Modelling of 25 storey building with the specified properties using ETABS

Challenge 6 – ETABS modelling of a 25 storey building

Model a 25 storey building on ETABS with structural properties as specified below. Ground floor or plinth floor level can be taken at a height of 1.5 metres from the base. Each of the successive 25 storeys has a storey height of 3 metres.

Structural Element Sizes

• Beams : 300 × 400 mm
• Columns : 800 × 800 mm
• Slab : 150 mm thick

Material Properties

• Grade of Concrete : M30
• Grade of Steel Reinforcement Bars : Fe 415

Loading

• Dead Load on beams from infill wall : 10 kN/m (Let us assume the same for roof floor in view of parapet)
• Live load on floor : 3 kN/m2 (Let us assume the same for roof floor)

a) Buildings are assumed to be pinned at the base

b) All columns in all storey are of the same size

c) All beams in all storeys are of the same size

d) Building is located on Soil type-II and in Zone-III. Assume other factors if required.

Carry out the following exercises:

• Check if the translational fundamental natural period of vibration in both the x and y direction is approximately: Tx1">Tx1Tx1= 4.4 second Ty1">Ty1Ty1= 4.2 second

This check will help confirm if modelling is done correctly. Some deviations from the above values is possible (± 2%). But any major deviation will suggest an error in modelling.

• Check if the following provision in Table 5 of IS 1893 (part 1) – 2016, on torsional irregularity satisfied:

The natural period corresponding to the torsional mode of oscillation must be less than the two fundamental translational modes of oscillation along each principal plan directions.

• Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied

• Check if provision on inter-storey drift limitations in clause 7.11.1.1 satisfied. Please note that this check is for Serviceability Limit State and hence is for situation when stucture is subjected to unfactored seismic base shear

ANSWER:

AIM:

• To Model a 25 storey building on ETABS with structural properties as strcuctural properties:

• To Carry out the following exercises:

  • Check if the translational fundamental natural period of vibration in both the x and y direction is approximately: Tx1">Tx1Tx1= 4.4 second Ty1">Ty1Ty1= 4.2 second

  This check will help confirm if modelling is done correctly. Some deviations from the above values is possible (± 2%). But any major deviation will suggest an error in modelling.

  • Check if the following provision in Table 5 of IS 1893 (part 1) – 2016, on torsional irregularity satisfied:

  The natural period corresponding to the torsional mode of oscillation must be less than the two fundamental translational modes of oscillation along each principal plan directions.

  • Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied.
  • Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied

INTRODUCTION:

ETABS is the abbrevation of " Exteneded 3D analysis of buildiing system". It is a product of Computers and structures, Inc.Which is reconginsed globally at the pioneering leader in strctural engineering analysis and design software for structural and earthquake engineering.

The innovative and revolutionary new ETABS is the ultimate integrated software package for the strctyural analysis and design of buildings.The latest Etabs offers unmateched 3D object based modelling and visualization tools, Blazingly fast linear and nonlinear analytical power, sophisticated and comprehensive design capabilites for a wide range of materials,and insightful graphic display, reports and schematic drawings that allows user to quickly and easily decipher and understand analysis and design results.

PROCEDURE:

• Intially open the etabs software and click on the new model option.
  
• It will appears a model initialization window, then select the Use Built-in settings with option and fill the units and codes as per the detailes we used.
  
• Then again it will appear another window-New model quick template. BY using this tempate select the grids and storeys and respectivelty it dimensions also.
  
  
  
• Hence the grid and storey details will appear .
  
• After thet, we have done the material prooperties. So to input the material properties go to the Define tab and then select the materials property and then goto the add material property option.
  
• Creating of concrete material as per the details given.
  
  
  
• After that Creating of Steel material as per the details given
  
  
  
• Hence the materials are added and then click ok.
  
  
  
• Now we have to add the frames members to the strcture. So, We go define tab --> selection propeties--. frames sections.
  
  
  
  
• NOw it will open the frame properties window . then click on the add new material property.
• NOw we have add the beam details, reinforcement details and cover to the reinforcement is also added.
  
  
  
• Similarly, the deatils of columns are also filled.
  
  
• Hence,The materials are added inthe frame window which is shown in the below figure.
  
  
  
• Now, We have add the slab details. go to define tab- section property-slab sections-slab property data dailogue box opens. In that we have fill the detailes as per the question.
  
  
  
  
• All the properties for the frame members has added.so,we have to place the strctural members.i., beams,columns, and slabs.
• For adding the frame members to its. there is a tools which is placed left side of the etabs software.
• With the help of the tools all frame members are added.
• Firstly we have place the columns all over the storeys by taking the quick column slection tool.select the all column postions. it should be added automatically.
  
• Next we have place the beams by using the qucik beam selction tool.make sure that all beams are selected and it in all stories.
  
• Similarly the slabs are also slected.
  
• Now, its time to assign the loads on the frames.FOr, go to define tab-load patterns- Define load patterns window will appear.Initially the dead and live are added onit self.no wwe have to added the brick wall load s and earth quakes load in both directions.
  
  
  
• Now we have provide the mass source value to the sesmic weight.as per the required details.
  
  
• Now we have crearte the diaphgram to the srtucture.
  
• After that we need to define the load combinations.For this Go to define tab-load combination.and select the concrete frame design select and click ok.
  
  
• Then it will generate the auomatic load combinations as per the codal provision.
  
• Now select the all floors by go to the select tab-select-object type-Floors -ok. then all floors are slected.
• Then go to the assign tab-shell lods- uniform-live load-3-apply-ok.
  
  
  
  
• Now select the all beams by go to the select tab-select-object type-beams -ok. then all beams are slected.
• Then go to assigntab- frame loads- Distributed -load pattern-brick wall load-load-10-apply ok.
  
  
  
• We have to keep the supports as pinned, so we have sleect the all joints in base storey.Then go to assign-joints-restraint-select pinned joint.
  
  
  
• Finally go to the analyse tab-check model- It is checked for any errors and warnings.
  
  
  
  
• Now the model is ready for the analyse.so we can run analysis.
• Hence run anaylsis has been completed.

Now we have check the details are given questions.

• For that, initially go to the display tab-show tables -analysis result-structure output-modal information-modal periods and frequencies.
  
  
  
• Check if the translational fundamental natural period of vibration in both the x and y direction is given in question.
  according the above table
  
  • For mode1 In x directrion is 4.41 sec
  • For mode2 In y direction is 4.22 sec

• Check if the following provision in Table 5 of IS 1893 (part 1) – 2016, on torsional irregularity satisfied:

  The natural period corresponding to the torsional mode of oscillation must be less than the two fundamental translational modes of oscillation along each principal plan directions.

  • it stasifed The transional mode3 time period should be lesser than x and y direction of time periods-as shoen in the below figure.
• 
• Next coming to the vertical irregularity of codal provisions IS 1893-2016(part-1) table-6 clause-7.
  
  
  • From the above table, as per the codalprovisions.yes it is stasifying the first three modes together should be contribute at least 65% in mass participation factor in each direction.
  • Again fromthe above table, as per the codalprovisions. no its not stasisfying the fundamental lateralnatural periods in two principal plane directions are away from each other by at at least 10%.
    taking the xdirection mode 1 as 4.416*0.1=3.97 so, its not stasisfying.
• Finally last check is Inter storey drift of codal provision is IS1893-2016(part-1) clause7.11.1.1.
  
  
  • here we get as 0.0032 which is less than 0.004.so it is also stasisfy the storey drift doesnot exceeds0.004 times the storey height for base shear with no load factors.

RESULT:

The analysis are done for the 25 storey building and specified all the checks were carried out.This 25 storey building satisfy the all check expect oncheck i.e, second provison of clause 7 in table 6 of IS 1893 part-1-2016. regarding vertically irregularity.Which is given as the fundamental lateralnatural periods in two principal plane directions are away from each other by at at least 10% of the larger value.

REPORT :

Criteria		Desirable solution	Excerise Result
Fundamental translational natural period	x-direction	4.4sec	4.41sec
	y-direction	4.2 sec	4.22sec
Torisional Irregularity	IS1893-2016 part-1 table-5	Torsional mode time period should be lesser then x and y directions Time period.	YES
Vertical irregularity	IS1893-2016 part-1 table-6 clause-7	the first three modes together should be contribute at least 65% in mass participation factor in each direction.	YES
		the fundamental lateralnatural periods in two principal plane directions are away from each other by at at least 10%	NO
Inter-storey drift	IS1893-2016 part-1 clause-7.11.1.1	Storey drift shall not exceed 0.004 times thestorey height for base shear with no load factors.	0.003(YES)