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: Tx1Tx1= 4.4 second 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

ANS:

AIM: To model a 25 storey building with the given properties using ETABS.

Given Details:

Beams – 300x400mm

Columns – 800x800 mm

Slab – 150mm

Grade of concrete – M30

Grade of steel reinforcement – Fe 415

Dead load of walls -10 kN/m

Live load on the floor – 3kN/m^2

Procedure:

Step1: First open the software and create a new model using the file menu.

Step2: Next Model initializing settings will open and use the built-in settings to continue the process. Next, a new window will open and create Grids using custom grid data and create as required.

Step3: Now we have to give story data as required. And then click on ok finally the model frame will create.

Step4: Now we have to create the required concrete and rebar materials using material properties in the define tab.

Step5: Now we have to define the frame section properties and create a new section and assign and check the properties as required.

Step6: Now we have to create the slab section property.

Step7: Now we need to add the columns to the model using the quick draw column.

Step8: Next we need to add the beams using quickdraw beams.

Now we have to add the slabs using Quickdraw floor Option.

Step9: Now we have to create the supports, so we have to go to the base plan and select joints as below and then in assigned menu select restraints in joints. Now we have to select the pin joint and apply.

Step10: It will look like this after application.

Step11: Next we have to select the load pattern and add Dead, Live, Brick wall load, and earthquake load as shown below.

Step12: Next, we have to edit the earthquake load as below and give the details w.r.t code parameters.

Step13: Now we have to assign the shell loads using the UDL load. And we have to consider the loads 3kN/m^2 up to 24 floors and 1.5 kN/m^2 at 25 floor.

Step14: Now select the object type as beams and apply the distributed frame load and a new tab will open their select brick wall and click on apply.

Step15: Now click on the toggle to see in 3D view how the load had applied on the model.

Step16: Next in the mass source option in the define option and select the show or modify mass source option and then add the load pattern in mass source data.

Step17: Next from the in define option select the load combinations a new window opens and select add default design combo option.

Step18: Select concrete frame design and click on ok then we can see the combinations which are created.

Step19: Select the slab objects and select the diaphragm in shell loads in assigned menu. After that select, the D1 and click apply.

Step20: Next, we have the check the model by clicking on the check model. Next, a new window will open and select all options and click ok.

Step21: After the model is checked the following model will appear if there is no warnings in the model. Then we have to do a run analysis in analyze menu.

Step22: Next we have to see the deformed shape click on the deformed shape and select the load case as required to see here I am selecting the live load and click on ok then the deformed shape of live load will appear on the screen.

DEAD LOAD

BRICK WALL LOAD

EARTQUAKE LOAD

Step23: Next in the display menu select the show table option and select modal participating ratio click ok then a table will appear.

Step24: In display option click on show tables and go to analysis result and then structure output modal info and finally click on modal period and frequencies.

We found,

Tx = 3.75sec

Ty= 3.89 sec.

Step25: In display now select the story response plot then keep the load as eqy and switch to max story drift and max is noted as 0.00204.

As per clause 7.11.1.1, the max drift value is 0.004 but we get 0.002 in ETABS, so the structure is OK.

RESULT: The 25-storey building had successfully modeled using ETABS and the results are interpreted which are asked in the question and required data is checked according to the Earthquake load codebook.