Structural Modelling using Etabs 2018

Aim:- To model and analyze the G+7 residential building from the given architectural drawings using the ETABS 20.1.0-20.

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.

Procedure:-

Step:1

• First we have to open the etabs software.
• Next click on the file option at the left side top corner and select the new model, as shown below.

• After selecting the new model the new tab opens, in that tab we have to select 'Use Built-in Settings with' option.
• After setting the model Initialization the templates tab will opens and, select the Grid only and press ok.
• Next we need to do the settings in Grid system data, as shown below.Next we need to add the stories upto 7 story in the Story Data.
• The 7 stories are added in the Story Data, as shown below.

Step:2

Define Material Properties

• Next we need to define option and select material properties, as shown below.

• After selecting the material properties the new tab appears, then we add new materials by selecting the Add new material option, as shown below.

Step:3

• Now we need to add material type as concrete and grade as M30.
• Next we need to check the material property data, as shown below.

Step:4

• Now we need to add new material type as rebar and grade as HYSD Grade 500.
• Next we need to check the material property data, as shown below.

Step:5

• Now we need to add new material type as rebar and grade as HYSD Grade 415.
• Next we need to check the material property data, as shown below.

Step:6

• Now we need to select the section properties and click on the frame sections, as shown below.

Step:7

• After selecting the frame sections the new tab will be visible, in that we need to select the Add New Property, as shown below.

• After selecting the Add New Property, the new tab appears.
• In that new tab we select the Rectangular shape type in concrete, as shown below.

• Next the frame section property data will be visible, In that we add beam size as B300x400.
• Next we need to select the Modify/Show Rebar option as shown below.
• After selecting the Modify/Show Rebar option the new tab appears, In that we select the design type as M3 Design only (Beam).
• Next we select longitudinal bars with the grade of HYSD500.
• Next we select Confinement bars with the grade of HYSD415.

• Again we have to select Rectangular shape type in concrete, as shown below.

Step:8

• Next we have to add the column size as 400X400 in the frame section property data, as shown below.

• Again we have to add the another column size as 400X600 in the frame section property data, as shown below.

Step:9

• Next we select the slab section option from the section properties, as shown below.

• Next the slab properties tab will be vissible, In that we select the Modify/Show Property option.
• In that we need to put the slab name as Slab 125, it means slab with the thickness of 125mm.
• And we take the concrete grade as M25, as shown below.
• Next we have to click the ok option.
• Again add 115mm slab.
• Now we take the slab thickness separately for staircase with the thickness of 175mm.

Step:10

• Next we have to add the wall properties in the wall property data, as shown below.
• Give 300mm wall thickness.

Step:11

Draw Column,Beams,Slabs,Walls

• Next we need to add the columns using the Quick draw columns option, as shown below.

Step:12

• Next we need to add the beams using the Quick draw beams option.
• Next we need to add the secondary beams using the Quick draw beams option.
• Next we add the shear walls in required locations in the residential building.

Step:13

• Next we need to add the slabs using the Quick draw floor option.
• Give Desire opening to the floor.

Step:14

Joints to the Base

• Now we go to the base plan and select all base joints.
• Next we select the Restraints from joint option.
• Now we need to select the fixed joint and click on apply and then click on close button, as shown below.

Step:15

Load Patterns

• Next we need to select the load patterns from the define option.
• Now we should add Dead load, live load, Brickwall load, and earthquake load, as shown below.

Step:16

Assigning Loads

• Next we need to select the distributed load from the frame loads.
• Then after the new tab will appear, In that we select load pattern as Brickwall, and we take uniform load as 3.5 kN/m and then click on the apply button and close.
• Give 1KN/m for balcony wall.

Step:17

• Next we have to click on the assign option and then select shell loads, from the shell loads we select the Uniform option.
• Here we apply the 3KN/m^2 live load for the staircase portion, varanda,balcony and lift core area.
• Next we apply the 2KN/m^2 live load for the remaining portions in the residential building, as shown below.

Step:18

Live load Reduction

• Next we have to select live load reduction factors from the design option.
• Now we add the reduction factor by decreasing 10% from 1st floor to 7th floor, as shown below.

Step:19

Defining Mass source

• Next, from the define option we select the mass source.
• Next we add the load patterns in the Mass Source Data, as shown below.

Step:20

Assigning Diaphragms

• In the select option we select object type option, as shown below.

• After selecting the object type option, the new tab will be visible, In that select the floors and click on the select button and close.
• Next we have to select the Diaphragms from the shell option.
• After selecting the diaphragms the new tab will appear, in that select D1 and click on the apply button and close.

Step:21

Defining and Assigning Pier Lebel

• Next we have to select the Pier label from the shell option.
• Before going to the shear wall design we have to assign the names for the shear walls(P1,P2,P3,P4,P5,P6,P7,P8), as shown below.

Step:22

Defining Load Combination

• Next, from the define option we select the load combinations.
• After selecting the load combinations the new tab is visible, In that we select 'Add Default Design Combos' option.
• Next we select "concrete frame design" & "concrete shear wall design" in the 'Add Default Design Combinations', as shown below.

• Now we can see here that the load combinations are visible, as shown below.

Step:23

Checking Model

• Next we have to check the model by clicking the check model option.
• After the model is checked, then the warning tab will be visible and it tells that there is no warning messages, as shown below.

Step:24

Defining Response Spectrum Function

• Now we select the Response spectrum from the Functions from define option.
• After selecting the Respnse spectrum the new tab is visible, In that we choose IS 1893 2016 from the 'Choose function type' and click on the Modify/Show spectrum option.
• After selecting the modify/show spectrum option the new tab will be visible, In that we give the Function name as 'IS FUNCTION' and remaining details will be set by the software itself,we don't need to change any of the details in that response spectrum function tab, as shown below.

Step:25

Adding Response spectrum in Load case type

• Next we have to select the Load cases from the Define option.
• We select the 'Add new case', as shown below.

• Now we have to enter the details of load case in the 'Load case data', as shown below.

Analysing Model

• Now we have to run analysis.

Step:26

Checking Table Results

• Next, from the display option we select the show tables option.
• After selecting the show tables option the new tab will be visible.
• Now we select the Base Reactions and click on the ok button.

• Next the Base Reactions table will be visible, as shown below.

Output Case	FX KN	FY KN
Ex	2366.0789	0
Ey	0	2366.0791
RSx	1090.7506	0
RSy	0	984.4788

• Here we have to check that EQ should be closer to the RS, to get the closer to each other we should calculate that, `frac{Ex}{RSx} x Scale factor of RS
• Now substituting the values from the table, at X-direction `frac{2366.0789}{1090.7506}`x 9806.65
• At X-direction we get, 21272.58

• At Y-direction we get, 2366.0791/984.4788 x 9806.65
• At X-direction we get, 23568.32
• We put the above values as scale factor for response spectrum at X and Y directions in the load case data.
• After we enter these values for response spectrum as scale factors at X and Y directions in load case data, then the EQ is closer to the RS from the base reaction table, as shown below.

Step:27

• Next, from the display option we select the show tables option.
• After selecting the show tables option the new tab will be visible.
• Now we select the Modal Participating Mass Ratios and click on the ok button, as shown below.

• Now the Modal Participating Mass Ratios table will be visible, as shown below.

1. As per IS 1873 clause 7.1,the natural period corresponding to fundamental torsional mode of oscillatio should not be greater than sum of two fundamental translational mode of oscilation(Tx+Ty>Txy)-from table 1.131+1.045=2.176>0.832.hence no torsional irregualrity.
2. IS 1873-clause 7.1,table 6 the frist three model contribution should be more than 65% of mass participation factor in each principal plan direction.Here it is 0.68>0.65.
3. Under same table,the fundamental lateral natural period of building in two principal plan direction should differ by atleast 10%.Here Tx=1.131 and Ty=1.045,differ by 8.2%,hence Its fails.
4. From modal number,maximum required is 12 number as it capture more than 90% of mass in all 6 degrees of freedom.

Step:28

• Next we select the Story response plots from the Display option, as shown below.
• The story response for maximum story drifts at X & Y directions, should not be more than 4%.

Step:29

• Next we open the select plan view tab and select the base floor, as shown below.

• Next we have to open the reactions tab, then we select the eartquake load towards X-direction(EQX) in the load case, then click on the ok buttion as shown below.
• Now the base shear reactions will appear, as shown below.
• When we divide the base shear taken up by the shear wall divided by the total base shear of building will get the % of the shear forces taken up by the shear wall.
• And if that is less than 80%, then the more shear walls we need to add to the structure.

Check for aspect ration for both column and shear wall.

Column-the aspect ratio should be less than 0.4.(aspect ratio=force/cross section area*fck).

Lets consider for first load combination(1.5DL),force 2576kN.

Aspect ratio=2576*1000/400*600*30=0.35< 0.4,hence ok.

RESULT:

• The structural model is designed for given architectural planning using etabs.
• Frame model which satisfy both codal provision are analyses.
• Columns,shear walls and beam are procided in possible symmetrical way without much offsets.
• Analyses is done for modal number,base shear,storey drift,aspect ratio,irrgeluarity etc.,
• As per the analyses result,building is bit flexible in y-axis,as shear wall are sufficient add addiitonal column as provided in y-direction to meet the maximum storey drift limit .