Structural Modelling using Etabs 2018

Que.

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.

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.

Ans.

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 structural model must comply with provisions of IS 1893 and IS 13920.
• To 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 software that caters to multi-storey building design 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 advance system under static or dynamic conditions may be evaluated using ETABS
• Fundamental to ETABS modelling can be done of floors to vertical direction.
• once modelling is complated ETABS automatically generate and assign code based loaing conditions for gravity, sesimic, wind  and thermal forces.User may specify an unlimited number of load cases and combinations.
• Output and display formats are also practical and intutive.Momant, shear and axial force diagram, presented in 2D and 3D view corresponding to that data set.
• Here in this challange we have to model an entire G+7 building with floor plan using ETABS software.

Procedure:-

• Initially open the given AutoCAD file and locate position of beams, column and shear wall

• Now, open ETABS file and provide grid and storey information as required and given

• Now, deife material property for concrete and reinforcement.

• Define section property of column, beam and wall.........For this go to define tab -----> Section property -----> Beam 300X450mm and column 400X600mm

• Now, define slab properties......Define -----> section properties -----> Slab section -----> Slab 125 and 150

• Now, define wall properties......Define -----> section properties -----> wall section -----> Wall 250

• Hence we have to define material as well as section properties, so now we need to place the components in the suitable positions.
• So. for this we have to draw column and place them to suitable position (C 400X 600)
• Similarly, place the beam (B 300X450 ) shear walls at suitable locations without obstructing the parking area.

• After this we need to place the slabs, for starcase slab we use slab150 and for remaining area we will be using slan125
• 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 loads cases

              a. Brickwall loas assigned as 3.5KN/m

              b. Floor finishes as 1.5KN/sq.m

              c. Live load as 2KN/sq.m and 5KN/sq.m for terrace area as it empty and lift unit

              d. Also provide the liveload reduction factor as per IS- 875 Part II. Design -----> Live load reduction                    factor.

• Now define mass sources

• After defining mass source, then we have to define model case, Keep max. no of mode as 20
• Next we need to define the responce spectrum function. Define -----> Response spectrum -----> function name: RS function -----> Ok

1.  Then go to load case -----> add new case ----->RSx(U1) -----> load case type -----> response spectrum ----->then fill load applied deatils, add another load case as RSy (U2)

• Now assign -----> Shell ----->Diaphrams ----->D1 ----->Apply
• Then assign pier labels
• Now go to define ----->load combinations ----->add default load combination -----> choose concrte frame design and concrtee shear wall design -----> convert to user combination

• Put all input and then analyse model

• Now we run the anaysis
• Once the analysis over, go to display -----> show table -----> anaysis result -----> structure output -----> modal information -----> model mass participation ratio

1.   Mode1 - 69.14% ;  Mode2 - 63.96% ; Mode3 - 63.03%
2.   Hence, the mass participation of translation mode (first two fundamental mode) is greater than torsional mode (third mode)

• Now, in display choose base. go to display -----> Show table -----> anayse result -----> structure output -----> base reaction

1.   Eqx obtained=1159.66KN and RSx=1163.24KN.......hence, scale factor=(1159.66/1163.24) =0.9969
2.   Similarly, Eqy=1265.27KN  and RSy=1128.56KN......hence, scale factor=(1265.27/1128.56) =1.12
3.   Now, keep scale factor

• Now taking both Eq andRS value, using same scale factor, Eqx and Eqy can be removed from load case and combination

• Check interstory drift. For this diaplay ----> story response plot ----> max. strory drift

Here, for both RSx and RSy, max stroy drift is within 0.004 as given in IS 1893-2016

• Axial force diagram is given in display -----> force/stress diagram-----> frame/pier/spandrel/link/link forces

• Hence complete model is given below

Result:-

• The structure modal of G+7 building has been develop that complies with IS-1896 and IS13920
• After framing the layout, analyse has been carried
• all necessary check has been carried out and aslo verified the value with code.