 1 and rename it as Plinth Level
• Select plinth level height as 1.5
• Double click > Story 2 and rename it as Story 1 and keep height 3
• Double click > Story 3 and rename as Story 2 and keep height 3
• Double click > Story 4 and rename it as Story 3 and keep height 3
• Right click in window
• Select > Add story
• Select > Keep existing story height
• one dialogue box will open
• Fill the data as per shown below.
• Make story 1 as Master story.
• And make all the stories except plinth and base similar to storey 1.

• Hence both the grids and stories are set, Click ok.
• And it will shows the following result.

Step 2:-

• Keep all the unnecessary viewports close
• Select Plan view > Story 1
• To select the material
• Go to define tab
• Select > Material Properties.

• Click > Add new material
• Select Region as India
• Material Type as Concrete
• Standard as Indian
• Grade as M30.

• Click > Ok
• One dialogue box will appear
• Fill datas as following.

• Click on modify materail property design data.
• Apply light weight concrete.

• Click > OK
• The concrete material is added
• Again go to add material
• Add the rebar for longitudinal reinforcement.

• Click ok
• New window appears.

• Click ok.
• Similarly add the rebar for shear reinforcement.

• Click ok.
• Now the materails are added.

Step 3

• Go to Define tab
• Select > Section properties
• Select > Frame sections To add the sizes of beams and column.

• Click add new property in the that the window that opens.
• Select > Rectangular concrete
• Select Property name as B 300 X 400
• Material as M30
• Select section dimension Depth as 400 and Width as 300.

• Now click on modfiy rebar tab.
• Then fill the datas as folllows.

• Go to properties modifier
• IS 1893 ( Part1 ) : 2016 clause no 6.4.3.1 suggests MI about axis for beam should be 35 %.

• Click OK.
• Now add column as new elememt im the frame sections.
• Select the rectangular sections in the window that opens.

• Click ok.
• A new window appears and fill it as follows.

• Select modify rebar.
• Fill it as follows.

• Go to properties modifier.
• IS 1893 ( Part1 ) : 2016 clause no 6.4.3.1 suggests MI about axis for beam should be 70 %

• Click ok.
• Beams and columns are added.

• Go to define tab
• Select > Section properties
• Select > Slab section
• Click > Add new property
• Propert name > Slab 150
• Slab material > M30
• Modeling type > Membrane
• All the slabs are two way slab, so no need to keep one way slab on.

• Click ok.

STEP 4

• we start with columns
• select to All story
• Go to Plan view
• select story 1
• Take Quick draw column command
• Provide column at proper grids.

• It will shows the following result.

• Then these column are joined by Beams
• Open first story plan view
• select to All story
• select quick draw beam command
• Select appropriate property

• Click on all grids to provide the beams
• It will shows the following results

• Next slabs are provided
• Go to first story plan view
• Keep as Similar stories
• Go to quick draw floor command
• Select appropriate property
• Click in between grids to provide the slab
• It will shows the following results.

• Select appropriate property
• Click in between grids to provide the slab
• It will shows the following results.

Step 5

• To assign the base of building as Pinned
• Go to plan view
• Select Base plan
• Select > One story
• Select all the joints

• Now Go to assign
• Click Joints
• Then click on Restraints
• Select the base as pinned.

• Click on Apply and the ok.

Step 6

• Now add the load pattern
• Go to define
• Select Load patterns
• Add the loads as per shown below.

Step 7

• Select Eqx load
• Then click on Modify lateral load tab.
• Make the setting as shown below.

• Then Select Eqx+ load
• Click on Modify lateral load
• Set all the things as per shown below

• Then select all the other load patterns.
• Make the settings accordingly.

Step 8

• Now assign the live load
• Keep as Similar stories
• Select all the shells.
• Go to assign tab
• Select as Shell loads
• Select as Uniform
• The above settings will shows the following result.

Step 9

• Now assign the loads of infill walls.
• Click on select tab.
• Select > Object type > Beams > Select > Close.
• All the beams are selected.

• Go to assign > Frame loads > Distributed.
• Select load > infill walls.
• Set as per shown below.

• Click apply and then ok.
• This will shows the following result.

Step 10

• Now assign the mass source.
• define tab>mass source
• select modify existing mass source.

• Click ok

Step 11

• Generate the load combination
• go to define tab > Load combination.
• Click > Add default design combos
• Put tick on Concrete frame design
• Put tick on Convert to user combinations

• Now the load combinations are generated as follows.

Step 12

• Now assign the diaphrams.
• Click on select>select>Object type>floor.
• Select and then close.

• Go to assign
• Select > Shell > Diphragms
• One dialogue box will open
• Click D1
• Click Apply and then Ok

STEP 13

• Model check.
• Click on analyse>Check the model

STEP 14

• Run analysis/f5
• Gives the following result.

STEP 15

• Check for deflections.
• Show deformed shapes.
• set for case and mode in the dialoge box opened.
• Select for different loads for deflection.

For Dead load.

For Live load

for Eqx

For Eqy

For Mode 1

For mode 3

Step 16

• Now for base reactions.
• Click display>show tables.
• Do the settings as follows in the window that appears.

• Click ok
• Finally shows the analysis result.

• Tx1= 4.416
• Ty1= 4.222

Step 17

• For modal results,
• Click display>show tables.
• Do the settings as follows in the window that appears.

• Click ok
• Finally shows the analysis result.

• Modal mass participation ratios obtained of first 3 modes of vibration in X direction are:

1. 0.8084
2. 0.1003
3. 0.0328

Step 18

• For story drift,
• Go to display>story display plot.
• Keep Display type as Maximum story drift.
• Also Case combo as Eqx
• Shows the following result.

Checks:

1.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

• Obtained natural periods are;(From the above tables)

1. Tx1= 4.416
2. Ty1= 4.222

• Hence obtained natural periods shows modelling is done correctly.

2.Check if the following provision in Table 5 of IS 1893 (part 1) – 2016, on torsional irregularity satisfied:

ie, 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.

• Obtained natural periods corresponding to translational modes are;(From the above tables)

1. Tx1= 4.416
2. Ty1= 4.222

• Natural corresponding to the Torsional mode;

1. 3.311 (Which is less than period corresponding to natural modes of oscillation)

• Hence results satisfies the prescribed provision in table 5 of IS code 1893(part 1)

3.Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied

1. Modal mass participation ratios obtained of first 3 modes of vibration in X direction are:

1. 0.8084
2. 0.1003
3. 0.0328

=>ie, 80.84 + 10.03 + 3.28 = 94.15% > 65%(as per IS Code 1893 )

2. The fundamental lateral periods of the bulding in 2 pricipal plan directions are away from each other by at least 10% of the larger value

1. Now the difference between X and Y time periods are, 4.416- 4.222= 0.194, which is 4% of the larger value(For fundamental translation periods of Tx1 and Ty1 it is not possible to have the difference greater than 10%)

• Hence satisfies the 1st criteria but not the 2nd criteria.

4.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

• From the graph story drift obtained as;

Maximum story drift from the graph= 0.005425 which slightly greater than 0.004

Results:-

The analysis and checks for the design have carried out and All the checks except clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, ie "The fundamental lateral periods of the bulding in 2 pricipal plan directions are away from each other by at least 10% of the larger value" and provision on inter-storey drift limitations in clause 7.11.1.1 of IS 1893, ie " The maximum story drift should not exceed not more than 0.004 the story height" have satiesfied.