Modelling of 25 storey building with the specified properties using ETABS
AIM:
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.
Answer:
Steps:
- 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 intialization
- Choose the built-in settings option.
- Now select the grid and story inputs from the New model quick templates dialogue box.
- In this dialogue bchoose ctom grid spacing and custom story datata which is used to provide the inputs specified above.
- Enetr X grid data as 5 at a distance of 4 metre and Y grid data as 4 at a distance of 4 metre.
- Now edit the stories by using the user defined storey input,26 storeys are incorportaed( plinth at 1.5 meter height+ 25 storey with 3 meter height each). Storey 1 has benn labelled as master storey and all above levels are labelled similar to that.
- Now we define the material properties.
- Define the materials of concrete M30 grade and steel of transverse reinforcement as 415 grade and longitudnal 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 ass 150mm
- 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 fllors option,all the slabs have been modelled keeping"similar stories" ON.
- 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 0.36,importance factor 1.25 and time period 0.5 seconds.
- Do the same for all the earthquake loads.
- 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.
- For roof it is 50% the total live load which is 1.5
- Similarly add live load of 10Kn/m^2 on all the beams.
- For that select all the beams from select object type beams.
- Goto the frame load and click on the distributed load and enter the value as 10 Kn/m^2.
- Define the load cases:
- Click on the load combinations.
- Click on the add default design combos.
- 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 strucrue is verified without errors and warnings.
- Using analyze>run analysis,the model is analysed and deflection patterns,BMD/SFD patterns are cross checked logically.It is understood that the worked model provides reliable results.
- Now click on Display>show tables>Analysis results>Structure ouput>Modal information>modal periods and frequencies.
Results:
- The time periods for fundamental mode-1Y direction and findamental Mode -1X direction are noted from the table and are as follows
