Modelling of 25 storey building with the specified properties using ETABS
AIM : Model a 25 storey building on ETABS with structural properties as given in the question and to cross check with IS 1893 :2016
INTRODUCTION : ETABS is one of the most powerful software tools for structural analysis. 3D modelling, visualization, and automatic code-based learning are some of the unique features of this software. ETABS also supports several analytical models like response spectrum analysis, time-history analysis, and line direct integration time-history analysis.
PROCEDURE :
- Open the ETABS software.
- Click the file menu and choose to create a new model option.
- After choosing a new model a dialogue box will appear as model initialization.
- Choose the built-in settings option and select the display units and codes.
- After model initialization select the grid and story inputs from the new model quick templates dialogue box.
- In this dialogue choose grid spacing and custom story data which is used to provide the inputs specified above.
- Enter X grid data at a distance of 4m and Y grid data as 4 at a distance of 4m.
- Now edit the stories by using the user defined storey input, 26 storeys are incorporated (plinth at 1.5m height+ 25 storey with 3m height each). Storey 1 has been labelled as master storey and all above levels are labelled similar to that.
- Select material properties under the define tab.
- Define the materials of concrete M30 grade and steel of transverse reinforcement as 415 grade and longitudinal reinforcement as 500 grade.
- Select Section properties under the define tab.
- Click on the frame section and create a new property as beam and input the values as 300X400mm.
- After the define properties for the column as 800X800 and slab thickness as 150mm
- Using the membrane property, slab size 150mm has been added to the list. Membrane property will help to consider only slab weights and floor weights in analysis of structure while no stiffness component of flange advantage is considered during calculation.
- Now draw a column of size 800X800mm at the intersection of the horizontal and vertical grid and beams with quick draw tool keeping all stories on.
- Beams drawn using quick draw beam tool keeping all the stories on.
- Using the quick draw floors option, all the slabs have been modelled keeping “similar stories”.
- Select assign and click on joint select pinned support.
- Fix he pin supports at the base.
- Now define the load patterns: click on the define ta and click on load patterns.
- Define the loads like dead load, live load, brick load, earth quake load in x direction and positive x and negative x and same loads in the Y direction also. Mention IS codes of respective loads.
- Click on modify lateral load, set range from base to 25th storey and seismic zone factor as 0.16, soil type II & importance factor 1.
- Define the load cases:
- Click on the load combinations.
- Click on the add default design combos.
- Now go to mass source from the define tab.
- Modify the mass source and tick mark the required loads.
- Add load patterns and assign to the model.
- Assign the loads and select similar stories.
- Click on shell load under the assign tab.
- Click on live load and give value as 3kn/m^2.
- Click on apply.
- Similarly add live load of 10Kn/m^2 on all the beams.
- For that select all the beams from select object type beams.
- Go to the frame load and click on the distributed load and enter the value as 10 KN/m^2.
- Now create the diaphragm by going to the assign tab then shell and select diaphragms.
- Analyze the model using analyze option then click on check model, the modelled structure is verified without errors and warnings.
RESULT :
| Criteria | Desirable solution | Exercise result | |
|---|---|---|---|
| Fundamental Translational natural period | X-direction | 4.4sec | 4.43 |
| Y-direction | 4.2sec | 4.24 | |
| Torsional irregularity | IS 1893 :2016 (Part-1) Table 5 | Torsional mode Time period should be lesser than X and Y direction time periods. | YES |
| Vertical Irregularity | IS 1893 :2016 (Part-1) Table 6 Clause 7 | First three mode together should contribute at least 65% in mass participation factor in each principal direction | YES |
| Fundamental lateral natural period in two principal plan direction are always from each other by atleast 10% | NO | ||
| Inter-storey Drift | IS 1893 :2016 (Part-1) Clause 7.11.1.1 | Storey drift shall not exceed 0.004 times the storey height for base shear for no load factor (4X10 ^-3) | YES does not exceed |
