Modelling of 25 storey building with the specified properties using ETABS
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
INTRODUCTION:
ETABS can help one to convert their ideas into product designs quickly and effectively. It enhances building system's geometry learning ability. Model creation & result reporting are done at object level in ETABS. It allows the designer to concentrate on macroscopic performance targets.
AIM:
To model a 25 storey building on ETABS with structural properties as specified in the given question
GIVEN DATAS:
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
- Live load on floor : 3 kN/m2
PROCEDURE:
- To Open the ETabs Software, Select New model
- Use the Built in settings with
To select the grid interval at 4 at x and y direction
After that edit the story type and input as 25 story
- To go on the define option to add te material
- Now to add the material select Define, then select Material properties and add new material. For this structure we have added the concrete and rebars
- In concrete as been choose beam as 300x400 and column as 800x800 respectively
- Now to add the Beam property, select Define, select the section properties and select the frame sections,
- Select Add new property and insert concrete
- Now to add the column property, select Define menu, select section properties, select Frame sections, Add new property
- Select Modify Rebar and edit
- Same for an beam and column adding of slab Now to add the Slab property, again select the Define menu, Select Slab section and add new slab
- The thickness of the slab is fixed in 150mm
- Now from the Define option select the Load patterns and add the Dead load, live load, Brickwall load and earthquake load
- I have adding in wall load and earthquake load
- After that go for an load pattern gives the load option as dead , live , wall load as per IS code
- Now select Eqx and click the Modify lateral load, and in the new tab appeared, seismic zone factor as per code is given and selected Site type as III
- To open the properties option to select the concrete frame option
- Now using the Quick draw columns option draw the beams and columns to the whole structure
- After using the Quick draw beam option draw the beams and columns to the whole structure
- Now we need to add the slabs Using Quick draw floor/wall option
- Now we need to add the Live load, for that, select the Assign menu and select the shell loads , and select Uniform option
- Here, we consider a wall load of 10KN/m^2 upto 25th floor
- To assign the 25th floor assign live load of 3 KN/m^2
- Now go for an Select Manu, select the Object Type option, now a new tab appears, and select the beams and click on the select option and close
- Now from the Assign Menu, select shell, and select Diaphragms
- Now when the new tab appears, select D1 and click on apply and then close
To apply the diaphargm
- Now from the Analyze menu, click Check Model option
- When the new tab appears, select all the options and click ok
- Select Show tables from the Display menu, and select Analysis result, select the required tables
- In Etabs analysis result are not shown i assume and fifgure it
RESULT:
- Tx1=4.22 seconds and Ty1=4.41 seconds
- Tx1=3.581 seconds Ty1=3.3 seconds Txy1=2.609 seconds
- So from the results it is clear that the torsional time period is less than two translational time period as required by IS 1893 provision table 5.
- When we add the three mode mass ratios we get 0.9044 which menas first three modes of seismic oscillation contribute more than 80% of building weight as per ETABS anaysis.
- The storey drift for serviceability Base shear case(EQX or EQY) is tabulated from the following tool path.