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.

PROCEDURE:

STEP1

• Open Etabs
• Create new file->use built in settings
• A new tab will open->select user grid system(use spacing)

• Click OK

STEP2

• Now go to user defined floor system->enter the no. of floors you want

• CLick on OK->Now the grid system will be visible.

STEP3

• Now go to define->material properties

• Click on add new materials to add HYSD500,HYSD415,M30

   //similarly add 415 and M30

STEP4

• after adding material properties->we add beam and column sizes
• Go to define->section properties->select rectangular section
• Add new property->a new tab will open->enter the name C400x500

• Click on add new material->enter the B300x500
• enter the types of rebars

• Similarly add different sizeof columns

STEP5

• Now we add slabs and walls
• go to Define->section property->walls section
• Add new property->enter the name SW250
• wall material as M30->enter the thickness of wall

STEP6

• Now we add Slabs->define->section property
• slab section->add new proprty->enter the name of slab->enter the thickness

//Similaryly do for the stair slabs with thickness 125 (Tick the special one way load distribution for stairs slab)

STEP7

• NOw we have to add columns and beams
• Click on quick draw columns-
  Make sure to change the selection type to "all stories"
  select the columns where you want that column to be added
  Select the columns you want to change orientation->Assign->shell->local axes
  Enter the rotation angle you want to rotate the column.

  

  STEP8

  • Now similarly->select quick draw beams->select the beam type(B300x500)
  • select all the frames and the beam will be applied to all floors
  • Go to edit->Replicate(to replicatebeams at a distance)->a new tab appears
  • enter the distance in dx or dy you want

  

  

  • Use the values to replicate at distance of different beams to achieve the design.

  

  • Go to base plan->select the columns (change slection to one story)
  • Go to assign->joints->restraints(Add fixed support)

   STEP9

  • Now we add shear walls to the structure

  Note-"We remove the column where the shear walls are added"

  • change the selection to all stories->select quick draw walls->select the SW250 frame rpoperty
  • Apply walls at the parts required in the builidng as per your calculation
  • Make sure not to obstruct the parking way of cars and not disturb the architectural design

  

  STEP10

  • Now we apply slabs->Go to quick draw slabs/floors
  • select the slab150 and select the slab areas you want
  • The slabs wiil be applied to all the floors

   

  STEP11

  • Now we label the the piers -.>Assign->shell->pier labels
  • select the shear walls and assing the pier labels individually

  

  STEP12

  • Now we enter the load patterns
  • Define->load patterns->a new tab appears 
  • input the live ,dead ,brickwall,and seismic loads

  

  • CLick on EQ and modify lateral load

  

  //For EQ loads ,modify the lateral loads ,Given Calculated time period Ta=0.52 (calculated as per IS 1893 part1 7.6.2) by Ta=0.09*h/d^(1/2)

  //Importance factor is 1.2

  STEP13

  • Next we apply the loads on the frames
  • Select->object types->beams(keep selection to all stories)
  • Go to Assign->Frame load->distributed load
  • a new tab appears->select brickwall->apply load of 3.5KN

  

  STEP14

  • Next we apply live loads on slabs
  • Select->object types->floors
  • Assign->shell loads->uniform loads->select live and input 3KN for stairs slab,walking path and elevator slabs
  • //Similarly apply live load of 2KN on the Remaining slabs

  

  STEP15

  • Next we have to apply live load reduction factor
  • Design->Live load reduction factor->a new tab will open

  

  • CLick on User defined to define by yourself-> add the reduction factor according to IS 875 part2 3.2.1

  

  

  STEP16

  • Now we add mass source->Go to define->mass source
  • click on modify mass source->a new tab will open(give live load of 25% when the live load on floor is greater than or equal to 3KN)

  

  

  STEP17

  • Now we define load combination->define->load combination
  • click on add default design combo->select concrete fram design & concrete shear wall designs (Editable)

  

  • Now we add the diaphragm
  • Select->Object types->floors
  • Assign->Shell->Diaphragm(a new tab opens)
  • select D1 and click OK

   STEP18

  • NOw go to define->modal cases->go to modify case
  • increase the number to 30 modal cases

  

  • Now we check the modal
  • Go to analyse->check modal
  • A message will be shown with check results(if any error occurs it'll be shown)

  

  STEP19

  • NOw we add response spectrum
  • Define->fucntion->response spectrum                              //A new tab will open
  • VHange the code to IS 1893:2016->Add new function->name it as "IS FUNCTION" and remainign data will be set automatically

  

  • Next we apply load cases
  • Define->load cases->add new case ,a new tab opens
  • Name it as RSx->load case type as "Response spectrum"->CLick OK

  //Similarly we add new case for RXy with Load name as U2

  STEP20

  • Now we have to run the analysis->Analyze->run analysis

  

  STEP21

  • After the analysis is done ->show tables->modal participation mass ratio & base reactions

  

  • For the structure to be stable the response spectrum (RSx & RSy) must be nearly same as of Seismic forces (EQx & EQy)
  • For response spectrum to be equal we use a formula [(EQ/RS)*Scale factor],The scale factor here is 9806.65 we got in load case data
  • [(3851.9553/1476.219)*9806.65]=25588.87 for RSx
  • for RSy=29986.47
  • he obtained data is then replaced by the scale factor(9806.65) which gets us the value of RS closer to EQ.The resultant BAse raction table will be as shown

  

  STEP22

  • Go to display->show tables->modal participating mass ratio
  • The table shown below
  • The natural time period of Building is around 1.039sec which is acceptable for a 7 storey builidng(nearly 0.89sec for 5-10 storey)
  • A Minimum of 25 mode needed in this case as we achieve 90% value for RX in 25 mode

  

  STEP23

  • now to check the max storey drift
  • Display->storey response plot->Display type->Max storey drift->Case as EQx
  • It's safe as the max drift less than is 0.004

  

  • storey response plot->Display type->Max storey drift->Case as EQy
  • Drift along Y direction is also safe

  

  RESULT:The analysis is done and the proper proper design shear walls are also given successfully

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