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">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

AIM :

• To model a 25 storey building on ETABS with given structural properties
• To check if the translational fundamental natural period of vibration in both the x and y direction is approximate, Tx1 = 4.4 seconds Ty1 = 4.2 seconds.
• To check if the provision in Table 5 of IS 1893 (part 1) - 2016, on torsional irregularity is satisfied.
• To check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) - 2016, regarding vertical irregularity is satisfied.
• To check if provision on inter-storey drift limitations in clause 7.11.1.1 is satisfied.

Introduction:

• ETABS is an engineering software product that caters to multi-story building analysis and design.
• Modeling tools and templates, code-based load prescriptions, analysis methods and solution techniques, all coordinate with the grid like geometry unique to this class of structure.
• Basic or advanced systems under static or dynamic conditions may be evaluated using ETABS ETABS modeling is the generalization that multi-story buildings typically consist of identical or similar floor plans that repeat in the vertical direction.
• Modeling features that streamline analytical-model generation, and simulate advanced seismic systems.
• Once modeling is complete, ETABS automatically generates and assigns code-based loading conditions for gravity, seismic, wind, and thermal forces.
• Users may specify an unlimited number of load cases and combinations.

Procedure:

• First we have to open the etabs software.
• Click on new model.

• "Model initialization" dialogue box will open.
• Go to the "built-in settings with" option and change the different options as "Select Display unit > Metric Si", "Steel section database > Indian", "Steel design code > IS 800:2007", "Concrete design code> IS 456:2000" as shown below.

Creating grids and storeys :

• "New Model Quick Template" dialogue box will open.
• Check the "Custom Grid Spacing" and click on "Edit Grid data".

• The "Grid System Data" dialogue box will open.
• Check on the "Display grid data as ordinates" option and provide the grid's data as given in the question and then click "OK"

• Now check the "Custom Story Data and click on "Edit Story data".
• The "Story Data" dialogue box will open.
• Click on Story land rename it as "Plinth Level" and give plinth level height as 1.5m.
• Click on Story 2 and rename it as "Storey 1" and give storey height as 3m.
• Again click Story 3 and rename it as "Storey 2" and give storey height as 3m.
• Again click Story 4 and rename it as "Storey 3 and give storey height as 3m.
• Now Right click in the window and select add story" and Select "Keep Existing Story Height"
• The "Add Story" dialogue box will open.
• Fill in the required data as per the question requirements.
• Click "OK" and rename all other storeys.
• The following result will shown:

Adding materials:

• Close all viewports and select Plan view and on "Storey 1"viewport on the window.
• To select the material, Go to the "define" tab and Select "Material Properties".
• Click on "Add new material".
• Select Region as "India".
• Material Type as "Concrete, Standard as "Indian" and Grade as "M30" and then click 'OK'
• The "Material Property Data dialogue box will open.
• Check the Data as per requirement or modify it accordingly.
• Click "Modify Material Property Design Data" and Select "Lightweight concrete"
• Click "OK". The concrete material is added.
• Again go to add material and add the rebar for longitudinal reinforcement

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

• Provide the data requirement and then click "OK".
• Similarly, add the shear reinforcement.
• provide Grade 415.

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

• similarly create for HYSD500 material.

Adding Columns, Beams and Slabs

For beam.

• Go to the "Define" tab and Select "Section properties Select and then click on "Frame sections".
• Click on "Add New Property" Select "Rectangular concrete".
• Change Property name to "B-300 X 400"
• Provide Material "M30' and give dimensions as "Depth - 400' and Width - 300
• Select "Modify rebar" and fill in the data as per requirement.

• Click "OK" and the beam is added.

column

• Now, add another element "Column" by Clicking on "Add new property"

• Select "Rectangular concrete", Rename Property name as "C-800 X 800" provide Material "M30" and give section dimension as "Depth = 800" and "Width=800".

• Click "OK" and the column is added.

Slab

• Now for Slab, Go to the "define" tab and Select "Section properties" then Select the "Slab section".
• Click on "Add New Property".

• Change Property name as "Slab 150". Slab material as "M30" and Modeling type as "Membrane" and provide the thickness of slab as 150mm

• Click "OK" and the Slab is added.

Drawing Columns, Beams and Slabs

Drawing Columns :

• Go to the Plan view of Story 1 and select the "All story" option at the bottom.
• Take the "Quick Draw Column" command and select the column "C-800 X 800".
• locate column at the intersection of the grid

Drawing Beams :

• Again open the first story plan view and select the "All story" option at the bottom.
• Go to the "Quick Draw Beam" command and Select Beam "B- 300 x 400".
• click on grid lines in betwwen columns

Drawing Slabs :

• Again open the first story plan view and select the "Similar story option at the bottom.
• Click on the "Quick Draw Floor" command and Select Slab "Slab 150".
• click inbetween the grids where slab should be located

Adding Support

• The building is assumed to be pinned at the base.
• For assigning pinned support, go to plan view and select "Base plan"
• Select the "One Story" option at the bottom
• Select all the joints and then click on the "Assign" tab and Select "Joints" then Select "Restraints" and Select the base as "Pinned".

Adding Load Pattern :

• Click on the "Define" tab and select "Load patterns"
• Add different loads i.e., Dead load, Live load, Infill wall load, Earthquake load in both principal directions and Earthquake load with eccentricity in both principal directions.
• Select "Eqx" load and click on "Modify Lateral Load"
• Fill in all the factors as per the conditions given in the question.
• Then click "OK.
• Now Select "Eqx+" load and click on "Modify Lateral Load".
• Provide Eccentric Ratio as "5% and all other parameters are the same.

Prespective view:

• Similarly follow the steps for live load on the roof

v

Assigning Infill Walls Load to Beams :

• Go to the "Select" tab and click on "Object type".
• Now Click on "Beams" and then click "Select"

• All the beams are selected and for assurance check the bottom left corner.
• Now go to the "Assign" tab and select "Frame Loads" and then "Distributed".
• Select "Infill Walls" as the load pattern name and give the value of "10 kN/m" in the uniform load section

• click ok.

Persepective view:

Assigning the Mass Source :

• Go to the Define" tab and Select "Mass Source .

• Select the "Modify/Show mass source" option
• specify seismic mass as per code and click ok.

Generating the Load combinations :

• Go to the Detine' tab and Select Load Combination

Assigning the Diaphragm to the Floor :

• Go to the "Select" tab and click on "Object type"
• Now go to the "Assign" tab Select "Shell" and then click on "Diaphragm".
• Shell Assignment - Diaphragm" dialogue box will open.
• Select "D1" and click on "Apply" and then click "OK". The diaphragms are applied. Shell Assignment - Diaphragm

3D view:

Checking Model :

• Go to the "Analyze" tab and click on the "Check the Model" option
• Select all the checks which are required to be checked and then click "OK".

• model is ready for analysis.

Run Analysis :

• After checking, click on the "Run Analysis" Icon or press the "F5" function key.

Checking Deflection :

• Click on the "Show Deformed Shapes" icon or press the "F6" function key.
• The "Deformed Shape" dialogue box will open, select the load for which the deflection is required and then click on apply.

Checking Modal Results :

• Go to the "Display" tab and select "Show Table".

• Select the "Model Participating Mass Ratio" Table and then press "OK"

Storey Response plot :

RESULT :

• The 25-storey building has been modelled and analyzed on ETABS with the structural properties and load conditions provided in the questions.
• The requested data are verified as per Indian seismic standards.