Structural Modelling using Etabs 2018

Q1). 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.

AIM :

To model and analyze the G+7 residential building in zone 5 from the given architectural drawings using the ETABS 19.

INTRODUCTION :

ETABS is an engineering software which is used to design 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 are all the features of this Etabs software.

PROCEDURE :

• Open Etabs software and go to File then New model then click on that.
• Hence new model page will open then select Use built in settings and provide the data displayed in the screenshot attached then click ok.

• After that Grid system data dailog box will open .Provide the grids as shown in attached picture.
• Then click ok.

• Enter the story details as per mentioned in the question.Make story 1 as master story and other stories similiar to story 1.
• Then click ok to proceed.

• Now you can see the model has been created as a grid system as per data entered.

• Go to Define then Materials to create materials required for the model.
• A dailog box will open ,click on the Add new material and enter the details of the required materials.

• Then go to Define again then Section properties then Frame sections to add the frames for the model.

• Create a new frame and name it as per data required. For beams select the M3 Design option and define the rebar material as Longi.bars as HYSD500 and Confinement bars as HYSD415.
• then click ok.

• Similarly do the same steps for columns also.
• And then click on the Modify/Show modifiers.

• There provide the Moment of Inertia about 2 and 3 axis as 0.35 and tortional content as 0.001.
• Enter 0.7 value for moment of inertia for column.
• Then click ok.

• For Column select the design type as P-M2-M3 design and assign the longitudinal and confinement bars.
• Then click on Modify/Show rebar and enter moment of inertia value as 0.7 for 2 and 3 axis.

• Do the same step for other columns also.

• Now you can see the created frame sections.

• For slab,
• Go to define then section properties then slab sectiions

• Add the new slab section and enter the required details as thickness 125mm
• Slab material as M25 them click ok

• Also add slab for staircase . Do the same steps and enter thickness as 200mm.

• Now you can see the created slabs.
• click ok.

• Then for wall sections
• Go to Define then Section properties then wall sections.
• Enter the details in the dailog box opened.
• wall material as M25
• Modelling type as shell thin then click ok

• Hence walls are also added to the model .

• Now to assign the columns
• Click on the Quick draw column option and draw the columns as required
• Select from the properties option and assign the columns

• For beams click on the quick draw option then select the appropriate properties of the beams which are required and then assign the beams in the model.

• Now apply the secondary beams in the model with the help of the plan attachment which is given.Refer to that plan and draw the secondary beams.

• Now assign the shear walls in the model by clicking on the draw walls option.

• After shear walls have been assigned ,then assign the slab surface in the model.
• For the stair case area add the STR_slab which we have assigned.

• Now select all the columns that are provided.
• Go to Assign then Joint then retraints to assign fixed support system.
• Then select the fix support form the dailog box and then click ok
• Then go to define then load patterns .click on that

• Then assign the loads as displayed in the attached screenshot

• Then go to Assign then Frame loads then select Distributed.
• Then select the load pattern name as Brick walls and assign uniform load of 3.5kn/m and then click ok.

• Hence assignes loads are now visible in the modal.

• Then for shell loads
• Go to assign then shell loads then uniform
• Provide load pattern as Live , enter uniform load as 3kn/m for stair and lift area.
• Then click ok.

• Provide load pattern as Live , enter uniform load as 2kn/m for other area.
• Then click ok.

• Hence floor loads are also assigned.

• For reducing liveload by 10% ,
• Go to design then live load reduction factors
• Add the loads as per reduction to be provided.
• Then Click ok.

• To assign the mass source
• Go to Define then click on the mass source

• Add load patterns as per shown in the attached screenshot.
• then click ok .

• Now for the diaphragms assignment
• Go to the Assign option then go to shell then Diaphragms
• Select D1 from the dailog box then click ok to proceed.

• Hence assigned diaphragm is now visible in the model.

• For assigning pier labels to the shear walls
• Go to Assign then go to shell then pier label.

• Add the pier label name first as P1,P2,P3,P4,P5,P6,P7,P8 and then assign the pier label to the different shear walls.
• Now to add load combinations.
• Go to define then click on the load combinations.

• Add the load combination by selecting on the Detail design combinations as concrete frame design and concrete shear wall design.
• Click ok .

• For Response spectrum assignment
• Go to define then Functions then go to response spectrum
• Provide the values and name as in the attached screenshot.

• Then in the load case data tab ,provide first for RSx then do the same for RSy.
• Then Click ok.

• Finally now run the analysis of the building.
• Before analysis please check the model.

• Deformed shape of building after the analysis done will look like this.

• To see the result of the analysis, Go to display then click on the show tables option.

RESULT :-

Hence the model has been analysed and the following results are achieved for given conditions

• Modal Mass Participation for first 3 modes must be 65%
• Hence achieved.

• Mode 1 and 2 differs by 10%

• It is also achieved.
• Principal modes must be greater than Torsional mode.
• Achieved.

• Inter storey drifts must be limited to 0.004
• ACHIEVED

• Now open the reactions tab, then select the eartquake load towards X-direction(EQX) in the load case, then click on ok .
• The base shear reactions are now shown
• When we divide the base shear which is taken by shear wall divided by the total base shear of building , it will get us the % of shear force taken up by the shear wall.
• If it is less than 80%, then more shear walls are need to be added.
• Here in our building it is sufficient.

RESULT :-

The G+7 building has been modelled and analysized succesfully using the E-TAB Software.