Structural Modelling using Etabs 2018

Q: 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:
• Brick wall 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.

Sol:

Aim: To conceptualize a framing plan layout and model the building in Etabs.

• 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.

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:

• First you need to open the etabs software.
• Then click on the File option in the top left corner and select New Model as shown below.
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• After selecting a new model, a new tab will open where you need to select the option "Use built-in settings" as shown below.
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• After setting up model initialization, in the Templates tab that opens, select Mesh only and click OK.
• Next, we need to configure the grid system's data as shown below.
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• Next, we need to add up to 7 stories to our story data as shown below.
• Added 7 layers to historical data:
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• The plan view is displayed on the etabs screen as shown below.
• Next we need to open the 3D view as shown in the image below.
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• Next you need to define parameters and select material properties as shown below.
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• After selecting material properties, a new tab will appear, add a new material by selecting the Add new material option.
• Select concrete as material type and M25 as its grade and check the material property data.
• Similarly add two new materials for rebars by selecting rebar as material and HYSD grade 415 and HYSD grade 500 respectively.
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• Now you need to select section properties and click on the frame section.
• Define two beam sections of dimensions B250X450 and B300x500 by selecting add new property and selecting rectangular section.
• Select M25 in the material drop down, edit the depth and width values. Decrease the values of moment of inertia about axis 2 & 3 to 0.35 and change the tortional constant to 0.001.
• Then open the modify/show rebar and select beam in design type.
• Assign the respective rebars to longitudinal and confinement bars.
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• Similarly add two column sections of dimensions C400x400 and 400x600.
• Assign M25 as material, change the depth and width value.
• Open the modify/show modifiers & change the moment of inertia about 2 & 3 axis to 0.7.
• Open the Modify/show rebar settings and assign the respective rebars definitions to longitudinal and confinement bars.
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• Then select the slab section option in section properties and create two slab sections one for floor areas and one for staircase area of thickness 125mm and 225mm respectively.
• Assign slab material as M25 concrete and modeling type as Membrane to both of them.
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• Now go to wall sections in section properties and create wall sections of thickness 250mm.
• In this case the modeling type will be shell-thin.
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• Next you need to add columns and beams using the Quick Draw Columns and quick draw beams option option as shown below.
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• Next we need to add secondary beams using the quick draw beam option.
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• Then we add shear walls and slabs at the desired locations of the residential building as shown in the image below.
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• Now let's go to the basic plan and select all the basic connections.
• Next we select the constraints for the union option as shown below.
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• Now we need to select the fixed connection and apply and click on the close button as shown below.
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• Next, we need to select the load model from the set option as shown below.
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• Now we need to add Dead load, Live load, Brickwall load and Earthquake load as shown below.
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• Next, we need to select the distributed loads from the frame loads as shown below.
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• Then, after the new tab appears, we select the load model as Brickwall, we set the uniform load to 3.5 kN/m, then click the Apply button and close.
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• Next we have to click on the assign option and then select shell loads, from the shell loads we select the Uniform option, as shown below.
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• Here we apply a live load 3kn/m^2 for the stair section, veranda and elevator core.
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• Then we apply a live load of to the rest of the residential building as shown below.
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• Next, we need to select the live load reduction factor from the design options as shown below.
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• Now we add the reduction factor by reducing it by 10% from stage 1 to stage 7, as shown below.
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• Next, from the definition options, we select the quality source as shown below.
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• Then we add the load model to the mass source data as shown below.
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• In the select option, we select the object type option as shown in the figure below.
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• After selecting an object type option, a new tab will be visible. Select the floor and click the Select and Close button.
• Next, we need to select the aperture from the case options as shown below.
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• After selecting the aperture, a new tab will appear, select D1 in it, then click the Apply button and close.
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• Next we need to select the Pier tab in the hull options as shown below.
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• Before we proceed to design the shear walls, we need to assign names to the shear walls (P1, P2, P3, P4, P5, P6, P7, P8) as shown below.
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• Now we select the load combinations from the define tab and select the ‘Add Default Design Combo’ option from the new tab that appears after selecting the load combinations.
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• Then ‘concrete frame design’ and ‘concrete shear wall design’ are selected in the ‘add default design combinations’.
• The load combinations are now visible.
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• Then the select the define option and select the modal cases from there.
• The modal cases are then defined, the name of the case is given as Modal 1 and the maximum number of modes is given as 20.
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• Now the model has to be checked by selecting the check model option.
• Then to define the response spectrum the IS 1893 2016 is selected from the ‘choose function type’ and select Modify/Show spectrum option, as shown below.
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• After selecting the Edit/Show Spectrum option, the new tab will be visible because we named the function name "IS FUNCTION" and the rest of the details will be set by the software itself, we don't need to enter details. do not modify the Response Spectrum Function tab, as shown below.
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• Then a new load case has to be added by selecting load cases from the define tab and define the new load case in the ‘load case data’ as shown.
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• Finally run the analysis and obtain the tables from the display option.
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• Select the base reactions from the list of tables.
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• Then the basic reaction table will be visible as shown below.
• Here we need to make sure EQ should be closer to RS, to make them closer we need to calculate it, ( ) X Response spectrum scale factor.
• Along x-direction () x (9806.65) and in Y-direction x 9806.65.
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• In the X direction we get 30969.6
• In the Y direction we get 27835.15
• We use the above values ​​as scale factors for the response spectra in the X and Y directions from the data of load case.
• After entering these values ​​for the response spectrum as scale factors in the X and Y directions from the load case data, the EQ is closer to the RS in the basic response table, as indicated below.
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• Similarly get the modal participating mass ratios table and the story response plots from the display option.
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• The floor response for the maximum floor displacement in the X and Y directions must not exceed 4%.
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• Next, we open the Select plan view tab and select the ground floor as shown below.
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• Next, we need to open the Response tab, then we select the seismic load in X direction (EQX) in the load case, and click on the OK button, as shown in the figure below.
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• The base shift response will now appear as shown below.
• By dividing the base shear absorbed by the shear wall by the total base shear of the building, we will obtain the percentage of the shear absorbed by the shear wall.
• If less than 80%, we need to add more shear walls to the structure.
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Results:-

G+7 residential buildings successfully modeled and analyzed using ETABS 2018.