Modelling of 25 storey building with the specified properties using ETABS

AIM:  To model a 25 storey building on ETABS with structural properties as specified below.

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. 
• In this project we are modelling the 25 storey building and concuct design analysis with respect to loads and behavior of the structure 

 

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: $T_{x1}$= 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

PROCEDURE:-

• Open the ETABS software.
• Click on New model to create new model

• After choosing a new model a dialogue box will appear as model intialization.
• Choose the built-in settings option and select the display units and codes as below;

 

• In the "New model quick templete" select the "custom grid spacing'  as below 
• Make  X grid data at a distance of 4 metre and Y grid data as 4 at a distance of 4 metres

• Then in same dialog box itself click on  "custom story data "
• Then make make first level after base as "plinth" level from 1.5 m from the base 
• Rest take as its in height prespective 
• Click on the "FLOOR 3" and add 22 stories to make 25 storey building and name it all sties after plinth as the "FLOOR 1,2,3,4,5,6........24 " and name upmost story as "ROOF " And click OK 

• After the our ETABS screen appear as below;

 

DEFINING MATERIAL PROPERTY:-

• Now , click on define choose "material properties."
• To create material like concrete and steel to be used in the model.
• Define the materials of concrete M30 grade and steel Rebar reinforcement as 415 grade

• Now we successfully added the material properties as below;

DEFINING BEAMS AND COLUMNS:-

• Select "Section properties" under the" define" tab.
• Click on the "frame section' and add new property as beam and input the values as 300*400
• Go to the "reinforcement"  and give design type and rebars as below
• Also look at the property modifier if we work in as ultimate project (make inertia for 0.35 for beam)

 

• Similarly add the colums as beams
• Define properties for the  column as 800*800 

 

• Now we successfully added the frames i.e columns and beams

 

DEFINING SLAB:-

• Now select "Section Properties" under "Define" Tab.
• Select "Slab Sections".
• Select Add new properties in Slab Properties.
• (make modelling type as membrane)

• Now we successfully added the slab

LOAD PATTERN:-

• Now we are adding "load pattern"
• go to the "define" click on "load pattern "
• Add the load as per below showing ;
• Mke sure the give direction and eccentricity to the Eqx and EqY loads 

MASS SOURCE:-

• Mass should be considered for seismic lateral movement
• Go to "define" tab select mass source
• Select modify/show "mass source"
• Slect speified load patterns
• Considered deal load as 100%, LL-25%, wall load or super DL-100% as per code

 

LOAD CASES AND LOAD COMBINATIONS:-

• Check for "load cases" as we assign properly or not, go to "define" tab and select "load cases"
• Go to "define" tab and  select "load combinations"
• Select add default design combo
• Select following properties and press ok

 PLACING THE BEAMS AND COLUMNS:-

• Select quick draw column from left side column
• At bottom left properties object will open 
• Make sure Select all stories from the boottom
• Select property-Column 800*800
• And draw column on grid points 

 

• Similarly, now select quick beam drawn option
• From properties object  select property- Beam 300*400
• Select all stories
• Place the beam on the grids one by one

 

PLACING OF SLAB:-

• Select the slab icon tp draw the slab on similar stories 
• Make sure select similar story not all stories
• Draw the slabs one by one by clicking the middle of the slabs drawn portion 

APPLIYNG LOADS:-

load on frame;

• Now go to select tab in which  select properties and then select frame section and select B300*400
• After selecting beams go to assign tab , select frame loads and  select distributed
• Load pattern name - Type wall, uniform load - type 10KN/m as given 

 Applying Load on slab:-

• Now select slab sections apply the Live load 
• go to select tab and  select properties  in that  select slab section i.e select SLAB 150
• Then go to assign tab  and select shell loads in which  select uniform loading 
• load pattern name-  select live, select load -3kn/m^2

 

 

 

• Similarly appling load on the diaphragm of the slab 
• Select slab section again
• Similarly, go to select tab and  select properties  in that  select slab section i.e select SLAB 150
• Go to assign tab and click on  shell and select diaphragms then select D1 from the dialog box and click ok to aply it

 

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ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer 

 

• The analysis model appeared like this as shown below;

• Then for sheet table visibility in model exploree go to display in which click on the show table click on strcutural output and click ok to makw appeared in the home 

FUNDAMENTAL TRANSLATIONAL NATURAL PERIOD:-

• Then ,go to model explorer - select structure output -  select model information - select modal periods and frequencies by selecting right click of mouse and then table ans check the values 
• Satisfied with Check of  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

CHECK FOR TORSIONAL IRREGULARITY:-

• Now go to modal participating mass ratio and check the values 
• also satisfied with Check of  the following provision in Table 5 of IS 1893 (part 1) – 2016, on torsional irregularity satisfied

 

CHECK FOR INTER STOREY DRIFT:-

• Go to display command and select story response plot 
• then select display type - max story drift, case combo-EqX and EqY  to see the result as below;

•  Similar proces to be followed For EqY

 

RESULT :-

We have created ETABS modelling of a 25 storey building and the result obtained as follows;