Structural Modelling using Etabs 2018

Question

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.

Answer

Aim:

To model an apartment with all seismic consideration, based on given architectural input and to know how to check the seismic performance of an apartment using ETABS

Introduction:

To model and analyse the G+7 residential building with the given architectural drawing using ETABS

Data required for Etabs analysis:

• Pinned support,Base + 9 story (ground to terrace) + 1 mumty
• Column 300x600mm & 300X750,Beam 300x450mm,Slab 150mm thick,Shear wall 300mm thick
• Live load 2kN/m2,Floor finish 1.5kN/m2,Wall load 3.5kN/m,Water tank 20KL over mumty equivalent to 200KN overall load

Conceptual design consideration before analysi:

• Re-entrant and cut-out check and modification (compromise)
• Vertical irregularity (soft story)
• Planar irregularity (looks symmetrical)
• 2% shear wall area with respect to build area
• Stiffness modifier for column,beam & shear wall (0.35 for beam, 0.7 for vertical)

Key point to remember while modeling:

• No slab, no wall load in ground floor
• Proper end releases in beams as per engineer intent
• No interior wall load in terrace
• Comparison of static and dynamic forces and revising the factor

Procedure:

Step 1) Create Model Reference in AutoCAD

• Changed the column size, position & orientation without disturbing the parking area and floor area, it doesn’t affect the floor area and parking area
• Created shear wall according to my opinion
• This drawing is used as a reference drawing for etabs model
• I have overlapped the floor plan to the new designs plan

Step 2) Create New Model in ETABS

• Click on New Modal from ETABS home interface
• Select Unit Built in Setting from Modal Initialization dialog box
• Change display unit as METRIC SI
• Region for default material as INDIA
• Steel selection database INDIAN
• Steel design code IS-800:2007
• Concrete design code IS-456:2000 enter OK

Step 3) Create Grids & add a stories

• A new dialog box opened as New Modal Quick Templates
• Select Custom Grid Spacing and click on the Edit Grid Data
• Modify the X & Y Grid Data from the Grid System Data dialog box and click OK

Step 4) Define Material

• The grid arrangement of the new modal will open
• Go to Define → Material Property
• Define Material → Add New Material
• Add New Material → Material Type Concrete → Grade M30 click OK
• Material Properly Data dialog box will open, click OK
• Again, click on Add New Material
• Add New Material dialog box will open, select Material Type Rebar and select Grade HYSD 550 & 415 click OK
• Material Properly Data dialog box will open, click OK

Step 5) Add Column, Beam & Shear Wall

• Go to Define → Frame Section → Section Property
• Click on Add New Property from Frame Properties dialog box
• Click on Rectangular Section for Beam from Frame Property Shape Type
• Change the Property Name as B300X450 and Material M30 and section dimension Depth as 450 & width as 300 from Frame Section Property Data, click on Modify/Show Rebar under Reinforcement
• Change Design Type and Rebar Material, click OK
• Again, Add New Property for Column and select Rectangular Section
• Change the Property Name, Material and Dimension and Modify/Show Rebar similarly

Step 6) Add Slab

• Go to Define →  Slab Section → Section Property
• Click on Add New Property for Slab
• Change the Property Name, Slab Material, Modeling Type and Thikness of Slab

Step 7) Load Pattern

• Go to Define → Load Patterns
• Add Wall & Floor Fininsh Load as Super Dead type
• Simalry add EQX & EQY Load as Seismic type and select IS-1893:2016
• Modify the lateral load and uncheck the other direction except X for EQX and Y for EQY

Step 8) Define Mass Source

• In Define → Select Mass Source
• Click on Modify/Show Mass Source
• Check mark only Specified Load Pattern
• Add wall, live and dead load

Step 9) Response Spectrum

• Go to Define → Functions
• Open response spectrum
• Modify the spectrum details

Step 10) Check Load Case

• Go to Define →  Load Cases
• Check load cases and click OK
• Modify the model

Step 11) Load Combinations

• Go to Define →  Load Combinations
• Add Default Design Combination
• Check on Concrete Frame Design,Concrete shear wall Design and Convert To User Combination

Step 12) Draw Column and Shear wall

• Select Quick Draw Column
• And change the Properties

Step 13) Assign Load

• Select all Beam
• Assign Frame Load as a Distributed
• Load Pattern Name Wall → Uniform Load 3.5kn/m
• Similarly select slab
• Assign shell load as uniform
• Load Pattern Name live → Uniform Load 2 kn/m
• Added floor finish and water tank load

Step 14) Add Diaphragms

• Select Slab
• Assign Shell as Diaphragms

Step 15) Base Support

• Goto the base plan
• Select all the joitns
• Assign → joints → restrian
• Select fast restrain and click ok
• All the joints are fixed

Step 16) Assign Peir Lebal & live load reduction

• From define added pier labels
• Assign one by one on shear wall
• Add live load Reduction factor on each floor

Step 17) Check Modal and Run The Analysis

• Here I got no warning so that modal ok, we can run analysis
• After completion of anaysis we got max. & min. deflection

Step 18) Check Result

• Form table checked the modal infromation and compare the result
• First two fundamental modal mass grater than the torsional mode
• Modal mass participation for first 3 modes dominates at least 65% (Achieved for X-axis only)
• Mode-1 and Mode-2 differs by 10% (Achieved)
• Principal modes be greater than Torsional mode (Achieved)
• Inter story drift ratio limited to 0.004 (Achieved)

Result:

To model and analyse the apartment with all seismic consideration, based on given architectural input and to check the seismic performance of an apartment using ETABS and attach the model.