Structural Modelling using Etabs 2018
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.
ANS:
Procedure:
- Open the ETabs software.
- Click the file menu and choose to create a new model option.
- Choose the built-in settings option and select the display units and codes
- Select Custom Grid spacing and custom story data.
- Select Material properties under define ta
- Now select Section Properties under Define Tab.
- Select Frame Sections.
- Select Add new properties in Frame Properties.
- Now Draw columns of size 400X400 mm at the intersection of the horizontal and vertical grids and beams with quick draw Column keeping all the stories on.
- Now draw columns of size 400X650 mm at the intersection of the horizontal and vertical grids and beams with quick draw Column keeping all the stories on.
- Now Draw the Beams.
- Draw beams of size 250X450mm at the intersection of the horizontal and vertical grids and beams with quick draw beam keeping all the stories on.
- Next we have to Draw secondary beams.
- Next we add the shear walls in required locations in longitudinal building.
- Now Draw the Slab.
- Draw slab of size 130mm thickness, Draw slabs with quick draw floor/wall keeping all the stories on.
- Now we go to base plan and select all the joints.
- Now we select the Restraint from joint option, as shown below.
- Now define the Load patterns.
- Click on the define tab and click on load patterns.
- Define the loads like dead load, live load, brick load, earthquake load in X direction and same loads in Y direction also.
- Mention IS codes of respective loads.
- Next we need to select the distributed load from the frame loads.
- Then after the new tab will appear, in that case we select load pattern as Brickwall and we take uniform load as 3.5 Kn/m an then apply.
- Next we have to click on assign option and then select shell loads and select Uniform option.
- Here we apply 3 Kn/m2 live load for the staircase portion, verandah and liftcore area.
- Here we apply 2 Kn/m2 live load for rest of the portion in the slabs.
- Next we add live load reduction factor from the design option.
- Now add the reduction factor as decrease of 10%from 1st to 7th floor.
- Now go to Mars Source from define tab.
- Modify the mars source and tick mark the required loads.
- Add load patterns and assign the model.
- Insert the dead load as multiplier to 1, live load as multiplier to 0.25 and wall load as multiplier to 1.
- Now go to Load cases in define Tab.
- Now create the Diaphragm by going to the assign tab then shell and select diaphragm.
- Next we have to select the pier lable from shell option.
- Now go to Load combinations in define Tab.
- Select add default design combos.
- Select concrete frame Design.
- Next we add model cases from define option.
- Give odeal case name as Model1 and we give the maximun number of modes as 20.
- Next we need to check the Model.
- Now select the response spectrum from Functions option in define Tab.
- We choose IS 1893:2016 from choose function Type and click on Modify/Show spectrum option.
- Now go to Load cases in define Tab.
- Add new case
- Analyse the model using analyse option then click on check model the modelled structure is verified without errors and warnings.
- Now click on display -> show tables -> Analysis result structure output -> Base Reactions
- Now click on display -> show tables -> Analysis result structure output -> model information -> model periods and frequencies.
- Select the Story Response Plot from Display option.
X- Direction :-
Y- Direction :-
- Next we open the Base floor in Plan view
- We have to open Reaction tab, we select the earthquake load towards in X-direction in load case.
- When we divide base shear taken up by shear wall divided by total base shear of Building will get % of shear forces taken by Shear Wall.
