Modelling of 25 storey building with the specified properties using ETABS

Aim - To model a 25 storey building on ETABS with structural properties.

Introduction -

1) ETABS is an engineering software product that caters to multi-story building analysis and design.

2) 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.

3) Basic or advanced systems under static or dynamic conditions may be evaluated using ETABS.

4) For a sophisticated assessment of seismic performance, modal and direct-integration time-history analyses may couple with P-Delta and Large Displacement effects.

1) Structural Element Sizes

i) Beams - 300 × 400 mm

ii) Columns - 800 × 800 mm

iii) Slab - 150 mm thick

2) Material Properties -

i) Grade of Concrete - M30

ii) Grade of Steel Reinforcement Bars - Fe 415

iii) Dead Load on beams from infill wall: 10 kN/m (Let us assume the same for roof floor in view of parapet)

iv) 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.

Procedure -

Step 1)

i) Open the Etabs software from deskstop icon

ii) Once software is open - Click on New model

Step 2)

i) Once you click on New model

ii) A Model Initialization setting will open

iii) Select - Metric SI units

iv) Select section database - Indian

v) Select Steel code - IS 800-2007

vi) Select Concrete design code - IS 456-2000

Step 3)

i) Once you click Okay

ii) A following dialog box of grid settings will open

ii) In New Model Quick templates under grid dimensions select the custom grid spacing

iii) Once you click on Custom grid spacing

iv) Click on Display grid data as spacing

Step 4)

i) In New Model Quick templates under Story dimensions

ii) Select the custom story data and then click edit story data.

iii) Now input the storey details

iv) As given in question and Story 1 was selected as the Master story

v) And was applied to rest story from 2^nd story to roof

vi) Click on Okay.

Step 5)

i) Once you click on Okay

ii) A plan and 3D view of model is created in model space

Step 6)

i) Now we have to define the materia properties

ii) Click on Define

iii) Click on Material properties

iv) Add New material as Concrete

v) Select Grade of conccrete - M30............................( given)

vi) Standard as Indian

vii) Click on Okay .

viii) Click on okay

ix) The remaining data is as per IS code

Step 7)

i) Similarly we have to define the materia properties for Steel

ii) Click on Define

iii) Click on Material properties

iv) Select New material as Rebar

v) Select Grade of Steel - HYHD - Grade Fe415...................... ( given)

vi) Standard as Indian

vii) Click on Okay.

viii) Click on Okay

ix) The remaining data is as per IS code

x) Material properties is added

Step 8)

i) Now we have to Define the section properties ( Column and Beam )

ii) Click on Define

iii) Select - Section properties

iv) Click on Frame Section

v) Click on Concrete - Rectangular

vi) Click on Add new property

vi) Give property name - Beam 300x400............( given)

vii) Material type - M30

viii) Section Shape - Concrete Rectangular

ix) Depth - 400 mm

x) Width - 300 mm

xi) Click on Modify / show Rebar

xii) Select M3 Design Only (Beam)

xiii) Select the rebar materials as HYHD Fe415 in both the direction

xiv) Click on okay.

xv) Similarly we have to follow the same steps for Column also.

xvi) Property name - Column 400 x 400 mm

xvii) Material - M30

xviii) Depth - 400 mm

xix) Width - 400 mm

xx) Click on Modify / show Rebar

xxi) Select M3 Design Only (Column)

xxii) Select the Rebar materials as HYHD Fe415 in both the direction

xxiii) Click on okay .

Step 9)

i) Now we have to define Slab properties

ii) Click on Define

iii) Select Section Properties - Select Slab properties

iv) Click on Slab Section

v) Give property name - Slab 150

vi) Slab material - M30

vii) Modeling Type - Membrane

viii) Type - Slab

ix) Thickness - 150 mm

Step 10)

i) Now we have keep the 3D view also to see the properties

ii) Now we have to add the columns and beams

iii) Click on Quick Draw Column option

iv) Select the Column properties which we have defined earlier

v) Draw the columns at the grids as shown in below

vi) Note that - All stories option should be selected which is at the Bottom

vii) Similarly we have to draw beams also

viii) Select Quick Draw Beam option

ix) Select the Beam properties which we have defined earlier

x) Draw the beam as shown below

Step 11)

i) Now we have to add the slabs

ii) Select Quick draw floor

iii) Draw the slabs as shown below

iv) 3D view after assigning the material and section properties

Step 12 )

i) Now we have to assign the base connections

ii) Base connection is given as Pinned type

iii) Click on Assign - Select Joint - Select Restraints -

iv) Select 2nd one - Pinned type

v) Before that - Go to Plinth level - Change the All storey option to One storey as shown below

vi) Click on Okay.

Step 13)

i) Now we have to assign the loads

ii) Select Define

iii) Click on load patterns

iv) Define load pattern dialogue box will open

v) Add the Following loads and Select the IS code for Seismic Case as IS -1893

vi) Following Modification needs to be done in case of Seismic load

vii) Select Zone factor - Zone III - 0.24 ..............................................( given)

viii) Select Soil type - Type II ............................................................( given)

ix) Follow the same for remaining seismic directions

Step 14)

i) Now we have to apply the live loads.

ii) In Assign menu- Select Shell Loads

iii) Click on Uniform loads

iv) Load Pattern as - Live load

v) Load - 3 Kn/m^2

vi) We can see that Floor load has been assigned to all the floors

vii) Now we have to assign Brick wall load for beams

viii) Select Assign

ix) Click on Frame loads - Uniformly Distributed loads

x) Select load pattern as Brick wall

xi) Apply 10 Kn/m load ........................................................(given)

xii) Load has been assigned

Step 15)

i) Now we have to assign Mass source for Modal calculations

ii) Click on Define menu

iii) Select mass source options

iv) Mass source dialogue box will open

v) Add the loads

vi) Dead load - 1

vii) Brick wall - 1

viii) Live load - 0.25 ( Because we only considered some fraction of Live load in calculation of seismic weight )

So live load , upto 3 Kn/m2 - 25%

above 3 Kn/m2 - 50%

Step 16)

i) Now we have to assign Load combinations

ii) For that Click on Define menu

iii) Select Load Combinations

iv) Load Combination box will open

v) Click on Add Default Design Combos

Step 17 )

i) Now we have to assign Diaphragm

ii) Click on Assign

iii) Select Shell - Select Diaphragm

iv) Select D1

v) Click on Apply

vi) Click on Ok

vii) A Diaphragm has been assigned

Step 18)

i) Now we have to create a Modal Analysis

ii) Click on Define

iii) Select Modal cases

iv) Click on Modify

v) Load Case Name - Modal

vi) Load case type - Eigen

vii) Mass Source - Which we have already defined

viii) Click on Okay

Step 19)

i) Before Run Analysis we have to check the model

ii) Click on Analyze

iii) Click on Check Model

iv) A structure is verified without any error and Model has been checked .

Step 20)

i) Now Click on Run Analysis

ii) Once the analysis is done you will see the deform shaped as below

Step 21)

i) Now we have to check the mode as per IS 1893 .

ii) For that click on Display - Show tables

iii) Click on Analysis Result - Select Structural Output

iv) Select Modal Information - Modal Participation and Mass ratio

v) For we have to see the Results of storey drift for Base shear case(EQX or EQY)

vi) Click on Display -Storey response plot

vii) Keeping load case to EQY and selecting max story drift the Maximum drift value is 0.0020

Results -

i) The modeling of G+25 storey has been completed and successfully Analyzed

Parameters		Checks AS per IS 1893	Results
Fundamental Translation Natural Periods	X - Direction	Tx = 4.4 seconds ( given)	4.416 seconds
	Y - Direction	Ty = 4.2 seconds ( given)	4.222 seconds
Torsional Irregularity	IS 1893-2016 ( part 1) TAble 5	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.	Torsional Mode of Oscillation is less than the two fundamental modes of Oscillation i.e Mode 1 = 4.416 Mode 2 = 4.222 Mode 3 = 3.311
Vertical Irregularity	IS 1893-2016 ( part 1) TAble 6 Clause 7	The first Three modes together should contribute at least 65% in mass participation factor in each principal direction	As we could see that 1st Mode itsel contribute more than 65% i.e Mode 1 = 80% Hence Safe .
		Fundamental lateral natural periods in two principal plane direction are away from each other by atleast 10%	As we could see that 1st two modes are not separated each other by 10% i.e Mode 1 = 4.416 Mode 2 = 4.222 Difference is not more than 10% Hence Rechecked
Inter Storey Drift	IS 1893-2016 ( part 1) Clause 7.11.1.1	Storey drift shall not exceed 0.004 times the storey height under tha action of base shear Vb with no load factors	As we could see that the Storey drift is less than 0.004 i.e 0.0020 Hence okay.