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">Tx1��1= 4.4 second Ty1">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

SOLUTION:

Open the Etabs software

select a new model

provide units & design code,concrete design code.

now arrange the grids in X,Y directions 4m spacing.

Add story upto 25 story, height of each story is 3m and plinth level is 1.5m.

After setting the grid arrangement and story, plan view and 3d view of the model appear.

Now click on the Define ->material propert->add new material that is M30

Add another new material as ->HYSD415

Now select the define->section propertys->frame section

create a new beam section select the shape give the size as B300x400

depth 400mm,width 300mm

add column propery select shape, size as C800x800

modify the reinforcement as shown below.

Again select define->section propert->slab section.

add new propert name it as S150 thickness of slab is 150mm

load patterns select define->load patterns

now add the loads as dead, live,wall,EQX,EQY by give codes

For EQX provide direction and eccentricity in x direction, soil type as type 2 and zone 3 assume other data same as in EQY also.

select define->mass source

provide the loads dead ,live, wall load as per codes.

by this we get to know how much mass should we considered for seismic lateral moment.

Check for load cases all are arranged or not

click on Define->load cases

create the load combination for concrete frame.

click on Define->load combination.

Now we get to modal select quick draw column,chose the property make sure that work in all story option.

select the grids and draw the column or use replicant option to draw the column.

After completing column select qucik draw beams do the as column.

For slabs click on plan->select the story1->chage it to similar story.

select the quick draw floor->chose S150->select the model for slab.

for selecting of beams, click on select->properties->frame section->B300x400

Assign frame load click on assign->frame loadapply the load.

Now select all the slab click on select->properties->slab section->S150.

Now assign shell loads click on assign->shell load apply load.

again select slab to assign diaphragms, click on assign->diaphragms select D1.

Now run analysis as it ask save the model after that we get model analysis.

RESULT:

• 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

Yes the time period of vibration in both x and y same.

• • 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.

Yes, It is less than mode 1&2.

• • Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied

  

Yes, first 3 modes contribute 65%.

No,The fundamental lateral natural peroids does not satisfied.

• Check if the provision on inter-story drift limitations in clause 7.11.1.1 is satisfied. Please note that this check is for Serviceability Limit State and hence is for situations when the structure is subjected to unfactored seismic base shear.

yes it achive less 0.004.