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��1= 4.4 second Ty1��1= 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
Designing a structural model for a 25-storey building involves several steps, and it typically requires a structural analysis and design software like ETABS. Below are the general steps you might follow, but please note that this is a simplified guide and you should consult with a structural engineer for a comprehensive and accurate design.
- Model Geometry:
- Open ETABS and create a new model.
- Set up the geometry of the building. Define the number of stories, the height of each story, and the overall height of the building.
- Define Materials:
- Define the material properties. In this case:
- Concrete: M30
- Steel: Fe 415
- Define Section Properties:
- Define the section properties for beams, columns, and slabs.
- Beams: 300 × 400 mm
- Columns: 800 × 800 mm
- Slab thickness: 150 mm
- Assign Sections to Members:
- Assign the defined beam and column sections to the corresponding members in your model.
- Define Supports:
- Assuming the building is pinned at the base, set the supports accordingly.
- Define Loads:
- Apply dead loads and live loads to the structure.
- Dead Load on beams from infill wall: 10 kN/m
- Live Load on floor: 3 kN/m^2
- Define Analysis Parameters:
- Set up the analysis parameters such as the type of analysis (static or dynamic), load combinations, and other relevant parameters.
- Run Analysis:
- Run the analysis to obtain the internal forces and displacements.
- Design:
- After obtaining the analysis results, proceed with the design of members (beams and columns) for the specified loads and material properties. ETABS will provide the required reinforcement for the members.
- Check Code Compliance:
- Verify that the designed elements comply with the relevant building codes and standards. Ensure that the design meets the strength and serviceability requirements.
- Review and Adjust:
- Review the analysis and design results and make any necessary adjustments to the model or member sizes if required.
- Generate Reports:
- Generate reports that summarize the analysis and design results, including member sizes and reinforcement details
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