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

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.

PROCEDURE:-

Step 1: Open new model

• Open Etabs software>New model
• Use built in settings
• Display units: Metric SI
• Steel section: Indian
• Concrete: IS 546:2000

Step 2: Grids

• In X direction 5 grids with each spacing of 4m
• In Y direction 4 grids with each spacing of 4m
• Grids>Custom grid spacing>Edit grid data

Step 3: Model storey

• Number of stories: 25
• Typical storey height: 4m
• Bottom storey hright: 1.5m

Step 4: Add the materials

• Define> Material properties> Add new material
• Concrete and Rebar material are added

Step 5: Add Beam property

• Define>Section properties>Frame sections
• Add new property>Concrete

Step 6: Add Column property

• Define>Section properties>Frame sections
• Add new property>Concrete

Step 7: Add Slab property

• Define>Slab sections> Modelling type: Membrane

Step 8: Add the columns

• Keep it to all stories
• Select Quick draw columns

Step 9: Add beams

• Keep it to all stories
• Select Quick draw beams

Step 10: Add Slabs

• Keep it to similar stories
• Select Quick draw slabs

Step 11:

• Go to plan>Base
• Select One storey
• Select all the joints
• Go to Assign>Joined>Restrains
• Select pinned

Step 12: Loadings

• Define>Load patterns

• Time period= 0.5s
• Site type: III

• To assign the live load to the building
• Assign>shell load>Uniform> 3kN/m2

• Brick wall load
• Select beams>Assign>Frame section>Distributed load 10kN/m

• Define>Mass source>Modify>Specify load patterns

• Define> Load ombination> Add> Concrete frame

• Go to select>object type>Floors
• Assign>Diaphragms>D1

• Go to Define> Modal cases> Eigen

Go to Analyze> Check model

• Run Analysis

• Now Go to Display> Show tables> Analysis> Show Output > Model participating mass ratio

RESULT:-

Mode participating mass ratio for 1st 3 nodes

0.0001+0.8018+0 = 0.8019

Therefore it is more than 65 percent.