Structural Modelling using Etabs 2018
AIM:
The architectural drawings for a G+7 residential building in zone 5 has been provided. The floor plan is the same for all 7 floor levels. Possible column positions have also been provided. Conceptualize a framing plan layout and then model the building in Etabs. The following architectural drawings have been provided:
- Typical floor plan – The location and thickness of the brick walls and the use of the
space (for estimating live load) can be obtained from this plan - A building section through the staircase and lift core is provided
- Parking layout in the ground floor – the column/shear wall arrangement must not
obstruct entry/exit of vehicles.
The following loadings are to be taken into account: - Brickwall made of AAC blocks
- Finishes – floor tiles of 75 mm thickness
- Live loads as per IS 875 part 2
- Water tank of 20 KL above the staircase at Mumty level
- Lift Machine room at mumty level above lift core
The structural model must comply with provisions of IS 1893 and IS 13920.
Run a modal response spectrum analysis and check analysis results of the etabs model for inter-storey drift requirements, vertical & planar irregularities, minimum shear wall requirements,maximum axial load ratio for column and shear walls, effective moment of inertia for beams
and columns etc.
Please note that the column positions shown in the architectural typical floor plan are only to provide an initial starting point for modelling. Participants will have to change its size, introduce shear walls, and add new vertical elements after running the analysis. You will have to run the analysis multiple times until a structural model is obtained that meets structural code requirements without compromising architectural functions. Also, there is no one ‘correct’ structural system for this challenge. There can be multiple possible solutions for this problem.
PROCEDURE:
Open Etabs software edit story & grid systems
Add upto 7 story data
Open the created plan in 3D view
Now define option & select material properties.
Add new material as concrete M25
Add new material properties as rebar & HYSD &Grade 415
Add new material type as rebar & grade as HYSD 500
Click define tab >section properties>frame section>Add new property>Rectangular shape type concrete>Add column size as
B250*450
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.
Select Rectangular type of concrete again
Add column size as 300*500
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.
Add column size as 400*400
Add another column size as 400*600
Select define tab>section properties>slab section>modify/show property option>give slab name as slab 125>concrete grade M25>ok
Add wall properties as shown below
Add columns using quick draw column option
Add beams using quick draw beam icon
Add second story beams using the quick draw beams
Add the walls in required locations
Add the slabs using the Quick draw floor/wall option
Go to base plan & select all base joints
From assign tab select joints ,restraints
Select the fixed joint ,click apply & close button
Select load pattern from define option
Now add Dead load,live load,wall load & seismic load
Select distributed load from the frame loads
New tab appears in that select wall load & apply uniformly distributed load as 3.5kn/m^2
Unser assign tab click assign shell load apply a uniform distributed load of 2kn/m^2
Select Live load reduction factor under design tab
Add the reduction factor by decreasing 10%from 1st to 10th floor
Select mass source under define option
Add load patterns in mass source data
Under select tab ,select object type ,a new tab appears choose floors in that & close
select the Diaphragms from the shell option, as shown below.
After selecting the diaphragms the new tab will appear, in that select D1 and click on the apply button and close.
Next we have to select the Pier label from the shell option, as shown below.
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.
Next, from the define option we select the load combinations, as shown below.
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.
Next we select the Modal cases from the Define option, as shown below.
After selecting the Modal cases the new tab is visible, In that we give modal case name as Modal 1 & we give the maximum number of modes as 20, as shown below.
Next we have to check the model by clicking the check model option, as shown below.
After the model is checked, then the warning tab will be visible and it tells that there is no warning messages, as shown below.
Now we select the Response spectrum from the Functions from define option, as shown below.
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, as shown below.
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.
Next we have to select the Load cases from the Define option, as shown below.
Next the Load cases tab will be visible, In that 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.
Now we have to do the run analysis, as shown below.
Step:-30
- Next, from the display option we select the show tables option, as shown below.
- After selecting the show tables option the new tab will be visible.
- Now we select the Base Reactions and click on the ok button, as shown below.
Next the Base Reactions table will be visible, as shown below.
Here we have to check that EQ should be closer to the RS, to get the closer to each other we should calculate that, (EQRS)×(EQRS)×Scale factor of Response spectrum.
Now substituting the values from the table, at X-direction (2844.6348900.7656)×(9806.65)(2844.6348900.7656)×(9806.65), at Y-direction (2844.63481002.1982)×9806.65(2844.63481002.1982)×9806.65
At X-direction we get, 30969.
At Y-direction we get, 27835.15
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.
Next, from the display option we select the show tables option, as shown below.
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.
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%.
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.
RESULT:-
The G+7 residential building has been modelled and analyzed successfully using the ETABS 2018.
