Modelling of 25 storey building with the specified properties using ETABS

 

Modelling of 25 storey building with the specified properties using ETABS

• Question : 

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: $T_{x1}$= 4.4 second $T_{y1}$= 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

 

•  Answer :-

 

Step 1

• Open the ETAB software from the start menu
• Click > New Model
• One dialogue box will open
• Select model initializasation option as > Use Build-in setting with
• Select Display unit > Metric SI
• Steel section database > Indian
• Steel design code > IS 800:2007
• Concrete design code > IS 456:2000

Step 2

• To set the grids and story
• Select > Custom grid setting
• Click > Edit grid data
• 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

• Select > Custom story data
• Click > Edit storey data
• one dialogue box will open
• Double click > Story 1 and rename it as > Plinth Level
• Select plinth level height > 1.5
• Double click > Story 2 and rename it as > Story 1 and keep height > 3
• Double click > Story 3 and rename it 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

• Click > OK
• Rename all the storeys as per shown below
• Select master story > Yes only to > Story 1
• Keep all other remaining story > No
• Keep all other storeys similar to > Story 1
• Keep Plinth > Similar to > None

• It will shows the following results

 

Step 3

• 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 > India
• Material Type > Concrete
• Standard > Indian
• Grade > M30

• Click > Ok
• One dialogue box will open
• Fill the data as per shown below

• Click > Modify material property design data
• Select > Lightweight concrete

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

• Click > Ok

• Click > Ok
• By this similar way, add the rebar for shear reinforcement

• Click > Ok

• Click > Ok
• All the three materials are added

 

Step 4

• To add the sizes of beam, column and slab
• Go to Define tab
• Select > Section properties
• Select > Frame sections

• Click > Add new property

• Select > Rectangular concrete
• Select Property name > B 300 X 400
• Material > M30
• Select section dimension Depth > 400 and Width > 300

• Select > Modify rebar
• Fill the data as per shown below

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

• Click > Ok
• The beam is added
• Now, add another element > Column
• Click > Add new property

• Select > Rectangular concrete
• Select Property name > C 800 X 800
• Material > M30
• Select section dimension Depth > 800 and Width > 800

• Select > Modify rebar
• Fill the data as per shown below

• Go to properties modifier
• As per IS 1893 ( Part1 ) : 2016 clause no 6.4.3.1 the MI about axis for column should be 70%

• Click > Ok
• The column is added
• The beam and column is added

• To add the structural element > Slab
• 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
• The slab is added

 Step 5

• To start the drawing, start with columns
• Keep > All story
• Go to > Plan view > Story 1
• Take Quick draw column command
• Select the appropriate column
• Provide the column, by clicking to all the intersection point of grids
• It will shows the following results

Step 6

• To draw the beam
• Open first story plan view
• Keep > All story
• Go to quick draw beam command
• Select appropriate property
• Click on all grids to provide the beams
• It will shows the following results

Step 7

• To draw the slab
• Open first story plan view
• Keep > 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

Step 8

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

• Click > Apply
• Click > Ok

Step 9

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

• Select Eqx load
• Click > Modify lateral load
• Set all the things as per shown below

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

• Similarly modify lateral load for all other eq loads

Step 10

• To assign the live load
• Keep > Similar stories
• Select all the shells
• Go to assign tab
• Select > Shell loads
• Select > Uniform
• Set as per shown below

• It will shows the following results

Step 11

• To assign the loads of infill walls
• Go to select tab > Select > Object type > Beams > Select > Close
• All the beams are selected
• Go to assign > Frame loads > Distributed
• Select load > Brickwall
• Set as per shown below

• Click > Apply
• Click > Close
• The infillwall load is applied

Step 12

• To assign the mass source
• Go to define tab
• Select > Mass source 
• Select > Modify existing mass source

• Click > Ok

Step 13

• To generate the load combination
• go to define tab
• Select > Load combination
• Click > Add default design combos
• Switch on > Concrete frame design
• Switch on > Convert to user combinations
• The load combinations are generated

Step 14

• To assign the diphragms
• Go to Select > Select > Object type > floor > Select > Close
• Go to assign
• Select > Shell > Diphragms
• one dialogue box will open
• Click > D1
• Click > Apply
• Click > Ok
• The diphragms are applied

Step 15

• To check the model
• Go to analyze
• Select > Check the model

• The model has been checked

Step 16

• The model is ready for analysis
• Go to run analysis
• It will shows the following results

Step 17

• After analysis, we need to check deflection
• Go to show deformed shapes
• One dialogue box will open
• Select the load for which, we want to see the deflection

Step 18

• To see the base reactions
• Go to display
• Select > Show tables

• Click > Ok
• It will shows the following results

Step 19

• To see the modal results
• Go to display
• Select > Show tables

• Click > Ok
• It will shows the following results

 

• Result :-

• Mass participating ratio

• Deflections for various loads

 

• Base reaction