Structural Modelling using Etabs 2018

Aim:

• To conceptualize a framing plan layout and then model the given G+7 building situated in zone 5 in Etabs.
• To develop the structural model that comply with provisions of IS 1893 and IS 13920.
• To run the modal response spectrum analysis and to 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-storey building design and analysis.
• Modelling tools and templates, code-based load prescriptions, analysis methods and solution techniques, all coordinated 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.
• Fundamentals to ETABS modelling is the generalisation that multi-storey buildings typically consist of identical or similar floor plans tat repeat in the vertical direction.
• Once modelling is complete ETABS automatically generates and assigns code-based loading conditions for gravity, seismic, wind and thermal forces. Users may specify an unlimited number of load cases and combinations.
• Outputs and display formats are also practical and intuitive. Moment, shear and axial force diagrams, presented in 2D and 3Dviews wirth corresponding data sets, may be organised into customisable reports.
• Here, in this challenge we are going to model an entire G+7 building with the floor plan using ETABS software.

Procedure:

• Initially open the given AutoCAD file and locate the positions of columns beams and possible loaction of shear wall.

After selecting the new model the new tab opens, in that tab we have to select 'Use Built-in Settings with' option, as shown below.

• 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, as shown below.
• The 7 stories are added in the Story Data, as shown below.

• Next the plan views are visible in the etabs screen, as shown below.
• Next we need to open the 3d-view, as shown in the below figure.

• 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.

• Now we need to add material type as concrete and grade as M25.
• Next we need to check the material property data, as shown below.
• 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.

• 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.

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

• Now, open the Etabs file and provide the grids and storey information as required and given.

• Next we need to define the material property for concrete and reinforcement.

• Then, define the section property for column, beam and wall. For this, go to define tab --> section property --> frame section --> Beam 300X450mm and column 400X600mm.

• Now, define the slab properties. Define --> section properties --> slab sections --> Slab150 and slab 125.

• Next thing that we need to define is the wall properties. Define --> section properties --> wall sections --> wall250.

• Hence we have now defined the material as well as section properties, so now we need to place the components in the suitable positions.
• So, for this go to quick draw columns and place the columns at suitable positions(C400x600).
• Similarly place the beams(B300x450) and shear walls at suitable locations without obstructing the parking area.

• After this we need to place the slabs , for staircase slab we use slab150 and for remaining area we use slab125.
• Now make the staircase slab as one way slab.

• Next, we need to provide loads before carrying out the analysis.
• Define --> load patterns.(Include wall and load floor finishes as super dead loads)
• After defining assign the load cases.
  • Brickwall load is asssigned as 3.5kN/m.
  • Floor finishes - 1.5kN/m2m2
  • Live load - 2kN/m2m2 and 5kN/m2m2for terrace as it contains mumty and lift unit.
  • Also provide the liveload reduction factor as per IS875 part II.Design --> Live load reduction factor.

• Next we need to define the mass source.

• After defining mass source, next we have to define the modal case. Keep the max no. of modes as 20.
• Next we need to define the response spectrum function. Define--> Response spectrum --> Func. name: RS function -->ok
  • Then go to load case --> add new case --> RSx (U1)--> load case type - Response spectrum-->Then fill load applied details.similarly add another load case as RSy (U2).

• Now, Assign --> shell --> diaphragms --> D1 --> Apply.
• Then assign pier labels.
• Now, go to define --> load combinations --> add default load combinations --> choose concrete frame design and concrete shear wall design --> convert to user combination.

• All the inputs have been provided, now we can check the model. Analyze --> check modal.

• Now, we can run the analysis.
• Once, the analysis is over, go to display --> show tables -->analysis result --> structure output --> modal information --> modal mass participating ratio.
  • Mode 1 - 69.14% ; Mode 2 - 63.96% ; Mode 3 - 63.03%
  • Hence, the mass participation of translational mode (first two fundamental modes) is greater than torsional mode(third mode).

• Now, in display choose base reactions. Go to display --> show tables -->analysis result --> structure output --> base reactions.
  • Eqx obtained is 1159.66kN and RSx = 1163.24kN. Hence, the scale factor = 1159.661163.24=0.99691159.661163.24=0.9969
  • Similarly, Eqy = 1265.27kN anf RSy = 1128.56kN. Scale factor = 1265.271128.56=1.121265.271128.56=1.12
  • So, now, keep these values as scale factor.

• Now, both Eq and RS values are made same using the scale factor hence, the Eqx and Eqy can be removed from the load case and combinations.

• Now, we need to check the interstory drift. For this display --> story reponse plot -->maximum stry drift
  • Here, for both RSx and RSy the max story drift is within 0.004 as given in IS1893-2016

• Now, the axial force diagram is given by display --> force/stress diagram --> frame/pier/spandrel/link forces.

• Hence the completed modal of the G+7 building is as given below:

Result:

• The structural modal of the G+7 building has been developed that complies with IS1896 and IS13920.
• After framing the layout, analysis has been carried out.
• Necessary checks have been carried out and also verified the values with the code